Flap and Elevator Experement.

I did this experement. The wing flaps go DOWN when the elevator goes UP.

10 degree down flap and 45 degrees up elevator the airplane makes sharp turns. Inside and outside loops are 15 ft radius.

20 degree down flap and 45 degrees up elevator the airplane turns but not as shape as before. Inside and outside loops are 20 ft radius.
30 degree down flap and 45 degrees up elevator the airplane is very hard to turn it is impossible to do a loop. I think I might be able to get the airplane inverted if I fly over the top then come down the other direction upside down.
40 degree down flap and 45 degrees up elevator the airplane will not turn. Full up makes the airplane rise up higher elevation but the fuselage stays almost parallel to the ground. Same thing with down the airplane elevation gets lower and the fuselage stays almost parallel to the ground. The airplane sure does land nice with 40 degree flaps I LOVE the landing, "WOW".

The flaps seem counter productive. I know flaps will give the wing lift but the radius of the turns gets larger with more flaps. The airplane turns best with 10 deg flaps.

I did another experement. The wing flaps go UP when the elevator goes UP.

10 degree up flap and 45 degrees up elevator the airplane turns sharper than ever before. Inside and outside loops are 10 ft radius. I can do 10 inside loops change directions then do 10 outside loops. Horizonal and vertical figure 8's are easy.

20 degree up flap and 45 degrees up elevator the airplane turns much sharper, I'm ready to fly combat. Inside and outside loops are 5 ft radius.

30 degree up flap and 45 degrees up elevator the airplane makes some extremely sharp turns. The airplane will do a loop in a 5 ft circle. First loop is fine but the 2nd loop the airplane looses a lot of speed and its hard to control.
40 degree up flap and 45 degrees up elevator I am afraid to try this it will probably rip the wings off in the turn.

When flying the pattern square loops are much easier to do when the flaps and elevator both go in the same direction. My turns are actually sharp turns a square loop is actually square and not circles with 4 flat spots.

Why does everyone fly with flaps that move in the opposite direction of the elevator? I don't get it??? It seems to me an airplane with NO flaps would do turns and square loops much better.

The airplane is a Sig Twister. Fox 36X engine with 11x5 prop. Balance is exactly where the plans show it. Fuel tank is behind the engine. Balance is with no fuel in the tank. Fuel tank holds 3 oz. of fuel.

This experement gave me an idea for another experement. The engine exhaust pressure could be used to over power a spring and hold the wing flaps LEVEL against a STOP during flight. When the engine stops the spring will lower the flaps for a NICE landing.

What airplane are you talking about? What is the airfoil, the percentage of flap area to wing and tail area to total wing area?

AND

What is your CG? Somehow I have a feeling your cg is too far forward.

Gary,

Interesting as far as it goes. What you are describing is a very severe case of a well known phenomenom known as adverse pitching moment. It's what makes a flying wing turn in the direction the flap (we call it an elevator, but it's really a flap)moves. A cambered wing (or a wing with a deflected flap) has a pitching moment that must be countered by an opposing load on the tail before a pitch in the opposite direction can be accomplished. For instance, if your pushrod fails to the elevators on a flapped stunter when you give "up" control the flaps will go down and the airplane will pitch down as a result of the resulting pitching moment. Been there and done that. Generally breaks a lot of balsa.

On the other hand I flown and watched fly a lot of very good stunt ships that turn just fine with opposing flap and elevator motion. Mine are pretty much all one to one (or 45 degrees of flap for 45 degrees of elevator and every degree in between) and they fly pretty well.

It is entirely conceivable, however, that the situation you describe could, in fact, occur if the aircraft is not trimmed to suit its design characteristics and wing loading.

Len is on the right track but didn't ask all the necessary questions.

Almost certainly the CG is well forward of optimum for competitive stunt use. So I'll take that as a given.

The more important data for me would be the wingloading (how much the ship weighs and how large the wing area is); how large the tail area is in relation to the wing area and; very important, how large are the flaps as a percentage of the wing area?

A combination of very low wing loading, far forward CG, small area tail and large flaps could well result in the results you describe.

It is important to realize that the only significant reason for the use of flaps on a stunt ship is to allow rapid pitch changes without stalling with a heavier airframe. If an airplane is light enough and the flaps large enough and deflected far enough the flaps can indeed be counterproductive and retard the rate of pitch change.

The farther forward the CG is the greater the negative pitching moment that results from the arm between the aerodynamic center of the wing and the center of gravity. In other words, the farther forward the CG the more down load is required on the tail to maintain level flight ... let alone start a pitch change for a loop or square. When the up elevator required to provide that download at the tail is mechanically slaved to deflect the flaps the adverse moment of the flaps is added to the negative pitching moment of the AC/CG displacement and the problem is magnified.

In the worse case condition you could achieve what you describe. An airplane which with full up elevator has barely enough download on the tail to keep the nose from falling ... thus maintaining a level body angle ... but the resulting deflection of the flaps increases the lift of the wing to be greater than that required to maintain altitude and the result is a ship that will rise in altitude with the body angle flat.

Another consideration. Remember, flap deflections increase the lift available from the wing compared to the undeflected condition. Thus a wing that, without flaps, would stall under a given control input and loading condition, is able to produce enough lift to avoid stalling and complete the desired pitch change maneuver.

If, however, you increase the weight or decrease the deflection you will eventually find yourself unable to support the load with the wing and a stall will occur due to the required angle of attack exceeding critical-stall-angles.

The reverse is also true! If you have an airplane whose wing loading is low enough you could in fact deflect the flaps in the same direction as the elevators and the rate of pitch change would accelerate as you describe. This will, in fact, even allow you to maneuver pretty briskly with the forward CG. At some point, however, as the weight increases or the adverse flap deflection increases the wing will become incapable of developing the lift necessary to support the load of the maneuver and a stall will occur.

Our combat friends will support this example. For a short period in the late '50s and '60s true flying wings were the cat's meow for combat. With elevators attached to the trailing edge of the wing it was thought that the ultimate maneuvering machine would be created. The Half Fast was the most extreme example with its full span elevator.

What they quickly realized was that the same wing was much more effective if the elevator was removed from the trailing edge of the wing (where it was actually decreasing the lift of which the wing was capable and, therefore, limiting the potential turn rate)and attached to booms or raised above the wing or almost anywhere except on the trailing edge. The fact was (and is) that maneuvering flying wings depend on flap induced pitching moment to produce the directional change the combat guys desired. The sad reality was that using pitching moment for directional change was pretty much like trying to do outside loops in a Piper Cub (which has a classic flat bottomed Clark Y sort of airfoil)very, very ineffective.

So, Gary, what you discovered isn't magic or a revelation or anything. It's just aerodynamic reality and proof positive that proper design and trim are essential for competitive CLPA flying.

So, what exactly does your test airplane look like?

A little reading would have saved you all that trouble.

>A little reading would have saved you all that trouble.
Dave,

Tried the link but didn't find an obvious route to info germane to this discussion. What link and article are you suggesting?

Cool. It's good to do real experiments. Thanks for giving us the results. I did this experiment myself some time ago. Last year I tried moving just part of the flap the same direction as the elevator. It worked OK.

Your elevator doesn't have enough authority. As Ted said, you might move the CG back or make the tail bigger. Another thing you could do is tape the crack between the stabilizer and elevator. Also, the pushrod or control linkage may not be stiff enough, so the elevator blows down. If you make some changes, you will probably enjoy the airplane more. You will be able to get it to turn tighter with opposing flaps than it did with the flaps and elevator going the same way.

Gary, it will be also helpfull if you better define "sharp turn". Are you speaking about fuselage angular speed (pitching rate) or maneuver radius?

Also, it would be interesting to know the percieved response for and comparison to outside maneuvers as well as inside maneuvers in the various scenarios described in this "experiment". Or am I misreading the description which seems that only inside maneuvers were flown?

>Also, it would be interesting to know the percieved response
>for and comparison to outside maneuvers as well as inside
>maneuvers in the various scenarios described in this
>"experiment". Or am I misreading the description which
>seems that only inside maneuvers were flown?

Following up with what Kieth here mentions, sometimes we have our flaps and elevators off (or even the alignment of stabilizer with wing or wing to thrustline or...

The bottom line is we sometimes need to "adjust" the elevators or flaps up or down slightly just to get things to fly evenly inside and outside. If, for instance, you had already inadvertently given yourself some positive incidence to the wing or flap, this would also throw the experiment off.

We are still waiting to hear what plane you were using for the experiment. What is the area and weight? What is the percentage of flap to wing? What is the percentage of tail area to wing (and elevator to stab?) Where is your cg?

I didn't see anybody ask "How long is the tail moment?". If the flap and elevator hinglines are only an inch or two apart, I would expect better results if both go the same direction. At some point, that changes. Older flapped models (perhaps the Super Clown and Sterling Mustang & Yak?) may have too short a tail moment. Steve

>I didn't see anybody ask "How long is the tail moment?". If
>the flap and elevator hinglines are only an inch or two
>apart, I would expect better results if both go the same
>direction. At some point, that changes. Older flapped models
>(perhaps the Super Clown and Sterling Mustang & Yak?) may
>have too short a tail moment. Steve

Although I agree that the tail moment is also a consideration, I find the comments about the Sterling Mustang and yak interesting. People in the past have stated that these fly "better" without coupled flaps. I have built both with coupled flaps (still have two Mustangs from the 50s that I built) and they are excellend flyers with coupled flaps. The interesting thing is the second Mustang was a dud. I could start an outside loop from near level flight with the first one. The second one just didn't turn. I tried all sorts of things and then finally noticed that the pushrod to the flap was bending. I cut into the plane and replaced that pushrod and it became as solid as the first one. These things came with very sloppy controls, and I surmise that most problems that people experienced with these were from that factor. But when built right, even with as short a couple as these have they are excellent flyers with coupled flaps. Oh, and I used K&B Greenhead 35s for power. I still don't think you can overpower an airplane (within reason). You just need to watch that you don't make it too heavy.

In his original post he said it was a Sig Twister with a Fox and the CG in the plans shown position.
Bare

good experiment Gary. A little aeronautic reading would explain your results. Wild Bill Netzeband's articles covered this back in the '70's. Basically the flaps pitch the nose down when hooked up conventionally in a stunter. Too much flap and they can overcome the elevator. A heavier plane with a larger elevator will handle more flap movement than a light plane, which you obviously have.

I did something similar with a profile carrier way back when. Put a nice thick wing on it with a 30% wide flap and a huge stabilizer/elevator. With 30 deg. of flap the thing would fly about 20 degrees nosedown and level. I got it down to about 10 mph without hanging it on the prop. It looked more like it was standing on its nose!! Was a fun experiment. The plane probably could have lifted 5-6 lbs. and still flown level it had so much lift.