Positive Wing Incidence-Why ?

[Billa]

Hello,

A friend of mine recently test flew his 102" span Extra 300S with rather bad results - this is not a plane which is on the market. He has a 3W 106 upfront. Wing incidence is positive 1.5 to 2 deg. All other thrusts and indences are zero except for the mandatory right thrust. CG set at about 32% of MAC. I have exactly the same bird and am wondering what changes to make to the setup - have a ZDZ80 for power.

His plane took off with in 10 feet (1/4 throttle) and headed upwards at about an 80 deg angle. He pushed in down elevator and down trimmed all the way with the plane still climbing a little.

The fuselage is fibreglass and has fillets for the wing and the stab so changing the wing/stab incidence is not an easy option at all.

I am sure the designer must have had a reason for the positve incidence but he is not accessible to us. Would some one be kind enough to explain why the positive incidence is there in the first place and what can be done with engine thrust etc to alleviate the problem.

TIA,
Aamer

[Boulder]

Aamer,

You could add about 2 degrees of down thrust, but I'm not sure that will cure the problem. This is the first time I've heard of an Extra with positive incedence in the wing.

I'm sure you will get some good answers here.

[Billa]

That was my first thought too but I don't know how that will effect the down lines etc - I would first like to know why it is there ? Thanks for the input.

[WOODisGOOD]

Aamer,
I think your best option is to move the wing to 0. The only purpose of changing the wing incedence is to change the angle of the fuselage as it flys. You could also try moving the stab to match the wing but I think you would be better off moving the wing to 0.

[Boulder]

	Quote: Originally Posted by Billa
	That was my first thought too but I don't know how that will effect the down lines etc - I would first like to know why it is there ? Thanks for the input.

The only way to know is try it, that's the problem...

Tony's answer is the optimum way to fix it, but if I read your question correctly, the fuse has built in fillets for the wings, which means cutting the fuse apart and re-attaching the fillets to the correct incidence.

Is it possible to post a side shot of the fuse so guys would know what you are working with?

[jtec/radiowave]

I agree with Tony. You need to see if you can get the wing to 0 with the rest of the plane. negitive engine thrust won't help the down lines, without power it will see the 2 degrees positive and want to pull to the canopy as it builds speed.

Al
JTEC/RADIOWAVE

[Billa]

Ok. These shots should clarify the gravity the situation I am in. The fillets are an integral part of the structure but I have also more or less resigned to the fact that this modification will be most necessary.

Is everyone sure there is no advantage to be derived from this positive incidence ?

Thanks,
Aamer

(Resized the snaps - they were too big, sorry !)

[Boulder]

That's gonna' suck Billa,

[Boulder]

That's gonna' suck Billa,

[Boulder]

This is gonna' suck Billa,

These guys are right, and they're the experts without a doubt. They both design and market their own kits. The only reason I said to try motor thrust is to keep you from cutting up your fuse, but it is the right way to fix the problem.

Follow the advice of the experts.

[Vortex]

might as well live with it

[GremlinX]

I cant see it ??