Why doesn't this launch stage work?

[quasarrgames]

Well, technically it does work. If flown correctly it can get over 27 tons to orbit, and on its own it can reach escape velocity. It has one big problem, though:

If i turn it at all during ascent, the prograde marker slips sideways, like it should. The problem is, the ship keeps leaning toward the prograde marker, meaning that the marker slips sideways more, and the ship keeps leaning sideways more, until the ship makes a violent parabola into the ocean.

To illustrate:

My hands were off the controls when i took this picture. The SAS was just doing all it could to prevent the leaning, but it didn't work.

I've tried everything i could think of; making the ship shorter, controlling it manually (it's not the SAS' fault), making it more streamlined, adding an overabundance of control surfaces and reaction wheels that it really shouldn't need... nothing helps at all.

So, that's why i'm asking for your help. Do you know what could be the cause of this? If you can help me, you shall be reputationally rewarded.

P.S. it worked fine in 1.0, but this problem popped up in 1.0.2, presumably because of the ominous looking bullet point called "aerodynamics"

[Guest Darth Gerbil]

The cause of your problem is physics. If you turn to low down in the atmosphere, where it is denser, your vehicle will be forced to stay in the airstream. (Because the vehicle you are flying is aerodynamically stable, meaning there is more drag at the back.) Basically if your center of mass and center of lift are too far apart, then you will have difficulty turning. To solve your problem you must:

- Turn higher in the atmosphere.

- Increase your thrust/weight ratio. (Total thrust divided by mass times gravity.)

- Bring your center of mass closer to your center of lift and vice-versa. Remember to always have your center of lift behind center of mass.

You could bring the com and col closer by putting fins at the top. (Maybe?)