The Lift Equation - Part 1
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- Опубликовано: 11 сен 2024
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This video's topic covers part 1 of 2 of the Lift Equation. This subject can get pretty detailed if you ask an aerodynamicist. But for this video I want to keep it to just the basics. It's important to understand where Lift comes from so that pilots can understand what they can and cannot affect, either directly or indirectly. The lift equation itself is made up of 4 key elements. The first one being the Coefficient of Lift (CL). CL is a measure of the amount of lift a particular airfoil shape can produce. This is determined specifically by the shape of the airfoil itself and the Angle of Attack (AOA). Shape of an airfoil includes factors like blade span, camber, whether it's symmetrical or non-symmetrical, etc. Obviously this cannot be affected while in flight. But the second part, AOA can be. As the flight controls are manipulated the Angle of Incidence (AOI) changes. These changes in AOI combine with induced flow velocities which result in Angle of Attack. So although AOA is an aerodynamic angle which we don't directly control, it is affected by AOI, a mechanical angle that we control directly with cyclic and collective inputs. For a better look at this I'd recommend checking out my Compensation for Dissymmetry of Lift video ( • Compensation for Dissy... ).
The next element of the Lift Equation is surface area. This refers to the general surface area of the airfoil or rotor disk. The larger the area, the more lift (considering all other parts of the equation remain the same) and vice versa. This is generally thought to be unchanged,purely a factor of blade design, and unaffected by the pilot. However, consider blade coning and its effect on surface area. As the rotor cones, it's surface area decreases. During normal rotation the rotor system usually stays relatively horizontal and sometimes cones slightly about 2-5 degrees. This indicates more centrifugal force than lifting force. If lifting force begins to exceed centrifugal force, coning angle increases, surface area decreases, and lift is reduced. Some factors that affect rotor coning are: low rotor RPM, high gross weights, and excessively high G-forces. As a pilot you can directly affect all 3 of these which reduce blade surface area.
That wraps up part 1 of 2 if the Lift Equation. Thanks for watching and don't forget to check out Part 2 ( • The Lift Equation - Pa... )! As always, safe flying!
If you enjoyed the video or have any questions or comments, hit the like button and comment below.
If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook - amzn.to/2ifPlnZ
If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - amzn.to/2ifQGLx
I understand the coefficient but when we get to the surface area, are we working in cm and meters or feet and inches.
Depends on what unit you want in your answer, if you want newtons then just use SI units in the calculations
Brother can you tell what will be the coefficient of lift value of an NACA 23012 airfoil with to different angle of attacks
Nice one
I wouldn't necessarily say Surface Area is controlled by the pilot in a normal sense. Its more of a resultant of the pilots control, not a primary or direct control. In an airplane you use flaps and slats to directly change the surface area, yes, but you would not fly the aircraft to the ground only using flaps, only AOA and V squared but speed is set at a constant approach speed. Same with a helicopter. Im not gonna think, "Hey i'm landing, i want my blades to cone" Its just a byproduct of flight. Id more or less think "Ill change my AOA" saying i need more lift, not by saying "i want less surface area." But in reality id say "Holy shit i'm descending to fast"
Parker Raimondo. I think we're saying the same thing. Pilots cannot directly control surface area in flight, but they can affect rotor RPM, excessive G loading, and high gross weights, all which influence the amount of coning. It's a far more directly affectable component of lift in fixed wing aircraft.
Hey Jacob,
Currently at AH-64E IPC. Tried to argue the change in SA as taught in this video. I got crushed. There's no manual where this is taught and it appears to be completely incorrect. Even when there's coning the actual surface area hasn't changed. The lifting area (disc) has changed, but that's not what the equation is referring to.
I'd love to be wrong. Do you have any reference that directly correlates Surface as being able to be changed as result of coning?
I would think the change would be in the angle of attack when coning occurs. I'm a fixed-wing guy, so take it for what it's worth. The blade is going to feel the relative wind differently when coning occurs. The surface area has not changed. The way the airfoil feels the wind has.
When the blades are spinning normally, all of the lift would be directed upward. When the blades begin to cone, some lift would be directed horizontally instead of straight up. That may be where the loss of lift comes from when coning occurs.
if velocity is squared it seems more influential to life. so if coning reduces surface area, but increases velocity, wouldn't that be better or equal?
*lift
So if your angle of attack is 6 degrees up would you use that number 6 X surface area and on.
Where do you get this music from? I might need a playlist while I'm blasting across the wasteland after the nuclear war
Why is there a 1/2 in front of the density??
my lord = excellent = u r from which country ? please suggest a book =than u sir
Is the surface area the whole rotor disc area? Or is it just the surface area of each rotor blade added up?
James Downs. Surface area can refer to either. The length (root to tip) and width (from leading edge to trailing edge) affect how much surface area or lift each blade can individually produce. This comes down to blade design and cannot be affect by the pilot in a helicopter. The total surface area of the disk takes into account the entire rotor system and how much lift the system as a whole can produce. The pilot can affect surface area of the disk by affecting the amount of blade coning. Great question!
Thanks for your answer... and thanks a lot for your whole series of videos.
As a helicopter pilot I am not sure you can affect surface area. If my rotor disk is 60ft this does not change with coning. My lifting area is changed however the surface area maintains 60ft. Thoughts?
@@jasonbouchard8914 I may be wrong but I wouldn't have thought coning would have much effect on disk area, either.
As I'm sure you know, but to the o.p. I would say that both disk area (A) and blade area (or more usually, solidity, denoted sigma) figure in basic performance equations. For example, it is standard to define a thrust coefficient CT for the rotor in terms of disk area as in pi*R^2. To make sense of this in terms of blade aerodynamics, this is divided by solidity to give something akin to an average lift coefficient for each blade.
By the way - I enjoy these videos and they are teaching me alot that although I will never be able to put it into practice is really enjoyable.
@@helicopterlessonsin10minut10 FYI, likewise for me, in the "Conservation of Angular Momentum" video, when you mentioned "blade diameter shrinkage" I pictured the thickness or "waistline" of the blade shrinking... Then I thought it must be the length of the blade getting smaller, retracting somehow, like when it's cold out?... (Eventually I saw a video by George Costanza that straightened me out.)
The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force. Low pressure creates force normal to the cord (contact surface), and it name is "aerodynamic force" because is made from the air (aero) in motion (dynamic), or wind relative to the wing (object).
The force object receives is always normal to the contact surface and air pressure always acts normal to the surface of the body. This has long been well known, and I don't know why in flight theories and aerodynamics books this is (mostly) omitted.
What happens when there is a vertical gust
Maybe start with a disclaimer that says you should understand certain terms and concepts before watching this video. I happen to understand AOA because of a previous video I watched, but all of the other stuff (cambers?, "obviously we cannot affect this while we're in flight"???) What are you talking about? because I'm seriously interested and have no reference...
He posted an airfoil characteristic video that may give you better understanding of those things.
I have a playlist titled “All videos in order” that should clear things up. The whole channel is meant to be progressive.
Man, this should be on a t-shirt. ;)
Lol! It’s on a shirt and coffee mug in the Teespring Swag attached below the video.
What song was that as the intro?
Mazing how we have formulas to tell us the lift, but know one has conclusively given us an explanation of flight?
Flight is the process of breaching beyond the point of gravity where as you begin to breach it's pull and lift off a solid surface. In a way swimming counts as flying, but conventionally swimming is it's own thing since that fluid is a liquid and not a gas. Flying doesn't have to be in any fluid at all either. It can be in the vacuum of space.
🔥🔥🔥🔥🔥❤️❤️❤️
How do u calculate *Cl value*
Harder to explain here and a physics textbook would be an easier source. But here’s the jist: Multiply fluid pressure by velocity squared and divide the product by 2. Multiply the surface area with the preceding product. Divide the lift force by the product.
@@helicopterlessonsin10minut10 upload a video that show how to calculate power needed to hover
That will generally come from your aircraft operators manual. There should be cruise charts and hover performance charts. Each aircraft varies so it’s best to find your specific aircraft.
@@helicopterlessonsin10minut10will I get answer in Newtons or kilograms after multiplying cl, velocity, air density surface area and 0.5 ..
How to dermine Rotor RPM ?
Stealhty1. As a pilot you monitor it on your instrument panel. It's usually labeled as "NR."
I like the stranger things intro music. Haha