Reflex flaps capability is very common in flapped gliders, but outside of gliders I am only aware of the Maule which has this feature. https://aviation.stackexchange.com/a/37753/20394 shows the advantage gliders gain from reflex position, so presumably this would hold for more aircraft than just gliders.

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I can see how with certain types of flaps, such as fowlers, the mechanism would be impossibly complex. But for other types with a simple pivot this must be more attainable.

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    $\begingroup$ This is a good question, although I'll admit I'd never heard of a reflexed flap mechanism prior to reading your question here. :) $\endgroup$ – ifconfig Jan 18 at 22:48

I'd guess that it's because gliders are optimised for low speed in rising air and their aerofoils have lots of camber. Reflexed flaps allow them to reduce the camber for high speed flight, but the resultant aerofoil isn't as good as a proper low-camber, high speed aerofoil.

RC power models generally have plenty of power to spare and either don't care about drag or it only matters at high speeds. Their aerofoils are generally low (or zero) camber already so they don't need reflex flaps to achieve it.

  • $\begingroup$ Reflex reduces lift, so whether there is camber or not shouldn't eliminate the effect from reflexed flaps. Considering the extents people go to to pick up a knot or two of airspeed, it seems reflex might be a solution. Perhaps it is only worth the cost when you have a plane designed to spend significant periods at both slow and fast speeds? Most small planes only fly slowly to land or right after wheels up. $\endgroup$ – Kenn Sebesta Jan 20 at 1:46
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    $\begingroup$ Reducing lift isn't the same as reducing drag. If you start from an aerofoil that's optimised for high speed, adding reflex would just add drag. Reflex is a compromise to make a low speed aerofoil act a bit more like a high-speed aerofoil, not a magic bullet that makes everything faster. Gliders are designed for low speed and need it, power planes are designed for cruise already, so they just use flaps for low speed. $\endgroup$ – Robin Bennett Jan 20 at 9:07
  • $\begingroup$ "...power planes are designed for cruise already," Is this generally true? On one hand, it makes sense that a cruise plane would be optimized for cruise, but on the other hand there are all kinds of design features which detract from cruise. For instance landing gear, which imposes a huge weight and/or drag penalty yet is only useful for the 3 minutes at the beginning/end of a 5 hour flight. So my earnest question is "are power planes' airfoils able to be optimized purely for cruise, without consideration of slow-speed lift?" $\endgroup$ – Kenn Sebesta Jan 20 at 13:42

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