Spacecraft tips over while throttling in space.

[Olsson]

Hello,

I've made a spacecraft which I'm having some issues with. When I'm in space and I'm doing a normal burn my spacecraft will tip over/forward as I throttle up. If I engage the ASAS the craft will point itself a few degrees away from where the point I locked the ASAS too. I just want to understand why and how I can prevent this from happening. The center of thrust and the center of mass looks good so I don't think thats the problem. Any advanced spacecraft builders that can explain to me why this happends and what the cause might be?

Picture of craft: http://i.imgur.com/A4rTi.jpg

[EndlessWaves]

I'd suspect it is a centre of mass/thrust problem, some modded parts only update their mass in flight (particularly fuel tanks) so the VAB's indicators wouldn't be accurate.

Does this happen if you make it symmetrical top and bottom?

[Beowolf]

I had a ship that tumbled as fuel burned off, as EndlessWaves suggested. It was easier to debug after I added a fuel dump part so I could get rid of most of my fuel while still on the pad. I used the one in ORDA, but there are several.

/Balance was so far off that, if I turned on the gyros in orbit, they'd work backwards and she'd gradually tumble faster and faster until she broke apart. That part was kinda cool, though not the mission profile I had in-mind.

[sal_vager]

Olsson, it's possible your craft is just slightly weighted on one side, it might fly straight if you tried it without all the extras you have fitted.

[Olsson]

Well the three of you were right. It was a balance issue even though it was minimal it did affect. Like sal_vager said it was specifically the extras that created the problem, I moved them all to the bottom and I tried to place them symettrically, the spacecraft doesn't fly precisely straight in space now but it's much better than before and the ASAS works perfectly atleast. I'll continue to develop on this spacecraft and try to fix it completely. Thanks again!

[T10]

If it's parts such as landing gear, legs, parachutes, wings or other such stuff, you could try adding more extras to the other side of the rocket. I did this to counterbalance the big landing gear on my spaceplane, by calculating the 'bottom' mass, and simply adding extra parts to the top. It solved a tumbling spaceplane in upper atmosphere/space.

[sal_vager]

Olsson, I know you said it does not fly perfectly in space, but there is another factor that can affect you in the atmosphere, that factor being the drag of the various side mounted components, even ladders have a small effect.

But in space there is no drag, so it must be something else, I find with some large designs that the craft can twist under acceleration but that should not happen with your small design, but just in case, see what happens if you brace the nacelles with struts or mount them on decouplers so they don't touch the main section of the craft.

[Markus Reese]

I think it is a weight inbalance. Do you have a z02 tank on the other side as well? When you get to such small weights, asymetry has much more of an effect.

[draeath]

Seems to me it would be nice to have "ballast" components we could place and manually adjust the mass of. These could be used to troubleshoot/resolve center of mass troubles.