Control surface differential

[extreme_stu2@yahoo.com]

Would or is there anybody out there that can tell me what is meant be differential, in regards to control surfaces,ailerons,rudder,etc!.😕

[OV10]

Differential control is with regard to ailerons.
This site is a wealth of good info in the RC airplane world and the link is directly to your question.

http://www.rc-airplane-world.com/aileron-differential.html

[fhhuber]

Differential, usually referring to ailerons...

Refers to one control surface moving more degrees than the other, usually the one moving up has more travel than the one going down.

this has a few effects.

The most common use is for combating an effect called "adverse yaw". The aileron moving down will add drag. The one going up might actually reduce drag. That tends to pull the nose around opposed to the commanded bank which can result in : stall, snap-roll and spin. The adverse yaw is most noticeable at lower airspeed high AOA and with flat bottom or under-chambered wings.
Differential throw reduces the added drag on the downward moving aileron, sometimes allowing the upward one to be in the region where it is adding drag before the downward moving one's drag is significant.

It can also be used to correct for a precision aerobatic plane that tends to roll around a line above the canopy instead of through the spinner. It doesn't take much differential aileron to correct this.

some planes need NO differential.
some benefit from a small amount.
Some can use extreme differential to the point of virtually zero downward aileron movement.

[WintrSol]

It is interesting to note that the latest wing design, being tested by NASA, actually has 'proverse yaw'; IOW, you get some wingtip thrust, rather than drag, when the wing is commanded to roll. This eliminates the need for a rudder to correct for yaw, so a stable flying wing is possible, assuming the design can scale from the test models.

http://www.uasvision.com/2014/03/19/nasa-dryden-students-achieve-proverse-yaw-through-wing-tip-aerodynamics/

[Grossman56]

That reminds me, I was going to ask this. When I roll my Pandoras, they will roll to the right a lot faster than the left, I'm gathering due to the prop factor. Is there any way to balance that out while using one channel for ailerons, or would I have to assign each aileron servo to a separate channel?

Grossman56

[WintrSol]

Can we assume that you have checked the range of motion of the ailerons, and that they are the same in both directions? If so, you can try shifting the end points in the transmitter, if it is programmable.

[Grossman56]

DX8, travels are equal, I'm not sure how to shift the end points.

Grossman56

[WintrSol]

I meant the mechanical motion of the ailerons. There could be a mechanical reason the movements are not identical, such as the position of the servo arms, relative to the servos. For example, if you sight down the surface of the wing, does one arm lean slightly forward, and the other slightly aft? I make sure both of mine lean slightly forward, the same amount, so that the differential is mechanical, and the ailerons go up more than down.

Once you have seen to that, if you connect the ailerons to separate channels in the receiver, you can create a mix in the transmitter to control each at the same time. Once that is done, you can change the end points of each channel independently; I don't know how to program the Dx8, but do know, from other discussions, that it is part of the programming logic. It may have a different name, like travel limits, or some such.

[Grossman56]

Got you WintrSol, I've considered using a separate channel for each aileron, but was curious as to whether there was another way, I'll check the mechanical motion if for nothing else, to cross that off the list of possibilities. Thanks for the tip.

Grossman56

[KitBuilder]

You;ll always roll faster one way than the other... motor torgue and the corkscrew effect of the air over the rudder... the second being the reason you need to hold rudder on taildraggers on take-off.

[PappaBear]

To have the same rate of roll in both directions, you will have to increase the aileron defection in one direction more than the other. If you use two channels to set up the ailerons is easy to do. Simply increase the throw in one direction more than the other, job done.

Using two channels to set up the ailerons makes for a very versatile set up and so easy to make adjustments. I do it every time with every model.

Martin.

[Grossman56]

What I ended up doing is going into the aileron servo set up and increasing the percentage in one direction to balance it out. You'll see when in the DX8 program that when you hold the stick over it will show the value of that direction, opposite direction will show the value of that direction.

Grossman56

[gooniac33]

In simple terms.... making the up aileron deflection more than the down deflection. The aileron that goes down too far will induce adverse yaw. So when you roll to the right the nose will move to the left as well. You can do differential in the radio by making sure that each aileron is in a separate port so that you can use the differential function in the radio. If you have the ailerons on a Y harness then you can prevent adverse yaw with mixing in rudder. There are lots of other ways to do it too but I said I would keep it simple...LOL

[Grossman56]

I have an aileron/rudder mix dedicated to a switch in all of my airplanes. Depending on the wing type, the amount will vary, the highest being on a flat bottom wing and the lowest on a symmetrical/ tapered wing