Is there anyway so i can put my fuel lines or struts in more symmetric manner

[mwlue]

I'm having hard time placing the fuel lines and struts. and they keep my rocket spins even with mechjeb killroll enabled....

Thank you.

Edited July 6, 2013 by mwlue

[stupid_chris]

Fuel lines aren't loaded in the physics simulation, just like struts, they're virtually massless while flying, and even if they did, the aerodynamics model is far from being precise enough to cause it to affect your trajectory, so it's not them that are causing your roll issue. Could you post a screenshot of your whole rocket?

Edited July 5, 2013 by stupid_chris

[mwlue]

here it is:

Thank you.

[numerobis]

Fuel lines won't matter.

Struts will: you want to place the struts perfectly symmetrically (use symmetry mode). This being impossible, you'll have some imbalances, though you can keep them to a minimum.

In your rocket, you have almost nothing to fight a roll moment. On the one hand, that's not really an issue: you can roll all you want, it just helps you go straight, so that pitch and yaw imbalances tend to cancel themselves out. But if you really want to fight the roll, you'll need some way to apply a roll force. Your main options: control surfaces, or SAS units (not ASAS: ASAS is a computer, SAS is a roll-cancelling unit).

[Tiron]

Yep, engine gimbaling can't really do roll. You need something else on there to deal with it, because with a rocket that size a command pod's built in SAS isn't strong enough, let alone a probe core.

And regular SAS isn't nearly as good for this as it used to be: At some point, probably in 0.20 or one of its patches, they removed the Integral component from it, essentially making it a bigger version of the command pod's movement-damping-only built-in SAS.

Mechjeb's killrot can't, so far as I know, use SAS torque itself, and doesn't really like to turn on the SAS anyway. You'd need an ASAS unit as well to make effective use of regular SAS.

Control fins really work better for this anyway... I normally use Delta Deluxe fins if I can, as they're low drag and light weight, with high amount of lift. If their control forces are too weak I'll switch to Canards.

[mwlue]

Arr ok, thanks all for the feedback. gonna put some fins at the tail then .

Thank you.

[Sid]

Locking the gimbals on the outboard engines helps a lot. To save the hassle of locking each motors gimbals individually I set it up as a custom action in the VAB so it's just one key press when on the pad.