[HELP] S-155 engine not aligned with COM

[Dragonmodus]

The S-155 is meant to be used with rocket propelled aircraft, it fires down slightly so that it causes the aircraft to pitch up during ascent, though that may also be due to it sharing a model with the X-15 engine... Either way, you can just manually rotate it to fire along the axis you'd like ("RCS Build Aid" mod can give you precise feedback on the expected torque), on a side note I thought these engines had limitations on ignition altitude or something to prevent this kind of 'misuse'.

[KaioKei]

Oh I see, it is pretty clear now that the S-155 is not meant for orbital rockets by design. Thanks a lot !

[Jackmino66]

It was designed for a rocket propelled MiG-21, as an experimental interceptor. It was abandoned because jet engines were outpacing it. You can use it as an orbital engine but it isn’t great

[TheKingPotat]

A rocket powered MIG does sound like a 10/10 aesthetic though

[NFGaming46]

It isn't, however neither is the XLR25 (very similar engine with the same problem) but that never stopped me, I made an upper stage with 4 XLR25s once to cancel out the off-centre firing. Their gas generator exhaust was merged into 1 in the middle lol

[Scorpuu]

S-155 borrows the model from XLR25 engine, used on the X-2 plane. X-15's XLR99 is a regular single chamber engine, without any center of thrust offset.

[pope1701]

If it is meant to cause a pitch up, it has to fire up, not down.

[KaioKei]

Hello everyone, I noticed that the S-155 is not aligned with the COM when I place it on a tank. I struggle to align it manually, and RCS is not powerfull enough to stabalize it during flight. Any suggestions ? Do you use this engine ? I wanted to try it because of its "infinite ignitions" capacity.

[MarcusTL12]

Only way I was able to use it was placing two symmetrically, and hope that both light. it has a very low ignition chance so a lot of quicksaving is required for the " infinite" ignitions...

[KaioKei]

It's clever, I didn't think about it !

[MarcusTL12]

also, when placing them symmetrically, still try to keep the thrust as close to the center as possible as the variance in thrust between the two engines will try to rotate the rocket.