X-15A-2 Engine
The XLR-99 engine on the X-15A-2 SE.
Pilot operation of this system is the same as on X-15 airplanes. However, depending on flight configuration, helium for purging of the engine compartment may be obtained from either the 0.491-cubic-foot bottle (located in the 29-inch fuselage extension) or the 2.4 cubic-foot bottle [11, fig. 3-2] (located on top of the engine shroud, just aft of the upper vertical tail).
Note: Helium for purging of the engine compartment (or extinguishing an engine fire) is obtained from the 0.491-cubic-foot bottle (located in the 29-inch fuselage extension) on the X-15A-2 SE addon. Helium pressure in the 0.491-cubic-foot bottle can be monitored on the auxiliary pneumatic and control pressure gauge [21, fig. 5-3] on the center pedestal.
In addition to the 74.4-gallon spherical supply tank, hydrogen peroxide monopropellant (90% H2O2) is stored in four 10.85-gallon spherical supply tanks, two on each side of the fuselage, adjacent to the engine compartment, in the side fairings. Monopropellant from these tanks is transferred into the 74.4-gallon tank, which in turn supplies monopropellant to the engine turbopump.
To pressurize or jettison the propellant in the external tanks, the fuel selector switch [8, fig. 5-6] must be at EXTERNAL, when the desired function is selected with the vent, pressurization, and jettison lever [11, fig. 5-4]. The external tanks are vented, regardless of the position of the fuel selector switch, when the vent, pressurization, and jettison lever is moved to VENT.