|The X-15 ejection seat in the aircraft|
Because the rocket motor of the X-15 ejection seat had to be powerful to propel the pilot clear of the X-15's hypersonic shockwave, a novel means was used to transfer loads from the pilot's rear end to the seat pan. Each X-15 program pilot sat on a weather balloon filled with plastic beads and wiggled into it like a bean bag. A vacuum was applied which held the shape of the balloon. Once the pilot stood up, plaster of Paris was poured into the depression, creating an exact copy of the pilot's rear end. A block of Balsa wood was then carved to precisely fit the mould and this became the seat cushion of the X-15's ejection seat- not only was it custom fit which allowed the optimum transfer of shock loads from the pilot's body to the seat pan, it also made for a very comfortable seat!
|Scott Crossfield in the MC-2 pressure suit|
(NASA/Dryden Flight Research Center)
Once the articulated arms deployed into place, the emergency oxygen supply took over pressurization of the suit and a heating unit activated to keep the pilot's helmet visor clear of ice. Once the canopy was blown off and the seat traveled up the rails, special wings on the sides of the seat deployed to stabilize the seat in the high-Mach airstream. In a conventional ejection seat, a drogue chute would be deployed to slow the seat down but at the X-15's speeds, such a chute would have melted instantly, so the X-15's seat deployed a pair of telescopic booms that projected aft and outward from the bottom of the seat to provide aerodynamic braking and helped the wings stabilize the seat.
|Rocket sled test of the X-15 seat- note the deployed booms|
One little-known fact was that the X-15 cockpit was pressurized with nitrogen instead of oxygen as was used in the Mercury and Gemini spacecraft. The pilot breathed oxygen from the his suit which was only pressurized upon ejection. This meant the cockpit was fireproof, something that NASA tragically learned with the launch pad fire on Apollo 1.
The X-15s set an absolute speed record of Mach 6.7 and an absolute altitude record of 354,000 feet which qualified several of its program pilots for astronaut wings. Fortunately the ejection system was never needed and the one fatality, Michael Adams, occurred when his X-15 lost control and broke up on re-entry into the thicker levels of the atmosphere and the X-15's complex ejection system might not have saved him.
Interestingly, the David Clark MC-2 pressure suit served as the basis for the space suits for the Mercury and Gemini programs. The aluminized fabric exterior of the MC-2 suit carried over to the space programs and heavily influenced Hollywood cinematic depictions of space suits well into the 1970s.
Lockheed's Contribution to the Space Shuttle Program
The Boeing 747 SCA Shuttle Carrier Aircraft
Flight Testing on the Cheap: The Groundbreaking M2F1 Lifting Body
How the Shuttle Orbiter Lost Its Jet Engines
Source: Eject!: The Complete History of U.S. Aircraft Escape Systems by Jim Tuttle. MBI Publishing, 2002, p136-143.