Need help fixing my rocket/ship

[Shoggies]

im just kinda wondering why my ship flips out when it hits orbit. i have the main booster tilted slightly so that it corrects the ships weight. but when it hits space it just keeps

making these REALLY bad turns. Iv thought about placing a reaction wheel behind the nose cap but came here first some im not dumbling around parts on my ship and end up wasting my time. / The cargo bay does hold a small probe but i had these issues before and after equipping it with its load.

[Kelderek]

Are these bad turns happening while you are thrusting with engines, or are you talking about just using SAS to orient your ship? If your engines are firing while trying to turn and you are getting bad turns then that means your center of thrust (CoT) is not pointing through your center of mass (CoM). You might need to move fuel around or make changes to the design in the VAB.

[Friend Bear]

So, shuttles are not easy and I made a cool one here for reference (sorry it is in Coub form, I am at work and don't have all the video pieces anymore, anyways): https://coub.com/view/3ep4i

Use that as reference for the extremes you go to for attaining orbit concerning CoM, paying attn to the little, horizontal thruster. Given, this shuttle does not have an engine under the tank, the theory is the same.

For a shuttle, practically anything is possible when in the atmo, especially with wings like yours. But once you reach or near orbit, you have no atmosphere to work with so your thrust is everything.

That being said, make sure your thrust is pushing directly into your center of mass (CoM). When in the build screen, turn on CoM and Thrust and see if the arrow points directly away from the CoM.

Remember, at launch it is not a big deal so you do not need to really test CoM and thrust for the full build. Remove the thrusters on the side to simulate higher altitude since that is where you start running into problems.

Now see if thrust points into CoM.

Remove some of the fuel from the main tank with those thrusters still removed.

Again, see if thrust points into CoM.

Remove more fuel, repeat. Ultimately, you get to a point where it is inevitable the CoM will not have thrust directly underneath it. When that happens, consider limiting thrust on the more powerful engines to balance with the smaller, shuttle engines.

As you near orbit, thrust into CoM becomes more and more important. Even it barely being off can destroy any acceleration. Lessen the thrust each booster gives off in the construction by right clicking and sliding the limiter down. That will make them burn longer and you can get higher with a more stable build, but make sure there is still enough thrust to weight and the balance is not completely thrown. Thrust limit the main engine as well (you will more often do this during flight, far into the launch, since it matters less initially). That engine is far more powerful than your two shuttle engines and will generally counter them no matter the amount of thrust. You can limit thrust on liquid fuel while in the launch phase; just right click the part and drag it.

It takes some time to figure out a good balance, but you got it.

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Reaction wheels are a very good idea. I would place one or two on the top of the fuel tank.

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OH also!

Remember, it is a shuttle. You need a vertical stabilizer on that bad boy if you want to fly it safely in the atmo. Plus, have you tested the shuttle by itself to make sure it can fly? You don't want to go through all this effort only to find it is unflyable.

Edited October 14, 2015 by Friend Bear

[DeMatt]

Add another vote for "needs a rudder on the shuttle", which in turn means "needs an equivalent-but-opposite rudder on the fuel tank".

The shuttle could probably do with a reaction wheel, yes. A Mk2 Drone Core will not only give you reaction wheels but also unmanned control, and will fit nicely into the stack. The Advanced Inline Stabilizer (the medium reaction wheel) would probably need to be hidden in the cargo bay.

You also might want more RCS blocks - remember, for every set you put on one side of your center of mass, you want another set on the opposite side.

[Saltless Lemons]

I am getting the feeling that your rocket is directed by those control surfaces (which don't function without an atmosphere). You could try putting more RCS thrusters on, especially around the tank. I would also put a tail fin on, it helps a lot. By the sounds of things though, the ship itself is pretty well balanced, so props to you for that, it ain't easy balancing a moving center of mass with the center of thrust, while also accounting for the lift that wings generate. Well done.

Edited October 27, 2015 by Saltless Lemons
I didn't look properly :P

[Amoun]

It's a balancing act really.

I am practicing and trying to perfect my shuttle as well.

In the beginning I gave up trying to figure out the angles and made it almost a rocket-like vehicle with the shuttle sandwiched in the middle. It was good enough to dock, made it to my SS and then back down to the complex. Now I am playing around with the real-life like shuttle design and was able to get away with using two engines (one on shuttle and another on the tank and have the fuel drain evenly to make sure that the spin does not happen.

Anyway, this sounds a lot like Center of Mass issue. While you are in the atmosphere and when you launch your weight shifts while the trust doesn't and in the atmosphere your wings (or control surfaces rather) can kinda compensate for that shift but when you are in the atmosphere it does not do you any good. (Imagine trying to balance a broom upright on your palm, same idea). This is why the shuttle and the people who design them sometimes have two sets of engines. Main ones to help get to orbit and then a smaller set for vacuum flight. Definitely test the shuttle in flight before slapping it onto a launch vehicle....especially the reentry, that's when things can get interesting (at least for me).