On my latest design I decided to go with the airfoiled flap because it seemed more logical considering it's part of the wing and therefore the total airfoil shape. Now granted there were other design factors involved but the end result was very little flap movement was needed to eliminate any trace of a stall in the hardest of corners. This was exactly what I was looking for because a small flap movement gives much less drag exactly where you don't want drag slowing the model.

Ahhh,  no, but the airfoiled flaps look much better on simi-scale airplanes
I don't do it though because sheet flaps are a lot easier to construct and mount.

Jim Pollock   

FWIW and IMHO only...

Flaps do two good things for us if properly utilized.

First, they provide the means to develop the "necessary" amount of lift to support our stunt ships in maneuvers without excessive wing area.  IOW, you can build an airplane with a higher wingloading that will fly better overall than will a lighter airplane with more wing area.  This is particularly valuable in windy conditions where every square inch of area allows the wind to accelerate the model in maneuvers. This is the "stunt kite" phenomenon that allows people to fly downwind maneuvers more or less endlessly--with a dead engine.  All that area does the same thing with the engine running--except you wish it wouldn't!

Second, flaps provide a very helpful form of negative pitching moment (they want to turn the airplane the opposite direction desired) which, when coupled with a properly located center of gravity, provides feel to control inputs that would be missing with that same CG location without flaps.  Stated another way; if you design/build a flapless stunter with a tail large enough to stabilize the airplane in level flight with a CG at around 25% of the Mean Aerodynamic Chord ([MAC]--just think average chord) there will be very little "feel" from control inputs and the airplane will feel squirrely, or tail heavy.  Make the flaps movable, however, and the effort expended to overcome the negative pitching moment from the deflected flap will materialize as "feel" at the handle--a VERY important factor for flying competitive maneuvers.

It is very important, however, to recognize that using flaps on a stunter and simultaneously balancing the ship more nose heavy will prove detrimental when flying in high winds.  This is because the other primary source of negative pitching moment is the result of the CG and the Aerodynamic Center (think Center of Lift) of the wing not being in close proximity to one another (at roughly 25% MAC).  Every increase in G loading due to maneuvers will be generated at the CG and multiplied by the distance between the CG and the CL.  With a nose heavy ship those increases will try to open up maneuvers--which will demand more control input to maintain the desired maneuver radius and back and forth like a dog chasing its tail.  In high winds with a forward CG you can literally run out of control authority.  That's usually at the point the pilot bails out of the maneuver...if he's lucky.

This combination of factors is the primary reason that stunt flaps can and do produce better overall stunt patterns than do ships without flaps.  Getting the required lift without flaps is no big deal, you just make the wing bigger.  As mentioned above, however, doing so isn't the best solution if precision patterns in all weather conditions is your goal.

Ted Fancher

p.s. one more thing.  With respect, I'm not a fan of making a big winged stunt ship and gradually adding flap movement until the airplane doesn't stall.  As Brian mentioned in his post, achieving that "no stall" condition required very little flap movement and I'm reasonably sure that flying good, recognizable stunt patterns could have been achieved with no movement of the flaps.  I also feel confident that, without significant flap movement, the best CG location for flying great patterns would be too far forward to be viable to fly equivalent patterns in high winds. 

Just my opinion.

Actually Ted you're quite right because before I got around to making the flaps moveable (I'd wasted about a month trying to get a proper engine run) I flew it in a state championship and my helper overheard the judges commenting on how sharply it turned. At the end of the first round I was in the lead ahead of Peter White, who's one of Australia's top fliers, and that's something I'd never achieved before. That made my day .

YOu know, Brian.  Your airplane is a real good resource if you're interested in doing some experimenting.  It would be real cool to find out what your set up is now (primarily: weight, wing area, flap size, tail area, where the CG is located at the average chord, and what the ratio of elevator to flap movement is now set up the way you like to fly it.  Just keep a record of how its set up and how it feels to fly it.

Then it would be fun to try moving the flaps more and more and making whatever adjustments you feel are necessary to restore it to the best flying state of trim for that status.  (Just thought of this--the handle should be left alone.  All the adjustments to maximize the performance to your test would have to be done with the aerodyamics of the airplanes).  Maybe try three stages far enough apart to make the changes obvious and verifiable.  Right now you've got maybe less very little flap for a given elevator deflection.  Try it that way, with zero flap like you flew it at that contest. with a one to two ratio (flap/elev) and finally with a one to one ratio.

My educated guess is that as you increase the flap movement the response rate will decrease.  My suggested action would be to regain the rate of turn desired (as much as possible) by moving the CG aft.  I'm going to guess that with zero flap you were flying with the CG at right around 15% of the average chord.  I'm further guessing that at 1 to 1 ratio you'll like the CG back around 25% (this assumes your tail area is around 25% or so of the wing area).

Gotta go eat.  back later.

Ted