Jetplane Physics Troubles

[Streetwind]

So this is my first real, proper jetplane. Yes, it mostly involved sticking parts together at random. Considering that, it actually flies quite well.

What it doesn't do, however, is launch off the runway.

If I launch the plane off of a clamp high up and let the turbines spin up a little, I can get enough speed to stay airborne and fly. But when I am on the runway, on my wheels, and try to accelerate I invariably see my plane make a very sudden and very sharp turn to the side at some point. Which side varies, sometimes left, sometimes right. If I have no supporting wheels on the wingtips, the plane immediately crashes and explodes; if I do, it just drivers straight off the runway. It doesn't matter if I gently increase my thrust or if I go full throttle. And it happens before I have enough speed to take off.

I saw the same phenomenon on an earlier test run with rocket parts. I assumed it was because I was not using proper airplane parts, but now it just feels like the physics simulation is giving me the middle finger for no reason I can discern.

Why is this happening, and how can I stop it from happening?

EDIT: I should maybe link the screenshot before posting...

Edited January 5, 2014 by Streetwind

[SnappingTurtle]

Unity's wheel physics aren't great, and those engines are causing a large pitch-down moment because they're mounted high up. They're probably putting too much pressure on the wheels and causing your problems on the runway, and it's also why you're having trouble rotating upward. The tail wheel is very far back increasing your takeoff rotation problem. You could shoulder mount the wings and put the engines under them to reduce the torque the engines cause and move the tail wheel further forward. Finally, those tail fins at the back don't look like the canards. You need elevators.

[Streetwind]

Torque from the engines? I had no idea that was even a thing, shows what I know I also spent a good 5-10 minutes simply trying to figure out how one could possibly shoulder-mount wings. They don't attach that way! Until I remembered the rotation keys. Aircraft construction sure is an advanced topic.

Anyway, I now have this. And to my great surprise, it actually worked. It handles a bit like a highly caffeinated rodent, despite already using the smallest control surfaces, but I actually managed to take off (barely) and land (was actually easier than taking off). I'm still not quite sure how everything interacts, but thanks anyway - this helped a great deal!

[TMS]

This may be cromulent to your interests: http://forum.kerbalspaceprogram.com/threads/52080