Second Stage Wobble

[Rizons]

The Joint between the Terrier Engine and the TR-18A Decoupler wobbles when I try to do the Gravity Turn to my rocket.

Already Did:

• Strutsss
• Placing a stabilizer below the Decoupler. 
• Distributing torques to the first stage and second stage.
• Not having a second stage at all. (But hey, It worked)

Its just annoying when I try to do the Turn and the whole rocket wobbles and oscillates, then the mission fails.

[bewing]

Have you tried "Grandparent" autostruts?

A strut makes a joint perfectly rigid. If you placed struts across the joint that is flexing, and it still flexes, something is broken in your game download, most likely. Could you attach a craft file, please? (You need to use a service such as pastebin to do that, FYI.)

 

[Kryxal]

How soon are you turning and how sharply?

[Palaceviking]

Second stage centre of drag syndrome. 

[Rizons]

19 hours ago, Kryxal said:

How soon are you turning and how sharply?

Probably 10 Degrees every 10 Seconds.

19 hours ago, bewing said:

Have you tried "Grandparent" autostruts?

A strut makes a joint perfectly rigid. If you placed struts across the joint that is flexing, and it still flexes, something is broken in your game download, most likely. Could you attach a craft file, please? (You need to use a service such as pastebin to do that, FYI.)

Haven't tried that yet. I tried connecting the struts to the fuel tank below the decoupler and above the terrier engine, and the wobble reduces but still frustrates me.

[Geschosskopf]

3 hours ago, Rizons said:

Probably 10 Degrees every 10 Seconds.

Haven't tried that yet. I tried connecting the struts to the fuel tank below the decoupler and above the terrier engine, and the wobble reduces but still frustrates me.

Have you tried using Kerbal Joint Reinforcement?  But if you don't like mods, then it's either that the rocket has some stability problem or your ascent profile needs tweaking....

So, is that 10 degrees every 10 seconds done in steps of 10 degrees all at once?  If so, that's likely the problem right there.  You should really never let the nose get more than about 5 degrees off the prograde marker, especially in the lower half of the atmosphere.  If you do, the aerodynamic pressure on the rocket's side will cause bending, breaking, and/or flipping.  Instead, you want to move keep the nose right on the circle of the prograde marker (which is about 5 degrees or less) and keep it there with a series of very small adjustments ever few seconds until you're pitched over to the angle you want at that altitude.

 

[Kryxal]

If you can get your turn to be closer to an actual gravity turn, it will reduce stresses on the joint.  This means you make a small turn early, hold attitude till prograde catches up, then just follow prograde.  If you do it well you can have your rocket climbing the whole way, but mostly building speed sideways, and have your periapsis above ground before getting your apoapsis where you want it.

By the way, if your rocket is built with sufficient drag at the back, you won't even need SAS to maintain this.