X-15-1 Add On Rocket Aircraft For Flight Simulator X
This package contains 2 versions of the X-15-1 with the interim XLR-11 rocket engines and two versions of the aircraft with the million-horsepower XLR-99 rocket engine.

X-15A-2 Add On Rocket Aircraft For Flight Simulator X
This package contains 3 versions of the X-15A-2 with external propellant tanks and the mighty XLR-99 rocket engine.

X-15-2/3 Add On Rocket Aircraft For Flight Simulator X
This package contains 2 versions of the X-15-2 and two versions of the X-15-3 aircraft, all equipped with the mighty XLR-99 rocket engine.