Sorry to derail the thread - I'm a big fan of this mod, I'm having some issues getting it to play nicely with the SABRE combined Jet / Rocket engines from the popular B9 Aerospace Pack. They're one engine with a toggle-able mode, so their parts files have the parameters for jets (atmospherecurve with velocitycurve) as well as the parameters for a rocket (another atmospherecurve contained within its own ModuleEngines). From tests with other rockets I've worked out how thrust is affected by this mod, and it seems pretty simple. I'll write it here, just in case I'm wrong someone can correct me: The Isp atmospheric to Isp vacuum ratio is the fraction that the base thrust is multiplied by, when you're at 1 atmosphere. I haven't done any tests to work out how it interpolates to get the value at intermediate pressures, but I don't think it's relevant to figuring this out. Before getting to what seems to be going wrong, here are (what I think) are the relevant lines from the B9 engine's part file: (These are from the jet mode) maxThrust = 640 atmosphereCurve { // Atm.P. Isp iTan oTan key = 0 1805 0 2.51E+07 key = 7.5E-06 1969 0 0 key = 0.0006 1658 0 0 key = 0.11 1853 0 0 key = 1 1600 -400 0 } (these are from the rocket part) maxThrust = 860 atmosphereCurve { key = 0 375 key = 1 330 } So, here's the weird part. The Thrust Corrector mod works perfectly for the engine when it's in jet mode. On the runway, thrust is reduced to 88% (1600/1805) of its unmodded value. Switching to the rocket mode, I'd expect the rocket's thrust to drop to 88% as well (330/375). The problem is, the thrust actually goes to a shockingly-low 14% of its unmodded value on the runway. The only way I can think of to reproduce the measured thrust reduction is to use the %F multiplier from the jet engine when it's not moving (0.85), use the jet engine's base thrust instead of the rocket's base thrust (0.85*640/860), and then either the rocket Isp to jet Isp ratio for both components at sea level, or both components at vacuum (both ratios end up with a final thrust reduction of 13%). Obviously, something wacky is going on here, and it seems to be stemming from the fact that there are two ModuleEngines nested within one module that B9 uses to switch between engine modes. It just seems doubly strange to me because I would think that if the Thrust Corrector handles the jet engine correctly, then I'd expect it to either handle the rocket correctly or treat the rocket exactly the same as it does the jet. Instead it seems to be pulling just one Isp value from the rocket, and otherwise pulling a bunch of data from the jet. Does anybody have any better ideas what might be going on, or what tests I could do to figure out what's going on? It's not the end of the world if I can't get these engines working, but they did look like they'd be fun for good-looking SSTOs. Thanks for reading, and extra thanks if you've got any ideas!