How an X-15 flight worked

An X-15 flight lasted about ten minutes, and the rocket engine ran for only about a minute and a half of it. Everything else was coasting, re-entering and gliding. The pilot had to manage energy the whole way down, because there was no engine for a go-around.

1. Captive carry

The X-15 hung under the wing of an NB-52 and rode to launch altitude with the pilot already aboard. Launch points lay along a tracked range of dry lakes; flight 191, for example, was released over Delamar Dry Lake.

2. Release at about 45,000 ft

The B-52 dropped the X-15 at about 45,000 ft and more than 500 mph. The pilot's first seconds were spent stabilising the aircraft as it fell clear of the carrier, then lighting the engine.

3. Ignition and boost

The XLR99 produced up to 57,000 lbf and could be throttled. The shape of the climb set the kind of flight. Altitude flights pulled up steeply after ignition. Speed flights climbed at a shallow angle and then levelled off, trading height for velocity. Either way the engine burned out after about 80 to 90 seconds, with the aircraft already moving at several times the speed of sound.

4. Ballistic coast and the apex

After burnout, an altitude flight kept climbing on momentum alone. Near the top the air was too thin for the control surfaces, so the pilot used the hydrogen-peroxide reaction controls to hold the aircraft's attitude. On the highest flights the pilot saw the curve of the Earth. Walker's flight 91 peaked at 354,200 ft.

5. Re-entry

Dropping back into the atmosphere meant holding a precise nose-up angle. Too shallow and the aircraft skipped; too steep and it overheated or overloaded the structure. The Inconel X skin took the heat. Pilots measured heart rates of 145 to 185 beats per minute in flight, which researchers put down mostly to pre-launch stress.

6. Energy management and the glide

Once in dense air the X-15 was a very fast glider. Pilots flew a planned descent to a dry lakebed, the biggest of which is Rogers Dry Lake at Edwards, using energy-management techniques that NASA credits as essential to the Space Shuttle. Other lakes, such as Mud Lake in Nevada, served as emergency landing sites.

7. Landing

The pilot jettisoned the lower ventral fin, lowered the gear (a nose wheel and two rear skids), flared and touched down fast on a lakebed with miles of room and no obstacles. Chase aircraft followed the descent.

Fly the same profile

Project X-15 follows these steps in its thirteen-step flight guide: drop, ignite, throttle, pull-up, boost, coast, re-entry, glide to the lake, ventral fin, gear, flare and rollout. Magenta guide boxes mark the ideal path for an altitude flight and a speed flight. Start a flight or compare your results with the real X-15 records.