I know what aileron differential is, why it is used, and how it works to a degree, but the when of their use have me confused.

I have an 80" Midwest Cap 232, just changed to a Futaba 9C to get a little more fine control over the Super Seven I was using. I wasn't confortable with the mixing for the twin servos.

Now to achieve a smother roll, it has ben sugested to use this fuction. yet no one has explained to me if the aileron top travel is the one reduced, or the bottom.

Just to coverthe bases the ailerons are hinged in the middle, and not like the hing of the new composits which is all on top.

I'm wondering if this is a guessing game of are there some fundemental guidelines that could help me learn the correct use.

thanks

bob

I never understood why anyone with center-hinged ailerons would want to use differential. Any argument would have to be valid both inverted and upright, and I haven't heard one that works both ways.

However, with top-hinged ailerons, one might use differential to even out the effective travel, and that one would be valid both inverted and upright.

Just my 2¢ worth,
Dave Olson

I doubt if it was a pattern or fun fly pilot that suggested you use that. It's only really meant for upright only type models.

It works wonders for my semi symetric airfoil planes, in this case you increase the travel of the down going aileron. The differential travel is built in mechanically by placing the servo arm toward the front of the aircraft when in the neutral position.

For what it's worth. The down travelling aileron effectively increases the camber on that wing half. The resulting increase in camber increases the lift on that wing panel. Due to the interaction of lift and induced drag, the wing with the down aileron will incur more drag than will the opposite wing. The higher drag will tend to yaw the nose in the direction of the down aileron. This requires correction rudder in order to produce truly axial rolls.

This induced drag simply is a function of the increased lift and will apply to all configurations. There might be some additional drag factors depending on hinge location, as top mounted hinges will have less area on the down aileron due to part of the aileron being blanked by the trailing edge, but the aerodynamic forces due to lift still apply.

RCS

Differential is wanted on models such as Piper Cub with barn door ailerons, where the adverse yaw problem can become severe.

On a 3D or precision aerobatic model, differential is undesireable, as you don't want the varying preformance between upright and inverted. Its also difficult to impossible to get a good axial roll with substantial differential when you have a symetrical airfoil. (Differential makes it easier to get a good axial roll with a flat bottom wing...)

Where the aileron is hinged has just about NOTHING to do with if you ant differential or not... the effect of the differential on how the aircraft flys compared to the way the aircraft is intended to be flown determines if you want it and how much you want. You can hinge the aileron on a Pattern model along the upper surface... it will work. But you'd still NOT want differential. You can hinge the aileron of a Cub at the center or the bottom of the wing... and it would still be wise to put some differential in.

You can almost go by the airfoil as to the differential desired. Flat bottom asks for 20% to 50% differential. Semi-symetrical asks for less (5% to 20%). Fully symetrical asks for none. Thats a decent way to come up with initial settings if you have nothing else to go by.

Again... it depends on how you plan to fly the model... If your fully symetrical wing model is never going to be flown inverted... you may desire differential to make it less likey for you to stall a wing on final approach.

I have an Eastbourne Monoplane with an undercambered airfoil with about twice as much up as down and does axial rolls with the best of them.I doubt if the full size could without collapsing. The purists in the club don't think much of my flying style

my thanks to all of you for your comments and perspectatives.

I'm wasn't sure that someone wasn't telling me a story or not.

A straight and true model with the correct incidences, balanced is still the best option for a smooth flying airplane.

bob

Aileron differential is usually needed on scale models... long-spanned planes like Cubs and Airknockers with scale barn-door ailerons need it, just as the full-scales do for the same reason, and also using rudder with the ailerons is a nifty flight "feature" just as with the full-scales for planes of that configuration.
Those types are about the only models I have flown that really need it.
For very slow-flying planes, it can be nice to have, but in unusual amounts, like all up and no down. The drag of the down-going surface can drag that side around oppositely to the command, or create a tip-stall. Both disconcerting.

I am setting up a SIG Rascal Forty. It says in the manual to set aileron throw equally up and down.

However, it is a high wing, long span aircraft like a Cub or Aeronca or Cessna, etc.

So, would it be beneficial to ignore the manual and set it up with aileron differential? [sm=confused.gif]

Doesn't take much to put in differential. Why not try it without first, then put it in, then you can see the difference for yourself. If it's a flatbottom wing about twice as much up as down would be a good place to start. The old Ercoupe had 10 degrees down and 30 up if I remember correctly. A mediocre plane can be made to do decent axial rolls with differential

Good point!

On my 100" glider i used the 'EPA' to set my differential!!(2 servo setup), the plan said 15 degrees up 10 down, boy that was very bad!, the glider would start to make the turn, as it did adverse yaw kicked in, the nose would try to spin the opposite way to the turn!!! all in all very scary stuff! screamed a few times as it stalled and lost all it 'e' lol.
I now run it with 15 deg's up and 2 deg's down! and 5% rudder mixed to rons fly's real sweet now.


Jim.

We setup a new Kange Monocoupe - top hinged - long wing - short fuselage
excellent kit! and excellent instructions on setups .
their take was quite good on the differential-
lotsa up -little down.
On some Pattern designs - guys would go on and on and on about minute differential .
All crap-
typically - the flier was holding in elevator trim and the roll would barrel due to that - NOT the differential.