aileron differential?

[dick hanson]

calculating it --is pretty much--worthless.
Understanding the concept is all you need
The top hinged model with the huge open gap -(The comp model) has a lot of messed up air in that crack. I once tried to seal the darn things but that proved to be a real problem to get correct.
So -- the efficiency of up/down is different -and you have to compensate with up-down differences . cut n try.
If the models really flew at ZERO AOA-- then differential would likely be -ZERO.
but some AOA is always present except for vertical flight
and even then there may be a bit -

Ideally --the axial roll is on the spinner try moving the holding stick on a hand fly model and do some "rolls" - If the roll is not on centered - the plane looks wobbly. As others noted - the correct amount of differential is a moving target .
Learn to fly and trim for "hands off" level flight
then try all the various roll attitudes - inverted to inverted -upright to upright - vertical -up-down - slow and fast .
You will find that you learn to automatically add a little elevator as you go.
The setup you go for may be different from what someone else likes . and you both may do perfect looking rolls .
I hate to say it but to get it right takes actual study and practice -
If study does not appeal to you - get a computer game -

[Colonel Klank]

IMHO

To trim for aileron differential:

Go high.
Set motor to idle
Up elevator until stall
Straight downline
Have someone watch your plane (the spinner) while you aileron roll on the downline
He will surely see some wobble
Add aileron diff until the wobble is reduced to minimum

It will take several flights to get it right

Downline takes motor thrust line out of the equation.

W. Patrick

[RTK]

I copied this off of a trim chart I use.


Fly model toward you; pull to vertical; neutralize controls, roll. NO ELEVATOR/RUDDER during the ROLL!!!.
A. No Heading Changes
B. Heading change opposite to roll command C. Heading change in direction of roll command
A. Differential settings OK B. Increase differential C. Decrease differential

Well it did not transfer quite right, here is the location.
http://www.rcaerobats.net/trim_chart.htm

[dick hanson]

Trim Charts -
those and a buck will get you a cup of coffee- maybe--


PS -don't forget the dollar-

[hillmanr2]

Thanks for the good discussion guys
I have differential dialed in to my extra but I didn't understands the concept behind it.
I used Peter Goldsmiths trimming procedure of flying directly into the wind, pulling a 45 up line and rolling the plane to see which way it "walks". To the right is to much and to the left is not enough.

[Ryguy]

This has always confused me. My radio can do differential in both directions. By adding differential, do I reduce the travel of the up going or down going aileron?

Also, the idea that AOA is what helps cause the walk in rolling manuevers has me bamboozled too, because my Byp Yak, along with most every other foamy I've flown, always wanders in the opposite direction that aileron is given, even in the downward half of rolling loops. I may be way off here, but when the AOA is negative, such as in the downward half or such manuevers, shouldn't the walk be in the other direction too if this is the cause of it? I'm quite bamboozled and in quite a conundrum.

[Colonel Klank]

	Quote: Originally Posted by Pale_Rider_Va
	IMHO To trim for aileron differential: Go high. Set motor to idle Up elevator until stall Straight downline Have someone watch your plane (the spinner) while you aileron roll on the downline He will surely see some wobble Add aileron diff until the wobble is reduced to minimum It will take several flights to get it right Downline takes motor thrust line out of the equation. W. Patrick

To set aileron diff, you have to exclude as many detracting forces as possible. Performing this on a downline with motor at idle not only takes out motor thrust line and P-Factor, but gravity also. On a pure, straight downline, gravity affects the tops and bottoms of the wing equally. (i think)

[3dubya]

	Quote: Originally Posted by Pale_Rider_Va
	To set aileron diff, you have to exclude as many detracting forces as possible. Performing this on a downline with motor at idle not only takes out motor thrust line and P-Factor, but gravity also. On a pure, straight downline, gravity affects the tops and bottoms of the wing equally. (i think)

I agree with that totally. I zero trim vertically, but sometimes the roll looks funny when a pile are done in a row vertically down ideling. It can be just a shape of the body thing that looks funny when rolled, and you need to offset the roll to improve the look of it. Unfortunately differential settings arespeed sensitive and mucked up anyway on the flats with induced elevator lift which ever Way Ur using it on the wing. When in doubt don't use it all with center hinged ailerons.

[Mithrandir]

	Quote: Originally Posted by Ryguy
	........ even in the downward half of rolling loops. I may be way off here, but when the AOA is negative, such as in the downward half .............

The AOA is not negative... the nose is pointed towards the ground, but the plane is continuing to loop around...
Reference frame here is the confusion...
In a rolling Harrier... straight and level across the field, the AOA (In Pitch) is transitioning from positive to negative (In the reference frame of the plane)...
There is also an "AOA" in the pitch dimension... also called "Beta"... the Beta is transitioning from Positive to negative... or rather... right to zero to left to zero... etc etc etc....

To help you visualize the rolling harrier deal better.... I will try to explain it more simply.....
Imagine the plane flying directly away from you in a rolling harrier.... rolling left... the wing that is on your right has the downward aileron... upright and inverted... the wing on YOUR right is down... this downward deflection increases the drag on the right side... the upward aileron is Decreasing the drag on the left... so... the model naturally drags around to the right........

[Ryguy]

Thanks for that explination, Mike, that helps my brain wrap around this effect. So how do you get rid of it? Adding aileron differential the way I see has virtually no effect because as soon as you roll inverted then the aileron with less down travel will suddenly have more because it is now going up.

I've asked for help on this subject on RCG a couple times and everyone was clueless as to how to fix it and how its caused. Every foamy I've flown has had terrible problems with this adverse yaw in rolling manuevers except my Fancy Foam Xcalibur. Right now the plane I'm trying to fix this on is my Byp Yak. I've tried everything I can think of adjusting aileron differential on it to no avail. What am I missing?

[dick hanson]

How the plane is trimmed is part of the equasion - CG positioning requires a load at the tail - large or small - positive or negative.
Mother nature -in the form of gravity - will make the PERFECT trim for any given atitude different for any other position.
This ain't a friggen computer game .
The aileron is a flap which is nothing but an extension of the airfoil
put one up -one down and we have changed the drag from one side to the other.
This fact -plus the fact that the rest of the model may swing in a cone about the cg, makes setting "best" differential a case by case thing.
Also
This is going to relate to gravity-depending on the position of the model
all agreed?
You must decide which attitudes (up/down / upright / inverted)are easy to correct -which are difficult .
because --in the end - you must correct for all except the one where differential is "perfect" .
Hint: light wing loadings are easier to set up and faster models are easier than slower ones
Why?
These conditions keep the wing at a lower angle of attack in all flying positions.
Foamies (near and dear to me ) are a different breed of cat because of the very slow speeds and super low wing loadings
Much of what you do with them , puts wings at attitudes which are usually considered stalled but the super low wing loadings allow for this. The working envelopes for aerodynamic rules are NOT the same for all sizes of models.
Try a good foamie and you will note that you can fly it with the CG -literally anwhere on the wing - just adjust speed till controllability is managable.
also--
Vectored thrust also plays a big part here.

[zoomer260]

I'm a dummy but don't you just have to "fly the Plane" to correct some things? I've met good pilots ( way better than I ever hope to be ) that used rudder and elevator to correct everything before they mixed out any of it. Sometimes you still have to fly the plane.