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Help with aileron differential

Old 03-11-2003, 10:07 PM
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Roger George
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Default Help with aileron differential

Is there a set percent of up and down for aileron differential. For example if the manufacture calls for 1/2" up and 1/2" down, do you use 120% up and 80% down for example, or is it all trial and error. Thanks
Old 03-11-2003, 10:48 PM
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Default Help with aileron differential

Depends on the plane. Most don't call for differential. I use it on my gliders, but not power. Works good on a cub though. What are you doing it on?
Old 03-12-2003, 02:38 AM
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CafeenMan
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Default Help with aileron differential

The further an airfoil is from being symmetrical, the better chance that it will benefit from differential as a rule of thumb.

Semi-symmetrical wings benefit from a little (maybe 1/2" up and 3/8" down). Flat bottom wings can use more (1/2" up, 1/8" down).

But to get it right you have to test fly/adjust, test fly/adjust until you like the way it flies.
Old 03-12-2003, 03:30 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by CafeenMan
.
I know i'm asking the right Guy here.
Why is it that they always say adjust for more UP and less down?
On one of my planes I tried everything and the best I can do on my trim is have only one aileron up and down.
The other is always centered.
If I trim to turn slow the other way then the other aileron is centered but now the right aileron has the right amount of up and down.
Using the stick both are fine and I have 1/2 up and 3/8th down.
Any suggestions?
Old 03-12-2003, 04:03 PM
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CafeenMan
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Default Help with aileron differential

The reason "they" say to trim for more up and less down is because it lowers the angle of attack of the wing. Flaps down = Stalls easily.

When I make adjustments to the ailerons, I start out with them both as close to center as possible. Sometimes they're off by just a hair because a half turn (clevis) one way is slightly too high and a half turn the other way is slighty too low.

If an adjustment is needed I adjust both ailerons the same amount. For example, if it has a left roll then I give the right aileron a half-turn up and the left aileron a half-turn down.

If you're ailerons aren't moving the same amount in each direction then the mechanical setup is wrong.

Also, if the wing isn't dead straight, then it will never trim properly. At best you'll be able to trim it for one speed and that's it.

What plane are you talking about?
Old 03-12-2003, 04:20 PM
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Chuckr53-RCU
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Default Help with aileron differential

I have a Futaba 8 channel radio and I can't set up differential unless both aileron servos each have their own channel...1 and 5 for example, so a Y-harness doesn't work for me.

The differential is setup so that both ailerons go up a greater amount than they go down so that when in a turn the "up" aileron creates more drag than the "down" aileron. This pulls the low wing thru the turn faster than the up wing...a coordinated turn. If you're setting up both ailerons to go both up and down 1/2" then your not getting the benefit of differential.

I have a TT Slow Cub .25 size with the differential setup so that the ailerons go up 5/8" and down 3/8". Each model will be different.

To get coordinated turns, I like setting up differential more than mixing some rudder deflection with the ailerons.
Old 03-12-2003, 04:23 PM
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Default Help with aileron differential

Sorry...I should have said the high wing goes thru the turn faster than the low wing due to the increased drag on the low wing...duh.
Old 03-12-2003, 04:24 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by CafeenMan
YUP,
I knew you would know.
The plane is the Avistar.
But from reading your post I see where I screwed up.
I never knew 1 turn on those fine threads would make such a big change.
I just received my GOLD N CLEVIS pack so i'll be changing over to those and now know that I should tweak with only 1 turn or less.
Thanks for the info. :thumbup:
PS;
Your info was great so I printed that out along with some other info I received for working with MoniKote
Many Thanks
Old 03-13-2003, 06:29 PM
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mulligan
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Default Help with aileron differential

Originally posted by Chuckr53
I have a Futaba 8 channel radio and I can't set up differential unless both aileron servos each have their own channel...1 and 5 for example, so a Y-harness doesn't work for me.

The differential is setup so that both ailerons go up a greater amount than they go down so that when in a turn the "up" aileron creates more drag than the "down" aileron. This pulls the low wing thru the turn faster than the up wing...a coordinated turn. If you're setting up both ailerons to go both up and down 1/2" then your not getting the benefit of differential.

I have a TT Slow Cub .25 size with the differential setup so that the ailerons go up 5/8" and down 3/8". Each model will be different.

To get coordinated turns, I like setting up differential more than mixing some rudder deflection with the ailerons.

You don't NEED a computer radio to set up differential- it can be done with ailerons on the same channel by setting up the geometry of the linkage.

Normally, the servo arm is perpendicular to the control rod when the control surface is in the nominal position. If you lengthen/shorten the control rod such that the servo arm is NOT perpendicular when the control surface is at the nominal position, you will create differential throws.

I always do this on throttles. I make the control rod a little longer than would be if the servo arm were perpendicular at mid-throttle. This gives a little better control at lower throttle settings, and faster response at high throttle where the engine responds less to throttle changes.

- George
Old 03-13-2003, 07:06 PM
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Default Help with aileron differential

Originally posted by Whirley Bird

YUP,
I knew you would know.
See? I knew mom was wrong about me!

I just received my GOLD N CLEVIS pack so i'll be changing over to those and now know that I should tweak with only 1 turn or less.
Changing clevis types or brands won't make a difference as far as adjustment difference per turn. 2-56 = 2-56.

The Sullivan clevises are very good though. Just be sure when you remove the keeper you put it someplace where it won't get lost when you remove them like a bowl on your workbench or a drawer in your field box.

Lastly, I didn't go into detail on the "always adjust up" thing. I don't live by rules like that. I try to get my control surfaces as close to center as possible.

Back to the left roll example. Let's say I give each aileron a half turn in the appropriate direction and that turns out to be too much - it now rolls to the right slightly.

If the left aileron is down a little, then I'll raise it a half turn. If it's ok, but the right aileron is up a little, then I'll lower the right aileron a half turn. If they both look ok, then eenie, meenie, minee, mo.
Old 03-13-2003, 07:08 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by mulligan



- George
I solved my problem by installing a round servo disk plus the advice from CafeenMan.
I never thought 1 turn on those fine threads would make such a big difference.
But I have my throws all setup now
Old 03-13-2003, 07:13 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by CafeenMan

Changing clevis types or brands won't make a difference as far as adjustment difference per turn. 2-56 = 2-56.

I know that,
It's just that I like better quality items on my plane and not have t worry about some nylon or plastic $1.00 item is going to give out and cost me a plane
Old 03-13-2003, 07:21 PM
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CafeenMan
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Default Help with aileron differential

OK, the way you worded it in your last response I thought maybe you thought a better clevis would give a finer adjustment. Didn't mean to insult your intelligence though.
Old 03-13-2003, 07:22 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by Chuckr53
Sorry...I should have said the high wing goes thru the turn faster than the low wing due to the increased drag on the low wing...duh.
Yes,
I'm not an expert but I flew many hang gliders and the cross bar would shift and creat more lift on the low wing because the high wing is flying faster.
Because the gliders don't have a rudder the cross bar moves side to side and changes the wash out and wash in of the wing tips as needed when making turns
Old 03-13-2003, 07:30 PM
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Default Help with aileron differential

Originally posted by CafeenMan
I'm printing all this stuff out Guys.Thanks for all the info.
CafeenMan,
The plane in question here is the WIZ-BANG Avistar
Not much of a plane to you Guys but I did put a lot of TLC nto it and the covering is superior.
Looks like a GEM and this weekend I hope to have the tail dragger conversion installed but I forgot to order the small wheel for the back
Old 03-13-2003, 07:37 PM
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Default Help with aileron differential

Originally posted by CafeenMan
. Didn't mean to insult your intelligence though.
Intelligence??? `ME???LOL
You didn't insult me LOL
I just act like that most of the time LOL.
I was really not aware that 1 half turn on that super fine threaded rod made such a big change.
Learning to land this tail dragger should be fun but i'm always ready and expect the expected so I stocked up on 12 props
Do you drink a lot of coffee?
Old 03-13-2003, 07:37 PM
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CafeenMan
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Default Help with aileron differential

You don't need no freakin' pansy tailwheel! Real men use a skids!

Actually, a plane with a skid will taxi better than you think. Make a stearable skid so you can put a wheel on it when you get it.
Old 03-13-2003, 07:38 PM
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CafeenMan
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Default Help with aileron differential

Taildraggers aren't difficult. Don't sweat it. I think they're easier than trike gears for the most part. Landing isn't any different. Just fly your plane and have fun.



PS. No, I don't drink coffee.
Old 03-13-2003, 07:48 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by CafeenMan
The reason "they" say to trim for more up and less down is because it lowers the angle of attack of the wing. Flaps down = Stalls easily.

The above I don't understand.
Lowers the angel of attack of what half of the wing?
The lower or upper.
The lower wing is lower and flying slower right?
So I think you would want the angel of attack greater on the lower wing because the higher wing is flying faster.
How does the angle of attack change when the wing is secured at a specific angle and is presently fixed?
The wing is still flying but one side is flying slower.
And the angle of attack remains the same no matter how steep the turn.
Old 03-13-2003, 07:55 PM
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CafeenMan
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Default Help with aileron differential

OOPS! My mistake. Lowering the flaps (or aileron) RAISES the angle of attack of the wing. The centerline of the wing goes through the center of the trailing edge and the center of the leading edge.

If the fuselage doesn't change it's angle into the wind when the aileron goes down, then the wing with the lowered aileron (or flap) has a higher angle of attack and the wing with a raised aileron has a lower angle of attack than they did when the ailerons were centered.

I'm not explaining this well. Just draw a picture of an airfoil with the aileron level and draw a centerline through it.

Then draw it with the aileron lowered with a centerline through the center of the TE and LE and you'll see what I'm talking about.

For a more detailed explanation, see the Gurus in the Aerodynamics forum.
Old 03-13-2003, 08:00 PM
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Default Help with aileron differential

Whirley Bird,

I think you got the posts mixed up. Cafeen wasn't speaking about the coordinated turn, but rather the general reason differential is always for more up aileron than down.

- George
Old 03-13-2003, 08:48 PM
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Whirley Bird
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Default Help with aileron differential

Originally posted by mulligan
Whirley Bird,

- George
Hi George,
Yes,
thinkI responded to the wrong post with info from another post.
Thanks for the eye ball spotting

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