Also, why are the excursion of the ailerons much greater in the up position then when in the down. i.e. there is an aprox. 7 inch gap between the aileron and center line in the up position and only an aprox. 1-3/4 gap in the opposing one. Thanks to a great group.
In a word (well two words) 'adverse yaw.'
The Ercoupe is designed to minimize the things that require a separate rudder
control.
The chief issue, in turns, is 'adverse yaw.'
Remember your ground-school class and the discussion of the 4 forces?
Recall that there were two kinds of drag: induced and parasitic. Induced
drag, the drag generated by a wing when it produces lift, is what we want
to talk about here. In a nutshell, the more lift the more drag.
Now sit in your airplane.
Feed in left aileron to turn left. The right aileron goes down, making more
lift to raise the right wing. More lift equals more parasite drag. Now think
about what you're trying to do. Turn left, correct? Well, what effect does
more drag on your right wing have?
Correct, it makes you tend to turn right. Just what you didn't want to
do when you're banking left. A lot of old airplanes, if you don't add rudder
in the turn, won't turn at all and SOME WILL EVEN TURN THE WRONG
WAY.
How to fix that? Well, left (bottom) rudder, during the time the aileron
is deflected.
Okay, there's another way to do it.
If you deflect an aileron UP, it doesn't make induced drag. But it does
reduce lift (yes, and drag, but not so much as the down-going one
increases it, because let's face it folks, gravity is a one-way street).
So it turns out that this 'differential' aileron action gives you an
airplane which requires less rudder to counteract induced drag.
The result enhances both controllability and safety, because pilots
don't spend so much effort trying to coordinate their turns.
You'll find that most modern airplanes utilize differential ailerons, just
like the Ercoupe. 172s and Cherokees do. I think it is more extreme
in the Ercoupe and you notice it more because the ailerons are so
danged big. The big ailerons are another way that Fred Weick balanced
the funny forces out. A big aileron doesn't need to deflect down very
much at all. That also explains the sweet handling.
Last of all, how is a differential aileron made? Well, all you have to
do is to install an aileron bell-crank with the arms at an angle other
than 90-degrees (acute or obtuse depends on how things are
rigged).
On the Ercoupe, it isn't just the ailerons which are differential.
Check out the rudders. They move way out, but barely move
in.
Greg
