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The traditional Bernoulli explanation of lift depends thoroughly upon a wing which, through differing geometry between the upper and lower wing surfaces, causes higher air velocity above and below, leading to a pressure differential, which in turn creates an upward lift force. Yet insect wings are nearly flat, and they seem to be capable of generating some lift to complement their direct application of downward force to the air. I get the strong sense this is one of those cases like static and kinetic friction where the first year university description turns out to be grossly oversimplified, and there's some deeper, more true to form explanation I'm missing.

How do insects achieve lift with flat wings, and what am I missing?

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  • $\begingroup$ A number of comments hidden. To answer a question, post an answer. $\endgroup$
    – rob ♦
    Commented Oct 24, 2021 at 20:03
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    $\begingroup$ Two comments. (1) The Bernoulli explanation of lift is about a pressure difference and about production of a downdraft from the wings; there are many erroneous explanations which begin with the air velocity difference. Read carefully; some links. (2) If you have ever touched an insect you have probably noticed its wings are not rigid; I’m not sure what it means to call a constantly-flexing surface “flat.” $\endgroup$
    – rob ♦
    Commented Oct 24, 2021 at 20:12
  • $\begingroup$ The "traditional" explanation is the "equal time fallacy". It's traditional and it's wrong. The first thing you need to understand is how wings actually work. Read av8n.com. $\endgroup$
    – Mike Dunlavey
    Commented Oct 26, 2021 at 20:41

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Note that uncambered wings on insects are flexible, and twist while being beaten up and down in air into complex 3-dimensional curves. The lift is generated by a cyclic mechanism called vortex shedding plus the interaction of the moving wing with the previously-shed vortex.

This is a tremendously complicated process which was not well-understood until the 1950's, through the work of von Karman.

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    $\begingroup$ Vortices also cause a local increase in viscosity, which substantially reduces the insect's terminal velocity. "Big whirls have little whirls that feed on their velocity; little whirls have lesser whirls & so on to viscosity" - Lewis Fry Richardson. $\endgroup$
    – PM 2Ring
    Commented Oct 25, 2021 at 1:27
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Maybe you look at this beautiful video and see, that insect flight is more complicated and not to be compared with airplanes, jus moving with the same form of wings an only going straight,https://www.youtube.com/watch?v=Cnn9CfsYJqc

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enter image description here As shown in the figure, we define that one side of the object at the curvature center of the curve is within the curve, such as A in the figure; The object on the other side of the curve is outside the curve, such as B in the figure. enter image description here As shown in the figure, the red curve represents the curve of the airflow around the wing from the top of the wing, and the wing and the curvature center of the curve are on the same side. Due to centrifugal force, the air flow tends to be far away from the upper surface of the wing, so the pressure on the upper surface of the wing decreases. The blue curve represents the curve of the airflow around the wing from the bottom of the wing, and the curvature center of the wing and the curve is not on the same side. Due to centrifugal force, the air flow tends to compress the lower surface of the wing, so the pressure on the lower surface of the wing increases. In this way, the pressure difference between the top and bottom of the wing also leads to the lift of the wing. The lift of insects' wings is also generated according to this principle. Because the air flow will also circle the wings along the curve, it will also generate centrifugal force and lift force. This is nothing special. So lift is not explained by Bernoulli's theorem.

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