5 December 1963: On Flight 97 of the X-15 Program, Major Robert A. Rushworth flew the number one aircraft, Air Force serial number 56-6670, to an altitude of 101,000 feet 30,785 meters) and reached Mach 6.06 (4,018 miles per hour/6,466 kilometers per hour).
The rocketplane was dropped from the Boeing NB-52B Stratofortress “mother ship” 52-008, Balls 8, flying at 450 knots (833.4 kilometers per hour) at 45,000 feet (13,716 meters) over Delamar Dry Lake, Nevada. Rushworth ignited the Reaction Motors XLR-99-RM-1 rocket engine, which burned for 81.2 seconds before shutting down.
The flight plan had called for an altitude of 104,000 feet (31,699 meters), a 78 second burn and a maximum speed of Mach 5.70. With the difficulties of flying such a powerful rocketplane, Rushworth’s flight was actually fairly close to plan. During the flight the right inner windshield cracked.
Bob Rushworth landed the X-15 on Rogers Dry Lake at Edwards Air Force Base, California, after a flight of 9 minutes, 34.0 seconds.
Mach 6.06 was the highest Mach number reached for an unmodified X-15.
56-6670 flew 81 of the 199 flights of the X-15 Program. It is in the collection of the Smithsonian Institution National Air and Space Museum.
From 1960 and 1966, Bob Rushworth made 34 flights in the three X-15s, more than any other pilot.
20 November 1953: At Edwards Air Force Base, California, NACA’s High Speed Flight Station test pilot Albert Scott Crossfield rode behind the flight crew of the Boeing P2B-1S Superfortress as it carried the Douglas Aircraft Company D-558-II Skyrocket supersonic research rocketplane to its launch altitude. As the four-engine bomber climbed through 18,000 feet (5,486 meters), Crossfield headed back to the bomb bay to enter the Skyrocket’s cockpit and prepare for his flight.
The Douglas D-558-II was Phase II of a U.S. Navy/Douglas Aircraft Company/National Advisory Committee on Aeronautics joint research project exploring supersonic flight. It was a swept-wing airplane powered by a single Reaction Motors LR8-RM-6 four-chamber rocket engine. The Skyrocket was fueled with alcohol and liquid oxygen. The engine was rated at 6,000 pounds of thrust (26.69 kilonewtons) at Sea Level.
There were three Phase II aircraft. Originally, they were also equipped with a Westinghouse J34-W-40 turbojet engine which produced 3,000 pounds of thrust (13.35 kilonewtons) and the Skyrockets took off from the surface of Rogers Dry Lake. Once the D-558-II reached altitude, the rocket engine was fired for the speed runs. As higher speeds were required, the program shifted to an air launch from a B-29 (P2B-1S) “mothership”. Without the need to climb to the test altitude, the Skyrocket’s fuel load was available for the high speed runs.
The D-558-II was 42.0 feet (12.80 meters) long, with a wingspan of 25.0 feet (7.62 meters). The leading edge of the wing was swept at a 35° angle and the tail surfaces were swept to 40°. The aircraft weighed 9,421 pounds (4,273 kilograms) empty and had a maximum takeoff weight of 15,787 pounds (7,161 kilograms). It carried 378 gallons (1,431 liters) of water/ethyl alcohol and 345 gallons (1,306 liters) of liquid oxygen.
The mothership, NACA 137, was a Boeing Wichita B-29-95-BW Superfortress, U.S. Air Force serial number 45-21787. It was transferred to the U.S. Navy, redesignated P2B-1S and assigned Bureau of Aeronautics number 84029. Douglas Aircraft modified the bomber for its drop ship role at the El Segundo plant.
Going above the planned launch altitude, the Superfortress was placed in a slight dive to build to its maximum speed. At the bomber’s critical Mach number (Mcr), the Skyrocket was just above its stall speed. At 32,000 feet (9,754 meters), Crossfield and the Skyrocket were released. The rocketplane fell for about 400 feet (122 meters) until the rocket engine ignited and then it began to accelerate.
Crossfield climbed at a steep angle until he reached 72,000 feet (21,946 meters), and then leveled off. Now in level flight, the D-558-II accelerated, quickly passing Mach 1, then Mach 1.5. Crossfield pushed the nose down and began a shallow dive. The Skyrocket, still under full power, built up speed. As it passed through 62,000 feet (18,998 meters) the Skyrocket reached its maximum speed, Mach 2.005, or 1,291 miles per hour (2,078 kilometers per hour).
Scott Crossfield was the first pilot to fly an aircraft beyond Mach 2, twice the speed of sound. During his career as a test pilot, he flew the Douglas D-558-II, the Bell X-1, Bell X-2 and North American X-15. He made 112 flights in rocket-powered aircraft, more than any other pilot.
18 November 1966: On Flight 175 of the research program, Major William J. (“Pete”) Knight, U.S. Air Force, flew the newly-modified North American Aviation X-15A-2, 56-6671, to Mach 6.33 (4,261 miles per hour/6,857 kilometers per hour) at 98,900 feet (30,245 meters). This is just 11 years, to the day, since Pete Everest made the first powered flight in the Bell Aircraft Corporation X-2 rocketplane, with more than 6 times an increase in speed.
On this date, NASA made an attempt to launch two X-15s, -671 and -672, using the NB-52A 52-003 and NB-52B 52-008. However -672, the number three ship, had to abort the mission.
Balls 8, the NB-52B, flown by NASA test pilot Fitz Fulton and Colonel Joe Cotton, USAF, carried 56-6671 to the launch point over Mud Lake, Nevada, approximately 200 miles to the north of Edwards AFB. (This was the lake where -671 was severely damaged in an emergency landing, 9 November 1962. It was returned to North American to be rebuilt to the X-15A-2 configuration and returned to flight operation 19 months later.)
At 1:24:07.2 p.m. local time, Pete Knight and the X-15 were dropped from the pylon under the right wing of the B-52. He ignited the Reaction Motors XLR99-RM-1 and began to accelerate with its 57,000 pounds of thrust (253.549 kilonewtons).
Since this was to be a high temperature test flight, it was planned to fly no higher than 100,000 feet (30,480 meters). The denser atmosphere would result in greater aerodynamic heating of the rocketplane.
With the two external propellant tanks carrying an additional 1,800 gallons (6,814 liters) of liquid ammonia and liquid oxygen, the engine ran for 2 minutes, 16.4 seconds. The rocketplane had accelerated to Mach 2. The external tanks emptied in about 60 seconds and were jettisoned. The tanks were equipped with parachutes. They were recovered to be reused on later flights.
The X-15, now about 25,000 pounds (11,340 kilograms) lighter and without the aerodynamic drag of the tanks, continued to accelerate. At its highest speed, the rocketplane was travelling approximately 6,500 feet per second (1,981 meters per second), more than twice as fast as a high-powered rifle bullet. Its surface temperatures exceeded 1,200 °F. (649 °C.)
Knight landed the X-15 on Rogers Dry Lake at Edwards Air Force Base. The duration of this flight had been 8 minutes, 26.8 seconds.
18 November 1955: Major Frank Kendall Everest, Jr., USAF, makes the first powered flight in the Bell X-2 research rocketplane, 46-674, at Edwards AFB, California. The rocketplane was airdropped from a Boeing EB-50D Superfortress, 48-096. Only one 5,000-lb. thrust rocket tube ignited, but that was enough to accelerate “Pete” Everest to Mach 0.992 (655.4 miles per hour/1,054.5 kilometers per hour) at 35,000 feet (10,668 meters).
The X-2 was a joint project of the U.S. Air Force and NACA (the National Advisory Committee on Aeronautics, the predecessor of NASA). The rocketplane was designed and built by Bell Aircraft Corporation of Buffalo, New York, to explore supersonic flight at speeds beyond the capabilities of the earlier Bell X-1 and Douglas D-558-II Skyrocket.
In addition to the aerodynamic effects of speeds in the Mach 2.0–Mach 3.0 range, engineers knew that the high temperatures created by aerodynamic friction would be a problem, so the aircraft was built from stainless steel and K-Monel, a copper-nickel alloy.
The Bell Aircraft Corporation X-2 was 37 feet, 10 inches (11.532 meters) long with a wingspan of 32 feet, 3 inches (9.830 meters) and height of 11 feet, 10 inches (3.607 meters). Its empty weight was 12,375 pounds (5,613 kilograms) and loaded weight was 24,910 pounds (11,299 kilograms).
The X-2 was powered by a throttleable two-chamber Curtiss-Wright XLR25-CW-1 rocket engine that produced 2,500–15,000 pounds of thrust (11.12–66.72 kilonewtons)
Rather than use its limited fuel capacity to take off and climb to altitude, the X-2 was dropped from a modified heavy bomber as had been the earlier rocketplanes. A four-engine Boeing B-50D-95-BO Superfortress bomber, serial number 48-096, was modified as the drop ship and redesignated EB-50D.
The launch altitude was 30,000 feet (9,144 meters). After the fuel was exhausted, the X-2 glided to a touchdown on Rogers Dry Lake at Edwards Air Force Base.
Pete Everest joined the United States Army Air Corps shortly before the United States entered World War II. He graduated from pilot training in 1942 and was assigned as a P-40 Warhawk pilot, flying combat missions in North Africa, Sicily and Italy. He was credited with shooting down two German airplanes and damaging a third.
Everest was returned to the United States to serve as a flight instructor. He requested a return to combat and was then sent to the China-Burma-India theater of operations where he shot down four Japanese airplanes. He was himself shot down by ground fire in May 1945. Everest was captured by the Japanese and suffered torture and inhumane conditions before being freed at the end of the war.
After the war, Everest was assigned as a test pilot at Wright-Patterson Air Force Base, Ohio, before going west to the Air Force Flight Test Center at Edwards Air Force Base, California. At Edwards, he was involved in nearly every flight test program, flying the F-88, F-92, F-100, F-101, F-102, F-104 and F-105 fighters, the XB-51, YB-52, B-57 and B-66 bombers. He also flew the pure research aircraft, the “X planes:” the X-1, X-1B, X-2, X-3, X-4 and X-5. Pete Everest flew the X-1B to Mach 2.3, and he set a world speed record with the X-2 at Mach 2.9 (1,957 miles per hour, 3,149.5 kilometers per hour) which earned him the title, “The Fastest Man Alive.”
Frank Everest returned to operational assignments and commanded a fighter squadron, two combat crew training wings, and was assigned staff positions at the Pentagon. On 20 November 1963, Colonel Everest, commanding the 4453rd Combat Crew Training Squadron, flew one of the first two operational McDonnell F-4C Phantom II fighters from the factory in St. Louis to MacDill Air Force Base. In 1965, Pete Everest was promoted to the rank of brigadier general. He was commander of the Aerospace Rescue and Recovery Service. He retired from the Air Force in 1973 after 33 years of service. General Everest died in 2004.
15 November 1967: Major Michael J. Adams, U.S. Air Force, was killed in the crash of the number three North American Aviation X-15 hypersonic research rocketplane, 56-6672.
Flight 191 of the X-15 program was Mike Adams’ seventh flight in the rocketplane. It was the 56-6672’s 65th flight. The flight plan called for 79 seconds of engine burn, accelerating the X-15 to Mach 5.10 while climbing to 250,000 feet (76,200 meters). Adams’ wife and mother were visiting in the NASA control room at Edwards Air Force Base.
Balls 8, the Boeing NB-52B Stratofortress, 52-008, flown by Colonel Joe Cotton, took off from Edwards at 9:12 a.m., carrying -672 on a pylon under its right wing, and headed north toward the drop point over Delamar Dry Lake in Nevada. The drop ship climbed to the launch altitude of 45,000 feet (13,716 meters).
The X-15 launch was delayed while waiting for the Lockheed C-130 Hercules rescue aircraft to arrive on station. This required Adams to reset the Honeywell MH-96 Automatic Flight Control System to compensate for the changing position of the sun in the sky.
56-6672 was launched by Balls 8 at 10:30:07.4 a.m., Pacific Standard Time. As it dropped clear of the bomber, the rocketplane rolled 20° to the right, a normal reaction. Within one second, Mike Adams had started the XLR99-RM-1 rocket engine while bringing the wings level. The engine ignited within one-half second and was up to its full 57,000 pounds of thrust (253.549 kilonewtons) one second later. The engine ran for 82.3 seconds, 3.3 seconds longer than planned, causing the X-15 to reach Mach 5.20 (3,617 miles per hour/5,821 kilometers per hour) and to overshoot the planned altitude to peak at 266,000 feet (81,077 meters).
With the X-15 climbing through 140,000 feet (42,672 meters), the Inertial Flight Data System computer malfunctioned. Adams radioed ground controllers that the system’s malfunction lights had come on.
The flight plan called for a wing-rocking maneuver at peak altitude so that a camera on board could scan from horizon to horizon. During this maneuver, the Reaction Control System thrusters did not respond properly to Adams’ control inputs. The X-15 began to yaw to the right.
As it reached its peak altitude, 56-6672 yawed 15° to the left. Going over the top, the nose yawed back, then went to the left again. By the time the aircraft has descended to 230,000 feet (70,104 meters), it had pitched 40° nose up and yawed 90° to the right its flight path. The X-15 was also rolling at 20° per second. The rocketplane went into a spin at Mach 5.
10:33:37 Chase 1: “Dampers still on, Mike?”
10:33:39 Adams: “Yeah, and it seems squirrelly.”
10:34:02 Adams: “I’m in a spin, Pete.” [Major William J. “Pete” Knight, another X-15 pilot, was the flight controller, NASA 1]
10:34:05 NASA 1: “Let’s get your experiment in and the cameras on.”
10:34:13 NASA 1: “Let’s watch your theta, Mike.”
10:34:16 Adams: “I’m in a spin.”
10:34:18 NASA 1: “Say again.”
10:34:19 Adams: “I’m in a spin.”
Adams fought to recover, and at 118,000 feet (35,967 meters) came out of the spin, but he was in an inverted 45° dive at Mach 4.7. The X-15’s MH-96 Automatic Flight Control System entered a series of diverging oscillations in the pitch and roll axes, with accelerations up to 15g. Dynamic pressures on the airframe rapidly increased from 200 pounds per square foot (9.576 kilopascals) to 1,300 pounds per square foot (62.244 kilopascals).
At 62,000 feet (18,898 meters), still at Mach 3.93, the aircraft structure failed and it broke up.
10:34:59 X-15 telemetry failed. Last data indicated it was oscillating +/- 13 g. Radar altitude was 62,000 feet (18,898 meters). The aircraft was descending at 2,500 feet per second (762 meters per second) and broke into many pieces at this time.
10:35:42 NASA 1: “Chase 4, do you have anything on him?”
10:35:44 Chase 4: “Chase 4, negative.”
10:35:47 NASA 1: “OK, Mike, do you read?”
10:35:52 Chase 4: “Pete, I got dust on the lake down there.”
North American Aviation X-15A-3 56-6672 crashed in a remote area approximately 5½ miles (9 kilometers) north-northeast of Randsburg, California, a small village along U.S. Highway 395.
Major Michael James Adams was killed. This was the only pilot fatality of the entire 199-flight X-15 program.
An investigation by NASA’s Engineering and Safety Center determined that, “. . . the root cause of the accident was an electrical disturbance originating from an experiment package using a commercial-off-the-shelf (COTS) component that had not been properly qualified for the X-15 environment. . .”and that there is“. . . no conclusive evidence to support the hypothesis that SD [spatial disorientation] was a causal factor. On the contrary, the evidence suggests that poor design of the pilot-aircraft interface and ineffective operational procedures prevented the pilot and ground control from recognizing and isolating the numerous failures before the aircraft’s departure from controlled flight was inevitable.”
—A Comprehensive Analysis of the X-15 Flight 3-65 Accident, NASA/TM—2014-218538 (Corrected Copy)