How to keep control

[Hiatsu2k8]

My spacecraft launches fine but when I reach a certain altitude it starts flipping and I can't stop it. Anyone have any suggestions?

[Aphox]

After you've been in flight for a while you've more than likely gained a lot of vertical speed, which makes your ship more and more unstable.

Attach an Advanced S.A.S. unit somewhere in your construction and press the T button before you launch turn on your SAS module. This will keep the rocket pointed up-right and give you some extra control. You can press and hold F to toggle it on and off while it's on to make minute adjustments. This also works while it's off.

Another thing you can do is add control surfaces (found in the command and control tab in the VAB) to the rocket to give it a little bit of maneuverability, which will allow the A.S.A.S. to operate a little better, depending on your design.

[Markus Reese]

More often the high altitude flipping is caused by asymetry. If you have fins or other aero control surface, they become ineffective at higher altitudes. You want to make sure your fuel burn doesn't offset your center of gravity, also make sure your center of thrust is inline with your center of gravity. Even one engine being slightly off angle will cause a spin out of control. I had this happen on a space plane where I had one engine above and one below mounted to radial decouplers. The below one was only slightly off center on the decoupler and I spun out of control once I lost the airflow control.

[EndlessWaves]

If this is happening at high altitude then control surfaces won't have much of an effect, you'll need to use RCS instead.

What sort of altitude are you at and how violent is the flip? If it's fairly fast then they may be an easily identifiable cause but if it's slower then those are harder to troubleshoot - it might be that your thrust isn't under your centre of mass, either because of some small addition to the rocket or because it's bending under power.

[RoboRay]

If you've got a whole bunch of fins and other draggy stuff up front, that may be the problem.

Pitch and yaw control surfaces need to be at one end or another of the ship to be effective, but putting them on the back allows their induced drag to add positive stability. Putting them up front causes their induced drag to create negative stability. Which is pretty much universally bad.

[iamaphazael]

Which engines are you using? Thrust vectored ones can help keep control in the upper atmosphere where there's still enough air to cause drag, but not enough for control surfaces to do much good.

[phoenix_ca]

Using RCS for stability on higher stages may indeed help. Also, turning-off ASAS may help stability. The problem with ASAS as it is is that it can cause severe oscillations in rockets that have a certain amount of instability (typically, anything that's tall and pointy...like a rocket). It corrects, but doesn't reduce the speed of it's correction until it passes over the point it was aiming for. Then it corrects just as hard back the other way, overshoots, and so-on. Both stock ASAS and MechJeb suffer from this. If it finally over-corrects too much, such that it can't correct it's over-correction, the result is the whole rocket flipping.

So if you notice this back-and-forth oscillation, taking manual control for a bit may help matters. You can use ASAS when the rocket is more inherently stable. Reducing throttle may also help.