I have been recently studying the shapes and characteristics of different high-lift airfoils that have been used for VTOL aircrafts. While studying these different designs today, a particular quadrilateral-shaped airfoil design popped into my mind and I am now very curious to know if this airfoil shape would be ideal as a high-lift airfoil for a VTOL aircraft, either as an airplace wing for a VTOL aircraft, or perhaps as a rotor blade for a high-lift helicopter.

I believe this airfoil should produce lift even though it will have a zero angle of attack as it moves through the air.

Please reference the following drawing:

enter image description here

It will produce a lot of drag but at the same time I believe that the air pressure differential should produce a lot of lift.

Would this quadrilateral-shaped airfoil produce lift with a zero angle of attack?


I have changed the main question from 'Would this quadrilateral-shaped airfoil be ideal for VTOL aircraft?' to 'Would this quadrilateral-shaped airfoil produce lift with a zero angle of attack?' because this is really the particular answer that I am seeking.

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    $\begingroup$ "I believe..." - on what basis? Have you put this in a wind tunnel and tested it? Why do you think that the engineers who have tested aerofoils haven't come up with this yet? $\endgroup$ – CatchAsCatchCan Sep 8 at 0:03
  • $\begingroup$ @CatchAsCatchCan, I said that because of my interest in VTOL aircrafts and due to my self-study of airfoils and aerodynamics over the past few years. I am actually planning to make a set of blades with this particular design on my 3D printer and install them on my drone to see if it will lift the drone up, but before I do so, I would first like to get some feedback on this design from actual aerodynamic experts. $\endgroup$ – user255577 Sep 8 at 0:16
  • $\begingroup$ Well, in the vertical phase of flight a VTOL aircraft wing has no forward speed, so no lift. Once it has transitioned to horizontal flight a VTOL aircraft is just an aircraft. Beware of Dunning Kruger $\endgroup$ – CatchAsCatchCan Sep 8 at 1:46
  • $\begingroup$ @user255577: I think you need to clarify something. By "blades", do you mean the propellors (or rotors?) on the motors? That's rather different than a wing. $\endgroup$ – jamesqf Sep 8 at 3:08
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    $\begingroup$ @user255577, "for every action there is an equal and opposite reaction". All lift generating airfoils create their upforce by producing a downforce. This is basic physics. $\endgroup$ – Michael Hall Sep 8 at 17:43

Draw a line from the leading edge to the trailing edge. This is the chord, and it has a positive angle of attack as the shape is oriented. Therefore your premise that this has zero angle of attack is incorrect.

Since you can produce lift with a positive angle of attack using a flat plate, it is reasonable to assume that this shape, as drawn, should produce some amount of lift. But if oriented so the leading and trailing edges were aligned, (zero AOA) it would not.

However, it will also have tremendous drag, and likely very poor stall characteristics with the sharp corner on the top surface causing premature airflow separation.

There are lots of proven airfoil designs out there. If this was a good idea someone would have tried it in the last 100 years.

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  • $\begingroup$ thanks for pointing that out about the chord line. I guess what I should have written is that the bottom surface of this airfoil will remain parallel with the ground as it moves through the air, or another way of saying it is that the airfoil will always be in the same position as it is shown in the drawing. $\endgroup$ – user255577 Sep 8 at 20:37
  • $\begingroup$ Understood. Just curious, you admit to not being an aviation expert, so why do you think this design might be a good idea? $\endgroup$ – Michael Hall Sep 8 at 23:52
  • $\begingroup$ I have to admit that the way I envisioned the air moving around this airfoil was wrong and that this airfoil will not create lift. $\endgroup$ – user255577 Sep 9 at 12:36

Would definitely create some lift if flying supersonic ;)

Otherwise, sharp edges force the flow to detach and thus destroy any lift capabilities of the shape.

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Yes, it will produce lift, just like any body that is asymmetrical w.r.t. the flow field will produce lift.

A program like XFOIL can estimate its lift and drag at various angles of attack and at various Reynolds numbers. If you wanted to convince a professional to build such an airfoil, they'd want such numbers first.

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  • $\begingroup$ Do you have a source for the claim that any asymmetric body produces lift? I think it's an interesting claim and would like to know more. $\endgroup$ – Sanchises Sep 8 at 18:00
  • $\begingroup$ Handwavingly, such a body causes vertical flow, possibly up, possibly down, but not zero; action-reaction means the body then experiences lift. Experimentally, a flat plate I tested in UIUC's low speed wind tunnel with one face slightly rougher than the other produced lift at AoA=0. Mathematically, you probably could build something pathological where all the lifts and torques cancelled out... I'd love to see such a beast. $\endgroup$ – Camille Goudeseune Sep 8 at 19:26
  • $\begingroup$ Ah yes, I was especially interested in your last bullet point. I guess the obvious counterexample would be an airplane that is trimmed for level flight in 0g (assuming most airplanes are not fully symmetrical). So I guess almost all asymmetric bodies produce lift. $\endgroup$ – Sanchises Sep 8 at 20:42
  • $\begingroup$ So, the Vomit Comet trimmed for hands-off flight during its parabolic segment? There's still some thrust and drag, but I guess it's as free of lift as a golf ball... $\endgroup$ – Camille Goudeseune Sep 8 at 21:51
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    $\begingroup$ A non-rotating golf-ball ;) $\endgroup$ – Sanchises Sep 9 at 5:55

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