I have to have a fair amount of up trim in my aerobatic trainer to keep level flight, it balances on the CG well and there are no twists in the airframe,

someone said that the Ailerons both might be down a little creating a flaps issue. they said with some planes when you turn on flaps the nose will drop,

does this sound ok.

so the fix would be to screww both ailerons up a bit?

Check the thrust line of the engine. If it has some down thrust that will cause the problem. Put a washer or two between the engine mount and firewall to bring it up. Center all your control surfaces and try flying it again.

thats why i love this place....


Thanks WBC you got it in one.

when you look at the side of the plane you can see the thrust line is REALLY wrong.

good find....

There are 2 things you need to check. The engine thrust line and the wing incidence.

I use the GP laser incidence and can check both wing incidence and engine thrust with it.

TYPICALLY, most planes use a 0 degree on the main wing and 0 degree on the horizontal stab for incidence (if different, it is normally stated on the plans) and FREQUENTLY about a 2 degree side offset on the engine with a 0 to 1 degree down offset.

Without an incidence meter, block the plane so the datum line (line running through the center of the plane) is level. Then use a small level to determine that the main wing and horizontal stab are level (or set where they should be if the plans state differently ).

Once you have determined that the wing incidence is correct, use the small level to determine if the engine crankshaft is level. If it isn't level, use washers for shims and either shim the motor mount or the engine. Your local hardware store will have a variety of washers in varying thicknesses in the fastner section.

Your trainer will most probably fly best with some downthrust, maybe as much as 3 degrees. As to your original question, would changing the ailerons to have both slightly up help; most probably and worth a first try for an easy fix. More probably you have to little angle of attack on the wing or possible to much angle of attack on the stabolator. If so change the one which is easiest to change, usually by shimming the wing as the stab is most probably glued in place. As to downthrust, trim out the airplane so it is flying level with half throttle. Now apply full throttle, if it tends to tuck under, you have to much downthrust, if it thends to balloon up, you do not have enough downthrust. It should just increase in speed with no dive or climb as you increase the throttle if the thrust line is correct.

Cranking the ailerons up will require MORE up elevator trim. This is called reflex. Or it is a quick and dirty form of reflex. Cranking the ailerons up will tame a snappy beast or it will help a floater sink better on landing. It will cause a flat bottom foil to behave like a semi symetrical one. And it will help make a semi foil behave more like a fully symetrical.