i built a twin boom "drone-like" like plane.
1/3 throttle and i try to launch it. the plane will glide for a short bit and then yaw to the left, as i try to increase throttle the left wing just drop and then crash. i try some right trim aileron trim and the plane will still do the same left wing tip stall.

whats going on ? what can i do to fix it?

Did you give your plane a thrust angle to counteract the props torque thrust?

no, i just try and mount it as straight to the fuse as possible.
i'll give that a try

If you are using a normal counter clockwise prop, then yes, its probably the torque. Also, It might just be stalling and dropping a wing. Maybe you should launch with more than just 1/3 throttle

Are your leading edges the same . This also might be a reason why it's happening. One wing may be stalling faster than the other an hence it crashes. But it probably is what the others said

test glide show that the plane want to yaw left, if i add throttle the plane will starting to yaw left even more.
i got it up to about 15 ft and lose control of it, the plane just go straight down and messed up the nose.

p.s : i think is just my limited flight time + the tail boom is glue on not straight ( maybe my eyeballing skill is horrible )

I'm having this left yaw issue. My test glides didn't reveal it, was only after adding power. Last night I got a second set of eyes on it and turns out when I installed my motor I didn't account for down angle either. I'm not sure I can access the motor to correct mine either. I've compensated by setting the sub-trim in my tx. If I can get to the motor I'll fix it properly.

It's better to do it properly for both ease of flight and above all safety.

Controls reversed ? Wing warped ?
Stand back and sight past the leading edges to see if the trailing edges are parallel.

Test glide with yaw implies that one or both vertical stabilizers are crooked.

Lacking some info here but...if the airplane won't glide straight you will only complicate problems witht the addition of power.

There are trim angle issues and torque issues if the two motors spin in the same direction.

Can you give us a photo or layout so we can better help?

Originally Posted by StewieRC

test glide show that the plane want to yaw left, if i add throttle the plane will starting to yaw left even more.
i got it up to about 15 ft and lose control of it, the plane just go straight down and messed up the nose.

p.s : i think is just my limited flight time + the tail boom is glue on not straight ( maybe my eyeballing skill is horrible )

Try this little experiment ....

Stick a small nail into the end of the right wing. Then test glide again. The nail wont hurt anything just create a small hole. If it works - leave it, if it doesn't take it out and squeeze foam with fingers and hole will dissappear.

I suspect that not only a lacjk of thrust line ... but if the model yaws / dips left without power that model is heavy on left side ... have you checked lateral balance ? The nail trick fixes that.

It could be any one of many things, especially if it's an own design scratch build which opens up the possibility of something being fundamentally wrong with the design. What about a photo and specifacation (size, weight, CG location etc).. Give us something to go on!

Steve

Originally Posted by ChillPhatCat

Test glide with yaw implies that one or both vertical stabilizers are crooked.

Or seriously under-sized?.. It could be lots of things.

This forum could do with a special rule for minimum data requirements for "why did my plane crash" type questions

Trim out the ails in the glide till it flies level. Most planes will not even fly at 1/3 throttle or just barely. It's probably just stalling out and dropping a wing because of lack of power. Try half throttle. Set the throttle before you launch it. It's the motor torque that makes the plane roll to the left when you add throttle after the launch. Big mistake when your on the edge of a stall.

Gord

Originally Posted by JetPlaneFlyer

Or seriously under-sized?.. It could be lots of things.

This forum could do with a special rule for minimum data requirements for "why did my plane crash" type questions

Very true, I wasn't totally with it last night... spent the whole day doing Gas Dynamics. You're right there are a lot more possibilities and it could even be a combination of a couple of them. It does sound like this plane was made by eyeball and not by ruler however.