13:27 are you sure? imho only the induced drag is reduced. The lift stay the same, and the maximum lift coefficient is limited by the reynoldsnumber. A higher reynoldsnumber (higher velocity) increase clmax. Please correct me if im wrong
He has it all messed up in his mind. Ground effect increases the pressure on the bottom of the wing, increasing the force of lift, because air has inertia and "builds up" in the region just forward, and below, the wing.
I'd love to see those topics revisited in more depth both with experiemetns and math. And maybe with simulations where experiments are not possible. Overall it's a bit too much for me to ingest for one short episode and I'd like to take it more slowely. Awesome work overall !
Oh dear… Wingtip vortices exist, certainly, but explaining induced drag as “vortices!” gives no insight, does not help explain why longer spans have lower drag, and leads to bad intuition (like, “end plates will block the formation of wingtip vortices and eliminate induced drag”). Your video has all the required facts; but trying to tie everything to the vortices, as you did, isn’t helpful. A better - much better - approach is to tie everything to the downwash. Downwash is necessary to create lift, as you note. If the speed of the airflow is constant, then downwash also implies a loss of horizontal momentum of the air, which is drag. THIS is the actual source of induced drag - as part of your video acknowledges, although for some reason you attribute the downwash to the tip vortices. Now, the lift per unit span is essentially proportional to the deflection angle of the airflow. The resulting induced drag per unit span is approximately. proportional to the square of the deflection angle. For a given total lift, the deflection angle is inversely proportional to the span, which means the total induced drag is proportional to 1/(span ^2) x span, I.e., odd proportional to 1/span. Aspect ratio, of course, is span^2/area, so if we fix the wing area then induced drag is proportional to 1/Sqrt(AR). By attributing induced drag to deflection angle we can deduce this relationship from first principles; talking about vortices won’t get us to this result. Also, because we know that induced drag is related to downwash angle, and thus to total lift and (effective) wingspan, we know the only way to reduce induced drag is to increase effective wingspan - which is what tip plates and winglets do (although less effectively than simply adding more wingspan). Well, what about those tip vortices? Sure, they exist, when you generate downwash near the wing, but not far beyond the wingtips, you wind up with a shear between the air that’s moving down and the air that isn’t. That shear, plus viscosity, results in vortex formation. And yes, the total energy tied up in the vortices does represent drag, but that energy is extracted from the downwash and we already know that the downwash creates drag by deflecting the airflow; worrying about vortex energy provides no additional insight. Your video touches on the idea that a 2D wing generates no downwash. This is misleading. A 2D wing is the limit of a 3D wing as span goes to infinity. For a fixed total lift, as span goes to infinity the lift per unit span, and therefore the downwash angle, goes to zero and in the limit there is no downwash. But if lift per unit span is held constant, calculating the 2D case directly involves dividing infinity by infinity, which may appear undefined; but calculating it as the limit of the 3D case as span goes to infinity is easy because the deflection angle stays constant - so in the limit there is, indeed, downwash. Anyway, from the point of view of offering an insight into induced drag, starting with vortex formation offers no insight; starting with downwash provides plenty of insight. Your box diagram at 5:24 should be re-ordered to Pressure Difference -> Downwash with two boxes beneath it, for Induced Drag and Wingtip Vortices, as both are consequences of downwash. Thanks for all the effort you put into these videos!
I'm an inventor who's been redesigning internal combustion. Now I'm getting into aero, including propulsion systems and wings. I think there's a better focus: the real enemy is span-wise flow. The solution appears obvious, and it's not kluges like fences and wingtips. I won't post "the obvious" here, but let me know if you'd like to see it privately (and shoot it down?)
@@RePeteAndMe I'm not going to post an email address here, so a private viewing may be difficult. However, if your focus is on spanwise flow I fear you are focused on the tail, rather than the dog - just as this video is. Far from the ground, lift requires downwash, and the downwash plus conservation of momentum is the source of the drag. The shear between the downwash region and the non-downwash region (beyond the wingtips) gives rise to a vortex, and the vortex gives rise to the spanwise flow. If you did have a scheme that successfully reduced spanwise flow, it would reduce the vorticity, which would require reducing the shear between the downwash and the non-downwash, which would require reducing the downwash, which would imply less lift per unit span - which you can really only achieve by reducing the span loading (i.e., for a given weight, increasing the span).
Could be. I’m just learning about wings and initial concepts rarely survive scrutiny. My propulsion concept uses a much improve piston engine and a different type of counter-rotation: A direct drive open fan is at the aircraft’s cone-shaped nose, which contains the engine and flight deck. The rear of the flight deck is the largest diameter of the fuselage. A planetary gear driven fan between said flight deck and the plane’s cabin counter-rotates at about 1/10 engine RPM. The plane’s nose spreads, slows, and smooths the front fan’s wake while entraining lots of air. The huge and slow rear fan bats said wake straight back, conveniently leaving a fuselage-sized hole for the plane to slip through.
@@FinbarSheehyYes, the wing a micron from the tip can't have any down wash or be involved with lift. Of course, span-wise flow is impossible to to delink from said micron of wing tip. If you have zero span-wise flow and zero lift at that last micron you have no "primary" vortex, right?
Winglets do not reduce the bulk vorticies, instead they convert a small amount of the tip pressure gradiant into thrust by "turning" the airflow rearward. None of the popular books describe what is going on correctly.
The elliptical wing has an efficient lift profile because the pressure gradient near the tip is low, and the skin friction area is also low near the tip, and the wing weight is low near the tip. These all add up to hauling around less drag, wasted pressure, and mass that do nothing positive for the airplane.
The induced drag is due to the tilting back of the lift vector, that is correct, but it does NOT depend on the aspect ratio meaning it does not depend at all on the chord of the wing, just the span Di = (L/span)² / π Q nothing to do with the chord meaning does not depend on the aspect ratio This is a common missconception because you should use the actual forces, not the coefficients Do the algebra! and you will see that the chord cancels out
Induced drag is my least favourite kind of drag, it shuns more compact wings due to high lift concentration and thus strong downwash, and benefits low lift concentration high AR less compact wing
At small angles of attack, there is almost no change in the drag coefficient of an infinite wing, and it is often assumed to be constant. You are correct though that at higher angles of attack, the drag coefficient of an infinite wing will increase significantly.
@@DesignYourOwnAirplanes-xd6lz Sorry, not correct. The force of gravity is only down, it does not provide movement forward through the air. Gravity alone cannot move a glider horizontally through the air. There is a force that provides the "thrust" but it's not gravity. I know what it is. Can you tell us what it is?
@@WAVEGURU since the glider flies on a downward glide slope instead of horizontally, there is a component of the weight vector that acts parallel to the flight path, providing thrust. If we only consider lateral motion and not vertical motion, there is a horizontal component of the lift force vector that can be said to provide thrust in the horizontal direction.
I am a commercial pilot working on my flight instructor certificate. This was a great refresher. Subscribing for more.
Very informative and well explained. Can't wait for the next video(s)
your video is so clear which helps me a lot.😀
Well done! This is an abstract topic and I think you described it well :)
13:27 are you sure? imho only the induced drag is reduced. The lift stay the same, and the maximum lift coefficient is limited by the reynoldsnumber. A higher reynoldsnumber (higher velocity) increase clmax.
Please correct me if im wrong
He has it all messed up in his mind.
Ground effect increases the pressure on the bottom of the wing, increasing the force of lift, because air has inertia and "builds up" in the region just forward, and below, the wing.
I'd love to see those topics revisited in more depth both with experiemetns and math. And maybe with simulations where experiments are not possible. Overall it's a bit too much for me to ingest for one short episode and I'd like to take it more slowely. Awesome work overall !
Oh dear… Wingtip vortices exist, certainly, but explaining induced drag as “vortices!” gives no insight, does not help explain why longer spans have lower drag, and leads to bad intuition (like, “end plates will block the formation of wingtip vortices and eliminate induced drag”).
Your video has all the required facts; but trying to tie everything to the vortices, as you did, isn’t helpful. A better - much better - approach is to tie everything to the downwash. Downwash is necessary to create lift, as you note. If the speed of the airflow is constant, then downwash also implies a loss of horizontal momentum of the air, which is drag. THIS is the actual source of induced drag - as part of your video acknowledges, although for some reason you attribute the downwash to the tip vortices. Now, the lift per unit span is essentially proportional to the deflection angle of the airflow. The resulting induced drag per unit span is approximately. proportional to the square of the deflection angle. For a given total lift, the deflection angle is inversely proportional to the span, which means the total induced drag is proportional to 1/(span ^2) x span, I.e., odd proportional to 1/span. Aspect ratio, of course, is span^2/area, so if we fix the wing area then induced drag is proportional to 1/Sqrt(AR). By attributing induced drag to deflection angle we can deduce this relationship from first principles; talking about vortices won’t get us to this result. Also, because we know that induced drag is related to downwash angle, and thus to total lift and (effective) wingspan, we know the only way to reduce induced drag is to increase effective wingspan - which is what tip plates and winglets do (although less effectively than simply adding more wingspan).
Well, what about those tip vortices? Sure, they exist, when you generate downwash near the wing, but not far beyond the wingtips, you wind up with a shear between the air that’s moving down and the air that isn’t. That shear, plus viscosity, results in vortex formation. And yes, the total energy tied up in the vortices does represent drag, but that energy is extracted from the downwash and we already know that the downwash creates drag by deflecting the airflow; worrying about vortex energy provides no additional insight.
Your video touches on the idea that a 2D wing generates no downwash. This is misleading. A 2D wing is the limit of a 3D wing as span goes to infinity. For a fixed total lift, as span goes to infinity the lift per unit span, and therefore the downwash angle, goes to zero and in the limit there is no downwash. But if lift per unit span is held constant, calculating the 2D case directly involves dividing infinity by infinity, which may appear undefined; but calculating it as the limit of the 3D case as span goes to infinity is easy because the deflection angle stays constant - so in the limit there is, indeed, downwash.
Anyway, from the point of view of offering an insight into induced drag, starting with vortex formation offers no insight; starting with downwash provides plenty of insight. Your box diagram at 5:24 should be re-ordered to Pressure Difference -> Downwash with two boxes beneath it, for Induced Drag and Wingtip Vortices, as both are consequences of downwash.
Thanks for all the effort you put into these videos!
I'm an inventor who's been redesigning internal combustion. Now I'm getting into aero, including propulsion systems and wings. I think there's a better focus: the real enemy is span-wise flow. The solution appears obvious, and it's not kluges like fences and wingtips. I won't post "the obvious" here, but let me know if you'd like to see it privately (and shoot it down?)
@@RePeteAndMe I'm not going to post an email address here, so a private viewing may be difficult. However, if your focus is on spanwise flow I fear you are focused on the tail, rather than the dog - just as this video is. Far from the ground, lift requires downwash, and the downwash plus conservation of momentum is the source of the drag. The shear between the downwash region and the non-downwash region (beyond the wingtips) gives rise to a vortex, and the vortex gives rise to the spanwise flow. If you did have a scheme that successfully reduced spanwise flow, it would reduce the vorticity, which would require reducing the shear between the downwash and the non-downwash, which would require reducing the downwash, which would imply less lift per unit span - which you can really only achieve by reducing the span loading (i.e., for a given weight, increasing the span).
Could be. I’m just learning about wings and initial concepts rarely survive scrutiny.
My propulsion concept uses a much improve piston engine and a different type of counter-rotation:
A direct drive open fan is at the aircraft’s cone-shaped nose, which contains the engine and flight deck.
The rear of the flight deck is the largest diameter of the fuselage. A planetary gear driven fan between said flight deck and the plane’s cabin counter-rotates at about 1/10 engine RPM.
The plane’s nose spreads, slows, and smooths the front fan’s wake while entraining lots of air. The huge and slow rear fan bats said wake straight back, conveniently leaving a fuselage-sized hole for the plane to slip through.
I spent a few days relearning a lot about aerodynamic forces and I finally came back to this comment and mostly understand it now, thank you!
@@FinbarSheehyYes, the wing a micron from the tip can't have any down wash or be involved with lift. Of course, span-wise flow is impossible to to delink from said micron of wing tip. If you have zero span-wise flow and zero lift at that last micron you have no "primary" vortex, right?
Winglets do not reduce the bulk vorticies, instead they convert a small amount of the tip pressure gradiant into thrust by "turning" the airflow rearward. None of the popular books describe what is going on correctly.
thank you for the great explanation ;)
The elliptical wing has an efficient lift profile because the pressure gradient near the tip is low, and the skin friction area is also low near the tip, and the wing weight is low near the tip. These all add up to hauling around less drag, wasted pressure, and mass that do nothing positive for the airplane.
The induced drag is due to the tilting back of the lift vector, that is correct, but it does NOT depend on the aspect ratio meaning it does not depend at all on the chord of the wing, just the span
Di = (L/span)² / π Q
nothing to do with the chord meaning does not depend on the aspect ratio
This is a common missconception because you should use the actual forces, not the coefficients
Do the algebra! and you will see that the chord cancels out
Induced drag is my least favourite kind of drag, it shuns more compact wings due to high lift concentration and thus strong downwash, and benefits low lift concentration high AR less compact wing
Surely an infinite wing also generated downwash? Simply by pushing air down by generating lift? Right?
At small angles of attack, there is almost no change in the drag coefficient of an infinite wing, and it is often assumed to be constant. You are correct though that at higher angles of attack, the drag coefficient of an infinite wing will increase significantly.
Great accent, simplified states of complex concepts ...
What force moves a glider forward through the air?
The weight of the glider provides the propulsion. In the basic glider physics video I provided a more in-depth explanation.
@@DesignYourOwnAirplanes-xd6lz Sorry, not correct. The force of gravity is only down, it does not provide movement forward through the air. Gravity alone cannot move a glider horizontally through the air. There is a force that provides the "thrust" but it's not gravity. I know what it is. Can you tell us what it is?
@@WAVEGURU since the glider flies on a downward glide slope instead of horizontally, there is a component of the weight vector that acts parallel to the flight path, providing thrust. If we only consider lateral motion and not vertical motion, there is a horizontal component of the lift force vector that can be said to provide thrust in the horizontal direction.
@@DesignYourOwnAirplanes-xd6lz Yes, you've got it now. What pulls the glider forward is the forward tilt of the lift vector.
@@WAVEGURUexactly. Gold star.
Great! ❤
Love this im building rc plane and i love studying for my rc plane
At the beginning of this video:
AIRPLANE = 1
CAMERA = 0
😊😊😊