Early in my CFI career I had an aerospace engineer as a student. I stopped charging him for ground school when it came to aerodynamics 😅. Thank you, Sven. If you see this, you were my favorite student/instructor!
This was a great video! I studied engineering in school, so I knew a lot of aerodynamics before I learned to fly. One of the really frustrating part of flight school was getting past the half-truths being taught about how wings work. Eventually I figured out that I just had to learn what they were teaching so I could parrot it back on the tests and pass the checkrides. It was doubly frustrating when I was prepping for my CFI and had to teach this garbage 🙂 I'm also a sailor. As you noted, sails are just airfoils. But more than that, the underwater fins on a sailboat (the keel and rudder) are also generating lift, except that it's hydrodynamic lift. And while sails are asymmetric airfoils, the keel and rudder are (almost always) symmetric. It gets interesting. One of the fun things is that if you take a sailboat that's standing still, like when you just released it from the mooring, you need to get both the sails and the keel flying. The sails will generally get attached flow before the keel does, and the boat will mostly be moving sideways. You need to turn the boat to reduce the keel's angle of attack until it un-stalls and then you can begin to sail normally.
I am a combustion engineer and private pilot, and I had to be careful in the same way regarding the FAA engine terms detonation and pre-ignition! (In reality light knock by itself is not damaging while pre-ignition is the kiss of death leading to immanent piston failure in the cylinder it occurs in. Although the actual technical meaning of pre-ignition this is aligned with is when combustion in a hot cylinder occurs prior to the ignition spark.) It was funny too when my CFI asked me why maneuvering speed for a given aircraft changes with the amount of weight that is onboard - I couldn't help but blurt out "That means the wings are not the weakest link!" Because the maximum force (lift) the wings can generated at a given indicated speed doesn't change with aircraft weight, but the lighter the weight of the airplane the more acceleration it will experience from that same lift force at that speed. And, since in theory the aircraft is certified to a given fixed G-level (acceleration rate) a lighter loaded plane will experience that acceleration rate with a lower amount of lift force and therefore at a lower speed.
Exactly. I'm a sailor too. The rudder plays a role too. It's a brake. Balance the sails and keel forces through proper sail trim and ballast location, and you can steer the boat without a rudder upwind. You'll go faster and take less of a beating if your balance the helm and trim your sails properly. My theory about aerodynamic lift and aircraft wings relates to airspeed, displacement and aingle of attack creating bouyancy as long as airflow remains laminar. How else to explain sustained inverted flight? Bernoili theory says an inverted airfoil will create it's lift vector towards the ground lol. Bouyancy says the shape of the airfoil plays a small role relative to airspeed, surface area, and angle of attack, but I'm an architect, not an aerospace engineer.... ;-) displacement and displacement and
it does sound like the airfoil is not that important to being able to fly, and that while a flat wing might be less efficient, and have a higher stall speed, it should still work,@@TheWilliamHoganExperience
My father was an aeronautical engineer and he always said "If you put a big enough engine on it, you can fly a barn door . . . broadside." Early in his career he did some work on airfoils for NACA [yes, that's with a C], but most of his career was designing gas turbine engines, so he may have been a bit biased.
I think you have to have some airflow that lifts the barn door up instead of pushing it down, but I agree...once you have that, you could put a strong enough push on it to get it flying.
Funny as I remember sticking things out of the car window as a kid, I built a rough model of a 707 out of cereal boxes and similar to the flat wing was only creating “lift” with aoa however when sticking a model airfoil out the window no pitch was consciously added but I could still feel the lift being generated from the proper airfoil shape. Interesting side note, I was kicked out of science class for debating the Bernoulli principle with my science teacher, even used similar wind tunnel footage to back up my argument.
@@carlosspiceyweineify you should have used a sail boat as your rebuttal. Take the airplane turn it on it’s side stick it down into the water, now the airplane becomes a sailboat. Every principle is the same for both of them, air flow, position of sail, position of the wing, no sail zone, stall zone. It’s all tied to the wing and sail, speed of air flow, fast over the wing, fast airflow around the sail, slow under the wing, providing pressure and lift, the sail, same thing. If you can fly, if you csn fly, you csn ssil.
Great video. I use to build foam planes for air to air combat, and since the whole purpose was to crash them, I'd just use a flat wing design. In order to get any sort of lift, we'd use higher RPM motors, and big batteries. They flew like bricks!
Thank you for this informative and straightforward video Captain! I'm a Ground Instructor at a school in the Philippines researching ways to better teach my PPL students. This video cleared my misconceptions regarding lift and now I get to teach my students accurate information about it 😁
@@crimony3054 About the only thing I particularly disagreed with was that the light high wing, full sized plane COULD fly, it just would need more power and possibly a bigger wing surface area. His graphic of a flat wing with a square, sharp cornered wing wasn't helpful as there's nothing to say you couldn't round off or taper down to a thin leading edge either. Sure, it wouldn't work on something like a Cesna 150 with it's stock, gutless engine but, give it more power, say about an extra 50 hp and it could. Of course stall speed would be higher too but, it would work. I'm sure as hell not intending to waste a fortune to test it but, the fact it does work fine on small scale DOES prove it can work on a larger scale too, it's just not 'the best way' to design a wing.
I think the moral of this story is that a flat wing will fly within a limit range of angle of attack. A curved wing will greatly extend the useful range of angle of attack, making the wing more versatile and practical.
Fabulous video. This 20-minute video puts 3 years of undergraduate Aerodynamics studying Aeronautical Engineering to shame. I remember the headaches I had trying to understand this stuff and unlearn the misguided falsehoods that had previously been taught. I have to say though that I shuddered at the Navier Stokes Equations, still. LOL. And when sticking flat plates out of car windows it's easy to confuse perceived lift for the drag you are actually inducing as you increase the angle of incidence. Thank you Magnar.
A great video! The development of early wings relied on trial and error to determine what worked best. A curved leading edge set at an angle to the oncoming air developed the most lift for the least resistance. It worked in a wind tunnel and it worked in practice. Mathematicians have been trying to catch up ever since. As you pointed out in the video, how and why a wing develops lift is determined by scale. Insects fly with wings that work well when air has the consistency of water, at that scale. Model aircraft can fly with flat boards for wings because they have an excess of power for their weight. Larger aircraft have to be encouraged to fly with finesse and wings that can be modified to be efficient during the different phases of flight with slats and flaps. There is no one size fits all explanation for how all wings work at all scales. For years, aerodynamicists insisted bumble bees couldn’t possibly fly, except they do, and very efficiently too!
I've had a number of aeroplanes that fly perfectly with flat wings but they're all very light small models made from Depron or other foam sheeting. Their main advantages are simplicity, low cost and, of course, fun :) A very interesting video that explains a lot. Certainly different aerofoils are suited to different applications - I like thick aerofoils in my models because low speed manoeuvrability is what I seek.
Fantastic video, brings back memories of Fluid Mechanics ME 2032, in college. My professor was doing a lot of research on wing aerodynamics and his teaching basically followed this video. So I am sitting here at 2:45 in the morning thinking about a course I took 43 years ago, thanks so much for the excellent explanation of lift.
Interesting. The importance of the curvature of the upper surface explains at lot, particularly why many WW2 fighters had wheel-wells extending almost a third along the wing-span, yet still, manged to get off the ground quite happily. Always wondered about that.
Regarding ordnance over or under the wing, airflow in a low pressure zone is more susceptible to flow separation. As you said both sides of the wing are crucial, at a given AoA a pylon on top of the wing might cause flow separation behind it, while the same pylon on the bottom has its flow still attached. In automotive applications rear wings are sometimes suspended from the top (swan neck wing) to make use of this effect, just in reverse.
The reason is the pylon introduces additional viscosity forces in the Boundary layer, which pulls the separation point upstream. Not important on the underside of a wing, because the whole point of a sharp trailing edge of the wing or flap is to force the flow to separate early.
Magnar, great video and visuals. Arguably the best practical video on lift. Permit me to defend the humble and unloved flat wing which is used on thousands of simple planes including the Cub. I'm talking about the horizontal stabiliser, of course. The little wing behind the big wing. It is simpler to manufacture and its efficiency can't be that bad or we would just camber it by inserting a few ribs. I see graphs for angle of attack vs coefficient of lift for flat wings that suggest they stubbornly continue to produce lift at high angles. Thus the plane can never lose stability or sufficient elevator authority to recover from a stall by pitching down. Is this a factor in their popularity? After 120 years of flight, the flat wing is all around us at least at smaller airfields.
Ah, the wonderful Cub! Yes, many small airplanes do indeed have a flat stabilizers. The purpose of the horizontal stabilizer is to produce a downward force. This is achieved by mounting the stabilizer with a negative angle of incidence, which means the stabilizer meets the airflow with a certain angle of attack. Moving the elevator up and down changes the curvature of the stabilizer, and hence the lift. While many old aircraft do have a completely flat stabilizer, most light airplanes do have a stabilizer with a thicker, symmetrical profile as it is aerodynamically more efficient and provides more strength. Hence, no need for struts.
Go to an airshow and watch so many aircraft, some of them normal aircraft, flying upside down with no problem. When I saw this as a young child I knew right away that the traditional explanation was at best only part of a more comprehensive explanation. I noticed then that those airplanes flying upside down maintained a relatively high angle of attack. So yes, the wings should have smooth curves to reduce turbulence, and we know from available observations that angle of attach can and does in certain situations provide enough lift to sustain flight. The Bernoulli physics also can dominate but as shown when ordinary planes fly upside down, it doesn't always dominate. Given a propulsive mechanism what matters when it comes to lift is what the air was doing before the passage of the aircraft and what the air is doing after the passage of the aircraft. The force of lift can be accurately calculated as the net rate of change in momentum experienced by the air in the vicinity of the aircraft (just point the force in the opposite direction, for every force there is an equal and opposite force). The rate of change in momentum of the air in the vicinity of the aircraft is actually the force exerted by the air onto the aircraft (just point the force in the opposite direction) . When you can see the vector describing the rate of change of momentum of the air then you can see how this vector can be resolved into downward and forward components. The downward component of the rate of change of momentum of the air is the lift and the forward component of the rate of change of momentum of the air is the drag. I did not get this out of a text book. I got it from observation and from experimentation when actually designing, building and testing flying devices.
There's a video of Alexander Lippisch taking about this. He uses a small smoke tunnel to demonstrate. A flat plate, given a bit of "A" incidence makes the air act as if it's passing over a camber. The air over the top is driven to pass the chord faster than the air under, even before the alpha slows and compresses the flow under it. The difference in pressure causes lift.
True that the continuity of mass flow causes air to accelerate over the top to faster than equal transit time speed because the pressure has dropped enough from the delayed transit to accelerate that lower density sufficient to keep flow rate out connected with flow rate in. This pressure drop bends the momentum of the.wider airflow at ambient pressure downward.
This is an incredible explainer! Not only does it present an incredibly thorough explanation of lift, it also manages to disprove nearly all of the common misconceptions about lift. I think the flat plate example at the end was really important, since most people's anecdotal experiences with lift are of this nature (sticking a hand out of a car window, sign being blown away by the wind, etc.), which could be a common source of misconceptions.
How do observations of the lift created from flat objects create misconceptions about how lift is created? In particular if there is a conception that a shape needs to be curved to create lift.
Great explanation on the theory of lift. I see that slide you showed with the system of differential equations, lift is not a simple proposition. On what you said about the importance of the shape of the wing leading edge: the gist of many STOL upgrades is to add a cuff, of which I have installed and flown a few, and can attest to the marked change in wing performance. As for a barn door flying: I am a structural engineer and often have to design for very high wind uplift forces on roofs, sometimes more than the weight of the building itself.
To make it simple for all: Airfoils are designed to reduce DRAG. LIFT is created only by deflection of air or fluid (Angle of Attack). By reducing DRAG of a surface even at high angles of attack, you increase efficiency and you can delay airflow separation. But the Lift is never created by airflow shape. This is why airplanes can even fly upside down without being sucked to ground.
Airfoil shape does matter though, in the sense that a more cambered airfoil creates more lift than one with lower camber at the same angle of attack. Look up Cl-alpha curves for the NACA 4412 compared to the 2412.
@@andreamusso1469 If you are aiming for maximum lift and low speed handling, power and meneuverablitly is more important than wind channel results. On my Savage Cup, the max. Lift was great before it was not. It had a very unpleasualble stall and got from tame to nasty way too fast...
@@Ozbird-72 What I mean is that angle of attack is not the whole story when it comes to lift. In fact, the traditional way of determining airfoil characteristics is by analyzing angle of attack, camber, and thickness separately. So it's not just your alpha that determines lift, otherwise there would be no difference between different airfoils.
6:37 I understand how bernoullis view also provides an explanation for the downwash but how does the newton way account for the pressure difference part?
I think he is referring to the pressure gradient force that must exist perpendicular to a streamline when that streamline is curved. From streamline curvature you can infer lower pressure inside the curve, higher pressure outside the curve.
The common misunderstanding is that either the "Bernoulli" pressure drop or the "Newton" downwash can explain lift. This is false. Both must be integrated to explain lift. The pressure drop bends the airflow at higher ambient pressure above, downwards. So the downward flow of mass results from the pressure drop's force. The force from one is numerically equal to the other. And you cannot have lift without both: a suction cup on a refrigerator can stay above the ground because the load stresses from its weight are contained within the fridge against the ground; if the fridge wasn't there, the suction cup's pressure difference would need to force air mass downwards (which obviously it isn't designed for). So, pressure is not enough without a rigid support structure. Mass momentum must be directed downwards to complete the other half of the requirement for lift.
Isn’t it really the second law, lift being a reaction force caused by the turning of the flow downward. This imparts an upward force which is lift. The greater the curvature the greater the pressure gradient which keeps the flow attached. The less curvature like in Whitcomb wings a greater adverse pressure as the flow moves back. Bernoulli applies to objects in a closed envelope. Flat wings fly just fine, as long as the α doesn’t get too high causing the flow to separate. Very good video.
2 года назад+4
You just called my favourite aeroplane a kitchen table.
So, the lower surface contributes to lift by being pushed upward by the incoming ram air, while the upper surface contributes to lift by creating a venturii effect between the upper wing surface and the undisturbed atmospheric pressure air in the higher air layers, that accelerates the air thats right next to the wing, creating lesser than atmo pressure ? Plus the smooth, gradually curving upper surface allows the air to flow smoothly without detaching and creating rotors that could hit the wing from above ? More or less ?
Wonderful vid, much better than the text books on wings course. In rotary wing flying, we refer to the combined downwash from the blades (rotating wings) as "induced flow". It is a column of descending air, drawn down, like a giant fan. This creates a large portion of the experienced lift, as evidenced by hovering in ground effect on this compressed column "air bubble" under the aircraft. It also temporarily reduces the lift when the transition to forward flight is made, as the aircraft moves off this compressed "bubble". (The lift increaess again for other reasons as air speed increases) This down wash is also observable on large aircraft with smokey engines (C130 for example). The distance and velocity of the descending air behind the aircraft is stunning. For interests sake, most modern rotary wing blades are symmetric, therefore they only produce lift with a positive AOA, and therefore also autorotate better in a unpowered situation with a low blade attitude (still positive AOA though). Finally, a nice experiment is to place a spoon under the kitchen tap, in the stream of water, observe the spoon move towards the side with convex curvature, and observe it redirect the stream of water towards the concave side; this is precisely the effect on the air.
Amazing Explanation ! One could have added that for supersonic flight, the flat plate is in fact the most efficient airfoil type because the air can flow around sharp corners by expanding after the bend. The sole reason fighter jets have cambered and thickened wings is because they have to go through the subsonic regime as well.
3d aerobatic foamy planes fly best with a flat wing and square leading/trailing edges. They get weird when you put a proper airfoil shape in the wing. But it is somewhat of an extreme example. They’re built with very light wing loading, a very aft center of gravity, extreme control surface deflection angles (~45 degrees), 2:1 or higher thrust to weight ratios and fly at a walking pace, in a stalled condition during much of the flight. I suppose it’s more akin to thrust vectoring than lift flying a wing, when the downward deflection of the prop wash deflecting off the wing and stabilizers is enough to keep the plane aloft as well as control pitch, roll and yaw. So while in my mind nothing flies better than my Crack Yak flat plank foamy model, I wouldn’t want to climb inside a full-scale with a flat plank wing.
I have thought about this issue for a while. I am a sailor. The sail structure does not create a very big difference between the path length over the back vs over the front. In watching your video there was a lot of emperic discussion of airflows, but I'm interested in what is the percentage of newton force vrs. Bernouli force in the wing. This really needs to be shown for airfoils, bicurved wings (which enter the air more smoothly than a piece of plywood) and sails. A piece of plywood tilted at an appropriate angle will fly, but may not be optimum. However, what is actually gained (in % of lift) by the airfoil? This value will vary depending by the angle of attack, but since planes fly upside down, it can't be huge if tilting the wing a bit more overcomes the effect. For your underwing loaded aircraft, are you sure this doesn't change the angle of attack? If so, where is the data?
There's is no percentage of Newton force vs Bernoulli force. Bernoulli's equation can, by mathematics, be derived from Newton's second law of motion, and vice versa. In other words, they are describing the same phenomenon: The relation between air pressure and velocity in an airstream. Lift is easier to understand when we apply Newton's third law. Scientinsts only use Bernoulli's equation to calculate the ratio between air pressure and velocity.
The "wing" in the wind tunnel at 1:59 has the same profile top and bottom, which makes it essentially flat, and is tilted up much higher relative to the incoming air than a wing would be in flight. And then again, your diagram at 4:27 shows a symmetrical wing tilted up toward the air flow which would work the same way as a flat wing at a high AOA. And your diagram at 5:39 shows low pressure up to the left but this area would actually be high pressure, and in fact higher pressure than below, because the air is getting deflected up more and compressed. Look at how the lines in the wind tunnel get squeezed together. The low pressure area is to the top right, after the air flows over the hump at the top of the wing, where a relative vacuum is created. The air under the wing slows down because it's hitting the resistance of a high pressure area under the wing, the air over the top speeds up because it's getting sucked into the rarefied space over the trailing top of the wing. If there was low pressure at the front of the wing then a plane with a symmetrical airfoil would need no thrust at all because the low pressure formed by the shape of the wings would pull it forward. When a plane flies through the air, is all the air in the sky above it pushed 3 feet to the tail of the plane? No, air below the wing is pushed forward. This is the drag. Also if you look closely at the airflow in the wind tunnel you will notice that the 2 lines that pass closest to the top of the wing are slowed down relative to all the airflows above them. And I guarantee that we extended those lines out that you would see that those lines over the wing are not accelerated, but in fact the lines below and directly above the wing were decelerated, which again, is drag.
WONDERFUL!! It all comes back to physics in the end!! When a discussion gets down to F=ma, I know we have found the right teacher! It is just a little disturbing to hear how many people have been mistaught or misunderstood some of the basic fundamentals of physics. We were taught Bernoulli's Principle by deriving it from Newton. Until you get to Quantum, everything goes back to Newton somehow.
Hi Magnar. That wooden model plane at about 18.30 in your video. Do you know what brand those little Micro Servos are that operate the ailerons. I want to get some like that. Can you advise? Thanks Brian
Great explanation in the entertaining video. Excellent presentation in relating the work of Bernoulli, Neuton, Navier-Stokes and others. The discussions and opinions (in comments) to these videos interesting and entertaining as well. The "flat wing" explanation (17:40) seemed a bit less complete, as only referenced a square leading edge airfoil, to which I agree with the conclusion. A round, or sharp leading edge would reduce air flow separation and drag. The thickness of the bubble and reynolds number at the scale of the wing plays a role. If the bubble is thin, it can act as an curved boundary for the air flow above. This not much different that a wing on a fighter jet at cruise speed. It also doesn't touch on flat surface aircraft like the F-117 Nighthawk. Model aircraft have the advantage of Reynolds numbers working in their favour, in addition to having a low wing loading, so less lift is needed (and efficiency of minor consideration). A discussion of Reynolds number would have been distraction here, as is a more advanced topic beyond the focus of this video. Nice work keeping this video focused, educational and entertaining.
You can get lift from a brick if you get it moving fast enough. Notice he says the flat wing fails because it "stalls". Okay, if it's stalling put some more power behind it and increase the velocity. That's why his belief that a scaled-up wing won't generate lift is faulty. A flat wing won't generate lift because you can't get it going fast enough to generate lift, not because it won't fly. Impractical for sure, but it will fly, and his reasoning is badly flawed.
Nit picking here; it seems, at first blush, the flat wing is not the problem but how you treat the leading edge. Needing angle of attack so air molecules can transfer momentum, being able to adjust the leading edge (say a nice wedge like the Starfighter's) would help your flat wing a lot. Then to confuse matters more, in really fast planes, shock waves created by the planes forcing its' way through the air provides the majority of lift (at least from what I've read - I don't really grasp it all that well) and in reality some planes get a huge percentage of their lift via the shape the body of the plane (e.g. F-14) and the upper side of those planes get very complicated. The thing gets complicated quickly. :)
You are absolutely correct. I included the F-104 in the video because it has an almost flat/symmetrical wing. It is optimized for supersonic speeds and doesn't work at medium and high angles of attack. At low and medium subsonic speeds, the leading edge flaps and trailing edge flaps must be deployed to provide enough lift.
RC fliers often use flat wing radio control planes to have fun because they are much easier to build. Square box fuselage and a flat wing are made very quickly.
I am with Frise. A kitchen table can produce lift. Inefficient, but that's not the question. A flat plate is a symmetrical profile with 0% thickness. Even if you add thickness and a horrible leading edge it still retains some of the properties of a symmetrical profile.
In fact, there was a Kickstarter project at some point that added a tiny motor and LiPo battery to any paper plane you made, and would let them fly until the battery ran out - under remote control no less...
Good description. Very important (3:09) that conservation of momentum (or the definition of force as "force = mass * acceleration", Newton) and conservation of energy (Bernoulli) are related. In fact, the basis is always the equilibrium of forces on the fluid element, and the transition to energy occurs simply by multiplying a force by a distance, and force * distance = work, i.e. energy. In the end, by Bernoulli it can be explained that the static pressure must decrease in a pipe constriction because the pressure energy p*v (with v as specific volume) or p/rho (with rho as density) must decrease, because the kinetic energy increases (forced by the channel contour via the continuity equation). But in reality this is terribly unclear, because we see a force (which, for example, is capable of lifting a column of liquid at the narrow point of a Venturi nozzle) - and where does this force come from? We can see the explanation here (approx. 5:05): The fluid element describes a curve, and similar to how a car driving around a curve experiences centrifugal forces, it is the same here with the fluid element. The centripetal force that keeps it on the track is applied by negative pressure or vice versa: The centrifugal force of the fluid element on the curved track causes the negative pressure. This is a purely mechanical explanation of the Bernoulli effect, which does not require the concept of energy and is immediately obvious. I don't quite agree with 6:26: "A wing creates lift, because it is deflecting air downwards." The statement sounds a bit like the lift is only produced on the underside, because only the underside deflects air downwards. Basically, the statement is correct: the aeroplane is moving in air, i.e. in a fluid. Therefore, the law of conservation of momentum for fluids must apply, which roughly reads: sum of all forces + sum of all momentum flows = 0. Momentum flow is the product of mass flow * speed difference. This means that the weight force of the aircraft must be balanced by an impulse flow of the same size. This can be clearly seen in a helicopter: It sucks in air above the rotor and blows it downwards at an accelerated speed. The aeroplane does something similar: on the upper side, it sucks air into the negative pressure zone of the wing, which is located above the wing, and on the underside, it deflects air downwards. The question is: How large is the mass flow and how large is the difference in speed? With a helicopter, the mass flow is small and the imposed speed difference is large. This is very inefficient. The same applies to the propulsion of aeroplanes: a pure jet propulsion system as used in military aircraft (which works on the principle of "small mass flow, large speed difference") is much less efficient than an engine with a large fan. What applies to the thrust force also applies to the weight force. Compared to helicopters, aeroplanes use "small speed difference, big mass flow" to compensate the weight force. It is therefore much more efficient to keep the mass of an aeroplane in the air than the mass of a helicopter.
I was a bit confused: "Very important...that conservation of momentum....and conservation of energy (Bernoulli) are related". It's true that they are related, but they also are distinctly separate properties that must be accounted for separately. For example, momentum is tied to direction, so the direction of momentum is conserved as well as the quantity, but energy has no direction. Also, energy is much more sensitive to changes in speed than momentum. So, the choice between mass or speed for making a given value of momentum makes no difference. For energy it makes a huge difference. (this has huge consequences for understanding the efficiency of wings for flight, and bypass ratios for fuel economy in turbine engines). "momentum (or the definition of force as "force = mass * acceleration", Newton)" Momentum is not the same as force. Force results in a change in momentum, and a change in momentum results from a force. "similar to how a car driving around a curve experiences centrifugal forces, it is the same here with the fluid element. The centripetal force that keeps it on the track is applied by negative pressure or vice versa: The centrifugal force of the fluid element on the curved track causes the negative pressure. This is a purely mechanical explanation of the Bernoulli effect, which does not require the concept of energy and is immediately obvious." The problem is, you haven't accounted for the increase in tangential speed around the curve, which Bernoulli, in terms of conservation of energy does address. Change of direction does require energy, but so does increased speed along the tangent of that curve. So, "compelled to follow a curve" doesn't work as an explanation for "Bernoulli" (conservation of energy). But in fact, you need to account for more than conservation of energy. "A wing creates lift, because it is deflecting air downwards....The statement sounds a bit like the lift is only produced on the underside". But deflection doesn't rule out deflection by the low pressure area above the wing. The fact is the total deflection of air (the total imparted change in vertical momentum of the air), is fully equal to the total lift force. "With a helicopter, the mass flow is small and the imposed speed difference is large. This is very inefficient. " That's a bit misleading. A helicopter relies on large mass flow with relatively lower speed of that flow. Of course there is an energy penalty for a helicopter in hover vs forward flight because forward flight allows even greater mass flow which increases efficiency. But helicopters can have relatively low power engines by increasing the blade size to increase the mass flow at the expense of the flow velocity (subject to other engineering limits). But both helicopter and fixed wing aircraft rely on large flow of air mass directed down.
One important aspect of the wing profile is the requirement for height sufficient to create a mechanical structure that is strong enough to lift the load of the aircraft. I wish your video had mentioned how this element factors into the engineering compromise of practical wing design.
Exactly. I have noted that every video I have seen on this subject ignores the fact that there is one constraint that always applies first.....it is that the wing HAS to have a finite thickness. This is implied but not stated in the final part where the 'flat wing' is shown not as a flat thin plate but as a rectangular box. I would expect that a thin plate would be more efficient for lift than box section shown, although lacking structural strength. Starting with a box section and then knocking off the corners and streamlining to reduce drag soon leads to a rough wing section. Aside from that I think this is a great video. Thanks Magnar!
Thank you for this. I always wondered about the details of Bernoulli vs Newton. I see that it is a bit complicated now, but makes sense. It is just different ways of viewing the same overall process.
I would disagree with: "It is just different ways of viewing the same overall process." I guess what I'm saying is, I disagree with the implication of the video's title: you can explain lift with one concept or the other. In truth you can't explain lift without the entire picture: to achieve a downward change in air momentum causing lift, the downward force causing that downward acceleration needs to be included in the explanation. The pressure difference is that force. But you can't explain lift only with a pressure difference either: you need to expel mass downward, because there is no external structure to support the load forces against the ground. So, the supporting force is the downward expelled mass, and it is expelled from the force of the pressure difference. As I wrote elsewhere today: quick summary: Lift is the asymmetry of a solid turning the air (explains both camber and AoA). Mass flow continuity means speed must increase proportional to the constriction A1/A2 (the ratio of two cross-sectional areas: an undisturbed incoming area of flow, to the effective constricted area of that flow due to asymmetry). This speed increase drives a conservation of energy, static pressure drop: pressure = constant - (1/2)x(mass density)x(v)^2 The total pressure difference is equal to lift. Which forces air mass down, also equal to lift: P x A = F = ma = d(mv)dt Or the force of pressure (as force per unit area times area), equals the change in vertical momentum of the air (again, both equal to lift). This directly ties asymmetry as the fundamental principle to both the "Bernoulli issue" and the "Newton issue".
How can I apply this to paper airplane design? Is it best to have a thick, rounded leading edge? (Having curvature over the full wing causes the planes to pitch down if not compensated by a tail.)
Apparently there are numerous aircraft, stunt planes, with flat wings, or at least symmetrical wings. Most of the lift is through the right angle of attack ... and they can fly upside down with the right angle of attack
The curvature of the wing, together with the angle of attack, is essential for lift. Aerobatic aircraft have pretty thick, asymmetrical wings. Some supersonic airplanes like the F-104 have almost flat wings, but they have flaps to allow for slow flight for take off and landing.
@@FlywithMagnar Well I'm sure you know better than I but I understand that some aerobatic aircraft have thin, flat wings. In any case, the fact that some planes can fly happily upside down says to me that the angle of attack is the primary factor in lift, and that wing curvature is secondary, perhaps contributing to efficiency.
Can I use this analogy. Cause this is how I visualise. When you through a skipping stone in water. Where the air is the LOW pressure and the water the HIGH(denser) pressure region. Every time the heavy stone needs to be in air it needs to hit the water with the flat and larger surface area. And every time it does hit the water it loses its energy. So aircrafts are fuelled to continue that motion, and with the help of flaps to continue the upward lift. Is it the boundary layer separation at the top surface of the wing that creates the pressure difference. 6:25 Or pressure difference is not important at all to create lift?!
You are talking about two different mediums: Water and air. While they have some common properties with it comes to fluid dynamics, they have very different density and viscosity. The stone is moving through the air because it has a high kinetic energy. And it skips the water because of the smooth surface of the stone and the relatively high density of the water. As the energy dissipates, the stone will eventually sink into the water. Therefore, you cannot compare skipping stones with wing lift. Regarding your quesiton: No, the boundary layer is often disregarded when lift is explained. It is the difference in static air pressure between the upper and lower surface of the wing that creates lift.
This is so true that will also explain the Magnus effect on a rotating object in an airflow. if you think carefully at this video contents the explanation of the Magnus effect will outcome better than it is usually explained.
You must understand upwash acts against downward atmospheric pressure , hence low pressure region around the maximum camber and leading edge. After this opposing upward pressure is redirected back downward , a pressure recovery is established on the upper surface reducing drag and increasing lift.
Ref to my comment at 15:34 in your video. I was saying that no matter what the shape of the wing, you get a low-pressure area on the top and a high pressure on the bottom. Low pressure does not suck the wing up, it's the higher pressure on the bottom that pushes the wing up. Instead of a diagram with a big arrow labeled LIFT pointing up above the wing, replace it with an arrow labeled PUSH pointing up below the wing and you have the same effect. Bernoulli describes the airflow but it's the pressure differential (Newton) that pushes the wing up.
Sorry but no. As the video rightly stated, it is neither the low pressure nor the high pressure that results in lift, it is the difference between the two. It is just a matter of semantics to argue about whether the wing is being sucked up or pushed up, the ‘net external force’ is the same either way. Nonetheless if you look at the pressure plot for a typical airfoil at moderate angle of attack you will find more ‘low’ pressure on the upper surface than ‘high’ pressure on the lower surface (shown in the video). Hence if you want to talk in terms of pushing and sucking - and you do - it is more sucking. And there is actually an engineering reason to be aware of that, but I will let you try and figure it out. As for the argument of whether to label an arrow “lift” or “push”, just label it how you want mate. But know that the word the industry has alighted upon since about 120 year ago is lift, so good luck convincing all the people who actually work with this stuff to switch over to the jargon of dhy5342 of youtube.
@@XPLAlN Regardless of 120 years of convention and labels, the scientific, physical forces of nature only recognize pressure as a force; "suck" does not exist. Only pressure can exert a force on an object such as an aircraft wing. Show me, if you can, any single instance where 'Sucking" or low pressure effects a reaction.
@@dhy5342 Lol. I know there are a few people who object to the word suck. I don’t care, it is a purely semantic argument because we define it to be what we want. It is arbitrary. As I said, use whichever word you wish to. But you believe “lift” should be replaced with “push”. You actually wrote it. And I am telling you that is not going to happen because all the people who need to actually work with this terminology are happy with what we have. So off you go with your words back under your little bridge, or span if you prefer to call it that, I don’t care which.
@@XPLAlN “Who is so deafe, or so blynde, as is hee, that wilfully will nother heare nor see.” ---John Heywood, 1546 "Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first." ---Isaac Newton, 1686 (Principia Mathematica Philosophiae Naturalis) 'Hear now this, O foolish people, and without understanding; which have eyes, and see not; which have ears, and hear not'" ---Christian Bible, Jeremiah 5:21 "Absent a rope or some other pulling method, there is no lift from above, only a push from below" ---dhy5342, 2023
First of all, in flight the air is not “traveling over the wing”. The air is just floating there minding its own business when suddenly this wing comes along and shoves it out of the way. I’ve never bought into the conventional theory of lift. Thank you for clarifying some of the flaws in the conventional reasoning.
Flow is relative to ones perspective. Think of a boat in the water, is the boat traveling through the water, or the water flowing by the boat? The view of this may differ if a boat is in a calm lake, or traveling upstream in a river that is flowing at the same speed as the boat. A observer on the show may have a different opinion that to the sailer in the boat depending.
The best way it was explained to me, is the air particles stay longer and accumulate together pushing up the wing. The particles on the top, just want to get out of the way, making less resistance - pressure.
My theory: bird poo and insect poo (both being flying creatures) is heavier than air when it dries. So when it is first poo-d (is that a word?) it falls on the upper surface of the wing. Once it dries, it becomes *almost* lighter than air. But when cooled with a draught of air, it becomes much lighter than air and lifts the aircraft into the air. This is why there is more lift on cold days. This why space rockets are usually white - they are covered in bird poo for extra lift. In some videos you can see the ice fall off that they use to cool the poo. Employers take note: I am available for hire by major airliner design bureaux, but only 3 days a week. The rest of the time I am too busy cleaning the poo off my car bodywork to prevent it skidding on fast corners and going over top of hills on motorways.
Ref 'flat wings' on a powered aircraft (I've posted this comment on its own) provided the leading edge shape is not two 90* (sharp) corners like a plank of wood, but rather has a rounded leading edge (more like a worktop 'nose') with the rounded shape upwards, then despite say 95% of the wind cord being 'flat' (top and bottom) it will of course fly perfectly well BUT will equally of course have a VERY 'nasty' (sudden/sharp) stall characteristic!!! This is one of the rerasons that as a general rule a quick glance at the wing shape (how 'fat' V how 'knife edge/skinny) in cross section lets you take a guess at the level of pilot skill required for that aircraft. (and yes my personal prefrence in paragliders is designs with VERY 'sharp' stall entry over wings with 'safe/soft' and highly delayed stall flight design.
11:46 about "..Symetrical wing has the Streamline compressed, both upper & underneath the Airfoil (with zero angle of attack) to create air pressure.." (??) In such case ("0" Degree of Attack) the plane in high altitude, still can glide-over but it will "stall", cannot maintain the same Alitude at Horizontal line of flight.. means decreasing height.!! Only (as you mentioned) positive Angle of (wind) Attack to be added, otherwise, the total Weight of aircraft will make (horizontal) flight "STALL/Fall-down"
Would you be able to comment on wing sections designed for tailless aircraft? They typically have a trailing edge that curves up to reduce the nose down pitching moment that conventional wing sections have. Do they still have a lot of downwash behind them? I guess they must.
The reason wings were made thick in the beginning was to accommodate a hefty spruce spar. Modern materials require less so. If you inspect modern airfoils, you will see thinner wings for less drag and more efficiency. A F18 would never fly if it depended on the Brenoulli effect for lift and would never exceed anywhere near a Mach 1 speed. Lift is dependent wholly on angle of attack and thrust. More thrust lower surface area equals more ZOOOOOOM!!!!!!
While thin flat wings may not be as aerodynamically efficient as more specialized airfoils, the (macroscopic summarised) Bernoulli effect and the more fundamental (microscopic detailed) Newtonian laws both apply and explain lift generation. The angle of attack is the key factor for generating lift with thin flat wings. Newton's equations of motion are generally valid (outside of quantum scales and relativistic speeds).
What comes first, on top of the wing, is the question. The low pressure comes first then the faster airflow. Nothing can accelerate instantly; the air is forced apart by the wing. The air in front of the wing impacting the air (which is actually the bottom of the wing), (remember there is always the angle of attack) is where the air is suddenly forced together, compressed. And at the same time the air is forced apart at the back of the wing (which is actually the top of the wing), where the air is forced apart faster than it can flow back together again, causing a vacuum, a low pressure. Now we know very well that when there is a pressure difference on either side of an object, that object wants to move in the direction of the lower pressure, because of the pushing force of the higher pressure. on one side and the pulling force of the lower pressure on the other side. Think about a door slamming shut. It slams shut because the air pressure on one side was greater than the pressure on the other side. This moving door can be seen as the wing of an aircraft that wants to do the same thing, that is to move from the higher pressure to the lower pressure.
Finally someone has provided an intelligent explanation, it is the angle of attack that generates a pressurev below the wing and therefore a lower pressure above the wing. I know very little about airplanes but the Bernoulli principle, bas I learned at school, does not make much sense. When, as a child, i used to throw flat stones above a pond of water, these would bounce up to half dozen times or more before sinking into the water, depending on the speed and the shape of the stone and the angle of impact. A wing glides on the air just as the stones glide on the water. The stones bounce at a much lower velocity than the aeroplane wings glide on the air because the water is much denser than the air but the principle is the same.
Unfortunately, stones skipping on water are at the interface between two different mediums, so that situation is quite different. "Bernoulli" just tells you how much pressure drop you get for an imposed speed increase. And the speed increase just keeps the mass flow rate continuous.
My A.E. son referred me back here and the conversation reminded me of this. I point your attention to John D. Anderson's Aerodynamics book. He shows flat wing experimental data from the Japan Society of Mechanical Engineers. From the lift curves it does show about half the lift, but if the power can muster 25% more airspeed, it should fly, but with a stall AoA around 10 degrees, you're margin is significantly reduced.
In the video, I discussed a flat wing with a sqared off leading edge. If the flat wing has a rounded leading edege, it will be able to produce more lift. In the video, I show the F-104. Without the maneuvering flaps, it will not not be able to fly, unless it is moving very fast. A flat wing with maneuvering flaps is a modern copy of the wings used in the first airplanes, wich in turn is a copy of a bird's wing. The nature has been, and still is, an insporation for the engineers.
@@FlywithMagnar It seems obvious that to have that squared off L.E. and T.E. is counter productive. The basic comparison with a flat wing is to one with little thickness, so the blunt L.E. doesn't cause such a problem. The Japan data is of a very thin wing similar to the common small. balsa model without the thick blunt edges causing more turbulence. . To land, the F-104 required engine air blown over the wing which was called Boundary Layer Control - BLC . However. . . The Wrights also observed that the L.E. shape had a profound effect and If I recall correctly, a squared off L.E. appeared to perform best in their tests, but I think it was hardly more than an inch or two thick.
To my knowledge, the Wright brothers never tested a wing with a squared off leading edge. They ended up with a thin, cambered airfoil with a rounded leading edge. Here is a good description of the evolution of the wing profile: greydanus.github.io/2020/10/13/stepping-stones/ Regarding the F-104, bleed air was not blown over the wing. It was directed over the flaps from a duct inside the wing. It is indicated with an orange circle in my video at 10:48.
@@FlywithMagnar RE: Wrights. I did not mean to imply the Wrights used a thick flat wing similar to what you show. They had some type of wooden, leading edge that we can call a spar. I don't recall reading its thickness, but its shape was definitely discussed in one of the many books written. I don't recall which, but I read all I could get my hands on, perhaps 20 years ago, about them and some others at that time. If I had to guess, I would first say the one 'official' book Orville wrote with Fred Kelly. I distinctly recall it mentioned. It was one example of the level of detail they went to.. It may have been in reference to the wind tunnel tests, or in a glider, or in a letter to Chanute, but they did look at LE shapes. I recall thinking about how much it could affect such a thin vertical dimension. Unfortunately, I don't recall exactly what was said - what shape was better or worse, but seem to recall that they saw some advantage to a squarer LE shape. I can't recall if I looked closely at the one at the Smithsonian when I visited, quite some time ago . Yes, I mis-spoke saying it was over the 'wing'. I built a plastic F-104 model back in the early 60s which is when I learned about it's BLC. I don't think I read s full description, or if I did, I've forgotten details. You imply it can't *fly* without flaps, but it is low speed flight that is the problem with the thin, small area wing. It couldn't *land* engine-out as there was a minimum RPM for the compressor to provide its effect. (of course it couldn't take off) .. The idea is also slightly similar to the 1943 Custer Channel Wing concept. That *was* an entire above wing augmented flow from the prop engine. that was further investigated in the early 2000s by a NASA funded project at Georgia Institute of Technology Research Institute. It had the problem in that at the low speed afforded by the augmented flow, It landed very nose up and the low speed flow over the control surfaces made low speed flight troblesome. I spoke with the Georgia Tech leader Bob Englar several years ago. A drawing he showed me had a forward-mounted, above wing jet engine of some type that did a true Coanda flow traversing the full chord, including flaps. Thanks. I see we've drifted far off topic. I simply wanted to point out that a thin, flat wing has a fascinating flow as shown in Anderson. Regards.
@@Observ45er A CL “of about half” will require 41% more airspeed to achieve the same lift. Not “25%”. But that is beside the point anyway. You could accelerate up to, say, 1.05 Vs, rotate, and yet be unable to sustain flight, or even maintain speed. You have to know the Vy, the drag, and the power available before you can answer this question. The TO and climb performance would certainly be in the range awful to nil. Hypothetically, you could just about make something like a C-172 fly with a flat wing (of the same area) and the rated power of an O-320, and an optimised prop. It seems plausible that a structurally adequate flat wing could be constructed at typical GA aspect ratio with a 6% thickness. However, it is a highly marginal case for such a thing to get airborne at representative operating weight of, say, 1 tonne. Nobody has tested such a ridiculous airfoil at the kind of Reynolds numbers we are talking about (3 million range) so the data is simply not available to nail down exactly how bad the performance would be. Nonetheless, the point I am making is that it has nothing to do with CLmax. If it cannot fly at its Vy, it cannot fly period.
6:03 In 2 dimensional flow, like a wing going from wall to wall, there is absolutely no downwash diferent from the upwash, as reflected from the ¼ wing chord, in other words no net down wash. The downwash is created as the inside flow from the vortex ring composed of the lifting circulation around the wing in clockwise direction, the starting vortex left behind and the two wing tip following vortices, which also create a significant updraft outside the vortex system, which is used by canadian geese to fly in that updraft, Newtons interpretation falls apart, because it sas not intended to be valid for a flowing medium, just a rigid single body.The proper , applicable equation IS the Euler Equation. The lift equation summarizing these conditions is indeed the Kutta Joukowski equation. In two dimensional flow there is no downwash, just the symmetrical flow due to the linear superposition of the uniform horizontal flow, the circulation and the displacement in thickness due to a source and sink distribution
The upwash and the downwash do not rule each other out. They complement each other. Please watch this video with Doug McLean: ruclips.net/video/QKCK4lJLQHU/видео.html The vortex from the wing tip does not produce lift, but induced drag. Yes, it is correct that birds flying in formation can utilize the upwards part of the vortex, but this happens behind the wing. Here are two questions I want you to answer: 1. Why are long, slender wings, like those used on gliders, more efficent than short, stubby wings? 2. Why do many aircraft have winglets that reduce the vortex?
@@FlywithMagnar I am familiar with Boeings McLean. Here is my Schadenfreude : ( my teacher was J. Ackeret) The winglets act to produce a larger effective span, by introducing a biplane effect. On a wing the apparent mass is proportional to the circular area over the wingspan, winglets extend the area upwards, like 2 circular areas slightly superposed . Only a reduction in induced drag L/D = spaneff÷2 × sqrt (pi/ Cd Aw) True, 2 vortices are created, spiraling each other, with the shear sheet behind the trailing edge wrapping around both. Read R. T. JONES Aerodynamics of wings. The strenght of the shear sheet is the span derivative of the almost elliptical lift distribution . Namely the circulation distribution, to locally satisfy the Kutta-Joukowski equation. A carefully designed visualization can be done in an extremely low turbulence wind tunnel Or a large one in Tullahoma Arnolds Air Force Research Lab. Tenn. huge wind tunnels.
@@FlywithMagnar Up wash in front of the¼ chord line and behind, the downwash in 2 dimensions are produced by the circulation in clockwise sense, so they are the same, in 3 dimensions the tip vortices downstream add another contribution to the downwash behing. According to the Biot Savart relation.
Could you please explain how a fighter can stay in the air when it's on its side, i.e., rolled 90 degrees, one wing pointing to the ground and the other to the sky, and going in a straight line? Where does the lift come from? And are fighters the only planes that can do this, and if so, why?
This is called a knife edge. The lift is created by the fuselage, which is pointed a bit up. The pilot must apply a lot of rudder to keep the nose up. A belly tank is a benefit as it will increase the lift.
Fighters often use ballistic manoeuvres as opposed to aerodynamic ones... At 500 mpg, you can do funny things just using inertia and ballistics... Like sitting in a bullet with control surfaces
Magnar, finally! A youtube video about lift with which I don't have any significant objection. And this is coming from a pilot who is also an aeronautical engineering and who used to teach Physics 1 and Aerodynamics 1 and 2 at college. Of course there is much more to say about lift that what's in this video, but for a youtbe video intended for a general audience of enthusiasts and pilots it is excellent: Clear, to the point, and more important: CORRECT! I have seen so many things wrong in official pilot training materials. (And I was one of the guys that critiqued your previous video on this, and you answered my comment)
Putting the back (convex) side of a spoon into a stream of water from the faucet causes a strongly felt force to move the spoon towards the stream as it attaches and flows smoothly over this convexity. Isn’t this a factor in flight?
@@BobbieGWhiz , this is the Coanda effect. It can be used to enhance lift, for example by using blown flaps. But a wing produces lift through pressure difference above and below the wing.
So if newtons third law explains that since air is deflected down and back from the trailing edge there is an equal and opposite reaction force upward and forward, then why does the effect of induced drag that further bends the downwash downward not result in the creation in more lift. In theory air is being deflected more downwards and would that not therefore mean the equal and opposite reaction to the downward directed air be upwards even more? I dont think induced drag and wing vortices increase lift, but this logic tells me it does. Where am I going wrong? I must be misunderstanding something
The vortex created at the wing tip does not create lift. Only drag. That's why a wing with a long aspect ratio (for example a glider) is more effective than a wing with a low aspect ratio.
Fair question. If I may expand a little on Capt Nordal’s reply. The short answer is: the tip vortex itself is a circulation, not a downwash, so it does not increase lift iaw Newton’s 3rd. The tip vortex will increase average downwash over the span. However, being a vortex it is circulating so there is no net extra downwash of air. The ‘up’ part is happening outside the tip. Nonetheless, the span gets the downwash part so that reduces the ‘effective angle of attack’, hence reduces lift (relative to a hypothetical no tip vortex case aka 2d section or infinite span). Ergo, for any given required lift, this shortfall has to be recovered by increasing the angle of attack somewhat. The net result is same lift but more drag for the real wing than the hypothetical no tip vortex case. That difference is ‘induced drag’. One of many references is Aerodynamics for Naval Aviators, p66, downloadable from the FAA website.
Are you planning a video about v-wing aircraft eg. The Vulcan and Concorde? Why is the same wing design effective for both when one is a slow heavy bomber and the other a supersonic passenger plane? Love the video presentations.
The delta wing is very good for supersonic flight, as the Concorde proved. Regarding the Vulcan, a delta wing was selected for the following reasons: 1) Less drag at transonic speeds (the Vulcan had a top speed of Mach 0.96). 2) Lot of space for fuel. 3) Space to embed the engines and the landing gear into the wing. 4) A very strong construction.
NACA 0012 has 0 camber and a thickness of 12%. The surface is not flat. airfoiltools.com/airfoil/details?airfoil=n0012-il While this profile is used on Jet Ranger, S-51 and other helicopters of "old" design, the majority of new helicopters have rotors with cambered airfoil because they are more effective.
@@FlywithMagnar 0 camber defines a flat profile chord... The NACA 0012 is a flat plate with an aerodynamic shape :-) Even R22, R44 and R66 use this one and it works fine
@@Ozbird-72, you might be confused by the definition of camber. NASA: "A cut through the wing perpendicular to the leading and trailing edges will show the cross-section of the wing. This side view is called an airfoil, and it has some geometry definitions of its own. The straight line drawn from the leading to trailing edges of the airfoil is called the chord line. The chord line cuts the airfoil into an upper surface and a lower surface. If we plot the points that lie halfway between the upper and lower surfaces, we obtain a curve called the mean camber line. For a symmetric airfoil (upper surface the same shape as the lower surface) the mean camber line will fall on top of the chord line. But in most cases, these are two separate lines. The maximum distance between the two lines is called the camber."
@@FlywithMagnar Zero camber means a flat, aerodynamic shape, but not a lifting surface. Unsymmetrical airfoils are better in defecting air downwards and optimise Lift. But they are not needed for lift at all.
When I was growing up in the '70's, I designed and built balsa wood airplanes. Some of the smaller ones had flat wings, and they flew ok. I knew that kites mostly worked in stalled states by redirecting wind on their bottom surfaces, so I knew that this was at least part of the source of lift for regular airplanes, and I knew about symmetrical airfoils on aerobatic aircraft. But of course you are right, asymmetrical airfoils that use both effects work better.
Fool in the video says it won't scale up, but that defies the wind tunnel experiments performed by the Wright Bros., who tested small wings in wind tunnels and scaled them up. Likewise, the Wrights scaled up the aerodynamics they refined with their kites and gliders. Doesn't scale -- now that's a laugh. 🤣🤣🤣🤣🤣🤣
@@crimony3054 I think he meant 'doesn't scale' more in the sense that you need to compensate for the bad airfoil shape with much more engine power, the catch is doubling the size os a wing makes its area 4x times larger, but it'll end up weighing 8x as much. TL:DR I think he meant the square-cube law.
Lift can be explanied in many ways. Newton's third law is one of them. Lift can also be explanied with the pressure difference under and above the wings.
I've a doubt. Why do some planes (like A300, where I experienced) fly level with a nose up attitude ? Anything to do with wing design, to have more airflow under the wings ?
Airliners usually cruise with the nose a couple of degrees up. The reason is twofold. One: The higher they go, the more fuel they save. Two: At high altitudes, the air is thin, resulting in a relatively low indicated airspeed. To compensate for this, they fly with the nose a few degrees up, as this increases the angle of attack, and with it, the lift coefficient. Wings are designed to be most efficient at a higer angle of attack (7-8 degrees for a straight wing), but this will result in a relatively low cruise speed. Therefore, some efficiency is sacrified for a higher cruise speed. The airflow under the wings contributes to some of the lift, but the airflow over the wings is more important. Here is a link to a video about the lift formula: ruclips.net/video/e43l2V_MFIY/видео.html
@@FlywithMagnar ... Yes, but if the airliners do most of their cruise flying with an attitude of 1 or 2 degrees nose up, they could have designed the wing to be mounted on the fuselage with an incidence of 1 or 2 degrees more. As an aeronautical engineer, I have always have this doubt myself. I found several explanations, and I don't know which of them if any are true. 1- The airplane is designed to fly with an attitude of no less than 0 degrees because flying a bit nose down is more uncomfortable for the pax than flying a bit nose up, so the whole range of cruise attitudes (different weight, altitudes, speeds and CG) are designed to have 0 degrees as the lower bound. 2- It is to reduce drag by better streamlining the aft fuselage with the airflow, which will not be horizontal but tilted downward due to downwash. Also the tail cone is tilted up so having the aft fuselage tilted down again aligns the tail cone with the airstream better. 3- To create a little bit of body lift, hence reducing a little bit of wing lift and reducing induced drag. I know this one HAS to be false. While the fuselage may create a little bit of lift by flying at an angle, it is super inefficient generating lift when compared with the wing, and it will create more drag for unit of lift. Any lift that you can take out of the fuselage and put it on the wing will result in a lower drag. 4- To provide a more nose-up attitude during landing and avoid a nosewheel-first touch down. If the plane flew with the fuselage 2 degrees less nose up at cruise, it would also touch down with the fuselage 2 degrees less nose up, and since it does touch down with about 2 or 3 degrees nose up to begin with, that would put the nosewheel dangerously close to touching down first. Not sure about this one. Tail strike seems to be a more common problem than a nose wheel landing. Also the problem could be solved by shortening the nose strut a bit.
@@adb012 Point 4.... They rarely come down with the same nose up attitude. In fact they point downwards, mostly, to lose altitude - which is my experience as a passenger.
@@RaviKumar-sn2lx ... I don't get your point. Airplanes touch down with the main landing gear first (the wheels under the wing) and they have a nose-up attitude at that point. Then, once the main gear is on the ground, they lower the nose and the nose gear touches down. If the wing was installed with, say, 2 degrees more of incidence, then, at any given speed and weight, the fuselage would fly so degrees more nose down or less nose up (because the wing, which is the thing that makes the lift, will have the same angle relative to the incoming airflow, so instead of the wing being installed on the fuselage with 2 degrees more of incidence, you can think about the fuselage being installed on the wing with 2 degrees more nose-down angle), and that would make the nose gear touch down first (or very close to that) unless you change somethin else like making the main landing gear longer or making the nose gear shorter.
so the biggest problem with flat wings is not how to explain lift but how to deal with stall , and of course we are talking about fixed wing , because as any bee or butterfly knows , turbulence can be an asset .On the other hand , a rocket table can pretty much ignore aerodynamics altogether .
You can add drag to the equation. Insect wings are neither 100% flat nor fixed. They can flap and swivel. So it would have been more accurate to use the aerodynamics that are applied to helicopters. Aircraft engineers are using turbulence to create lift. Examples are vortex generators (increases critical angle of attack) and leading edge root extensions (LERX) on fighter aircraft (creating a powerful vortex over the wing root).
4:33 The stagnation streamline meets the wing surface at a right angle! This is important to understand the stall warning sensor, giving the stall warning an electric signal. Please correct that image.
18:30 I'll add this to my mental list of examples how scaling (up or down something) can fail. The deeper reason for many purely mechanical and mostly static examples is that some things scale linear, others squared (like tensile strength) and others again cubed (like weight caused by mass). Therefore if you build an exakt replica of a bridge scaled down 1:10 and film it while putting more and more weight on it until it collapses you'll never get the same result like in reality. For the same reason you can't simply scale up a bridge by a factor of 2 and assume it now supports the double weight of traffic. Now, you say very small, light model airplanes actually CAN fly with flat wings but your next sentence is a larger plane can't and to me it sounds like you state a principle: _"No matter how strong an engine you put at it, it simply CAN'T."_ No I wonder - like I explained for the bridge - what is the deeper reason for this. My intuition tells me it's another application of the squared scaling of forces (when some material we practically have available breaks or in case of a wing how big it's surface is which produces force) vs. the cubed scaling of its weight. Is this right, or at least approximately right?
Your example with the bridge is to a certain degree similar with airplanes. In the video, I show an image of a model airplane with a wing made of square cut foam. The wing loading is very low, and the power to weight ratio is very high. Such model airplanes can fly. But if you scale up that wing and put it on a Cessna 172, it will not be able to fly. If you round off the leading edge and sharpen the trailing edge, the wing will provide more lift, but it will not be very efficient. You can scale up a model aircraft, but you cannot scale up the air molecules. Therefore, a model airplane will have different flying properties than a full size airplane.
Also, there is a logical point of confusion at about 5:08. You claim that because the particle is moving on a curved streamline that it proves F=ma applies and that this is the centripetal force. But one can't digest this because although it is true the particle can only follow a curved path (as well as speed up) if a force acts according to F=ma to cause that change in direction (and speed), there is not an identifiable centripetal force. And a centripetal force would not account for the increase in speed along the streamline. A centripetal force is a center directed force, such as gravity acting on an orbiting satellite. But the particle in your illustrated case, is being diverted from its horizontal momentum by the curvature of the wing. So, there is a logical disconnect here that makes one lose track of the explanation, again, because there is no identifiable centripetal force, or other any other force identified. Does the particle accelerate? Sure, but why does it speed up? Without any centripetal (center seeking) force here, what are in fact the forces both causing the change in direction and the acceleration along that change and direction? I think you'll agree, some more satisfactory answer is needed. Thank you.
Even before airfoil concept known for an aerplanes, people were aware of the tirck for flying a kite. What makes a paper kite fly in the sky? What are forces acting on kite, what cause it lift ?
Travelling in a car, I extend my arm outside. I flatten my hand. If I turn the leading edge of my hand up the air flow pushes my hand up. If I turn the leading edge down the air flow pushes my hand down.
There is a difference between a flat plate and a flat wing. The plate has a square edge, but a wing will have a streamlined edge if it's expect to function well in subsonic flow.
@@clintoncoker6 Seriously, are we really going to argue about word meanings here? It is flat if it can lie flat on a flat surface, whether or not the edge is rounded. Are you also going to tell me the countertop in my kitchen is not flat? Well, it is flat, and the edge is rounded, and it would make a better wing than one that has a squared-off edge.
@@satunnainenkatselija4478 Magnar said an airplane with a flat wing will not fly, which is inaccurate. If instead he had said a flat wing with a square leading edge would not fly very well, that would have been accurate. In this context flat means a surface without curvature, and the pertinent surface is the large area of the wing, which is curved (not flat) for most airplanes. Regardless of the leading edge treatment this is a flat wing, as opposed to the usual curved wing surface. But Magnar's drawing is really just a thick flat plate, not a wing intended to actually fly well. First of all, a flat plate is actually quite efficient at producing lift in supersonic flow. There is no flow separation, and the sharp corners produce expansion waves that are the source of pressure differential and aerodynamic forces. But nobody would expect that wing to work well at useful angles of attack in subsonic flow, even though it would still fly given enough airflow. However, all you have to do is taper the leading edge to expand the useful angle of attack range to allow a flat wing to work better. It will not be very efficient at low speeds, but it will fly. More than one aircraft has had a flat or nearly flat wing and flown to quite useful angles of attack, such as the X-15.
Bernoulli is not remotely related to lift generated by an aircraft wing. Wings generate lift in two different ways, depending on which side of the wing one is referring to. One side of the wing will be actively acting against the air reaching it by pushing it downward, often called Neutonian action/reaction. The other side of the wing (the upper side in normal flight) generates lift by first rapidly pushing the oncoming air upward. Then, taking advantage of the air's inertia, the wing surface then immediately does what I call "yanking the floor out" from under the air above it. The effect is mimicked, and can be felt, in a rapidly accelerating elevator as it begins its descent. An occupant will feel a bit lighter as the elevator begins moving downward, because for a short time, there is less pressure exerted by the feet against the floor of the elevator.
It is a standard wind tunnel exercise for aeronautical students to measure and plot the surface pressures at points around an airfoil. Then, using graphical methods the average pressure can be determined. When multiplied by the area of the airfoil this provides an estimate of the lift. At the same time, the lift can be measured directly by a balance. The estimate will agree with the direct measurement. Now for the Bernoulli part: the total pressure of the freestream can be measured directly. From this total pressure, each surface pressure data point can be subtracted to find dynamic pressure at that point. In other words, an estimate for airspeed at each point. If you then check this point with a pitot you find the estimate is remarkably good. This exercise is repeated by thousands of students each year. It then becomes denial of fact to continue to believe that Bernoulli is not remotely related to lift.
@@XPLAlN Engineers will engineer. That's what they do, and they are welcome to it. Somebody who throws a plate of spaghetti against a wall instantly knows all he needs to about the result. 1000 engineers trying to learn everything they can about it will never understand it fully. At some point they will give up and create some complex mathematical formula designed to make it look like they understand it.
All of this is true, which is more than can be said of almost everything youtube has on the topic, but it still says nothing about the actual effect responsible for lift generation. Deflection of air downward; a vertical component to pressure integrated over the wing surface; and non-zero circulation are all things that are necessary present if lift is, they just aren't an explanation of why it is. What does explain it is the effect of viscosity near a sharp trailing edge, which has the effect of forcing the rear stagnation point to be at the same place as the trailing edge. So long as this wouldn't be the case absent viscosity, this means that a circulation most exist around the wing (or equivalently, the flow has been deflected) and therefore lift is generated (See Kutta-Joukowski theorem). It also means that starting vortices are shed whenever the lift generated changes and the bound circulation adjusts to re-establish the Kutta condition.
Newton explains what is happening to the air and Bernoulli explains what is happening to the wing. Newton shows how the air is accelerated downwards and Bernoulli shows what effect accelerating that air has on the wing surface.
15;15. In case of FLAT curve, the induced pressure under & above the wing must be Equal (no difference) due to same curvature.. Only the underneath Flow is Engulfed/stagnant...in the opposite of Free flow on above that creates (positive) pressure difference. As already commented (below).. Bernoulli equation CANNOT be applied to "2" divided /separated Flows/streams of fluid(air, this case).. only explain each of them separately (either upper or lower of Airfoil.!!) None of them related except they are in the SAME PIPE/TUBE/TRENCH (non-separated/UNDIVIDed).., sire.
His video and explanation, but Isn’t the “lift” really just the result of the differential pressure created by the high and low pressure of the wing, and the lower pressure above the wing is creating a “vacuum”, so the wing is basically being “sucked” up by this vacuum?
On a real airplane, yes it will be able to fly, you said it yourself, like the model airplane, you just need to massively overpower the real engine. Will it be able to fly in a great controllable manner, without turbulence, without risk of accident? Will it be efficient? I believe these are different questions, right?
Same thing - the pressure difference makes the air move inside bringing the particles with it. Sucking something into a pipe means creating an underpressure in the pipe to establish the pressure difference, it's a colloquial term.
@@ottonormalverbrauch3794 Yes. But in colloquial terms talking about a blower because the normal pressure air flows into the pipe bringing the particles with them, would be confusing. Physically sucking does not exist since the lower pressure side does not exert force, but in colloquial terms it is handy. Sipping from a straw or sucking on the straw is a useful term for every day, saying "create an underpressure so the atmospheric pressure pushes the fluid into your mouth" would be useless from a conversation perspective. So just accept colloquial terms and scientific terms have their separate fields of usage...
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Early in my CFI career I had an aerospace engineer as a student. I stopped charging him for ground school when it came to aerodynamics 😅. Thank you, Sven. If you see this, you were my favorite student/instructor!
This was a great video! I studied engineering in school, so I knew a lot of aerodynamics before I learned to fly. One of the really frustrating part of flight school was getting past the half-truths being taught about how wings work. Eventually I figured out that I just had to learn what they were teaching so I could parrot it back on the tests and pass the checkrides. It was doubly frustrating when I was prepping for my CFI and had to teach this garbage 🙂
I'm also a sailor. As you noted, sails are just airfoils. But more than that, the underwater fins on a sailboat (the keel and rudder) are also generating lift, except that it's hydrodynamic lift. And while sails are asymmetric airfoils, the keel and rudder are (almost always) symmetric. It gets interesting. One of the fun things is that if you take a sailboat that's standing still, like when you just released it from the mooring, you need to get both the sails and the keel flying. The sails will generally get attached flow before the keel does, and the boat will mostly be moving sideways. You need to turn the boat to reduce the keel's angle of attack until it un-stalls and then you can begin to sail normally.
I am a combustion engineer and private pilot, and I had to be careful in the same way regarding the FAA engine terms detonation and pre-ignition! (In reality light knock by itself is not damaging while pre-ignition is the kiss of death leading to immanent piston failure in the cylinder it occurs in. Although the actual technical meaning of pre-ignition this is aligned with is when combustion in a hot cylinder occurs prior to the ignition spark.)
It was funny too when my CFI asked me why maneuvering speed for a given aircraft changes with the amount of weight that is onboard - I couldn't help but blurt out "That means the wings are not the weakest link!" Because the maximum force (lift) the wings can generated at a given indicated speed doesn't change with aircraft weight, but the lighter the weight of the airplane the more acceleration it will experience from that same lift force at that speed. And, since in theory the aircraft is certified to a given fixed G-level (acceleration rate) a lighter loaded plane will experience that acceleration rate with a lower amount of lift force and therefore at a lower speed.
Dude I'm working on CFI soon and I've got a lot of strange looks talking about this stuff!
I always wondered why the keel was so huge. Makes sense now!
Exactly. I'm a sailor too. The rudder plays a role too. It's a brake. Balance the sails and keel forces through proper sail trim and ballast location, and you can steer the boat without a rudder upwind. You'll go faster and take less of a beating if your balance the helm and trim your sails properly. My theory about aerodynamic lift and aircraft wings relates to airspeed, displacement and aingle of attack creating bouyancy as long as airflow remains laminar.
How else to explain sustained inverted flight? Bernoili theory says an inverted airfoil will create it's lift vector towards the ground lol. Bouyancy says the shape of the airfoil plays a small role relative to airspeed, surface area, and angle of attack, but I'm an architect, not an aerospace engineer....
;-) displacement and displacement and
it does sound like the airfoil is not that important to being able to fly, and that while a flat wing might be less efficient, and have a higher stall speed, it should still work,@@TheWilliamHoganExperience
My father was an aeronautical engineer and he always said "If you put a big enough engine on it, you can fly a barn door . . . broadside." Early in his career he did some work on airfoils for NACA [yes, that's with a C], but most of his career was designing gas turbine engines, so he may have been a bit biased.
NACA>NASA
I mean, it works for the F-15
I think you have to have some airflow that lifts the barn door up instead of pushing it down, but I agree...once you have that, you could put a strong enough push on it to get it flying.
The only substitute for power is more power
Funny as I remember sticking things out of the car window as a kid, I built a rough model of a 707 out of cereal boxes and similar to the flat wing was only creating “lift” with aoa however when sticking a model airfoil out the window no pitch was consciously added but I could still feel the lift being generated from the proper airfoil shape. Interesting side note, I was kicked out of science class for debating the Bernoulli principle with my science teacher, even used similar wind tunnel footage to back up my argument.
Unfortunately, too many teachers are bad at handling situations where students argue in contrast to the prescribed material.
Most teachers don't like questions that aren't in the book.
@@carlosspiceyweineify you should have used a sail boat as your rebuttal. Take the airplane turn it on it’s side stick it down into the water, now the airplane becomes a sailboat. Every principle is the same for both of them, air flow, position of sail, position of the wing, no sail zone, stall zone. It’s all tied to the wing and sail, speed of air flow, fast over the wing, fast airflow around the sail, slow under the wing, providing pressure and lift, the sail, same thing. If you can fly, if you csn fly, you csn ssil.
Flat wings can create lift if enough air is directed downward. If curved correctly the wings will do that more efficiently and with less drag.
@@giusdbg - I am sorry, I do not understand your comment.
My Kite!
Great video. I use to build foam planes for air to air combat, and since the whole purpose was to crash them, I'd just use a flat wing design. In order to get any sort of lift, we'd use higher RPM motors, and big batteries. They flew like bricks!
Lift is generated by the fact that the Navier Stokes equations are so ugly the earth pushes them away in disgust.
Hahah, 1 thumb up for you!
Thank you for this informative and straightforward video Captain! I'm a Ground Instructor at a school in the Philippines researching ways to better teach my PPL students. This video cleared my misconceptions regarding lift and now I get to teach my students accurate information about it 😁
He's wrong. More than once.
@@crimony3054 About the only thing I particularly disagreed with was that the light high wing, full sized plane COULD fly, it just would need more power and possibly a bigger wing surface area. His graphic of a flat wing with a square, sharp cornered wing wasn't helpful as there's nothing to say you couldn't round off or taper down to a thin leading edge either. Sure, it wouldn't work on something like a Cesna 150 with it's stock, gutless engine but, give it more power, say about an extra 50 hp and it could. Of course stall speed would be higher too but, it would work. I'm sure as hell not intending to waste a fortune to test it but, the fact it does work fine on small scale DOES prove it can work on a larger scale too, it's just not 'the best way' to design a wing.
I think the moral of this story is that a flat wing will fly within a limit range of angle of attack. A curved wing will greatly extend the useful range of angle of attack, making the wing more versatile and practical.
Fabulous video. This 20-minute video puts 3 years of undergraduate Aerodynamics studying Aeronautical Engineering to shame. I remember the headaches I had trying to understand this stuff and unlearn the misguided falsehoods that had previously been taught. I have to say though that I shuddered at the Navier Stokes Equations, still. LOL.
And when sticking flat plates out of car windows it's easy to confuse perceived lift for the drag you are actually inducing as you increase the angle of incidence. Thank you Magnar.
5:15 - What causes this centripetal force?
A great video! The development of early wings relied on trial and error to determine what worked best. A curved leading edge set at an angle to the oncoming air developed the most lift for the least resistance. It worked in a wind tunnel and it worked in practice. Mathematicians have been trying to catch up ever since. As you pointed out in the video, how and why a wing develops lift is determined by scale. Insects fly with wings that work well when air has the consistency of water, at that scale. Model aircraft can fly with flat boards for wings because they have an excess of power for their weight. Larger aircraft have to be encouraged to fly with finesse and wings that can be modified to be efficient during the different phases of flight with slats and flaps. There is no one size fits all explanation for how all wings work at all scales. For years, aerodynamicists insisted bumble bees couldn’t possibly fly, except they do, and very efficiently too!
I've had a number of aeroplanes that fly perfectly with flat wings but they're all very light small models made from Depron or other foam sheeting. Their main advantages are simplicity, low cost and, of course, fun :)
A very interesting video that explains a lot. Certainly different aerofoils are suited to different applications - I like thick aerofoils in my models because low speed manoeuvrability is what I seek.
Fantastic video, brings back memories of Fluid Mechanics ME 2032, in college. My professor was doing a lot of research on wing aerodynamics and his teaching basically followed this video. So I am sitting here at 2:45 in the morning thinking about a course I took 43 years ago, thanks so much for the excellent explanation of lift.
Glad you enjoyed it!
Interesting. The importance of the curvature of the upper surface explains at lot, particularly why many WW2 fighters had wheel-wells extending almost a third along the wing-span, yet still, manged to get off the ground quite happily. Always wondered about that.
That's also why ice on the upper surface can be a massive problem but on the lower surface nobody really cares.
Regarding ordnance over or under the wing, airflow in a low pressure zone is more susceptible to flow separation.
As you said both sides of the wing are crucial, at a given AoA a pylon on top of the wing might cause flow separation behind it, while the same pylon on the bottom has its flow still attached.
In automotive applications rear wings are sometimes suspended from the top (swan neck wing) to make use of this effect, just in reverse.
The reason is the pylon introduces additional viscosity forces in the Boundary layer, which pulls the separation point upstream. Not important on the underside of a wing, because the whole point of a sharp trailing edge of the wing or flap is to force the flow to separate early.
Magnar, great video and visuals. Arguably the best practical video on lift. Permit me to defend the humble and unloved flat wing which is used on thousands of simple planes including the Cub. I'm talking about the horizontal stabiliser, of course. The little wing behind the big wing. It is simpler to manufacture and its efficiency can't be that bad or we would just camber it by inserting a few ribs. I see graphs for angle of attack vs coefficient of lift for flat wings that suggest they stubbornly continue to produce lift at high angles. Thus the plane can never lose stability or sufficient elevator authority to recover from a stall by pitching down. Is this a factor in their popularity? After 120 years of flight, the flat wing is all around us at least at smaller airfields.
Ah, the wonderful Cub! Yes, many small airplanes do indeed have a flat stabilizers. The purpose of the horizontal stabilizer is to produce a downward force. This is achieved by mounting the stabilizer with a negative angle of incidence, which means the stabilizer meets the airflow with a certain angle of attack. Moving the elevator up and down changes the curvature of the stabilizer, and hence the lift.
While many old aircraft do have a completely flat stabilizer, most light airplanes do have a stabilizer with a thicker, symmetrical profile as it is aerodynamically more efficient and provides more strength. Hence, no need for struts.
Go to an airshow and watch so many aircraft, some of them normal aircraft, flying upside down with no problem. When I saw this as a young child I knew right away that the traditional explanation was at best only part of a more comprehensive explanation. I noticed then that those airplanes flying upside down maintained a relatively high angle of attack. So yes, the wings should have smooth curves to reduce turbulence, and we know from available observations that angle of attach can and does in certain situations provide enough lift to sustain flight. The Bernoulli physics also can dominate but as shown when ordinary planes fly upside down, it doesn't always dominate. Given a propulsive mechanism what matters when it comes to lift is what the air was doing before the passage of the aircraft and what the air is doing after the passage of the aircraft. The force of lift can be accurately calculated as the net rate of change in momentum experienced by the air in the vicinity of the aircraft (just point the force in the opposite direction, for every force there is an equal and opposite force). The rate of change in momentum of the air in the vicinity of the aircraft is actually the force exerted by the air onto the aircraft (just point the force in the opposite direction) . When you can see the vector describing the rate of change of momentum of the air then you can see how this vector can be resolved into downward and forward components. The downward component of the rate of change of momentum of the air is the lift and the forward component of the rate of change of momentum of the air is the drag.
I did not get this out of a text book. I got it from observation and from experimentation when actually designing, building and testing flying devices.
There's a video of Alexander Lippisch taking about this. He uses a small smoke tunnel to demonstrate.
A flat plate, given a bit of "A" incidence makes the air act as if it's passing over a camber.
The air over the top is driven to pass the chord faster than the air under, even before the alpha slows and compresses the flow under it.
The difference in pressure causes lift.
True that the continuity of mass flow causes air to accelerate over the top to faster than equal transit time speed because the pressure has dropped enough from the delayed transit to accelerate that lower density sufficient to keep flow rate out connected with flow rate in.
This pressure drop bends the momentum of the.wider airflow at ambient pressure downward.
This is an incredible explainer! Not only does it present an incredibly thorough explanation of lift, it also manages to disprove nearly all of the common misconceptions about lift. I think the flat plate example at the end was really important, since most people's anecdotal experiences with lift are of this nature (sticking a hand out of a car window, sign being blown away by the wind, etc.), which could be a common source of misconceptions.
How do observations of the lift created from flat objects create misconceptions about how lift is created? In particular if there is a conception that a shape needs to be curved to create lift.
Relative wind.
Great explanation on the theory of lift. I see that slide you showed with the system of differential equations, lift is not a simple proposition. On what you said about the importance of the shape of the wing leading edge: the gist of many STOL upgrades is to add a cuff, of which I have installed and flown a few, and can attest to the marked change in wing performance. As for a barn door flying: I am a structural engineer and often have to design for very high wind uplift forces on roofs, sometimes more than the weight of the building itself.
Thank you! At last someone who explains it the way I understand how this works. It made my day!
To make it simple for all: Airfoils are designed to reduce DRAG. LIFT is created only by deflection of air or fluid (Angle of Attack). By reducing DRAG of a surface even at high angles of attack, you increase efficiency and you can delay airflow separation. But the Lift is never created by airflow shape. This is why airplanes can even fly upside down without being sucked to ground.
No, airfoils always create drag when lift is created
@@biingyin5522 He didn't claim that drag was eliminated.
Airfoil shape does matter though, in the sense that a more cambered airfoil creates more lift than one with lower camber at the same angle of attack. Look up Cl-alpha curves for the NACA 4412 compared to the 2412.
@@andreamusso1469 If you are aiming for maximum lift and low speed handling, power and meneuverablitly is more important than wind channel results. On my Savage Cup, the max. Lift was great before it was not. It had a very unpleasualble stall and got from tame to nasty way too fast...
@@Ozbird-72 What I mean is that angle of attack is not the whole story when it comes to lift. In fact, the traditional way of determining airfoil characteristics is by analyzing angle of attack, camber, and thickness separately. So it's not just your alpha that determines lift, otherwise there would be no difference between different airfoils.
5:10 - So is this same theory as in 8:49? Because you mentioned Bernoulli. So I don't understand how it is applied?
6:37 I understand how bernoullis view also provides an explanation for the downwash but how does the newton way account for the pressure difference part?
I think he is referring to the pressure gradient force that must exist perpendicular to a streamline when that streamline is curved. From streamline curvature you can infer lower pressure inside the curve, higher pressure outside the curve.
The common misunderstanding is that either the "Bernoulli" pressure drop or the "Newton" downwash can explain lift. This is false.
Both must be integrated to explain lift.
The pressure drop bends the airflow at higher ambient pressure above, downwards.
So the downward flow of mass results from the pressure drop's force.
The force from one is numerically equal to the other.
And you cannot have lift without both: a suction cup on a refrigerator can stay above the ground because the load stresses from its weight are contained within the fridge against the ground; if the fridge wasn't there, the suction cup's pressure difference would need to force air mass downwards (which obviously it isn't designed for).
So, pressure is not enough without a rigid support structure. Mass momentum must be directed downwards to complete the other half of the requirement for lift.
@@davetime5234 👍
Isn’t it really the second law, lift being a reaction force caused by the turning of the flow downward. This imparts an upward force which is lift. The greater the curvature the greater the pressure gradient which keeps the flow attached. The less curvature like in Whitcomb wings a greater adverse pressure as the flow moves back. Bernoulli applies to objects in a closed envelope.
Flat wings fly just fine, as long as the α doesn’t get too high causing the flow to separate.
Very good video.
You just called my favourite aeroplane a kitchen table.
lol he's a savage
Those on the receiving end of its firepower had other names for it!
So, the lower surface contributes to lift by being pushed upward by the incoming ram air, while the upper surface contributes to lift by creating a venturii effect between the upper wing surface and the undisturbed atmospheric pressure air in the higher air layers, that accelerates the air thats right next to the wing, creating lesser than atmo pressure ? Plus the smooth, gradually curving upper surface allows the air to flow smoothly without detaching and creating rotors that could hit the wing from above ? More or less ?
Most interesting. And it makes me marvel even more at the genius of the design of Concorde's wings!
I Still doesn't understand why the flowvsticks to wing on both upper and lower side. Someone Please explain it
Wonderful vid, much better than the text books on wings course. In rotary wing flying, we refer to the combined downwash from the blades (rotating wings) as "induced flow". It is a column of descending air, drawn down, like a giant fan. This creates a large portion of the experienced lift, as evidenced by hovering in ground effect on this compressed column "air bubble" under the aircraft. It also temporarily reduces the lift when the transition to forward flight is made, as the aircraft moves off this compressed "bubble". (The lift increaess again for other reasons as air speed increases) This down wash is also observable on large aircraft with smokey engines (C130 for example). The distance and velocity of the descending air behind the aircraft is stunning. For interests sake, most modern rotary wing blades are symmetric, therefore they only produce lift with a positive AOA, and therefore also autorotate better in a unpowered situation with a low blade attitude (still positive AOA though). Finally, a nice experiment is to place a spoon under the kitchen tap, in the stream of water, observe the spoon move towards the side with convex curvature, and observe it redirect the stream of water towards the concave side; this is precisely the effect on the air.
Amazing Explanation ! One could have added that for supersonic flight, the flat plate is in fact the most efficient airfoil type because the air can flow around sharp corners by expanding after the bend. The sole reason fighter jets have cambered and thickened wings is because they have to go through the subsonic regime as well.
3d aerobatic foamy planes fly best with a flat wing and square leading/trailing edges. They get weird when you put a proper airfoil shape in the wing.
But it is somewhat of an extreme example. They’re built with very light wing loading, a very aft center of gravity, extreme control surface deflection angles (~45 degrees), 2:1 or higher thrust to weight ratios and fly at a walking pace, in a stalled condition during much of the flight. I suppose it’s more akin to thrust vectoring than lift flying a wing, when the downward deflection of the prop wash deflecting off the wing and stabilizers is enough to keep the plane aloft as well as control pitch, roll and yaw.
So while in my mind nothing flies better than my Crack Yak flat plank foamy model, I wouldn’t want to climb inside a full-scale with a flat plank wing.
I have thought about this issue for a while. I am a sailor. The sail structure does not create a very big difference between the path length over the back vs over the front. In watching your video there was a lot of emperic discussion of airflows, but I'm interested in what is the percentage of newton force vrs. Bernouli force in the wing. This really needs to be shown for airfoils, bicurved wings (which enter the air more smoothly than a piece of plywood) and sails. A piece of plywood tilted at an appropriate angle will fly, but may not be optimum. However, what is actually gained (in % of lift) by the airfoil? This value will vary depending by the angle of attack, but since planes fly upside down, it can't be huge if tilting the wing a bit more overcomes the effect. For your underwing loaded aircraft, are you sure this doesn't change the angle of attack? If so, where is the data?
There's is no percentage of Newton force vs Bernoulli force. Bernoulli's equation can, by mathematics, be derived from Newton's second law of motion, and vice versa. In other words, they are describing the same phenomenon: The relation between air pressure and velocity in an airstream. Lift is easier to understand when we apply Newton's third law. Scientinsts only use Bernoulli's equation to calculate the ratio between air pressure and velocity.
The "wing" in the wind tunnel at 1:59 has the same profile top and bottom, which makes it essentially flat, and is tilted up much higher relative to the incoming air than a wing would be in flight. And then again, your diagram at 4:27 shows a symmetrical wing tilted up toward the air flow which would work the same way as a flat wing at a high AOA. And your diagram at 5:39 shows low pressure up to the left but this area would actually be high pressure, and in fact higher pressure than below, because the air is getting deflected up more and compressed. Look at how the lines in the wind tunnel get squeezed together. The low pressure area is to the top right, after the air flows over the hump at the top of the wing, where a relative vacuum is created. The air under the wing slows down because it's hitting the resistance of a high pressure area under the wing, the air over the top speeds up because it's getting sucked into the rarefied space over the trailing top of the wing. If there was low pressure at the front of the wing then a plane with a symmetrical airfoil would need no thrust at all because the low pressure formed by the shape of the wings would pull it forward. When a plane flies through the air, is all the air in the sky above it pushed 3 feet to the tail of the plane? No, air below the wing is pushed forward. This is the drag. Also if you look closely at the airflow in the wind tunnel you will notice that the 2 lines that pass closest to the top of the wing are slowed down relative to all the airflows above them. And I guarantee that we extended those lines out that you would see that those lines over the wing are not accelerated, but in fact the lines below and directly above the wing were decelerated, which again, is drag.
WONDERFUL!!
It all comes back to physics in the end!!
When a discussion gets down to F=ma, I know we have found the right teacher!
It is just a little disturbing to hear how many people have been mistaught or misunderstood some of the basic fundamentals of physics.
We were taught Bernoulli's Principle by deriving it from Newton. Until you get to Quantum, everything goes back to Newton somehow.
Thank you for your feedback!
Pls. will you solve the Navier-Stokes-Equation for us? and pls in n+1 dimensions!
Hi Magnar. That wooden model plane at about 18.30 in your video. Do you know what brand those little Micro Servos are that operate the ailerons. I want to get some like that. Can you advise? Thanks Brian
I'm sorry, Brian, but I don't know.
Great explanation in the entertaining video. Excellent presentation in relating the work of Bernoulli, Neuton, Navier-Stokes and others. The discussions and opinions (in comments) to these videos interesting and entertaining as well.
The "flat wing" explanation (17:40) seemed a bit less complete, as only referenced a square leading edge airfoil, to which I agree with the conclusion. A round, or sharp leading edge would reduce air flow separation and drag. The thickness of the bubble and reynolds number at the scale of the wing plays a role. If the bubble is thin, it can act as an curved boundary for the air flow above. This not much different that a wing on a fighter jet at cruise speed. It also doesn't touch on flat surface aircraft like the F-117 Nighthawk.
Model aircraft have the advantage of Reynolds numbers working in their favour, in addition to having a low wing loading, so less lift is needed (and efficiency of minor consideration). A discussion of Reynolds number would have been distraction here, as is a more advanced topic beyond the focus of this video.
Nice work keeping this video focused, educational and entertaining.
You can get lift from a brick if you get it moving fast enough. Notice he says the flat wing fails because it "stalls". Okay, if it's stalling put some more power behind it and increase the velocity. That's why his belief that a scaled-up wing won't generate lift is faulty. A flat wing won't generate lift because you can't get it going fast enough to generate lift, not because it won't fly. Impractical for sure, but it will fly, and his reasoning is badly flawed.
Nit picking here; it seems, at first blush, the flat wing is not the problem but how you treat the leading edge. Needing angle of attack so air molecules can transfer momentum, being able to adjust the leading edge (say a nice wedge like the Starfighter's) would help your flat wing a lot. Then to confuse matters more, in really fast planes, shock waves created by the planes forcing its' way through the air provides the majority of lift (at least from what I've read - I don't really grasp it all that well) and in reality some planes get a huge percentage of their lift via the shape the body of the plane (e.g. F-14) and the upper side of those planes get very complicated. The thing gets complicated quickly. :)
You are absolutely correct. I included the F-104 in the video because it has an almost flat/symmetrical wing. It is optimized for supersonic speeds and doesn't work at medium and high angles of attack. At low and medium subsonic speeds, the leading edge flaps and trailing edge flaps must be deployed to provide enough lift.
RC fliers often use flat wing radio control planes to have fun because they are much easier to build. Square box fuselage and a flat wing are made very quickly.
I am with Frise. A kitchen table can produce lift. Inefficient, but that's not the question. A flat plate is a symmetrical profile with 0% thickness. Even if you add thickness and a horrible leading edge it still retains some of the properties of a symmetrical profile.
Do you think a paper plane can't fly? It would be capable of sustained flight with it's own means of propulsion and basic ailerons and rudder.
In fact, there was a Kickstarter project at some point that added a tiny motor and LiPo battery to any paper plane you made, and would let them fly until the battery ran out - under remote control no less...
Good description. Very important (3:09) that conservation of momentum (or the definition of force as "force = mass * acceleration", Newton) and conservation of energy (Bernoulli) are related. In fact, the basis is always the equilibrium of forces on the fluid element, and the transition to energy occurs simply by multiplying a force by a distance, and force * distance = work, i.e. energy.
In the end, by Bernoulli it can be explained that the static pressure must decrease in a pipe constriction because the pressure energy p*v (with v as specific volume) or p/rho (with rho as density) must decrease, because the kinetic energy increases (forced by the channel contour via the continuity equation). But in reality this is terribly unclear, because we see a force (which, for example, is capable of lifting a column of liquid at the narrow point of a Venturi nozzle) - and where does this force come from? We can see the explanation here (approx. 5:05): The fluid element describes a curve, and similar to how a car driving around a curve experiences centrifugal forces, it is the same here with the fluid element. The centripetal force that keeps it on the track is applied by negative pressure or vice versa: The centrifugal force of the fluid element on the curved track causes the negative pressure.
This is a purely mechanical explanation of the Bernoulli effect, which does not require the concept of energy and is immediately obvious.
I don't quite agree with 6:26: "A wing creates lift, because it is deflecting air downwards."
The statement sounds a bit like the lift is only produced on the underside, because only the underside deflects air downwards.
Basically, the statement is correct: the aeroplane is moving in air, i.e. in a fluid. Therefore, the law of conservation of momentum for fluids must apply, which roughly reads: sum of all forces + sum of all momentum flows = 0. Momentum flow is the product of mass flow * speed difference. This means that the weight force of the aircraft must be balanced by an impulse flow of the same size. This can be clearly seen in a helicopter: It sucks in air above the rotor and blows it downwards at an accelerated speed.
The aeroplane does something similar: on the upper side, it sucks air into the negative pressure zone of the wing, which is located above the wing, and on the underside, it deflects air downwards. The question is: How large is the mass flow and how large is the difference in speed? With a helicopter, the mass flow is small and the imposed speed difference is large. This is very inefficient. The same applies to the propulsion of aeroplanes: a pure jet propulsion system as used in military aircraft (which works on the principle of "small mass flow, large speed difference") is much less efficient than an engine with a large fan.
What applies to the thrust force also applies to the weight force. Compared to helicopters, aeroplanes use "small speed difference, big mass flow" to compensate the weight force. It is therefore much more efficient to keep the mass of an aeroplane in the air than the mass of a helicopter.
I was a bit confused:
"Very important...that conservation of momentum....and conservation of energy (Bernoulli) are related". It's true that they are related, but they also are distinctly separate properties that must be accounted for separately.
For example, momentum is tied to direction, so the direction of momentum is conserved as well as the quantity, but energy has no direction. Also, energy is much more sensitive to changes in speed than momentum. So, the choice between mass or speed for making a given value of momentum makes no difference. For energy it makes a huge difference. (this has huge consequences for understanding the efficiency of wings for flight, and bypass ratios for fuel economy in turbine engines).
"momentum (or the definition of force as "force = mass * acceleration", Newton)"
Momentum is not the same as force. Force results in a change in momentum, and a change in momentum results from a force.
"similar to how a car driving around a curve experiences centrifugal forces, it is the same here with the fluid element. The centripetal force that keeps it on the track is applied by negative pressure or vice versa: The centrifugal force of the fluid element on the curved track causes the negative pressure.
This is a purely mechanical explanation of the Bernoulli effect, which does not require the concept of energy and is immediately obvious."
The problem is, you haven't accounted for the increase in tangential speed around the curve, which Bernoulli, in terms of conservation of energy does address. Change of direction does require energy, but so does increased speed along the tangent of that curve.
So, "compelled to follow a curve" doesn't work as an explanation for "Bernoulli" (conservation of energy). But in fact, you need to account for more than conservation of energy.
"A wing creates lift, because it is deflecting air downwards....The statement sounds a bit like the lift is only produced on the underside". But deflection doesn't rule out deflection by the low pressure area above the wing.
The fact is the total deflection of air (the total imparted change in vertical momentum of the air), is fully equal to the total lift force.
"With a helicopter, the mass flow is small and the imposed speed difference is large. This is very inefficient. "
That's a bit misleading. A helicopter relies on large mass flow with relatively lower speed of that flow. Of course there is an energy penalty for a helicopter in hover vs forward flight because forward flight allows even greater mass flow which increases efficiency. But helicopters can have relatively low power engines by increasing the blade size to increase the mass flow at the expense of the flow velocity (subject to other engineering limits).
But both helicopter and fixed wing aircraft rely on large flow of air mass directed down.
One important aspect of the wing profile is the requirement for height sufficient to create a mechanical structure that is strong enough to lift the load of the aircraft. I wish your video had mentioned how this element factors into the engineering compromise of practical wing design.
Exactly. I have noted that every video I have seen on this subject ignores the fact that there is one constraint that always applies first.....it is that the wing HAS to have a finite thickness. This is implied but not stated in the final part where the 'flat wing' is shown not as a flat thin plate but as a rectangular box. I would expect that a thin plate would be more efficient for lift than box section shown, although lacking structural strength. Starting with a box section and then knocking off the corners and streamlining to reduce drag soon leads to a rough wing section. Aside from that I think this is a great video. Thanks Magnar!
Thank you for this. I always wondered about the details of Bernoulli vs Newton. I see that it is a bit complicated now, but makes sense. It is just different ways of viewing the same overall process.
I would disagree with: "It is just different ways of viewing the same overall process."
I guess what I'm saying is, I disagree with the implication of the video's title: you can explain lift with one concept or the other.
In truth you can't explain lift without the entire picture: to achieve a downward change in air momentum causing lift, the downward force causing that downward acceleration needs to be included in the explanation.
The pressure difference is that force.
But you can't explain lift only with a pressure difference either: you need to expel mass downward, because there is no external structure to support the load forces against the ground.
So, the supporting force is the downward expelled mass, and it is expelled from the force of the pressure difference.
As I wrote elsewhere today:
quick summary:
Lift is the asymmetry of a solid turning the air (explains both camber and AoA).
Mass flow continuity means speed must increase proportional to the constriction A1/A2 (the ratio of two cross-sectional areas: an undisturbed incoming area of flow, to the effective constricted area of that flow due to asymmetry).
This speed increase drives a conservation of energy, static pressure drop:
pressure = constant - (1/2)x(mass density)x(v)^2
The total pressure difference is equal to lift.
Which forces air mass down, also equal to lift:
P x A = F = ma = d(mv)dt
Or the force of pressure (as force per unit area times area), equals the change in vertical momentum of the air (again, both equal to lift).
This directly ties asymmetry as the fundamental principle to both the "Bernoulli issue" and the "Newton issue".
How can I apply this to paper airplane design? Is it best to have a thick, rounded leading edge? (Having curvature over the full wing causes the planes to pitch down if not compensated by a tail.)
Apparently there are numerous aircraft, stunt planes, with flat wings, or at least symmetrical wings. Most of the lift is through the right angle of attack ... and they can fly upside down with the right angle of attack
The curvature of the wing, together with the angle of attack, is essential for lift. Aerobatic aircraft have pretty thick, asymmetrical wings. Some supersonic airplanes like the F-104 have almost flat wings, but they have flaps to allow for slow flight for take off and landing.
@@FlywithMagnar Well I'm sure you know better than I but I understand that some aerobatic aircraft have thin, flat wings. In any case, the fact that some planes can fly happily upside down says to me that the angle of attack is the primary factor in lift, and that wing curvature is secondary, perhaps contributing to efficiency.
And yes, I am sure take off and landing are not handled well upside down.
Can I use this analogy. Cause this is how I visualise.
When you through a skipping stone in water. Where the air is the LOW pressure and the water the HIGH(denser) pressure region. Every time the heavy stone needs to be in air it needs to hit the water with the flat and larger surface area. And every time it does hit the water it loses its energy. So aircrafts are fuelled to continue that motion, and with the help of flaps to continue the upward lift.
Is it the boundary layer separation at the top surface of the wing that creates the pressure difference.
6:25 Or pressure difference is not important at all to create lift?!
You are talking about two different mediums: Water and air. While they have some common properties with it comes to fluid dynamics, they have very different density and viscosity. The stone is moving through the air because it has a high kinetic energy. And it skips the water because of the smooth surface of the stone and the relatively high density of the water. As the energy dissipates, the stone will eventually sink into the water. Therefore, you cannot compare skipping stones with wing lift.
Regarding your quesiton: No, the boundary layer is often disregarded when lift is explained. It is the difference in static air pressure between the upper and lower surface of the wing that creates lift.
Ryddig og konkret samtidig som det er lærerikt.
Topp jobb.
This is so true that will also explain the Magnus effect on a rotating object in an airflow. if you think carefully at this video contents the explanation of the Magnus effect will outcome better than it is usually explained.
You must understand upwash acts against downward atmospheric pressure , hence low pressure region around the maximum camber and leading edge. After this opposing upward pressure is redirected back downward , a pressure recovery is established on the upper surface reducing drag and increasing lift.
Ref to my comment at 15:34 in your video. I was saying that no matter what the shape of the wing, you get a low-pressure area on the top and a high pressure on the bottom. Low pressure does not suck the wing up, it's the higher pressure on the bottom that pushes the wing up. Instead of a diagram with a big arrow labeled LIFT pointing up above the wing, replace it with an arrow labeled PUSH pointing up below the wing and you have the same effect. Bernoulli describes the airflow but it's the pressure differential (Newton) that pushes the wing up.
Sorry but no. As the video rightly stated, it is neither the low pressure nor the high pressure that results in lift, it is the difference between the two. It is just a matter of semantics to argue about whether the wing is being sucked up or pushed up, the ‘net external force’ is the same either way. Nonetheless if you look at the pressure plot for a typical airfoil at moderate angle of attack you will find more ‘low’ pressure on the upper surface than ‘high’ pressure on the lower surface (shown in the video). Hence if you want to talk in terms of pushing and sucking - and you do - it is more sucking. And there is actually an engineering reason to be aware of that, but I will let you try and figure it out.
As for the argument of whether to label an arrow “lift” or “push”, just label it how you want mate. But know that the word the industry has alighted upon since about 120 year ago is lift, so good luck convincing all the people who actually work with this stuff to switch over to the jargon of dhy5342 of youtube.
@@XPLAlN Regardless of 120 years of convention and labels, the scientific, physical forces of nature only recognize pressure as a force; "suck" does not exist. Only pressure can exert a force on an object such as an aircraft wing.
Show me, if you can, any single instance where 'Sucking" or low pressure effects a reaction.
@@dhy5342 Lol. I know there are a few people who object to the word suck. I don’t care, it is a purely semantic argument because we define it to be what we want. It is arbitrary. As I said, use whichever word you wish to. But you believe “lift” should be replaced with “push”. You actually wrote it. And I am telling you that is not going to happen because all the people who need to actually work with this terminology are happy with what we have. So off you go with your words back under your little bridge, or span if you prefer to call it that, I don’t care which.
@@XPLAlN “Who is so deafe, or so blynde, as is hee, that wilfully will nother heare nor see.”
---John Heywood, 1546
"Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first."
---Isaac Newton, 1686 (Principia Mathematica Philosophiae Naturalis)
'Hear now this, O foolish people, and without understanding; which have eyes, and see not; which have ears, and hear not'"
---Christian Bible, Jeremiah 5:21
"Absent a rope or some other pulling method, there is no lift from above, only a push from below"
---dhy5342, 2023
@@dhy5342 Pure semantics. No substance.
First of all, in flight the air is not “traveling over the wing”. The air is just floating there minding its own business when suddenly this wing comes along and shoves it out of the way. I’ve never bought into the conventional theory of lift. Thank you for clarifying some of the flaws in the conventional reasoning.
Flow is relative to ones perspective. Think of a boat in the water, is the boat traveling through the water, or the water flowing by the boat?
The view of this may differ if a boat is in a calm lake, or traveling upstream in a river that is flowing at the same speed as the boat. A observer on the show may have a different opinion that to the sailer in the boat depending.
There doesn't seem to be a conservation of energy in my reality. There does seem to be a conservation of momentum in my reality.
What about COANDA effect, air will follow curved surface … ie a back of a teaspoon held under a running tap
@@47chester Sorry sir, you won't get anywhere in pilot training, checkrides, or earn a CFI cert citing Coanda effect it is irrelevant.
Pfft! Come on, man. Whether the wing travels through the air or the air travels over the wing is the same thing!
The best way it was explained to me, is the air particles stay longer and accumulate together pushing up the wing. The particles on the top, just want to get out of the way, making less resistance - pressure.
My theory: bird poo and insect poo (both being flying creatures) is heavier than air when it dries. So when it is first poo-d (is that a word?) it falls on the upper surface of the wing.
Once it dries, it becomes *almost* lighter than air. But when cooled with a draught of air, it becomes much lighter than air and lifts the aircraft into the air. This is why there is more lift on cold days.
This why space rockets are usually white - they are covered in bird poo for extra lift. In some videos you can see the ice fall off that they use to cool the poo.
Employers take note: I am available for hire by major airliner design bureaux, but only 3 days a week. The rest of the time I am too busy cleaning the poo off my car bodywork to prevent it skidding on fast corners and going over top of hills on motorways.
bird poo can be lighter than air but only if you reduce the volume of the air by compression
Ref 'flat wings' on a powered aircraft (I've posted this comment on its own) provided the leading edge shape is not two 90* (sharp) corners like a plank of wood, but rather has a rounded leading edge (more like a worktop 'nose') with the rounded shape upwards, then despite say 95% of the wind cord being 'flat' (top and bottom) it will of course fly perfectly well BUT will equally of course have a VERY 'nasty' (sudden/sharp) stall characteristic!!! This is one of the rerasons that as a general rule a quick glance at the wing shape (how 'fat' V how 'knife edge/skinny) in cross section lets you take a guess at the level of pilot skill required for that aircraft. (and yes my personal prefrence in paragliders is designs with VERY 'sharp' stall entry over wings with 'safe/soft' and highly delayed stall flight design.
Can u b using like a para sail wing on a wittle airpwane? Cause i b wounding tank veiw.❤
11:46 about "..Symetrical wing has the Streamline compressed, both upper & underneath the Airfoil (with zero angle of attack) to create air pressure.." (??) In such case ("0" Degree of Attack) the plane in high altitude, still can glide-over but it will "stall", cannot maintain the same Alitude at Horizontal line of flight.. means decreasing height.!! Only (as you mentioned) positive Angle of (wind) Attack to be added, otherwise, the total Weight of aircraft will make (horizontal) flight "STALL/Fall-down"
Would you be able to comment on wing sections designed for tailless aircraft? They typically have a trailing edge that curves up to reduce the nose down pitching moment that conventional wing sections have. Do they still have a lot of downwash behind them? I guess they must.
The reason wings were made thick in the beginning was to accommodate a hefty spruce spar. Modern materials require less so. If you inspect modern airfoils, you will see thinner wings for less drag and more efficiency. A F18 would never fly if it depended on the Brenoulli effect for lift and would never exceed anywhere near a Mach 1 speed. Lift is dependent wholly on angle of attack and thrust. More thrust lower surface area equals more ZOOOOOOM!!!!!!
While thin flat wings may not be as aerodynamically efficient as more specialized airfoils, the (macroscopic summarised) Bernoulli effect and the more fundamental (microscopic detailed) Newtonian laws both apply and explain lift generation. The angle of attack is the key factor for generating lift with thin flat wings. Newton's equations of motion are generally valid (outside of quantum scales and relativistic speeds).
What comes first, on top of the wing, is the question.
The low pressure comes first then the faster airflow.
Nothing can accelerate instantly; the air is forced apart by the wing.
The air in front of the wing impacting the air (which is actually the bottom of the wing),
(remember there is always the angle of attack)
is where the air is suddenly forced together, compressed.
And at the same time the air is forced apart at the back of the wing (which is actually the top of the wing),
where the air is forced apart faster than it can flow back together again, causing a vacuum, a low pressure.
Now we know very well that when there is a pressure difference on either side of an object,
that object wants to move in the direction of the lower pressure, because of the pushing force of the higher pressure.
on one side and the pulling force of the lower pressure on the other side.
Think about a door slamming shut. It slams shut because the air pressure on one side was greater than the pressure on the other side.
This moving door can be seen as the wing of an aircraft that wants to do the same thing,
that is to move from the higher pressure to the lower pressure.
Finally someone has provided an intelligent explanation, it is the angle of attack that generates a pressurev below the wing and therefore a lower pressure above the wing. I know very little about airplanes but the Bernoulli principle, bas I learned at school, does not make much sense. When, as a child, i used to throw flat stones above a pond of water, these would bounce up to half dozen times or more before sinking into the water, depending on the speed and the shape of the stone and the angle of impact. A wing glides on the air just as the stones glide on the water. The stones bounce at a much lower velocity than the aeroplane wings glide on the air because the water is much denser than the air but the principle is the same.
Unfortunately, stones skipping on water are at the interface between two different mediums, so that situation is quite different.
"Bernoulli" just tells you how much pressure drop you get for an imposed speed increase.
And the speed increase just keeps the mass flow rate continuous.
Very nice. I guess you can mount all sorts of things under the wings because the underside can't stall, or if it has, you may be inverted.
Yes but what about downwash?
My A.E. son referred me back here and the conversation reminded me of this. I point your attention to John D. Anderson's Aerodynamics book. He shows flat wing experimental data from the Japan Society of Mechanical Engineers. From the lift curves it does show about half the lift, but if the power can muster 25% more airspeed, it should fly, but with a stall AoA around 10 degrees, you're margin is significantly reduced.
In the video, I discussed a flat wing with a sqared off leading edge. If the flat wing has a rounded leading edege, it will be able to produce more lift. In the video, I show the F-104. Without the maneuvering flaps, it will not not be able to fly, unless it is moving very fast. A flat wing with maneuvering flaps is a modern copy of the wings used in the first airplanes, wich in turn is a copy of a bird's wing. The nature has been, and still is, an insporation for the engineers.
@@FlywithMagnar It seems obvious that to have that squared off L.E. and T.E. is counter productive. The basic comparison with a flat wing is to one with little thickness, so the blunt L.E. doesn't cause such a problem.
The Japan data is of a very thin wing similar to the common small. balsa model without the thick blunt edges causing more turbulence.
.
To land, the F-104 required engine air blown over the wing which was called Boundary Layer Control - BLC
.
However. . .
The Wrights also observed that the L.E. shape had a profound effect and If I recall correctly, a squared off L.E. appeared to perform best in their tests, but I think it was hardly more than an inch or two thick.
To my knowledge, the Wright brothers never tested a wing with a squared off leading edge. They ended up with a thin, cambered airfoil with a rounded leading edge. Here is a good description of the evolution of the wing profile: greydanus.github.io/2020/10/13/stepping-stones/
Regarding the F-104, bleed air was not blown over the wing. It was directed over the flaps from a duct inside the wing. It is indicated with an orange circle in my video at 10:48.
@@FlywithMagnar RE: Wrights. I did not mean to imply the Wrights used a thick flat wing similar to what you show. They had some type of wooden, leading edge that we can call a spar. I don't recall reading its thickness, but its shape was definitely discussed in one of the many books written. I don't recall which, but I read all I could get my hands on, perhaps 20 years ago, about them and some others at that time. If I had to guess, I would first say the one 'official' book Orville wrote with Fred Kelly.
I distinctly recall it mentioned. It was one example of the level of detail they went to.. It may have been in reference to the wind tunnel tests, or in a glider, or in a letter to Chanute, but they did look at LE shapes. I recall thinking about how much it could affect such a thin vertical dimension.
Unfortunately, I don't recall exactly what was said - what shape was better or worse, but seem to recall that they saw some advantage to a squarer LE shape.
I can't recall if I looked closely at the one at the Smithsonian when I visited, quite some time ago
.
Yes, I mis-spoke saying it was over the 'wing'. I built a plastic F-104 model back in the early 60s which is when I learned about it's BLC. I don't think I read s full description, or if I did, I've forgotten details.
You imply it can't *fly* without flaps, but it is low speed flight that is the problem with the thin, small area wing. It couldn't *land* engine-out as there was a minimum RPM for the compressor to provide its effect. (of course it couldn't take off)
..
The idea is also slightly similar to the 1943 Custer Channel Wing concept. That *was* an entire above wing augmented flow from the prop engine. that was further investigated in the early 2000s by a NASA funded project at Georgia Institute of Technology Research Institute.
It had the problem in that at the low speed afforded by the augmented flow, It landed very nose up and the low speed flow over the control surfaces made low speed flight troblesome.
I spoke with the Georgia Tech leader Bob Englar several years ago. A drawing he showed me had a forward-mounted, above wing jet engine of some type that did a true Coanda flow traversing the full chord, including flaps.
Thanks.
I see we've drifted far off topic.
I simply wanted to point out that a thin, flat wing has a fascinating flow as shown in Anderson.
Regards.
@@Observ45er A CL “of about half” will require 41% more airspeed to achieve the same lift. Not “25%”. But that is beside the point anyway. You could accelerate up to, say, 1.05 Vs, rotate, and yet be unable to sustain flight, or even maintain speed. You have to know the Vy, the drag, and the power available before you can answer this question. The TO and climb performance would certainly be in the range awful to nil.
Hypothetically, you could just about make something like a C-172 fly with a flat wing (of the same area) and the rated power of an O-320, and an optimised prop. It seems plausible that a structurally adequate flat wing could be constructed at typical GA aspect ratio with a 6% thickness. However, it is a highly marginal case for such a thing to get airborne at representative operating weight of, say, 1 tonne. Nobody has tested such a ridiculous airfoil at the kind of Reynolds numbers we are talking about (3 million range) so the data is simply not available to nail down exactly how bad the performance would be.
Nonetheless, the point I am making is that it has nothing to do with CLmax. If it cannot fly at its Vy, it cannot fly period.
6:03 In 2 dimensional flow, like a wing going from wall to wall, there is absolutely no downwash diferent from the upwash, as reflected from the ¼ wing chord, in other words no net down wash.
The downwash is created as the inside flow from the vortex ring composed of the lifting circulation around the wing in clockwise direction, the starting vortex left behind and the two wing tip following vortices, which also create a significant updraft outside the vortex system, which is used by canadian geese to fly in that updraft, Newtons interpretation falls apart, because it sas not intended to be valid for a flowing medium, just a rigid single body.The proper , applicable equation IS the Euler Equation. The lift equation summarizing these conditions is indeed the Kutta Joukowski equation.
In two dimensional flow there is no downwash, just the symmetrical flow due to the linear superposition of the uniform horizontal flow, the circulation and the displacement in thickness due to a source and sink distribution
The upwash and the downwash do not rule each other out. They complement each other. Please watch this video with Doug McLean: ruclips.net/video/QKCK4lJLQHU/видео.html
The vortex from the wing tip does not produce lift, but induced drag. Yes, it is correct that birds flying in formation can utilize the upwards part of the vortex, but this happens behind the wing. Here are two questions I want you to answer:
1. Why are long, slender wings, like those used on gliders, more efficent than short, stubby wings?
2. Why do many aircraft have winglets that reduce the vortex?
@@FlywithMagnar
I am familiar with Boeings McLean. Here is my Schadenfreude : ( my teacher was J. Ackeret)
The winglets act to produce a larger effective span, by introducing a biplane effect.
On a wing the apparent mass is proportional to the circular area over the wingspan, winglets extend the area upwards, like 2 circular areas slightly superposed .
Only a reduction in induced drag
L/D = spaneff÷2 × sqrt (pi/ Cd Aw)
True, 2 vortices are created, spiraling each other, with the shear sheet behind the trailing edge wrapping around both.
Read R. T. JONES Aerodynamics of wings.
The strenght of the shear sheet is the span derivative of the almost elliptical lift distribution . Namely the circulation distribution, to locally satisfy the Kutta-Joukowski equation. A carefully designed visualization can be done in an extremely low turbulence wind tunnel
Or a large one in Tullahoma Arnolds Air Force Research Lab. Tenn. huge wind tunnels.
@@FlywithMagnar
Up wash in front of the¼ chord line and behind, the downwash in 2 dimensions are produced by the circulation in clockwise sense, so they are the same,
in 3 dimensions the tip vortices downstream add another contribution to the downwash behing. According to the Biot Savart relation.
@@Arturo-lapaz , the Biot-Savart law is an equation describing the magnetic field generated by a constant electric current.
Could you please explain how a fighter can stay in the air when it's on its side, i.e., rolled 90 degrees, one wing pointing to the ground and the other to the sky, and going in a straight line? Where does the lift come from? And are fighters the only planes that can do this, and if so, why?
This is called a knife edge. The lift is created by the fuselage, which is pointed a bit up. The pilot must apply a lot of rudder to keep the nose up. A belly tank is a benefit as it will increase the lift.
Fighters often use ballistic manoeuvres as opposed to aerodynamic ones... At 500 mpg, you can do funny things just using inertia and ballistics... Like sitting in a bullet with control surfaces
Magnar, finally! A youtube video about lift with which I don't have any significant objection.
And this is coming from a pilot who is also an aeronautical engineering and who used to teach Physics 1 and Aerodynamics 1 and 2 at college.
Of course there is much more to say about lift that what's in this video, but for a youtbe video intended for a general audience of enthusiasts and pilots it is excellent: Clear, to the point, and more important: CORRECT! I have seen so many things wrong in official pilot training materials.
(And I was one of the guys that critiqued your previous video on this, and you answered my comment)
Thank you for your feedback! Buy making those videos and receiving constructive comments, I have learned a lot more.
It’s ok then if you don’t have any significant objections ! Who put you in charge ?
@@tonywright8294 ... What?
Putting the back (convex) side of a spoon into a stream of water from the faucet causes a strongly felt force to move the spoon towards the stream as it attaches and flows smoothly over this convexity. Isn’t this a factor in flight?
@@BobbieGWhiz , this is the Coanda effect. It can be used to enhance lift, for example by using blown flaps. But a wing produces lift through pressure difference above and below the wing.
@@FlywithMagnar Does the Coanda effect contribute to the movement of air over the top of the wing? Thanks much.
@@BobbieGWhiz For a plain wing, no. The Coanda effect is created by a jet blowing over a surface.
So if newtons third law explains that since air is deflected down and back from the trailing edge there is an equal and opposite reaction force upward and forward, then why does the effect of induced drag that further bends the downwash downward not result in the creation in more lift. In theory air is being deflected more downwards and would that not therefore mean the equal and opposite reaction to the downward directed air be upwards even more? I dont think induced drag and wing vortices increase lift, but this logic tells me it does. Where am I going wrong? I must be misunderstanding something
The vortex created at the wing tip does not create lift. Only drag. That's why a wing with a long aspect ratio (for example a glider) is more effective than a wing with a low aspect ratio.
Fair question. If I may expand a little on Capt Nordal’s reply. The short answer is: the tip vortex itself is a circulation, not a downwash, so it does not increase lift iaw Newton’s 3rd.
The tip vortex will increase average downwash over the span. However, being a vortex it is circulating so there is no net extra downwash of air. The ‘up’ part is happening outside the tip. Nonetheless, the span gets the downwash part so that reduces the ‘effective angle of attack’, hence reduces lift (relative to a hypothetical no tip vortex case aka 2d section or infinite span). Ergo, for any given required lift, this shortfall has to be recovered by increasing the angle of attack somewhat. The net result is same lift but more drag for the real wing than the hypothetical no tip vortex case. That difference is ‘induced drag’. One of many references is Aerodynamics for Naval Aviators, p66, downloadable from the FAA website.
Are you planning a video about v-wing aircraft eg. The Vulcan and Concorde? Why is the same wing design effective for both when one is a slow heavy bomber and the other a supersonic passenger plane? Love the video presentations.
The delta wing is very good for supersonic flight, as the Concorde proved. Regarding the Vulcan, a delta wing was selected for the following reasons: 1) Less drag at transonic speeds (the Vulcan had a top speed of Mach 0.96). 2) Lot of space for fuel. 3) Space to embed the engines and the landing gear into the wing. 4) A very strong construction.
BTW: 90 % of all helicopters still use a symetrical NACA 0012 airfoil for rotors, this is pretty much a flat plate with a rounded nose portion.
NACA 0012 has 0 camber and a thickness of 12%. The surface is not flat. airfoiltools.com/airfoil/details?airfoil=n0012-il
While this profile is used on Jet Ranger, S-51 and other helicopters of "old" design, the majority of new helicopters have rotors with cambered airfoil because they are more effective.
@@FlywithMagnar 0 camber defines a flat profile chord... The NACA 0012 is a flat plate with an aerodynamic shape :-) Even R22, R44 and R66 use this one and it works fine
@@Ozbird-72, you might be confused by the definition of camber.
NASA: "A cut through the wing perpendicular to the leading and trailing edges will show the cross-section of the wing. This side view is called an airfoil, and it has some geometry definitions of its own. The straight line drawn from the leading to trailing edges of the airfoil is called the chord line. The chord line cuts the airfoil into an upper surface and a lower surface. If we plot the points that lie halfway between the upper and lower surfaces, we obtain a curve called the mean camber line. For a symmetric airfoil (upper surface the same shape as the lower surface) the mean camber line will fall on top of the chord line. But in most cases, these are two separate lines. The maximum distance between the two lines is called the camber."
@@FlywithMagnar Zero camber means a flat, aerodynamic shape, but not a lifting surface. Unsymmetrical airfoils are better in defecting air downwards and optimise Lift. But they are not needed for lift at all.
When I was growing up in the '70's, I designed and built balsa wood airplanes. Some of the smaller ones had flat wings, and they flew ok. I knew that kites mostly worked in stalled states by redirecting wind on their bottom surfaces, so I knew that this was at least part of the source of lift for regular airplanes, and I knew about symmetrical airfoils on aerobatic aircraft. But of course you are right, asymmetrical airfoils that use both effects work better.
Fool in the video says it won't scale up, but that defies the wind tunnel experiments performed by the Wright Bros., who tested small wings in wind tunnels and scaled them up. Likewise, the Wrights scaled up the aerodynamics they refined with their kites and gliders. Doesn't scale -- now that's a laugh. 🤣🤣🤣🤣🤣🤣
@@crimony3054 Yep, his assertion that it "doesn't scale" lacked evidence.
@@crimony3054 I think he meant 'doesn't scale' more in the sense that you need to compensate for the bad airfoil shape with much more engine power, the catch is doubling the size os a wing makes its area 4x times larger, but it'll end up weighing 8x as much. TL:DR I think he meant the square-cube law.
On a sailboat, a keel is needed to create forward movement. Without a keel, the vessel is pushed sideways.
So, 6:24 you are saying it’s the Newton’s third law. But why do you need to mention pressure difference under and above the wings??? I don’t get it.
Lift can be explanied in many ways. Newton's third law is one of them. Lift can also be explanied with the pressure difference under and above the wings.
I've a doubt. Why do some planes (like A300, where I experienced) fly level with a nose up attitude ? Anything to do with wing design, to have more airflow under the wings ?
Airliners usually cruise with the nose a couple of degrees up. The reason is twofold. One: The higher they go, the more fuel they save. Two: At high altitudes, the air is thin, resulting in a relatively low indicated airspeed. To compensate for this, they fly with the nose a few degrees up, as this increases the angle of attack, and with it, the lift coefficient.
Wings are designed to be most efficient at a higer angle of attack (7-8 degrees for a straight wing), but this will result in a relatively low cruise speed. Therefore, some efficiency is sacrified for a higher cruise speed.
The airflow under the wings contributes to some of the lift, but the airflow over the wings is more important.
Here is a link to a video about the lift formula: ruclips.net/video/e43l2V_MFIY/видео.html
@@FlywithMagnar Thanks a lot for your explanation 👍
@@FlywithMagnar ... Yes, but if the airliners do most of their cruise flying with an attitude of 1 or 2 degrees nose up, they could have designed the wing to be mounted on the fuselage with an incidence of 1 or 2 degrees more.
As an aeronautical engineer, I have always have this doubt myself. I found several explanations, and I don't know which of them if any are true.
1- The airplane is designed to fly with an attitude of no less than 0 degrees because flying a bit nose down is more uncomfortable for the pax than flying a bit nose up, so the whole range of cruise attitudes (different weight, altitudes, speeds and CG) are designed to have 0 degrees as the lower bound.
2- It is to reduce drag by better streamlining the aft fuselage with the airflow, which will not be horizontal but tilted downward due to downwash. Also the tail cone is tilted up so having the aft fuselage tilted down again aligns the tail cone with the airstream better.
3- To create a little bit of body lift, hence reducing a little bit of wing lift and reducing induced drag. I know this one HAS to be false. While the fuselage may create a little bit of lift by flying at an angle, it is super inefficient generating lift when compared with the wing, and it will create more drag for unit of lift. Any lift that you can take out of the fuselage and put it on the wing will result in a lower drag.
4- To provide a more nose-up attitude during landing and avoid a nosewheel-first touch down. If the plane flew with the fuselage 2 degrees less nose up at cruise, it would also touch down with the fuselage 2 degrees less nose up, and since it does touch down with about 2 or 3 degrees nose up to begin with, that would put the nosewheel dangerously close to touching down first. Not sure about this one. Tail strike seems to be a more common problem than a nose wheel landing. Also the problem could be solved by shortening the nose strut a bit.
@@adb012 Point 4.... They rarely come down with the same nose up attitude. In fact they point downwards, mostly, to lose altitude - which is my experience as a passenger.
@@RaviKumar-sn2lx ... I don't get your point. Airplanes touch down with the main landing gear first (the wheels under the wing) and they have a nose-up attitude at that point. Then, once the main gear is on the ground, they lower the nose and the nose gear touches down. If the wing was installed with, say, 2 degrees more of incidence, then, at any given speed and weight, the fuselage would fly so degrees more nose down or less nose up (because the wing, which is the thing that makes the lift, will have the same angle relative to the incoming airflow, so instead of the wing being installed on the fuselage with 2 degrees more of incidence, you can think about the fuselage being installed on the wing with 2 degrees more nose-down angle), and that would make the nose gear touch down first (or very close to that) unless you change somethin else like making the main landing gear longer or making the nose gear shorter.
so the biggest problem with flat wings is not how to explain lift but how to deal with stall , and of course we are talking about fixed wing , because as any bee or butterfly knows , turbulence can be an asset .On the other hand , a rocket table can pretty much ignore aerodynamics altogether .
You can add drag to the equation.
Insect wings are neither 100% flat nor fixed. They can flap and swivel. So it would have been more accurate to use the aerodynamics that are applied to helicopters.
Aircraft engineers are using turbulence to create lift. Examples are vortex generators (increases critical angle of attack) and leading edge root extensions (LERX) on fighter aircraft (creating a powerful vortex over the wing root).
The best explanation I have seen on internet!
4:33 The stagnation streamline meets the wing surface at a right angle!
This is important to understand the stall warning sensor, giving the stall warning an electric signal. Please correct that image.
You are right. I will correct this in the first update. Thank you for notifying me.
flat wings do fly..
bernoullis principle is applied wrongly in this case
18:30 I'll add this to my mental list of examples how scaling (up or down something) can fail.
The deeper reason for many purely mechanical and mostly static examples is that some things scale linear, others squared (like tensile strength) and others again cubed (like weight caused by mass).
Therefore if you build an exakt replica of a bridge scaled down 1:10 and film it while putting more and more weight on it until it collapses you'll never get the same result like in reality. For the same reason you can't simply scale up a bridge by a factor of 2 and assume it now supports the double weight of traffic.
Now, you say very small, light model airplanes actually CAN fly with flat wings but your next sentence is a larger plane can't and to me it sounds like you state a principle: _"No matter how strong an engine you put at it, it simply CAN'T."_
No I wonder - like I explained for the bridge - what is the deeper reason for this. My intuition tells me it's another application of the squared scaling of forces (when some material we practically have available breaks or in case of a wing how big it's surface is which produces force) vs. the cubed scaling of its weight.
Is this right, or at least approximately right?
Your example with the bridge is to a certain degree similar with airplanes. In the video, I show an image of a model airplane with a wing made of square cut foam. The wing loading is very low, and the power to weight ratio is very high. Such model airplanes can fly. But if you scale up that wing and put it on a Cessna 172, it will not be able to fly. If you round off the leading edge and sharpen the trailing edge, the wing will provide more lift, but it will not be very efficient.
You can scale up a model aircraft, but you cannot scale up the air molecules. Therefore, a model airplane will have different flying properties than a full size airplane.
@@FlywithMagnar 👍 have a nice weekend, Martin
Also, there is a logical point of confusion at about 5:08. You claim that because the particle is moving on a curved streamline that it proves F=ma applies and that this is the centripetal force.
But one can't digest this because although it is true the particle can only follow a curved path (as well as speed up) if a force acts according to F=ma to cause that change in direction (and speed), there is not an identifiable centripetal force. And a centripetal force would not account for the increase in speed along the streamline.
A centripetal force is a center directed force, such as gravity acting on an orbiting satellite.
But the particle in your illustrated case, is being diverted from its horizontal momentum by the curvature of the wing.
So, there is a logical disconnect here that makes one lose track of the explanation, again, because there is no identifiable centripetal force, or other any other force identified.
Does the particle accelerate? Sure, but why does it speed up?
Without any centripetal (center seeking) force here, what are in fact the forces both causing the change in direction and the acceleration along that change and direction?
I think you'll agree, some more satisfactory answer is needed.
Thank you.
Even before airfoil concept known for an aerplanes, people were aware of the tirck for flying a kite. What makes a paper kite fly in the sky? What are forces acting on kite, what cause it lift ?
12:13 ; Yes, yes ..AOA. AOA is the Magic Word for creating Lift..the "Angle of Attack'.
Even a FLAT KITE can fly with positive Angle Of Attack (AOA.)
What about Coanda?
Travelling in a car, I extend my arm outside. I flatten my hand. If I turn the leading edge of my hand up the air flow pushes my hand up. If I turn the leading edge down the air flow pushes my hand down.
Best description I've seen! IV always laughed at the descriptions in college textbooks!
Funny how the separation bubble looks like an airfoil when visualized. It's almost like the bubble is trying to tell you what would work better.
There is a difference between a flat plate and a flat wing. The plate has a square edge, but a wing will have a streamlined edge if it's expect to function well in subsonic flow.
If it has a streamlined edge, it's not flat.
@@clintoncoker6 Seriously, are we really going to argue about word meanings here? It is flat if it can lie flat on a flat surface, whether or not the edge is rounded. Are you also going to tell me the countertop in my kitchen is not flat? Well, it is flat, and the edge is rounded, and it would make a better wing than one that has a squared-off edge.
@@satunnainenkatselija4478 Magnar said an airplane with a flat wing will not fly, which is inaccurate. If instead he had said a flat wing with a square leading edge would not fly very well, that would have been accurate.
In this context flat means a surface without curvature, and the pertinent surface is the large area of the wing, which is curved (not flat) for most airplanes. Regardless of the leading edge treatment this is a flat wing, as opposed to the usual curved wing surface. But Magnar's drawing is really just a thick flat plate, not a wing intended to actually fly well.
First of all, a flat plate is actually quite efficient at producing lift in supersonic flow. There is no flow separation, and the sharp corners produce expansion waves that are the source of pressure differential and aerodynamic forces.
But nobody would expect that wing to work well at useful angles of attack in subsonic flow, even though it would still fly given enough airflow. However, all you have to do is taper the leading edge to expand the useful angle of attack range to allow a flat wing to work better. It will not be very efficient at low speeds, but it will fly. More than one aircraft has had a flat or nearly flat wing and flown to quite useful angles of attack, such as the X-15.
14:30 one very important thing the Wright brothers figured out was how to design a propeller
Bernoulli is not remotely related to lift generated by an aircraft wing. Wings generate lift in two different ways, depending on which side of the wing one is referring to. One side of the wing will be actively acting against the air reaching it by pushing it downward, often called Neutonian action/reaction. The other side of the wing (the upper side in normal flight) generates lift by first rapidly pushing the oncoming air upward. Then, taking advantage of the air's inertia, the wing surface then immediately does what I call "yanking the floor out" from under the air above it. The effect is mimicked, and can be felt, in a rapidly accelerating elevator as it begins its descent. An occupant will feel a bit lighter as the elevator begins moving downward, because for a short time, there is less pressure exerted by the feet against the floor of the elevator.
It is a standard wind tunnel exercise for aeronautical students to measure and plot the surface pressures at points around an airfoil. Then, using graphical methods the average pressure can be determined. When multiplied by the area of the airfoil this provides an estimate of the lift. At the same time, the lift can be measured directly by a balance. The estimate will agree with the direct measurement. Now for the Bernoulli part: the total pressure of the freestream can be measured directly. From this total pressure, each surface pressure data point can be subtracted to find dynamic pressure at that point. In other words, an estimate for airspeed at each point. If you then check this point with a pitot you find the estimate is remarkably good. This exercise is repeated by thousands of students each year. It then becomes denial of fact to continue to believe that Bernoulli is not remotely related to lift.
@@XPLAlN Engineers will engineer. That's what they do, and they are welcome to it. Somebody who throws a plate of spaghetti against a wall instantly knows all he needs to about the result. 1000 engineers trying to learn everything they can about it will never understand it fully. At some point they will give up and create some complex mathematical formula designed to make it look like they understand it.
@@joepiol5105 …ok then, if that’s what you believe there is nothing more worth saying.
Great video!
All of this is true, which is more than can be said of almost everything youtube has on the topic, but it still says nothing about the actual effect responsible for lift generation. Deflection of air downward; a vertical component to pressure integrated over the wing surface; and non-zero circulation are all things that are necessary present if lift is, they just aren't an explanation of why it is.
What does explain it is the effect of viscosity near a sharp trailing edge, which has the effect of forcing the rear stagnation point to be at the same place as the trailing edge. So long as this wouldn't be the case absent viscosity, this means that a circulation most exist around the wing (or equivalently, the flow has been deflected) and therefore lift is generated (See Kutta-Joukowski theorem). It also means that starting vortices are shed whenever the lift generated changes and the bound circulation adjusts to re-establish the Kutta condition.
Accelerate mass downward; produce lift.
Simple.
The shape of the wing is the attempt to do that mose effectively and efficiently.
Newton explains what is happening to the air and Bernoulli explains what is happening to the wing. Newton shows how the air is accelerated downwards and Bernoulli shows what effect accelerating that air has on the wing surface.
15;15. In case of FLAT curve, the induced pressure under & above the wing must be Equal (no difference) due to same curvature.. Only the underneath Flow is Engulfed/stagnant...in the opposite of Free flow on above that creates (positive) pressure difference. As already commented (below).. Bernoulli equation CANNOT be applied to "2" divided /separated Flows/streams of fluid(air, this case).. only explain each of them separately (either upper or lower of Airfoil.!!) None of them related except they are in the SAME PIPE/TUBE/TRENCH (non-separated/UNDIVIDed).., sire.
His video and explanation, but Isn’t the “lift” really just the result of the differential pressure created by the high and low pressure of the wing, and the lower pressure above the wing is creating a “vacuum”, so the wing is basically being “sucked” up by this vacuum?
for ex : the flying cardboard at 20 degrees, has no lift, ... and a positive (upwards) drag.
On a real airplane, yes it will be able to fly, you said it yourself, like the model airplane, you just need to massively overpower the real engine.
Will it be able to fly in a great controllable manner, without turbulence, without risk of accident? Will it be efficient?
I believe these are different questions, right?
A similar question is whether a vacuum in a vacuum cleaner sucks the dust in or is it the atmospheric pressure pushing the particles in?😉
Same thing - the pressure difference makes the air move inside bringing the particles with it. Sucking something into a pipe means creating an underpressure in the pipe to establish the pressure difference, it's a colloquial term.
@@altoclef6688 Yes but it's the air particles from the higher pressure that do the work, a vaccuum has no energy to perform any sucking.
@@ottonormalverbrauch3794 Yes. But in colloquial terms talking about a blower because the normal pressure air flows into the pipe bringing the particles with them, would be confusing. Physically sucking does not exist since the lower pressure side does not exert force, but in colloquial terms it is handy. Sipping from a straw or sucking on the straw is a useful term for every day,
saying "create an underpressure so the atmospheric pressure pushes the fluid into your mouth" would be useless from a conversation perspective.
So just accept colloquial terms and scientific terms have their separate fields of usage...