X15

At a height of around 62,000 feet and a speed of roughly 3,800 feet per second, the X-15-3 aircraft broke up because the weights on it increased above their structural limits

A well-known and important figure in aviation history is the X-15. Its goal was to fly quickly and high, testing the aircraft and putting the pilots through challenges that might later face astronauts. In addition to being the first piloted aircraft in the world to reach hypersonic speeds, or more than five times the speed of sound, it made the first manned flights to the farthest reaches of space. In the 1960s, the X-15 was a crucial tool in the development of spaceflight, and X-15 pilots who flew at altitudes greater than 50 miles were awarded astronaut wings.

In total, 199 flights were made by the three X-15 aircraft between 1959 and 1968. It was a collaborative project between the US Air Force, US Navy, and US NASA.

Almost every X-15 flight experienced some sort of technical issue or malfunction; occasionally, there were many issues on a single flight. It is remarkable that during the 199 flights of the whole X-15 program, just one pilot, Mike Adams, perished.

Mike Adams was the twelfth (and last) pilot in the X-15 program, according to John Anderson and Richard Passman’s book X-15 The World’s Fastest Rocket Plane and the Pilots who Ushered in the Space Age.

Michael Adams, a veteran pilot with six prior X-15 flights, boarded the machine on November 15, 1967, for a mission intended to test a guidance display and carry out several experiments. He had practiced the specifics of this flight in the simulator for more than 21 hours. He descended to 45,000 feet at about 10 a.m. as usual and then climbed to 266,000 feet. After takeoff, an electrical disturbance caused the MH-96 dampers to trip out as the plane rose to a higher altitude.

The dampers were reset by Adams. To more precisely manage the experiments, he then changed the sideslip indicator’s mode to a vernier attitude control mode. In order to see his sideslip during the approach to landing, he intended to reset this back to indicate the yaw angle when returning to base. However, he was unable to see the airplane yawing at a crucial point in the flight as a result of this equipment shift.

After burnout, he experimented with wing-rocking while soaring, and as he neared his max altitude of 266,000 feet, the rocking became extreme. His instrument was accidentally adjusted to show pitch attitude rather than yaw, thus he was unaware that his yaw had drifted to 15 degrees. The aircraft began to yaw violently around 15 seconds later, and Adams informed Pete Knight that “the airplane seems squirrelly.”

He soon after claimed that he was spinning and experiencing strong accelerations. The ground crew was unable to provide assistance since they were mostly unaware of the airplane’s hypersonic spin characteristics. When Adams recovered, he was yawed 90 degrees, flying upside down, and descending at supersonic speed, according to the ground data that was later correlated with the flight data.

The Minneapolis-Honeywell adaptive flight control system (MH-96), which is on and locked in, causes the aircraft to oscillate between its limits, up and down, preventing Adams from correcting his attitude and flying his way home. Adams pulled out of the spin, and he probably would have had a successful landing, but for the fact that the MH-96 was on and locked in. The X-15-3 aircraft broke up at a height of around 62,000 feet and a speed of roughly 3,800 feet per second because the weights on the aircraft increased above their structural limits. In close proximity to Johannesburg, California, it struck the desert floor. There was talk about Adams having slight vertigo; this may have prevented him from seeing the yaw buildup or from resetting the yaw indicator to the yaw setting.

Adams’s death shows the dangers of flight testing a new aircraft in previously untested regions of flight, and of flying experiments in which certain research-data measuring instruments may have caused an electrical disturbance that affected the MH-96 from operating at its top quality and in conditions it was not designed for. All of these factors could have had an impact on the disaster.

Because his flight was above 50 miles high, Adams was posthumously awarded an astronaut rating. Despite being the only accident in 199 flights, the tragedy was a setback for the X-15 program. The disaster had a significant role in the decision to end the X-15 program because the goals for the aircraft had been met. Only seven more flights were scheduled after that.

Photo by NASA

The Hot Peroxide warning light on Knight’s X-15 turned on when he was doing some rudder pulses to collect data with the yaw damper off following the burnout at a speed of Mach 5.5.

A well-known and important figure in aviation history is the X-15. Its goal was to fly quickly and high, testing the aircraft and putting the pilots through challenges that might later face astronauts. In addition to being the first piloted aircraft in the world to reach hypersonic speeds, or more than five times the speed of sound, it made the first manned flights to the farthest reaches of space. In the 1960s, the X-15 was a crucial tool in the development of spaceflight, and X-15 pilots who flew at altitudes greater than 50 miles were awarded astronaut wings.

In total, 199 flights were made by the three X-15 aircraft between 1959 and 1968. It was a collaborative project between the US Air Force, US Navy, and US NASA.

The X-15 was launched midair from a B-52 “mothership” at a height of around 45,000 feet, similar to other rocket aircraft. After its potent rocket was detonated, the X-15 soared to the uppermost point of the atmosphere before gliding powerlessly to a dry lake bed.

The average flight time was ten minutes.

William “Pete” Knight, one of the pilots who flew this unique research aircraft, had the most memorable experience of all the X-15 pilots. In fact, he did achieve the maximum Mach number for the X-15 on October 3, 1967, according to John Anderson and Richard Passman in their book X-15 The World’s Fastest Rocket Plane, and the Pilots who Ushered in the Space Age. He accomplished this while flying the X-15A-2, which was covered in a white ablative heat shield and had extended fuel tanks as well as additional external fuel tanks that increased the full thrust time from 90 to 141 seconds.

As part of the research program to create a scramjet (a supersonic combustion ramjet engine), a dummy model of NASA’s high-speed research engine (HRE), was attached underneath the aircraft for the sortie.

Knight finally took off at 1:20 PM, after spending almost an hour under the B-52’s wings, and headed for Mud Lake, where he was dropped after two failed launches. Pete remembers reading about the initial launch attempt in X-15: Extending the Frontiers of Flight by William H. Dana and Dennis R. Jenkins. “Reached up and hit the launch switch and immediately took my hand off to [go] back to the throttle and found that I had not gone anywhere. It did not launch.”

Knight made another effort two minutes later, and this one ended with a good release. He then increased his speed and climbed with a high lift at an angle of attack of 12 degrees (the angle between the wing chord and the direction of the free stream airflow) until he reached a climb angle of 32 degrees (the angle between the horizontal and the flight path). At 102,100 feet, he leveled off and accelerated to 6,600 feet per second (Mach 6.7), which is still the top speed for a manned powered aircraft.

However, at a speed of Mach 5.5, Pete was doing some rudder pulses to collect data with the yaw damper off after the burnout when the Hot Peroxide warning light activated.

The X-15’s bottom surface was struck by a shock wave from the engine cowling, which prompted a warning. However, the attachment pylon was actually burned through by the strong aerodynamic heating in the impingement location, which separated the dummy scramjet from the aircraft. Additionally, the vertical tail was also affected by the shock waves, which resulted in some melting and skin rollover that badly damaged the aircraft and compelled Knight to shoot the remaining peroxide into the air to prevent its explosion.

The X-15 arrived at the so-called “high key” (actually the plan to reach an altitude of about 35,000 feet at a speed of 290 to 350 miles per hour on the highest approach to the runway at Edwards Air Force Base) at supersonic speed rather than the originally intended subsonic speed because Pete was preoccupied with this unpleasant excitement. Knight attempted to jettison the scramjet from its X-15 to lower the kinetic energy of the aircraft, but it didn’t appear to have any effect. As a result, Pete had to dissipate the extra kinetic energy by flying past the landing site, allowing aerodynamic drag to slow the aircraft, and then landing at the proper speed.

This trip was the X-15A-2’s final flight, and the aircraft is now on exhibit at the Wright Patterson Air Force Base in Ohio’s Air Force Museum.

However, what actually transpired with the mock scramjet? Without a doubt, Knight was fortunate to survive its record-breaking trip. If the dummy scramjet had stayed attached to the aircraft any longer, the shock wave would have blasted a hole into the main structure of the fuselage, killing the X-15 in flight. Instead, it was later discovered on the lakebed.

Photo by U.S. Air Force and NASA