Is this thread too old to post on?

It still works, go ahead

Thanks for bumping this. I never really understood aileron differential until now.

Hi Guys, I'm Julio, I live in Brazil and I'm the manufacturer of JC propellers. SUPER PROPS, found for sale in your country at Aircraft International.
My question about the AILERON differential is the following:
is there a percentage ratio to be applied to the aileron down compared to up?
TKS,
Julio

Originally Posted by jc super props

Hi Guys, I'm Julio, I live in Brazil and I'm the manufacturer of JC propellers. SUPER PROPS, found for sale in your country at Aircraft International.
My question about the AILERON differential is the following:
is there a percentage ratio to be applied to the aileron down compared to up?
TKS,
Julio

From my experience each plane is different. Do the aileron differential test to find out what the plane needs and go for it. See the attached trill chart .

Differential is all good and well for upright flying, but is reversed when inverted.

So you have set your model up with differential, meaning that the upward going aileron will travel more that the downward going aileron.

Now roll inverted to wings level. Now you have the horrible situation with the opposite of differential, whereby the upward (relative to the direction of lift) going aileron moves less than the downward going aileron.

Differential is great for planes that mostly fly upright.

You will never see differential aileron on an Extra or other full house aerobatic aircraft. Talking full size now. You will fly the plane keeping the ball in the middle.

what does differential do on a vertical down line when the wings aren't making lift??
as mentioned above... start from inverted and the differential starts out the wrong way..
Discover the correct CG and Decalage, then tune the differential... and best if you tune it until the roll is axial rather than pre-supposing more up than down.
(the truth is, the bulk of the "drag" comes from the lift vector over the aileron tilting aft... and both ailerons tilt that lift vector aft)
15 years later, I stick by my explanation...
https://www.flyinggiants.com/forums/...88&postcount=6


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)

(2021 Edit: I do think in the case of a rolling harrier.. the wings are stalled, quite a bit of wake.. so the aileron going "up" is going into a waked region not adding drag...almost the same as if the aileron were removed at that moment... maybe?... so the below part, I suspect is less true than I thought in 2006)

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....

I was going to start a new post but I will add another conundrum to the aileron diff question.

I am setting up a 126” carden 300. I know how to test for axial roll and what to correct for. My question is has anyone ever seen an aircraft that needs MORE down aileron than up? This is exactly what i am seeing with this bird. What would be causing this to act contrary?

Originally Posted by crashburn4ever

I was going to start a new post but I will add another conundrum to the aileron diff question.

I am setting up a 126” carden 300. I know how to test for axial roll and what to correct for. My question is has anyone ever seen an aircraft that needs MORE down aileron than up? This is exactly what i am seeing with this bird. What would be causing this to act contrary?

Comp-Arfs with the skin hinge aileron to the top wing skin will require more down deflection than up as the hinge pivot point is not centered in the wing cord.

Originally Posted by crashburn4ever

I was going to start a new post but I will add another conundrum to the aileron diff question.

I am setting up a 126” carden 300. I know how to test for axial roll and what to correct for. My question is has anyone ever seen an aircraft that needs MORE down aileron than up? This is exactly what i am seeing with this bird. What would be causing this to act contrary?

On a side note....do you have any pics of your new Carden to post?

Originally Posted by crashburn4ever

I was going to start a new post but I will add another conundrum to the aileron diff question.

I am setting up a 126” carden 300. I know how to test for axial roll and what to correct for. My question is has anyone ever seen an aircraft that needs MORE down aileron than up? This is exactly what i am seeing with this bird. What would be causing this to act contrary?

Ive seen it on the comp-arf's with top hinged ailerons as Zeeb said, as well as a few old designs that had the wing in a horrible location but the 126" Carden shouldn't need anything abnormal here.

When you initially set the aileron throw, did you measure it in inches or degrees? If you used a throw meter and measured in degrees was the airplane level? If you're going out and just adjusting off your baseline setup, its very possible that setup could be wrong. I'd double check what the actual throw is first then go from there.

Along with Marks point, make sure your mid travel throws are exact too. Even if max throws are equal, mid travel may not be.

Mark, I used inches to set it up. I will recheck the midpoints. It is requiring about 1.25 inches more down aileron than up in a right roll. The left is a little better for obvious reasons.

Originally Posted by crashburn4ever

Mark, I used inches to set it up. I will recheck the midpoints. It is requiring about 1.25 inches more down aileron than up in a right roll. The left is a little better for obvious reasons.

1.25" is wayyyyyy off, there's something else going on. Most of the time you should only need 1-3 degrees of a difference to smooth out any issues. What happens to the ailerons when you grab them by hand and try to force them back when they are deflected? I'd be willing to bet you're getting some kind of blowback on one surface at a specific deflection

I will try it next time! Thank for the tip! This thing needs to start behaving! Mocksville is next weekend!

Edit: just thinking about it a bit, I have put around 20 flights on the airplane and the roll rate regardless of speed (exeption of very low speed) is nearly identical. I will check it again tomorrow when I go out to the field and get a more precise measurement.

If it’s not blowback, Could it be a wing incidence thing? I don’t have much experience with measuring or knowing if it is correct / appropriate or not.