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Is there any proportion rule for aileron and flap chord proportions?

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Well-Known Member
Dec 31, 2009
Barcelona, Spain.

Most airfoils in ToWS hace an aileron or flap at 0,2 chord. So it is to be assumed, that sticking to that proportions might be OK. However in Pazmany's great book Light aircraft design, we have a very useful table below, providing some guidelines for elevator area in percent of stabilator area, for a given tail volume. And those are way higher than 0,2 C.

I believe that most aircrafts stick to ToWS proportions, regarding ailerons and flaps, but I have noticed that some gliders do not, like the ones below; Marske Pioneer, Horten's Piernífero and the Bergfalker. A possible reason for that, might be that of the simplicity of building a constant chord aileron, on a taper ratio wing.?
Regarding the Horten's glider, the proportion of the aileron is cleary higher than average. Maybe it is so to attach the ailerons straight to the D tube? But this might create flow separation at higher deflection?

So, is there any aerodynamic reason, like in Pazmanay's tail elevators table, for increasing the aileron or flap chord more than 0,2 C?



Pazmany elevator area.png