aileron differential?

[hillmanr2]

I understand the reason for aileron differential on a semi sym. or flat bottom wing but I can't rap my head around how it is useful on a symmetrical aerobatic plane?
When I'm inverted then isn't aileron diff. actually having the opposite effect?

I could use some explanation on this,
Thanks

[ConRadical]

I hope this helps...
Aileron movement can actually yaw the plane. To make the plain roll you're basically causing more lift on one side, that side being the side going up. The side that has less lift generally has less drag which means it'll be trying to move forward while the other wing will try to move backwards, thus yawing the plane. To correct this you use aileron diff, more up than down.

[hillmanr2]

	Quote: Originally Posted by ConRadical
	I hope this helps... Aileron movement can actually yaw the plane. To make the plain roll you're basically causing more lift on one side, that side being the side going up. The side that has less lift generally has less drag which means it'll be trying to move forward while the other wing will try to move backwards, thus yawing the plane. To correct this you use aileron diff, more up than down.

Thanks, but this is my point. When flying level the down aileron is less than the up aileron. when inverted the down aileron is more than the up aileron.

The part that confuses me is a full roll. As soon as the plane is past 90 degrees of the roll what happens to make aileron differential be of any use?

[ConRadical]

the drag i mentions is still created no matter what orientation the plane is in. As long as it's rolling it'll be getting the drag that causes the yaw... some aerobatic planes won't need aileron diff. keep in mind though the wing is fully symmetrical the plane is not. You have the canopy and the rudder also creating drag.
I'll see if i can get one of our IMAC HQ guys to hop in here and explain this a little better.

[TimDavie]

Hillman,
The differential is going to be different on each plane and setup. Wing placement, aileron center-hinged/top hinged, size of aileron etc. What I have typically found is the aileron in the down position creates drag and causes a yaw to that side of the plane(left aileron, right yaw). so it doesn't matter if the plane is upright or inverted. again, this will be different on each plane and setup.

[Mithrandir]

I think this might explain...

A model is stable. Usually this means that upright it will fly straight and level. Roll'er inverted and she will slowly dive towards the ground.
This stability is generally achieved by having the wing at some positive angle of attack with respect to the stabilizer. What differential does, is counteract this relative angle during the aileron input, so that the "Spiral" tendency is reduced.
The wing with the UP aileron has had its angle of attack with respect to the stab reduced more then the other side was increased because it started out with a positive angle initially.

(I think this is what prompts differential aileron)

Think about this... in a rolling Harrier, the wing is always lifting "UP"..... so if rolling left, the plane naturally wants to circle right.... in this instance, the wing that has the "Down" deflected aileron is dragging the plane to the right... (Down with respect to the earth and NOT the plane)... so upright or inverted, there is drag on the right side....
I bet if we mixed differential ailerons to the elevator, so that as the elevator was applied in the rolling harrier, the deflection of the down aileron was reduced, this tendency would be diminished... basically a dynamic differential mixed to elevator....

[hillmanr2]

Thanks guys I think I see a slight flicker on the old lightbulb

[dick hanson]

	Quote: Originally Posted by Mithrandir
	I think this might explain... A model is stable. Usually this means that upright it will fly straight and level. Roll'er inverted and she will slowly dive towards the ground. This stability is generally achieved by having the wing at some positive angle of attack with respect to the stabilizer. What differential does, is counteract this relative angle during the aileron input, so that the "Spiral" tendency is reduced. The wing with the UP aileron has had its angle of attack with respect to the stab reduced more then the other side was increased because it started out with a positive angle initially. (I think this is what prompts differential aileron) Think about this... in a rolling Harrier, the wing is always lifting "UP"..... so if rolling left, the plane naturally wants to circle right.... in this instance, the wing that has the "Down" deflected aileron is dragging the plane to the right... (Down with respect to the earth and NOT the plane)... so upright or inverted, there is drag on the right side.... I bet if we mixed differential ailerons to the elevator, so that as the elevator was applied in the rolling harrier, the deflection of the down aileron was reduced, this tendency would be diminished... basically a dynamic differential mixed to elevator....

That might help - the biggest assistance I have seen is thru -- lower wing loading - next lower aspect ratio wings
At very low aspect ratios - the airflow goes more spanwise--stabilizes better.
My new clipped wing EDGE is very good at rolling stuff.

[DA2000]

An increase in lift causes an increase in induced drag. The ailerons are effectively changing the camber of the wing. The down aileron increases camber, while the up aileron decreases camber. More camber means more lift, ie. induced drag (that's why that wing goes up!) The increased drag on the down aileron causes a yaw in that wings direction, thus the need for differential.

[dick hanson]

yeh - lift is drag and drag is lift -
sounds wrong -- but it's all in how and from what direction you look at it
consider the parachute

[fredo]

I think this is the reason why they invented top hinged ailerons (sometimes called differential ailerons).The down aileron disappears in the cavity of the wing therefore reduces its area and becoming less "draggy" that way you can have same travel on both ailerons. This is the idea right? Unfortunately it somehow doesn't seem to work on Composite ARF planes. It seems like the resulting effect is too much therefore they need opposite differential. More down travel than up. Strange. Does anyone know why is it? My opinion is, it probably takes a lot of calculating,testing and designing the right profile.

[DKjens]

I actually think Mike's (Mithrandir) explanation makes the best sense. Aileron differential actually aligns the resulting AOA of the wings with the AOA of the horizontal stab/elevators and thereby provides the foundation for axial rolls. I can see that wing position (low, mid, high) also has an impact on the amount and preface of the differential, since the airplanes resulting drag and weight position has an influence.

The explanations about adverse yaw doesn't cut it, because, as has been pointed out, when inverted the differentail dialed in while right side up would have the opposite of wanted effect.