ytell

What is the explanation for the differential ailerons effect in aerobatic model?

In a non aerobatic flight the extra drag from the down aileron causes the nose to yaw toward the high wing (out of the turn)

But why a continuous aileron input (model is rolling continuously), although the aileron with excess drag apears symmetrically on each side of the model (changes each half a roll) model heading will veer unless you compensate with more deflection on the down aileron?

Thanks,

Yoav

da Rock

Your next sentence indirectly describes how differential works, how it works both in excess and when present in an appropriate amount. Aileron differential is not always "extra drag". At different deflections it can provide the perfect amount of lift/drag for one wing. The other aileron may or may not be working as well. At other deflections each might provide too little or too much. It is not always symmetrical or in the correct amount from one aileron to the other. Depending on the pitch of the airplane, as well as other influences, the two ailerons can experience quite different airflows. i.e. symmetrical airfoil wings don't always encounter the same environment on both sides of the fuselage, which can account for why modelers apply differential adjustments to symmetrical airfoil wings. It's not a simple thing. An experienced modeler will test his trim adjustments and change them until they are appropriate and the isn't "excess" if possible. Also, airplanes really aren't affected by where the modeler is standing relative to the flight of the airplane. There really isn't a "side" away from the modeler or toward the modeler. Airplanes are affected by gravity, wind direction (when being flown relative to some point on the ground), and it's own characteristics. It's sides don't change relative to it's orientation.

If a model needs differential ailerons to cure a problem, the problem is often caused by forces differential ailerons introduce. Otherwise, introducing differential won't perfectly cure the problem.

karolh

Does the location of the wing in relation to the fuse, e.g. high versus low make a significant difference in the amount of aileron differential a model may requuire ?

Karol

pimmnz

Yes.
Evan, WB #12.

mithrandir

My Feedback: (2)

in an aerobatic plane, the differential is utilized to cancel the "Up Trim" a postively stable airplane has rigged between the wing and tail...

an aerobatic plane that has neutral pitch stability will need no differential...

it can occasionally be required to compensate for other asymetries such as an offcenter hingeline.

Bozarth

My Feedback: (15)

Please elaborate. Is the "Up Trim" creating a force up or down?

Kurt

da Rock

Positively stable in pitch is the description of a trim condition that returns the pitch of a model to level flight when the pitch has been displaced from level flight. There isn't an up or down in that description, but there is a 'toward the canopy' and 'toward the gear' orientation.

Bozarth

My Feedback: (15)

D.A. Rock,

I understand stability but I was hoping the previous poster would elaborate on his statements. I don't understand his comments.

Kurt

da Rock

I don't understand the comment either. But was hoping to save some time for everyone who might feel like looking up the definition.

mithrandir

My Feedback: (2)

really simple... the differential effectively decreases the relative angle of one wing more than it increases the angle of the other wing with respect to the stab.... (When ailerons are deflected)

It essentially nulls the "Positive" rigging during a roll...(between the wing and stab)

take a plane that is stable in pitch, and do a downline roll... it will still barrel or spiral a little.... (when theoretically the wing isn't lifting right?)

now take that same plane, find the "Down Elev" trim position so it truly dives straight down with no pull out..... and it will roll axially....

the differential nulls the positive rigging from the tail

another experiment is to put just a tiny bit of Down Elev mixing with aileron.... like 1%... with no differential... now do a roll....

there can be other causes to a peculiar rolling plane... example could be dihedral, a tall vertical... a highly fwd swept aileron hinge line....