Multi Stage Wobble

[Earl of Doncaster]

I'm building multi stage rockets, but I get disastrous wobble.

I've tried adding SAS modules and cannards, but can't stop the wobble.

It looks like a gigantic dildo.

How do I stop the wobble?

Thanks.

[Caribear]

Is it a wobble that starts slowly and then builds up until your rocket goes wildly out of control? Or a more of a "wiggling" down the length of the rocket?

One: you have to make 100% sure (I can't stress this enough) that your rocket is 100% balanced. Even a small equilibrium difference can cause huge problems. For example, if you place three similar components radially and then enter a gravity turn where the components during the gravity turn is off-centre, you WILL experience trouble.

Two: Are you using radial boosters? Again, make 100% sure they are perfectly aligned with one another and comprised of the exact same parts placed exactly.

Three: Tall rockets (especially) have a tendency to wobble based on (1) certain parts that do not "connect" properly and (2) bad structural rigidity. With large rockets you have to strut every section together properly or else you will experience wobble.

Four: Engine Gimballing can create that wobble.

If you can, post your craft file somewhere for me to DL, I'll happily test your rocket for you.

[Diving Duck]

My advice - go crazy with struts! It really does help. Connect stages together with several struts right at the edges for stability. Struts break on separation so do not worry too much about the struts snarling up stage removal.

Also if you are running liquid engines and can spare the loss in thrust, try throttling down a touch as it can help.

[bpivk]

Also don't make a heavy rocket, enable ASAS and launch. That can make big rockets wobble like hell. I usually launch the rocket without ASAS and center them manually and then enable ASAS. That reduces wobble considerably.

[Nats]

Add loads of strutting, lock the gimballing on side boosters, dont make your rockets too thin.

[Earl of Doncaster]

Thanks for the helpful replies.

It would seem that struts have got style and they got meaning.

[bpivk]

Originally posted by Krasny:

It would seem that struts have got style and they got meaning.

They don't have style (my ships look fugly with them) but they do have meaning. :)

[Caribear]

Also, I find it an quite the artform to build rockets: One can easily build a big launch rocket capable of lifting "x". What is much more difficult is building the same "x" lifter using less parts, less struts and to get it perfectly balanced.

Not that I mind, I spend hours tweaking single rockets.

[deDalei]

a lot of Struts work and good balance is the key for me and I start early with the struts ...

[jamesc70]

Once your rocket 'settles' on the launch pad, you can easily see where it isn't stable (it will move around).

Struts are the obvious answer, but if you have a large payload like a space station piece on top of a long rocket, the whole thing will spin a bit, even with struts. You could do things like attach girders to radial decouplers to 'lock' two stages together, or even place small vectoring engines on the higher part that fire on lift off (will help correct the spin).

[Caribear]

I build pretty huge rockets and to counteract spin I always use a multitude of RCS thrusters and apply liberally the moment I notice rotation. Very inefficient, but needs must.

[Couch Potato]

try to add struts connector. Always works for me...

[Alex Kerman]

you require additional struts

[Nachtus]

I have had this problem as well, I have noticed that the engine gimbal is about 80% of the problem in any of the wobbles, as well as stacking too many fuel tanks together. With heavier rockets you will find that the boosters are fighting the weight all the way up, also creating a wobble.

[Bubba Fett]

Use struts, but move them away from the rocket where more leverage will make more stability.
Ill usually radial mount a ring of 4 girders at the top and bottom of my main booster stage and a ring of them on my upper booster stage. Put your struts on the end of the girders and you can reach further than just strutting along the surface of the rocket and add a triangular brace of struts between them to stiffen the booster they're mounted on.

If you're using radial mount boosters (and who doesn't?) you might want to make sure gimbaling is off on the booster engines and just use the main engine gimbal. Too many engines steering can make heavy rockets wobble pretty bad. Don't forget to strut the boosters as well. To the main booster and to each other.

You should also get the subassembly loader/saver mod. Once you do come up with a stable rocket that doesn't wobble it's nice to be able to reuse it easily for any payload.

[ＤＨＣＰｃｏｎｆｉｇ]

Struts, struts out the ass. Place them between your fuel tank stacks and you will get a nice stable tall rocket. Put some on boosters as well to keep them from wobbling around on their coupling.