Tag Archives: 56-6671

5 November 1959

The Number 2 X-15, 56-6671, broke in half when it made an emergency landing while still partially loaded with propellants. (NASA)
The Number 2 X-15, 56-6671, broke in half when it made an emergency landing while still partially loaded with propellants. (NASA)

5 November 1959: During his fourth X-15 flight—the third in the Number Two ship, 56-6671—North American Aviation chief test pilot Albert Scott Crossfield made an emergency landing at Rosamond Dry Lake after one of the two Reaction Motors XLR11-RM-13 rocket engines exploded, causing an engine compartment fire.

The X-15 had been launched by the Boeing NB-52A Stratofortress, 52-003, at 0.82 Mach and approximately 45,000 feet (13,716 meters) over Bouquet Canyon Reservoir, about 35 miles (56 kilometers) southwest of Edwards Air Force Base. Scott Crossfield ignited both XLR11 rocket engines and began to accelerate and climb, but one of four combustion chambers of the lower engine exploded almost immediately. He shut both engines down after 11.7 seconds. Crossfield kept the rocketplane in a level attitude for the 114 seconds it took to jettison the liquid oxygen and water-alcohol propellants to lighten the X-15 for the landing. The tanks could not fully drain and the aircraft remained approximately 1,000 pounds (455 kilograms) overweight.

The X-15 approached the emergency landing site at Rosamond Dry Lake, about ten miles (16 kilometers) southwest of Edwards, while Major Robert M. White, flying a Lockheed F-104 chase plane, called out Crossfield’s distance from the dry lake and his altitude. As he neared the touch down point, Crossfield raised the X-15’s nose to decelerate.

“I lowered the skids and nose wheel, pulled the flaps, and felt for the lake bed.

“The skids dug in gently. The nose wheel slammed down hard and the ship plowed across the desert floor, slowing much faster than usual. Then she came to a complete stop within 1500 feet instead of the usual 5000 feet. Something was wrong; the skids failed, I was sure. . . Quickly I scrambled out of the cockpit. What I saw almost broke my heart. The fuselage had buckled immediately aft of the cockpit, two hundred and thirty inches back from the nose. Her belly had dragged in the sand, causing the abrupt deceleration on the lake. The rocket chambers which had exploded at launch were a shambles.”

Always Another Dawn: The Story of a Rocket Test Pilot, by A. Scott Crossfield and Clay Blair, Jr., The World Publishing Company, Cleveland and New York, 1960, Chapter 41 at Pages 383–384.

The scene at Rosamond Dry Lake after Scott Crossfield's emergency landing after an engine explosion. (NASA)
The scene at Rosamond Dry Lake after Scott Crossfield’s emergency landing following an engine explosion. (NASA)

It was determined that the engine had exploded due to an ignition failure, a relatively simple problem not connected to the design of the X-15. But there remained the question as to why the rocketplane had broken in half. The investigation found that the rapid extension of the nose wheel strut when lowered caused the oil inside the strut to foam and vaporize, providing almost no shock absorption. This was corrected and the check list changed to lower the gear sooner.

The total duration of this flight was 5 minutes, 28.0 seconds. The peak altitude was 45,462 feet (13,857 meters) and the maximum speed was 660 miles per hour (1,062 kilometers per hour).

56-6671 was taken back to the North American Aviation plant for repair. It returned to flight operations three months later.

Test pilot A. Scott Crossfield with the damaged X-15 (UPI/Harry Ransom Center
Test pilot A. Scott Crossfield with the damaged X-15 on Rosamond Dry Lake. (UPI/Harry Ransom Center, University of Texas at Austin)

© 2016, Bryan R. Swopes

4 November 1960

At the left, Boeing NB-52A 52-003 carries X-15 56-6670 while on the right, NB-52B 52-008 carries X-15 56-6671.(NASA)
At the left, Boeing NB-52A 52-003 carries X-15 56-6670 while on the right, NB-52B 52-008 carries X-15 56-6671. (NASA)

4 November 1960: This photo shows one of the four attempts NASA made at launching two X-15 aircraft in one day. This attempt occurred November 4, 1960.

None of the four attempts was successful, although one of the two aircraft involved in each attempt usually made a research flight.

In this case, Air Force test pilot Major Robert A. Rushworth flew X-15 , 56-6670, on its sixteenth flight to a speed of Mach 1.95 and an altitude of 48,900 feet (14,905 meters).

© 2016, Bryan R. Swopes

3 November 1965

North American Aviation X-15A-2 56-6671 on Rogers Dry Lake. In addition to the lengthened fuselage and external tanks, the nose wheel strut is longer and the windshields have been changed to an oval shape. A wheeled dolly supports the aft end of the rocketplane. (NASA)
North American Aviation X-15A-2 56-6671 on Rogers Dry Lake. In addition to the lengthened fuselage and external tanks, the nose wheel strut is longer and the windshields have been changed to an oval shape. A wheeled dolly supports the aft end of the rocketplane. (NASA)

3 November 1965: Major Robert A. Rushworth made the first flight of the modified X-15A-2 rocketplane, Air Force serial number 56-6671. After a landing accident which caused significant damage to the Number 2 X-15, it was rebuilt by North American Aviation. A 28-inch (0.71 meter) “plug” was installed in the fuselage forward of the wings to create space for a liquid hydrogen fuel tank which would be used for an experimental “scramjet” engine that would be mounted on the the ventral fin. The modified aircraft was also able to carry two external fuel tanks. It was hoped that additional propellant would allow the X-15A-2 to reach much higher speeds.

The first flight with the new configuration was an “envelope expansion” flight, intended to test the handling characteristics of the X-15A-2, and to jettison the tanks (which were empty on this flight) to evaluate the separation and trajectory as they fell away from the rocketplane in supersonic flight.

Boeing NB-52A Stratofortress 52-003, The High and Mighty One, with North American Aviation X-15A-2 56-6671 mounted to the pylon under its right wing. The external propellant tanks have been brightly painted to aid tracking after they are jettisoned. (U.S. Air Force)
Boeing NB-52A Stratofortress 52-003, The High and Mighty One, with North American Aviation X-15A-2 56-6671 mounted to the pylon under its right wing. The external propellant tanks have been brightly painted to aid tracking after they are jettisoned. (U.S. Air Force)

The X-15A-2 was dropped from the Boeing NB-52A Stratofortress 52-003, over Cuddeback Lake, 37 miles (60 kilometers) northeast of Edwards Air Force Base in the Mojave Desert of southern California. This was the only time during the 199-flight X-15 Program that this lake was used as a launch point.

The X-15 was released at 09:09:10.7 a.m., PST. Bob Rushworth ignited the Reaction Motors XLR99-RM-1 rocket engine and it ran for 84.1 seconds before its fuel supply was exhausted. This engine was rated at 57,000 pounds of thrust (253.549 kilonewtons).

The X-15 climbed to 70,600 feet (21,519 meters) and reached Mach 2.31 (1,514 miles per hour/2,437 kilometers per hour.)

The test flight went well. The external tanks jettisoned cleanly and fell away. The recovery parachute for the liquid oxygen tank did not deploy, however, and the tank was damaged beyond repair.

Rushworth and the X-15A-2 touched down on Rogers Dry Lake after a flight of 5 minutes, 1.6 seconds.

© 2016, Bryan R. Swopes

3 October 1967

Major William J. Knight, United States Air Force, with the North American Aviation X-15A-2, 56-6671. (U.S. Air Force)

3 October 1967: The 188th flight of the X-15 Program was the 53rd for the Number 2 aircraft, 56-6671. It had been extensively modified by North American Aviation to an X-15A-2 configuration following a landing accident which had occurred 9 November 1962. The fuselage was lengthened 28 inches (0.711 meters) to accommodate a liquid hydrogen fuel tank for a scramjet engine that would be added to the ventral fin, a new tank for additional hydrogen peroxide to generate steam for the rocket engine turbo pump, and external propellant tanks to allow the rocketplane to reach higher speeds and altitudes. The entire surface of the X-15 was covered with an ablative coating to protect the metal structure from the extreme heat it would encounter on this flight.

Minor issues delayed the takeoff but finally, after they were corrected, and with Pete Knight in the X-15’s cockpit, it was carried aloft under the right wing of Balls 8, a Boeing NB-52B Stratofortress, 52-008.

At 45,000 feet (13,716 meters) over Mud Lake, Nevada, the X-15 was droppeded at 14:31:50.9 local time. Knight fired the Reaction Motors XLR99-RM-1 rocket engine and began to climb and accelerate. After 60 seconds, the ammonia and liquid oxygen propellants in the external tanks was exhausted, so the the tanks were jettisoned to eliminate their weight and aerodynamic drag.

The X-15A-2 climbed to 102,100 feet (31,120 meters) and Pete Knight leveled off, still accelerating. After 140.7 seconds of engine burn, Knight shut the XLR99 down. He noticed that thrust seemed to decrease gradually and the X-15 continued to accelerate to 6,630 feet per second (2,021 meters per second), or Mach 6.72.

North American Aviation X-15A-2 56-6671 is carried to launch altitude under the right wing of the Boeing NB-52B Stratofortress 52-008. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 is carried to launch altitude under the right wing of the Boeing NB-52B Stratofortress 52-008. The scramjet is attached to the ventral fin. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 immediately after being released from the mothership, Boeing NB-52B Stratofortress 52-008, Balls 8, over Mud Lake, Nevada, 3 October 1967. The steam trail is hydrogen peroxide used to power the rocket engine turbopump. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 immediately after being released from the mothership, Boeing NB-52B Stratofortress 52-008, Balls 8, over Mud Lake, Nevada, 3 October 1967. The steam trail is hydrogen peroxide used to power the rocket engine turbopump. (U.S. Air Force) 
The North American Aviation X-15A-2 56-6671 ignites the XLR99 engine after being released from the mothership, Balls 8, 3 October 1967. (U.S. Air Force)
The X-15A-2’s XLR99-RM-1 rocket engine ignites after release from the mothership, Balls 8, 3 October 1967. (U.S. Air Force) 

Shock waves from the dummy scramjet mounted on the ventral fin impinged on the fin’s leading edge and the lower fuselage, raising surface temperatures to 2,700 °F. (1,482 °C.) The Inconel X structure started to melt and burn through.

Pete Knight entered the high key over Rogers Dry Lake at 55,000 feet (16,764 meters) and Mach 2.2, higher and faster than normal. As he circled to line up for Runway One Eight, drag from the scramjet caused the X-15 to descend faster and this set him up for a perfect approach and landing. Because of heat damage, the scramjet broke loose and fell away from the X-15.

Knight touched down after an 8 minute, 17.0 second flight. His 4,520 mile per hour (7,274 kilometers per hour) maximum speed is a record that still stands.

Firefighters cool down the ventral fin of the North American Aviation X-15A-2 56-6671 after its last landing on Rogers Dry Lake, 3 October 1967.(U.S. Air Force)
Firefighters cool down the ventral fin of the North American Aviation X-15A-2 56-6671 after its final landing on Rogers Dry Lake, 3 October 1967.(U.S. Air Force)

The X-15A-2 suffered considerable damage from this hypersonic flight. It was returned to North American for repairs, but before they were completed, the X-15 Program came to an end. This was 56-6671’s last flight. It was sent to the National Museum of the United States Air Force where it is part of the permanent collection.

In a ceremony at the White House, President Lyndon B. Johnson presented the Harmon International Trophy to Major William J. Knight.

The Harmon International Trophy at the Smithsonian Institution National Air and Space Museum. (NASM)
The Harmon International Trophy at the Smithsonian Institution National Air and Space Museum. (NASM)

© 2016, Bryan R. Swopes

21 August 1967

Major William J. Knight, U.S. Air Force, with the modified X-15A-2, 56-6671, at Edwards Air Force Base, California. (U.S. Air Force)
Major William J. Knight, U.S. Air Force, with the modified X-15A-2, 56-6671, at Edwards Air Force Base, California. (U.S. Air Force)

21 August 1967: On the 186th flight of the X-15 program, the modified North American Aviation X-15A-2, 56-6671, made the first of two flights with a heat-protective ablative coating, designed to protect the steel structure of the rocketplane from the extreme heat of flight at high Mach numbers.

After a landing accident which caused significant damage to the Number 2 X-15, it was rebuilt by North American. A 28-inch (0.71 meter) “plug” was installed in the fuselage forward of the wings to create space for a liquid hydrogen fuel tank which would be used for an experimental “scramjet” engine that would be mounted the the ventral fin. The modified aircraft was also able to carry two external fuel tanks. It was hoped that additional propellant would allow the X-15A-2 to reach much higher speeds. The external tanks were not carried on the 21 August 1967 flight.

With Major William J. (“Pete”) Knight, U.S. Air Force, in the cockpit, the X-15A-2 was airdropped from the Boeing NB-52B Stratofortress, 52-008, known as Balls 8, over Hidden Hills Dry Lake, just on the California side of the border with Nevada. This was Knight’s 11th X-15 flight, and the 52nd flight for 56-6671. The launch time was 10:59:16.0 a.m., PDT. Knight fired the 57,000-pound-thrust Reaction Motors XLR99-RM-1 rocket engine and accelerated for 82.2 seconds. The purpose of this flight was to attain a high speed rather than altitude. The X-15A-2 reached Mach 4.94 (3,368 miles per hour, 5,420 kilometers per hour) at 85,000 feet (25,908 meters) and reached a peak altitude of 91,000 feet (27,737 meters). Pete Knight touched down on Rogers Dry Lake at Edwards Air Force Base, just 7 minutes, 40.0 seconds after launch.

© 2015, Bryan R. Swopes