Alpha Jet flight problem

[mchurcher45]

I have a scratch built Aplha Jet with the F power pack. Conducted maiden flight today and plane flew well at 1/2 power but would start to climb under full power. It required full down elevator to fly level. The CG is 13-1/2 inches from the nose. The motor seems to have no offset either vertically or horizontally. Any recommendations about what might be wrong and how to fix it would be welcome.

Mike

 

[mrjdstewart]

CG needs to be moved forward or you need to check your trims.

good luck,

me

 

[mchurcher45]

I'll try both suggestions. Thanks. Somewhere in one of these forums, someone wrote that the CG for the Aplha jet should be 14 inches from the nose. I wonder why mine is different. Also, I was wondering if the motor alignment could also a problem. Thanks again.

 

[Merv]

I'm thinking your wing may not be at the correct angle. Try shimming up the back of the wing.

 

[SlingShot]

I'll try both suggestions. Thanks. Somewhere in one of these forums, someone wrote that the CG for the Aplha jet should be 14 inches from the nose. I wonder why mine is different. Also, I was wondering if the motor alignment could also a problem. Thanks again.

Yours is different because you set it up that way. You have control over the CG. The CG doesn't control you. Move the battery further forward or further back, as the case may be, to get the CG that YOU want.

 

[Hai-Lee]

I am with @Merv on this one! I would suspect strongly the wing and tail incidence angles. You can get the plane balanced in one particular speed range but then if you increase it the lift generated by the wing and tail are not increasing in equal proportions.

From your description I would either decrease wing incidence as mentioned by Merv or increase the tail incidence. The adjustment required might be quite small so do not make large adjustments but rather very small changes one after the after until it is correct.

have fun!

 

[mchurcher45]

The suggestion to shim the wing to change the angle of incidence had not occurred to me. I'll experiment with one change at a time to improve plane performance. Thanks, Mike