New rapier that runs on anything

[LABHOUSE]

Just make it be a normal rapier except with less thrust and have a fifth nozzle in the centre that can be turned on or off and be used to just shoot out anything left over like plain liquid fuel, (shooting it out like a water house so little efficiency) monopropelant, Xeon gas, oxidizer (left over), or intake air (when not enough for a jet). I cannot code but can model so I Can help. And the middle nozzle could be turned on and off and you could choose which fuel it uses.

[Lhathron the Elf]

Interesting idea. I would support this, but I don't think there is quite enough need for something like this in order for it to be put in the game.

[LABHOUSE]

But if you run out of fuel just switch to mono or left over oxidizer (from using it in jet mode)

[Franklin]

I think to keep it balanced against the other engines its "firehose" mode would need to be miserably inefficient. which might disappoint you all-in-all.

One of the counterweights to having multiple engines for multiple purposes is their combined weight jumps. A multi-tool like the engine you suggest would need to offset its static scaling-weight with really awful performance, I would think.

[nli2work]

try Interstellar. stock multiengine module only supports 2 engine modes.