Full-span flaperons as airbrakes?

On Mar 9, 12:59*am, Eric Greenwell wrote:
Bruce wrote:

The ASW-20 was the first to get the ailerons back up as the flaps went
on down, getting the plane into what a previous poster said is called
"crow mode" in the model world. *I think the biggest thing it does is
makes it so the ailerons won't stall once you are on the ground in two
point, tail low attitude. *I don't think it was done for added drag or
improved in flight handling. *You already get ENORMOUS geometric twist
when your inboard flap is down 50 degrees and your ailerons are still
down 8. *However, these flapped ships like to have the ailerons up
when sitting two point on the ground in order to have aileron
authority, and Schleicher got this (among so many other things) right
by putting them back up so you can leave the flaps all the way down
after you land. *That way, your left hand doesn't have to keep jumping
around in the cockpit grabbing different handles. *Set the flaps, use
the dive brakes and land. *No more needed hand changes.

Steve Leonard

And unfortunately Schleicher patented the mixer - so one of the more
effective safety innovations has not been widely used.

About 15 years ago, Gerhard Waibel told me they purposely did not patent
their system. They thought it was such an important safety feature it
should be available to the other manufacturers; to Schleicher's surprise
and dismay, none had ever used it, even though it was introduced on the
ASW 20 in about 1975.

Good to know that I didn't violate any patents. Years ago I installed
this feature on the RS-15 I owned. Actually, any HP series glider
with a flap/aileron interconnect can easily be set up to have this
behavior and I believe that many/most are. One needs only to modify
the cam slot in a piece of 3/16" aluminum plate. The guy to whom I
sold the RS wanted the ailerons to go "crow" at smaller flap
deflections. He was able to easily change it himself. In general, it
makes a huge difference in maintaining control during landing rollout
as described and the best part is crow mode happens automatically.
Just set the flaps and land. Dive brakes/spoilers? What are
those? ;-)

Regards,

-Doug

Thanks for all the good discussion.

I don't understand why flow separation above a full-span flaperon
would cause you to lose aileron control everywhere in the speed
braking region. Let's say you're at 45 degrees flap, and the flow has
separated on top, but you'd have plenty of pressure on them below. So
I'd guess the force on the control surface might be at 45 degrees or
so above horizontal. It seems you would still have some good aileron
control because raising or lowering opposite-side flaperons would
still change that force a lot, with its vertical component. It seems
the bigger problem might be yawing effects that would come with it?

Bret,

Model gliders have tried most of these control ideas at least once in
the past 20 years. It's much easier with the servos and computer
controlled radios to get almost any mixing arrangements you can think
of.

In the case of the full-span flaperon: Once the flap function exceeds
about 25 degrees down, the additional downward deflection of the
aileron function does NOT create much lift to make a roll, in fact it
adds a lot more drag and really increases the adverse drag. The
upward moving aileron function reduces the drag a little, but doesn't
remove much lift, again resulting an adverse yaw but no real rolling
effect. In the models you can change the "rate" of the controls
(increase or decrease the deflection relative to the control stick
input) and overcome some of the rolling problems but not very much.
We don't have any mechanism in our "big" sailplanes (that I know
about) that can increase the deflection of a surface at different
airspeeds or by selecting a mechanical detent on a control.

Having tried full-span flaperons in the model form, several times, I
can say I'd rather not try them on a full size, where my life is on
the line.

Mike