Stalling the stab/elevator

I have a DMECO All American Junior Stunt Trainer which is powered by a Torp 09 turning a Cox 7 x 3.5 prop. It is currently flying on 42 ft 008 lines which seem to be about the right length. It is too fast on 39 ft and loses tension overhead with 45 ft.

Although the airplane is several years old, I had come to the reasonable conclusion that it is too small, with too thin a wing, and probably too heavy (havn't weighed it) to fly very well. It had therefore not received the amount of fiddling with that an airplane thought to have competition possibilities (OTS in this case) would have received.

Last Sunday I was flying it and doing inside loops. In spite of my best efforts, the loops kept getting larger and larger and closer and closer to the ground. A friend watching remarked on the amount of elevator deflection he could see while I was looping (right in front of him).

I realized that I had not done any fine tuning on the controls and that I was probably stalling the stab and elevator by giving too much deflection. It is a large elevator and has about 45 degrees of movement either way. According to Frank Zaic, in his 1951-52 Model Aeronautic yearbook, Page 83, when the elevator stalls, it is almost like you had reversed control (my words) because you loose the lift of the elevator.

The opposing lift of the elevator, according to Zaic, is what is forcing the wing to fly at a higher angle of attach so as to generate enough lift to overcome the centrifugal force generated in a loop. So when the elevator stalls, the wing drops to a lower incidence angle and the airplane flys a much larger loop.

I flew the airplane again, more cautious with the controls, and it flew much better. I tried "overcontrolling" and duplicated, I think, the previous elevator stall. I could actually feel the elevator stall (or whatever) through the lines.

Anyway, I'm going to work on the controls and fly the airplane some more.

I've found that on most of the OTS models a good control set-up is a 3"bellcrank with the pushrod hole 7/16" from the pivot to the elevator horn 1" from the hingeline.This is,of course,the non-flapped models.I had an All American Sr. set-up this way and it flew quite well with no stalling or over controlling.As an experiment,I tried moving the pushrod hole farther out from the pivot point on my next plane thinking I could get a little more turn on the Climb,I should have left well enough alone,I have to fly it with a good bit of nose weight to calm it down.I've used this "slow" set-up on Ringmasters,All Americans,Barnstormers,a Circus King and even on my 38Special(non-flapped bi-plane)with much success,it just seems to be the most comfortable arrangement I've found.The 45 degree movement you mention is definitely too much,not only will it stall,but it's probably difficult to fly smoothly,or at least it would be for me.Try the slow set-up on you next plane,or cut into the one you've got if you don't mind a couple scars,I think it will fly better and easier.

Or perhaps try a closer spacing at the handle.

As a general rule of thumb, any control movement over about 30 degrees will add more drag than lift. We have checked several of our models (fully trimmed full-house stunters) and found that about 12 degrees of movement was all that was being given to snap a square corner. The rounds would use even less. Now, if you have a small elevator, a thin airfoil, no flaps, you may need more control movement. But you don't need drastic amounts. Some planes just aren't going to turn because the plane is too heavy, the controls too small, CG wrong, whatever. If you need to overcontrol, check the design. Something is wrong.

On a related note, I have a homebuilt "design" (actually it was just built, never realy designed) that has no flaps, but a rather large elevator that can be given almost 90 degree deflection in either direction. It does a maneuver I call a "whing-ding". I take it up to about 45 or 50 degrees and give it full up. The plane turns and stalls so violently that it just sits there spinning on the leadouts. It does slow "mini loops" that rotate around its axis with each one getting lower to the ground because the plane is no longer flying. I can do about 8 or 10 of these before I have to neutralize the controls, at which point the plane will begin flying again. It is not pretty, but it is a fun thing. No, I don't think it would get many points in competition unless this was "free style" and then I am not sure.

Leonard Neumann

As has been mentioned, I can confirm that huge 90 degree elevators doesn't guarantee anything unless the design is right. My last 1980s effort had this ludicrous arrangement and wouldn't even wing over. That was to do with having only 120 square inches of wing with my faithful PAW 0.09

Total disaster. I even tried strapping a great big chunk of lead to the tail, which made it real twitchy, but it still wouldn't turn!

It's probably the wing stalling because the elevator forces it to too high an angle of attack, and All American has too large an elevator which causes excess drag initially and slows the model in maneuvers, and with the tiny wing, it stalls rather easily.
the CG can affect the problem. The farther forward the CG, the more elevator travel you need, so ascertain the CG is back far enough to turn well. On the AA it should be 1"-1 1/4" back from the LE. This is also a tiny airplane as far as wing area goes and should weigh over 7 or 8 ounces max. The plans say 6.5. If it's heavier than that, that will increase the stalling tendency, too.
If you're not planning to fly OT Stunt with it, cut the elevator in half, chordwise. Reducing the drag there will increase your odds of having a good flying model. Also reduce your elevator travel to about 30 degrees each direction.
Bare

I finally got around to weighing the AA Jr Stunt Trainer, and it is 10 oz. No idea why it should be that heavy. Even so, I'm going to fiddle with the controls and see what it can be made to do.

How much does the Torp weigh? If it's in the 3-4 oz range, you might consider trying a lighter engine, like a TD or Medallion .049. Those engines have adequate power to easily pull the model and will shave a couple of ounces off the wing loading.
That model is actually too small for even these powerplants. Personally, if I were to build one, I would use a PAW 55 (.033) in it.
Bare

Bare is right about the size of the airplane vs powerplant. However, it was designed for an 09 and I wanted to see how that would work. If I put a TD 049 in the present airplane, I'd have to add nose weight to get it to balance, and would be no furthur ahead.

On closer inspection, I found that the hole in the elevator control horn is perhaps 1/64 ahead of the hinge line when at neutral. Down is OK, but up was about 45 degrees. I put a stop on the pushrod so that up only went to about 25 degrees, and moved the lines in to @ 2 1/2 inch separation on the handle.

Flying is much improved. The square-corner maneuvers: climb, dive, wingover, square loop, are recognizable. Loops, horizontal and overhead 8's are not bad at all. Where I was flying there is a deep gully across one side of the circle, and when the wind was right, I was able to fly some vertical 8's there. The engine run is not yet quite as consistant as I like. Once that is sorted out, I think the airplane will be able to fly the full OTS pattern in a recognizable manner.