Ailerons and Cambered Airfoils

[foamflyer]

I have heard that ailerons do not work on wings with cambered airfoils (such as those on slowfliers). Is this true? If so then why?

[Sparky Paul]

Strictly speaking, all airfoils are cambered; beginning with 0 to a lot! :)
Ailerons work poorly with high dihedral, which is typical of a park flier.

[foamflyer]

Yes, but I'm not talking about dihedral, I'm talking about a wing made out of a curved flat sheet.

???

[Marion]

Yes, they work on cambered airfoils.

[Sparky Paul]

Yes, but I'm not talking about dihedral, I'm talking about a wing made out of a curved flat sheet.

???
.
I explained why ailerons have a poor reputation generally on some wings.
You chose to omit the specific situation.

[DLD]

Any airfoil will work well with ailerons if the dihedral is about five degrees or less. If you are flyoing too slow for them to work, you're flying too slow! I've flown many highly cambered wings with ailerons and flaps, they work perfectly well. Good Luck,

David Layne

[Sail 'n Soar]

I assume you are speaking of ailerons on highly cambered airfoils, since all but symmetrical foils are cambered. If you are using a highly cambered foil, you are flying with a higher design CL. In that case, the delta CL/CL for a given aileron deflection, is going to be smaller. The will result in less roll relative roll moment for a given diflection. Flying the varioiusly cambered and symmetrical wings at the same CL should result in basically the same aileron effectiveness, assuming your aren't so far off design you have a major BL separation..

[Andy W]

Say what?

[Sail 'n Soar]

Say what?

Say a given ailereon deflection creates a change in CL of .1. If flying at a CL of .5 (low cambered foil at a couple of degrees angle of attack), then the aileron area of one wing will be at a .4 and the other at .6, a sizeable difference resulting in a strong rolling moment, with the one wing in the aileron area generating 50% more lift than the other. With strip ailerons, that represents the whole wing, or with conventional ailerons that represents roughly the outer 50% of the wing' that with the greatest impact on rolling moment.

Now if flying a more highly cambered airfoil at .9 (the only reason I can think of for going with a more highly cambered foil is to generate more lift, i.e., operate at a higher CL), the one wing will be at .8 and the other at 1.0, now a 25% vs the former 50% difference in lift in the wing aileron area. That difference will translate into less effective ailerons for a given deflection.

But fly the highly cambered foil at .5 and the aileron effectiveness will be the same as the lower cambered floil.

[capncrunch]

um, simple glossary:

If you are using a highly cambered foil, you are flying with a higher design CL.

CL -> Coefficient of Lift, or how much lift the wing makes per unit of wing area.

In that case, the delta CL/CL for a given aileron deflection, is going to be smaller. The will result in less roll relative roll moment for a given diflection.

delta CL/CL -> change in coefficient of lift divided by the (current) coefficient of lift. this is also known as the rate of change (of the lift coeff.), what he's saying is that since a wing of a certain size with a cambered flat section is going to have more lift than a full section airfoil, and therefore, the amount of difference created between the wing halves by the ailerons will be less for the cambered airfoil.

Flying the varioiusly cambered and symmetrical wings at the same CL should result in basically the same aileron effectiveness, assuming your aren't so far off design you have a major BL separation..

BL -> boundary layer. separation happens when the airflow separates from the body in question. major separation -> major loss of lift.

roll rate for a certain size of aileron at a certain deflection is related to the coefficient of lift. so if you have two wings with nearly the same CL, they should roll about the same.

-hope that helps.

barrett

[Sparky Paul]

You've all failed to note that a single-surface cambered foil will have a high Cd!
And the downgoing aileron will make that number worse regardless of what Cl does!
Can you say "adverse yaw"?
For such a surface, having a lot of differential, possibly 8:1, would make the plane fly better with ailerons.

[capncrunch]

right. there's a reason you dont see so many cambered surface foils anymore - they are rather inefficient, CL/CD ratio (lift to drag) being somewhat low, more lift but lots more drag.

-barrett

[davidfee]

Those highly cambered airfoils are actually pretty efficient for low Re/high Cl, even the curved plates are pretty good. That's why they are used on all Free Flight gliders (F1A, F1B, F1C, F1D, F1E, F1G, F1J, F1K...) Ok, so FF HLG's often use more of a flat plate... but they must be launched by hand... so low drag at higher speed is critical to maximize launch height... and the Re is so low they must glide fast as well.

You also see them in the heavy-lifting events, such as the SAE competition.

-David