Wobbling stages?

[kodemunkey]

I'm playing the demo in order to experiment with a rocket design that will get me out of the atmosphere, so that i can progress from drowning my crews in the ocean and killing them on mountain sides to marooning them on the moon and around the sun.

Anyway, some of my more developed two stage rockets contain 3 liquid rocket engines, with about 4 fuel tanks supplying each engine. During take off on x2 speed, i can see the tanks flailing about. I'm presuming there is a way to stop this? and can i use the the same 12 tank system to supply one central engine in the demo?

[bsalis]

Avoid x2 speed. It's hard on the physics.

If that's not enough, try using some struts.

This should probably be in How To.

Expect a Mod here to do that in 3... 2... 1...

[kodemunkey]

Struts eh? How do i use those effectivley?

[Cykyrios]

Thread moved to How To.

From what I understand, your rocket has a x3 symmetry (probably under a tricoupler?). When using such rockets, engines will tend to swing left and right, so you can use struts to keep them in place (click on one of the tanks, and then where you want to put the other point of the strut). It should help keep your rocket stable.

[kodemunkey]

I see, thanks for explaining that. I'll try it out when it's not hotter than a rocket exhaust outside

[Vanamonde]

Also, the longer a rocket is, the more it flexes. Struts will help somewhat, but it's often a good idea to build them shorter but wider.

[hubbazoot]

If you use engines that have thrust vectoring, they make handling way easier, but the rocket will flex every time an adjustment is made. If you do use longer rockets, make sure they're well balanced and use 2~3 struts to connect the booster stages to the center stage.

[kodemunkey]

I'm on the demo still, so struts are the way forward for now.

[Serratus]

One tip to rule them all (orbits): MOAR BOOSTERS.

Seriously, that was like a golden rule to me in my first attempts to orbit Kerbin

[kodemunkey]

More per stage? or more stages?

[Serratus]

In my experience You shouldn't really use solid rocket beyond the thickest part of the atmosphere. One thing You cannot stop them, and second they disrupt manoeuvring ability. So initial stage (but in 2-3 rows firing in sequence).

[kodemunkey]

I usually use liquid rockets to get off the ground with about 3 fuel tanks each, i suppose that could be my problem?

[Serratus]

Not really. Using liquid stages instead of solids is just a choice. They can last longer and help with control, but don't have that good power to weight ratio as boosters. I'd still put one set of boosters just to push me of the ground just for convenience. But that's not really required, unless Your rocket has slow ascend speed.

As to wooblines - too many SAS units in different parts of rocket can cause that as well as too much force. Try to keep g-force not higher than the middle on the display, but higher then the green zone. Also, if You have the main stage, it's typically a good idea to have 1/3 of engines gimbaled and the rest standard. So You don't get over-control.

Try making a single "core" of command pod;decoupler;ASAS,1SAS,RCS tanks,one fuel, gimbal engine;decoupler;3 fueltanks, gimbal engine;decoupler;6fuel tanks, gimbal engine.

Then put 4 radial decouplers on bottom stage and add those liquid stages with normal engines. Then if You want a row of solids on the outside. Then add struts where they should be. And Your generally set to go minus some minor adjustments.

This is not a spoiler, just an example of how I would do it but there are many different ways...

[EndlessWaves]

I usually brace against the direction of wobble, so if they're wobbling at the end of a stack I'd put the braces horizontally between the bottom of the stacks (on the last fuel tank). I don't actually know if it makes a difference but it looks best that way anyway.