Help with wobbling parts!

[Philae_Rosetta2021]

Hello, At the moment I am making a rather large Space Station. The core module is made up of 4 science modules, and a structural space station creator thingy, with cupola module and 2 storage containers. It is encased in a large 3.75m payload, but when I launch, at around 6000m, it starts wobbling and the spacecraft tips over. The rocket is 57m tall (roughly) but I have made bigger rockets that don't wobble. It seems that the Space station inside the payload it causing it to tip over as it tilts, even when I have secured it with structural space tape. Any thoughts on how to stop this, and why it is happening?

[Guest]

There’s usually several things it might be:

- too much mass lower down (doesn’t sound like this unless your 1st stage is huge)

- too much drag up top / not enough lower down (doesn’t sound like this as payload inside a fairing, but try fins on the bottom end)

- not enough struts (try autostruts) no idea what structural space tape is.(I think it’s this)

- being too aggressive during gravity turn (maybe this).

Some designs point blank refuse to cooperate regardless so in that situation I just pack on the fuel and launch straight up until into the darkest part of the altitude gauge where the air is thin before turning.

 

[AlexinTokyo]

Pictures of the craft (VAB, pad, and in flight) will help, but here are a couple of (possible) ideas:

• What's connecting the station payload to the fairing base?  I've found that that connection can be quite tenuous, and needs lots of care to prevent shennanigans from occurring.
• Are you using any form of autostrutting?  If so, what to what?

 

Edit: In response to FG's ninja, I'm focusing on the wobble here, rather than the flip (which I kind of assume is a result of the wobble).

Edited April 28, 2021 by AlexinTokyo

[Max von Kerman]

First, add more thrust to your first stage and add EAS-4 Strut Connectors to where two parts attach, if it still doesnt work, try using a kraken drive.

[Mystique]

I'd make a bet also on small to large part connection around where payload connected to decoupler, had similar problem when heavy and long payload started wobbling so much it actually clipped through fairing. 

So:

1. Add autostrut from part below first decoupler to grandpart/core in order to make this connection less wobbly.

2. Make sure you have reaction wheel around center of mass, perhaps on top of booster and below fairing to have enough control.

3. Check centers of mass and drag in VAB and add some fins to make sure center of drag is somewhat below CoM (not too much or you'll have troubles making gravity turn).

4. Add autostrut to root on main engine to reduce wobble caused by long craft.

5. If you're using side boosters - add autostrut to grandparent to booster itself + autostrut to root to nosecone if it's used and it's quite useful to and regular strut to tie each booster/SRB to its neighbor (i.e. from middle of SRB straight left and right to next SRBs) - that last part saved me from weird oscillations which were causing SRBs to start flying on their own.

Optional: maybe engine gimbal is overreacting and causing trouble, may be addressed by limiting gimbal.

By altitude of 6 km I can guess you may also be accelerating a bit too much (and going supersonic a bit early, while still in dense atmosphere, which causes aerodynamic troubles) and/or you may pushing angle of attack too early too much (4-5 degrees is usually safe).

Edited May 6, 2021 by Mystique

[Mahnarch]

I agree with the strutting and not too much acceleration.

 

Don't be the Hulk™ trying to push a kid on a bike.