How do I make this damned rocket behave?

[Specula]

I've made a rocket to take 2 Kerbals to Duna, land and come back safely. However, this rocket shakes itself apart constantly and despite the fuel lines feeding symmetrically through the bottom stage, the fuel does not, which sends my rocket into an insane spin when one of the final mainsails suddenly has half a tank of fuel left and the other doesn't. The connected large fuel tanks also like to sometimes fail. No idea why it's only sometimes though...

I've done what I can, but it's now beyond what I'm capable of fixing. Can anyone look at this rocket and tell me what it's problem is?

https://www.dropbox.com/s/ptpjteowmg4ie40/Wildcat%20Lander%20%2B%20Launcher.craft

[sgt_flyer]

hmm - a few points :first, lower your control surfaces - place them on your central booster. - you can also remove the ASAS on the outer boosters - 1 ASAS is enough per craft, more ASAS's won't cumulate their effects

then, try to add 3 struts between each fuel tank (vertically connecting them) also, disable gimballing on the outer mainsails before liftoff should reduce wobbling.

regarding the fuel flow, the fuel lines are not connected correctly - disable symmetry before adding them, or place your booster only using a x2 symmetry.

basically, the fuel lines in an asparagus on your rocket should be disposed like this : 1 fuel line from each of the two first boosters to fall go to the second set of booster, then, 1 fuel line per booster of the second set goes to the central tank. (two boosters to two boosters to central stage).

here's a modified version of your rocket (moved control surfaces, removed the boosters ASAS, strutting remade, and fuel lines fixed )

don't forget to disable gimballing on your outer mainsails before liftoff - i also added separatrons on your boosters, to prevent them from destroying your core stage on separation

note : with the fuel lines fixed, the first pair of liquid boosters runs out of fuel only a few seconds after the solid rocket boosters.

http://www./download/2zlguwkbbdspgag/Wildcat_Lander_%2B_Launcher.craft

Edited July 2, 2013 by sgt_flyer

[Specula]

hmm - a few points :first, lower your control surfaces - place them on your central booster. - you can also remove the ASAS on the outer boosters - 1 ASAS is enough per craft, more ASAS's won't cumulate their effects

then, try to add 3 struts between each fuel tank (vertically connecting them) also, disable gimballing on the outer mainsails before liftoff should reduce wobbling.

regarding the fuel flow, the fuel lines are not connected correctly - disable symmetry before adding them, or place your booster only using a x2 symmetry.

basically, the fuel lines in an asparagus on your rocket should be disposed like this : 1 fuel line from each of the two first boosters to fall go to the second set of booster, then, 1 fuel line per booster of the second set goes to the central tank. (two boosters to two boosters to central stage).

here's a modified version of your rocket (moved control surfaces, removed the boosters ASAS, strutting remade, and fuel lines fixed )

don't forget to disable gimballing on your outer mainsails before liftoff - i also added separatrons on your boosters, to prevent them from destroying your core stage on separation

note : with the fuel lines fixed, the first pair of liquid boosters runs out of fuel only a few seconds after the solid rocket boosters.

http://www./download/2zlguwkbbdspgag/Wildcat_Lander_%2B_Launcher.craft

Much appreciated, thank you. And yes I had the outer mainsails and tanks on 2x symmetry and did two pairs of them, same for the fuel lines. Couldn't figure out why they weren't behaving... Anyway, yes the SRBs are supposed to run out just seconds before the first two mainsails get dumped. Either way, thanks again!

[Johnno]

A few things - as sgt_flyer mentioned it'd be good to 'stitch' the tanks together vertically, but also I'd recommend a few struts horizontally between the outer tanks and inner tank.

The sepratrons on the decoupler below your lander (on the center tank) push the center tank into the lander, not sure if that's by design but if they're to push it away you'll have to turn them.

Decoupler on top of the lander is attached to the lander after use, you could turn it around to drop the dead weight.

I would recommend reinforcing the lander's engine stacks, a few more struts to connect them to the lander. Also after testing your launcher I did a few parachute tests on the way down, might want to swap the mk16-xl chutes for mk25s and possibly also move some of the radial parachutes onto the main lander body. I had a few RCS tanks/parachutes come off (even after a couple extra struts) during testing. From personal experience trying to slow down a heavy midsection with parachutes connected out on radially attached things can easily end in disaster.

The dish antenna above the lander's door - when deployed it may knock down exiting kerbals (happened when I tested it). From my experience you want to keep the area above the hatch clear, I had one incident where a kerbal hit his head so hard he died.

[Specula]

Much appreciated, thank you. Yeah... I got to Duna only to have every parachute rip off 500 meters off the ground. Things didn't go too well from there over the next few seconds...