What happens if I change the stab incidence

[Paul Williams]

I have a 30cc Sbach (hobbyking) and the plane flys with the tail low I have tried moving cog both ways and increasing down thrust but nothing works it flys terrible. I cant get any information from hobbyking regarding wing incidence but in desperation I am about to try changing the stabiliser angle to create more lift at the back. My question is will this work? The main wings can not be altered due to them fitting into pockets on the fuse.

[Paul Marsh]

You crash.

[cymaz]

Try a bit of packing to create downthrust on the engine, that should bring the tail up. If it doesn't help it can easily be taken out.

Edited By cymaz on 01/06/2013 19:05:59

[Shaunie]

If you fly faster does the tail come up?

If you lift the tail you will get less wing AoA and the plane will lose height. The only way to increase lift is more wing incidence or more airspeed.

What about drooping the ailerons slightly, maybe they are very slightly reflexed?

I have a Seagull Edge 540 (68" which was electric when I got it and flew with its backside on the ground. Having changed to an RCV91 (in itself a bit light on power but better than the electric setup) it now flies beautifully. I think perhaps it is now flying faster so it needs less AoA.

Shaunie

[Biggles' Elder Brother - Moderator]

Paul, this is really tricky question. There are all sorts of reasons why a model might fly tail down - only some of them concern the tailplane incidence.

First of all; the Sbach is a smashing model - I have a smaller one (55" span) myself. But they do seem to have a bit of reputation regarding fore-aft balance. It took me quite a lot of fiddling to get mine right. Now it is right I'd swear by it - flies brilliantly. But if its just a fraction out it flies like a dog. I've even had to mark on the battery tray exactly where the battery goes - normally I just rely on judging about the same spot - with the Sbach I have to be exact.

So why might it fly tail down?

1. Well one reason is as you say the tail is producing too much down thrust. Possible
2. The engine thrustline might be out - and some down-thrust is needed. Again possible.
3. The CoG too far back - possible not likely as the model would feel very unstable before you got to the point where tail lowering became obvious.
4. The wing incidence might be wrong and the model is having to generate an angle of attack. Again possible but not very likley as it would have to be miles out for that to happen.

Now some questions:

1. what happens inverted - is it still tail down?
2. What happens when you open the throttle up - does it zoom upward or just fly faster in the same tail down posture?
3. Also do you have a incidence meter? If so what is the decalage - ie the relative incidence difference between the wing and the tailplane?

With some of that info we might be able to eliminate some of the possible causes.

BEB

[Paul Williams]

Thanks guys, I have tried more down thrust I reckon that is right now because opening the taps does not make it head for the stars in fact it stays on the same level. It does pick up its tail if I fly it flat out its hard to put figures on it but that I assure you that is much faster than say a normal circuit speed. To be honest I have not noticed if it drags its tail inverted only that I have to push the stick up quite a bit to keep it level. I have a incidence meter but no figures to relate to, although as you say if I am looking at the relationship between the stab and main wings they are the same. I always wondered what decalage was thanks for that !! Should the stab have more or less AOA than the main wing? I dont know if this is relevant but it also takes a long run to get airborne then for a few secs everything feels woolly until it starts to gather air speed. I have a precision aerobatic edge 50cc that is so locked in it feels like it is on rails I know I should not compare the two but having flown a good plane this comes nowhere near. Which is a shame.

[Tartan81]

Post deleted for breaching the forum C of C.

I've PM'd you, tartan....

Edited By Pete B - Moderator on 07/06/2013 23:17:51

[Bandit]

I had a trainer that flew like that.

It was the marriage of two great names, the arising star and the boomerang, we called it 'the arising wang'....anyhow, the wing was the boomerang and the arising was the fuz. It flew ok but tail down so we packed the front (leading edge) of the wing up a bit and it greatly improved it to flying a normal stance.

It was easy on that trainer, god knows how you would change it on the Sbach coz they really nice pretty planes.

[Ian Jones]

If it takes a longer than expected ground run to get away and at low speed flies with it's tail down then it could be nose heavy, yes nose heavy.

When it's is nose heavy you have to feed in lots elevator to get it to climb and the change in pitch can be quite noticeable.

[Paul Williams]

Well I think maybe some one has found the problem, I mentioned I had fitted a Zen G38 engine thinking a bit more power would only help !! Well I was wrong the G38 weighs in at 2k which is twice the 980g of a dle 30 or rcgf 30 the result was extra weight on the tail to balance all this added up to a very overweight aircraft which flew terrible at low speeds. I take it all back Hobbyking I need a wing loading lesson and a new light weight engine.

Any one wanna buy a G38 just run in?

[Former Member]

[This posting has been removed]

[lakey]

Posted by Matsanga on 07/06/2013 23:02:50:

I had a trainer that flew like that.

It was the marriage of two great names, the arising star and the boomerang, we called it 'the arising wang'....anyhow, the wing was the boomerang and the arising was the fuz. It flew ok but tail down so we packed the front (leading edge) of the wing up a bit and it greatly improved it to flying a normal stance.

It was easy on that trainer, god knows how you would change it on the Sbach coz they really nice pretty planes.

"The arising wang" LMFAO