Ship spinning

[gor213]

I am having a problem with my ships spinning out before i reach orbit. Takes off fine, very solid and straight. However at around 13-18 thousand meters it begins to list to one side and is soon spinning out, even with advanced SAS turned on. I am new to the game and im not sure if there is something i am missing, but it makes getting to the mun difficult if i cant even get into orbit. Thanks!

[sal_vager]

Hi gor213, welcome to the community

You can counteract this with vectored thrust, gimballing engines in other words, also use winglets low down to 'bite' the air and help keep you straight, like an arrow .

[Vanamonde]

It really helps if you can post pictures of your ship.

[EndlessWaves]

It's a design problem with your ship, rather than something you're doing wrong in flight. At that altitude I guess you've got canards or other control surfaces that were keeping it in check at lower altitudes but are less effective in the thinner air.

You can fix the design problem (off centre thrust or wobble) or add space-capable control surfaces to keep it in check (SAS modules*, RCS thrusters). Spinning the ship as it ascends (Q or E) may also help.

* SAS modules are gyros and multiple ones work together. ASAS is a control computer and only needs a single one per ship.

[Markus Reese]

Hi there, somebody else posted the same problem, copy and paste reply ^.^

For that, it sounds like a weight imbalance combined with lack of controlable thrust. The ASAS just auto controls the rocket to keep it pointed where you want. SAS act as spin counters. The cause of the flippy rocket isn't related to this. At 13-18km, you start losing the ability for aerodynamic control. If you have a weight imbalance or are using all non gymbaled thrust, it can cause a tip to start to form with no way to control it. Try posting up a pic of the rocket and maybe we can see for an asymetric fuel tanks or what engines if you cannot see any of these. Try having some gymbal engines engage at this point so you can use thrust to help guide the rocket.

[EndOfTheEarth]

Things that will help stop spin and wobbling:

1) Vectored Thrust. The really big 3m engines have this, and make getting off the ground comparatively easy.

2) Winglets and an ASAS to help keep you pointed straight while in-atmosphere.

3) Normal SAS Modules, ESPECIALLY if you've got solid rocket boosters on your ship. These act like gyroscopes and help keep your ship pointed one way.

4) Structural support struts. Lots of them. A wobbling part or radial rocket will cause the rest of the rocket to wobble too...and it only takes so much wobbling before the whole rocket flips upside-down.

5) Do not turn on your RCS thrusters until you are out of the atmosphere. They will not help you otherwise, and likely only make things worse.

[Weatherman159]

I guess my problem is sort of related, so I'll just post it here.

So this:

gets into orbit just fine with enough fuel left over for whatever I'd like it to do up there, but it rolls like crazy once in orbit.

So I decided to add some SAS modules to counter that (one at the top under the command pod, the other is above the main engine).

Spins out like crazy around 3000 meters. I'm at a loss as to what could be causing this. The SRB's aren't exactly balanced out, but it didn't have any noticeable effect before the addition of the SAS modules.

Edited September 12, 2012 by Weatherman159

[EndlessWaves]

I'd suspect it's not the SAS modules themselves but the additional wobble induced by making the rocket taller/heavier at the top.

[RoboRay]

Those fins in the middle probably aren't doing anything useful. They can control roll from there, but they need to be further toward one end to handle pitch and yaw. Maybe spread the SRBs wider so you can put the fin in between them, at the base?

You may also want to tie all of the SRBs together with struts, not just the pair on each big tank. And maybe add struts from the outside top of the big tanks all the way up to the base of the command capsule to reduce wobble?

[hjalfi]

Yep. For control surfaces of any kind to be effective, they need to be as far away from the centre of gravity as possible. I typically put an ASAS right at the top, just under the capsule's decoupler, and a bunch of canards right at the bottom. Putting them on the SRBs isn't terribly effective because you're going to jettison them after twenty seconds, so you'll want them on your fuel tanks, but remember that they will rotate and bashing into your fuel tanks is unlikely to make for a good ascent.

With configurations like yours I've had good luck placing them on the side of the tanks; this lets me put them further down than if I placed them on the outside. And it makes the rockets much more stylish.