I changed the velocity curve to work better with RSS, so I can achieve 11 Mach @ 60km, using ultra light concorde like design. Still not very useful on spaceplanes, as too low Lift/Weight ratio on super thin atmosphere. But it is still cool to experiment and close enough to realism. Changed the last 2 values in the part.cfg velocityCurve { key = 0 0.2 0 0 key = 1350 0.3 0 0 key = 1500 0.8 0 0 key = 1700 1 0 0 key = 4000 0.3 0 0 key = 7000 0 0 0 }