Ejection seats are used to rescue a pilot when the plane is lost. Ejection seats are characterized by high dynamic pressured during the parachute inflation as the planes often fly low and fast. Some seats are also able to operate at supersonic conditions.
X-15 was a hypersonic rocket plane which flew at the edge of space. X-15 ejection seats were unlike any other aircraft or spacecraft ejection system. The escape system needed to function at a velocity up to Mach 4, dynamic pressure up to 1500 psi and altitude up to 120,000 feet.
Due to weight and time restrictions, it was not feasible to have an escape capsule for the pilot. Therefore, the MC-2 Pressure Suit was used as both breathing and windblast protection. The cockpit along with the suit below the neck was pumped with nitrogen for cooling and fire protection and pure oxygen was supplied in the helmet. There were serious concerns of nitrogen leaking into the helmet which fortunately did not materialise. It was expected that deployment at high Mach numbers would still lead to burns to the head, knees & toes.
The vertical ejection velocity had to be high so as to clear the pilot of the supersonic shock wave. This implied a high shock load along the spine of the pilot. In order to alleviate this, a plaster cast of the pilot’s bum was made and subsequently the custom seat was carved out of balsa wood. Arms and leg restraints were used for both injury and windblast protection at high Mach numbers. There was also a heating unit in the pilot’s helmet to keep the visor clear of ice build-up.
As a drogue parachute couldn’t be deployed at Mach 4, solid wings & telescopic booms that extended rear and outward were deployed from the seats after ejection to stabilise the ejection seat.
The pilot was attached to the seat until 15000 feet, after which the seat and the pilot separated and the pilot moved to the pressure suit oxygen supply. After which, the pilot chute and subsequently the main parachute are deployed.