Rocket spinning (spinning not flipping)

[Zander]

Hey,

I have seen some people make a threat asking about this but every time people think they mean flipping. I mean spinning around its axis like a top.

as soon as I get out of the atmosphere my rocket starts spinning around whenever I use the engines. I have 5 engines in a quincunx and no finns. Anybody know what causes this?

[Tidus Klein]

Try locking the gimbals on the 4 out side engines.

Other than that you could try going back in the editor and remaking them, some times ksp is just stupid and does random stuff, a quick dedisign even if its the exact same rocket can some times fix problems. But I would try the locking the gimbals first.

[SSSPutnik]

Struts can do weird things.

[Murph]

It might help if we knew more about your rocket. A picture and/or brief description would help.

Have you checked the centre of mass is safely in the middle of it, and aligned to the centre of thrust?

Is SAS enabled when the spinning happens?

Is there sufficient reaction wheel torque (probe cores alone are insufficient for large rockets)?

Are you using any mods?

Did you use the VAB editor's symmetry option when attaching the radial parts of the stack?

Are you trying to do anything clever in terms of construction? (e.g. something funky with engine positioning or alignment)

[Keldor]

I noticed this happening when I didn't add struts - I think the boosters were able to twist on their mounts, and thus the spinning was caused by the rockets.

[Murph]

I noticed this happening when I didn't add struts - I think the boosters were able to twist on their mounts, and thus the spinning was caused by the rockets.

Yes, radially attached components are attached by a single infinitely small (but strong) pin in physics terms. It can twist around if sufficient torque/shear is applied by the attached component. If the radially attached engine stacks are not braced with struts, they will not stay aligned under thrust.

[iDan122]

It is if struts are not placed correctly. Say you have a rocket with 4 boosters.

You place 4 strut attachment points on the center of a booster and place the other end in the place between the boosters.

That in KSP creates torque, so you have to place struts evenly on both sides of each booster.

Btw adding control surfaces will help by 90%

[Kasuha]

Spinning usually means your rocket is not symmetric. Most often this happens when you mount your external stage on radial decouplers "skewed", i.e. the fuel tank is not sitting on the center of the decoupler but on its side. The pull of the engine will skew the decoupler a bit and will add torsional force, making the rocket spin.

[el_coyoto]

I may be wrong, but even a perfectly symmetric and rigid rocket would need winglets or fins to keep it from spinning (even slightly).

Small rockets are not affected as much as big ones, but I still put winglets on the first stage of most of my rockets because I like them flying straight (it's much easier to do a good grav turn when the rocket doesn't spin).

This said, Kasuha is right, and, most often, severe spinning is due to buggy radial mounting or powerful engines under an insufficiently strutted/rigid stack. In the latter case, the engine thrust under an insufficiently rigid stack will make the part the engine is attached "wobble" around. This can be diagnosed by zooming on the part your engine is attached and check its behaviour in flight.

Do you have pictures of your rocket and/or its flight?

EDIT : carp, I missed the "as soon as I get out of the atmosphere" in the opening post. Not much to see here, sorry...

Edited December 17, 2013 by el_coyoto
words

[Zander]

It might help if we knew more about your rocket. A picture and/or brief description would help.

Have you checked the centre of mass is safely in the middle of it, and aligned to the centre of thrust?

Is SAS enabled when the spinning happens?

Is there sufficient reaction wheel torque (probe cores alone are insufficient for large rockets)?

Are you using any mods?

Did you use the VAB editor's symmetry option when attaching the radial parts of the stack?

Are you trying to do anything clever in terms of construction? (e.g. something funky with engine positioning or alignment)

center of mass is centered and aligned with thrust

SAS is enabled

No reaction wheels on my pod

yes quite a few

no radial parts at all except for the engines but they are on the bottom of the fuel tank and symmetry was used to attach them.

nothing weird i tried to put the engines on in a quincunx and used the symetry option so they should be pretty straight.

[Murph]

I may be wrong, but even a perfectly symmetric and rigid rocket would need winglets or fins to keep it from spinning (even slightly).

The OP is talking about out of atmosphere spinning, so aerodynamic widgets can't influence it (other than their mass). While winglets and fins can be very useful in-atmosphere, they are not a hard requirement  reaction wheel torque combined with thrust vectoring can be sufficient even on large rockets (although possibly not with mods, such as FAR).

I think it's sounding like insufficient bracing struts on the radially attached engine stacks. That, or insufficient reaction wheel torque relative to the total thrust. Or, an editor bug or construction goof which has allowed some asymmetry in the engines or some other form of misalignment.

Zander, what engines are you using? What's the mass and/or TWR when this happens?

Edited December 17, 2013 by Murph

[Zander]

I maybe wrong, but even a perfectly symmetric and rigid rocket would need winglets or fins to keep it from spinning (even slightly).

Small rockets are not affected as much as big ones, but I still put winglets on the first stage of most of my rockets because I like them flying straight (it's much easier to do a good grav turn when the rocket doesn't spin).

This said, Kasuha is right, and most often severe spinning is due to buggy radial mounting or powerful engines under an insufficiently strutted/rigid stack. In the latter case, the engine thrust under an insufficiently rigid stack will make the part the engine is attached "wobble" around. This can be diagnosed by zooming on the part your engine is attached and check its behaviour in flight.

Do you have pictures of your rocket and/or its flight?

This is not happening in the atmosphere, it is happening in space.

and no radial parts. I have 5 engines in quincunx on the first stage and 1 engine on the second stage so when the first stage is in space it spins but once I change to the second stage with only one engine the spinning stops so I am pretty sure its something to do with the engines.

[Zander]

Zander, what engines are you using? What's the mass and/or TWR when this happens?

Once again no radial parts. The rocket is composed of a single stack.

on the second stage i have 5 KW LR88s with a thrust of about 1000 kN each giving me a TWR initially of around 0.6 g which later increases to almost 2 g as fuel depletes.

[Murph]

Once again no radial parts. The rocket is composed of a single stack.

on the second stage i have 5 KW LR88s with a thrust of about 1000 kN each giving me a TWR initially of around 0.6 g which later increases to almost 2 g as fuel depletes.

The radial I'm talking about is the 4 engines around the outside. I was assuming that you had something like 5x (tank+engine), one central + 4 radial; but now I'm thinking you maybe have all 5 on the bottom of 1 supersize tank?

Your TWR isn't excessive, but 1000kN is certainly sufficient to produce some twisting in the engine attachments with stock components (I don't use KW myself, so into alien territory here for me).

[Noctrian]

I call this spinning "toilet-bowling", apart from disabling the gimbal on the outer engines, I don't know how to fix it. FAR seems to help if are willing to use it. I use a 3-splitter stack so I only have this problem in the beginning of asparagus staging.