Unmanned rockets flip?

[MultiFrapser]

Hello. I try to send some unmanned probes to Minmus, but for some reason all the suddenly I seem to have forgotten what to add in order to make it more stable? I know how aerodynamics work etc, I have fairings and all that but still it flips almost immediatelly after liftoff.

But, if I were to add crew to those rockets and pilots, it will work just fine. So what's the deal here does anybody know?

[Foxster]

A picture of the craft would be handy. 

[MultiFrapser]

Here are the two variants, both of them has the same problem. The smaller one doesn't have the probe connected to it because I deleted the original spacecraft with it on top of the main-stages

1. The lighter variant 

2. The larger variant 

[Human Person]

Sounds like the prope core is upside down? This would explain the strange flipping behavior (inverted controls) and that it's gone when the vessel is crewed (now it's controlled from the crew-pod).   

Edit: I just saw that the center of lift (blue marker) is over your center of mass (yellow marker).

Your rocket is aerodynamically unstable. Put the fins further down or remove them completely.

Edited June 4, 2017 by Physics Student

[Starman4308]

The fins are also relatively small and mounted high up on the craft. You want a top-heavy, bottom-draggy rocket for stability, which means fins as low down as possible on the stack.

There's also an excess of struts, though it's possible that that's because stock joints are much more wobbly than what I'm used to with KJR (Kerbal Joint Reinforcement).

EDIT: To be clear: while fins that small might work (you can often get away with rockets that are aerodynamically unstable, so long as you can still use gimbal and reaction wheels to keep it on course), they should definitely be as low as you can possibly mount them.

Edited June 4, 2017 by Starman4308

[Human Person]

If your engines have a decent gimbal range and you don't turn too aggressive low in the atmosphere, you should get away without any fins on this rocket.

Edited June 4, 2017 by Physics Student

[ZooNamedGames]

16 minutes ago, Physics Student said:

If your engines have a decent gimbal range and you don't turn too aggressive low in the atmosphere, you should get away without any fins on this rocket.

Cough I can get away with aggressive maneuvers lower in the atmosphere without fins on my rockets (but that's because I have no life and trail and error my way through the failures).

[MultiFrapser]

Ah thank you everyone, what could I ever do without these forums! I had a long break from KSP (been playing this since 2012, just check my profile page when I registered to the forums), so I forgot the physics and all that =D PS. The probe core was wrong on the lower spacecraft, or at least it felt to be because everything was inverted and that made me very confused when doing maneuver nodes and burns for them.