My nuclear tug spins (yaw) when engines on

[hanvyj]

Hi guys,

First post! I've got a nuclear tug design with two engines, the problem is it starts to spin (yaw, along the plane the two engines are in) out of control as soon as I have any thrust...

This suggests to me, one of the engines is either underpowered or they are angled in some crazy way. Surely if I'd mounted them wonky or something (which I'm pretty sure I haven't - used symmetry) it would spin on the pitch axes? Unless they were different heights... Anyway, rather than stab at it in the dark and have to launch into orbit every time I was wondering if anyone else has come across this problem with this engine configuration.

Thanks (this is the second to last stage, just the front bit is the tug itself:)

[krenshala]

Are the three fins part of the part that spins? I see that the right RV-N (in the picture) is lined up perfectly to try and flame that fin off, and that may be affecting the thrust symmetry.

Also, did you check the centers of thrust and gravity when building that part? It may simply be that the two of them aren't lined up on the same axis, which would definitely cause it to spin. The farther apart for their axis, the more force needed to counter that spin.

[espm400]

Where is your CoM in relation to your CoT? Although I've never experienced it before, I've heard if the CoM is above your CoT it tends to reverse the gimbaling on your engines. Try locking the gimbals on your engines and see if it still wants to spin.

[dlmarti]

I was wondering if anyone else has come across this problem with this engine configuration.

1. I have never seen a ship like that before, totally badass looking, but really really bizarre.

2. When you see it go out of kilter, hit F3, see if you have had a structural failure.

3. Check the fuel levels of each tank, when it goes wonky, you may have an imbalance.

4. Double check that you do not have a symmetry problem.

[stupid_chris]

I'm nearly sure your right nuclear engine is thrusting against that fin, and that is most likely the problem. What happens then is that the thrust from the left engine works while the left engine's thrust is being blocked, and that causes the spin you see.

[hanvyj]

Thanks everybody, I think you were right - reconfigured the winglets and all is good now. I never thought of the thrust being blocked. I thought things would just get destroyed first! Obviously not with the nuclear engines.