Spaceplanes

[Storm1]

I am not new to KSP but I need to ask this question. When building spaceplanes should the center of mass be in front or behind the center of thrust. I thought it was that you want the center of mass just behind the center of thrust but I saw some people's planes and the have the center of thrust behind the center of mass.

[vidboi]

It doesn't actually matter whether the centre of thrust is in front of or behind the centre of mass, this is known as the "rocket fallacy". As long as the thrust vectro is aligned so that it points through the centre of mass you're fine. What does matter is the positioning of the centre of life. This needs to be behind the centre of mass for the plane to be stable, however too far behind and you'll have difficulty controllign the plane and it may have a tendency to nose down. Essentially you want your centre of life to be just behind your centre of mass, and your thrust vector to point through your centre of mass.

[foamyesque]

I am not new to KSP but I need to ask this question. When building spaceplanes should the center of mass be in front or behind the center of thrust. I thought it was that you want the center of mass just behind the center of thrust but I saw some people's planes and the have the center of thrust behind the center of mass.

It's the centre of lift you want behind the centre of mass. Centre of thrust forward/back doesn't matter; only vertical and lateral distance from the CoM matters for it.

[El wonso]

Center of mass has to be at the same axis as the center of thrust. It cannot be above, below, to the left/right, that would cause your plane to to pitch or yaw in space.

It can be behind or ahead.

[K^2]

Actually, the way gimballing works in KSP, you always want center of thrust behind/bellow center of mass. The gimballing algorithm assumes this to be the case, so if you put CoT ahead of CoM, the controls for thrust vectoring are reversed.

Of course, if you turn off the gimball and only use surfaces for control, this doesn't matter.

[Kerbal01]

heres a simple SSTO that i made by re engineing a stock craft

http://forum.kerbalspaceprogram.com/showthread.php/37072-The-Ravenspear-Mk5

[numerobis]

Gimballing engines must not be ahead of the center of mass or you're in trouble, but other engines can be ahead of the CoM.

[Jod]

Aerospikes must always be ahead of CoM or the Drag resistance will screw you over at high speeds, literally. The rest of the engines - behind.

[bsalis]

Gimballing engines must not be ahead of the center of mass or you're in trouble, but other engines can be ahead of the CoM.

You can just turn the gimbals off then. Sometimes it pays to have some engines up front to help balance the dry mass.

[Storm1]

Ok thanks guys!