Tag Archives: Mach 3

4 February 1969

North American Aviation XB-70A-1-NA Valkyrie 62-0001. (U.S. Air Force)

4 February 1969: The North American Aviation XB-70A-1-NA Valkyrie, 62-0001, made its very last flight from Edwards Air Force Base, California, to Wright-Patterson Air Force Base, Ohio. NASA Research Test Pilot Fitzhugh L. Fulton, Jr., Lieutenant Colonel, U.S. Air Force (Retired), and Lieutenant Colonel Emil Sturmthal, U.S. Air Force, were the flight crew for this final flight.

On arrival at Wright-Patterson, Fulton closed out the log book and handed it over to the curator of the National Museum of the United States Air Force.

The Mach 3+ prototype strategic bomber and high-speed, high-altitude research airplane had completed 83 flights for a total of 160 hours, 16 minutes of flight time.

Lieutenant Colonel Emil Sturmthal, USAF and Fitzhugh Fulton, NASA, with the North American Aviation XB-70A-1-NA 62-0001 at Edwards AFB, California. (Chris Walmsley/Rockwell International)
Lieutenant Colonel Emil Sturmthal, USAF and Fitzhugh Fulton, NASA, with the North American Aviation XB-70A-1-NA 62-0001 at Edwards AFB, California. (Chris Walmsley/Rockwell International)

62-0001 was the first of three prototype Mach 3+ strategic bombers. (The third prototype, XB-70B 62-0208, was not completed.) The Valkyrie utilized the most advanced technology available. Materials and manufacturing techniques had to be developed specifically to build this airplane. It is a large delta wing airplane with a forward canard and two vertical fins. The outer 20 feet (6.096 meters) of each wing could be lowered to a 25° or 65° angle for high speed flight. Although this did provide additional directional stability, it actually helped increase the compression lift, which supported up to 35% of the airplane’s weight in flight.

The XB-70A is 185 feet, 10 inches (56.642 meters) long with a wingspan of 105 feet (32.004 meters) and overall height of 30 feet, 9 inches (9.373 meters). Fully loaded, the Valkyrie weighs 534,700 pounds (242,535 kilograms).

It is powered by six General Electric YJ93-GE-3 turbojet engines which were rated at 22,000 pounds of thrust (97.86 kilonewtons) at Sea Level, and 31,000 pounds (137.89 kilonewtons) with afterburner. The J93 was a single-shaft axial-flow turbojet with an 11-stage compressor section and two-stage turbine. It was 235.0 inches (5.969 meters) long, 55.0 inches (1.397 meters) in diameter, and weighed 4,770 pounds (2,164 kilograms).

The maximum speed achieved was Mach 3.1 (2,056 miles per hour, or 3,308.8 kilometers per hour) at 73,000 feet (22,250 meters). The service ceiling is 73,350 feet (23,357 meters).

The second Valkyrie, XB-70A-2-NA 62-0207, was destroyed when it crashed after a mid-air collision with a Lockheed F-104N Starfighter flown by NASA Chief Research Test Pilot Joseph A. Walker, 8 June 1966. Both Walker and the B-70’s co-pilot, Major Carl S. Cross, U.S. Air Force, were killed.

XB-70A Valkyrie 62-0001 is in the collection of the National Museum of the United States Air Force.

North American Aviation XB-70A-1-NA Valkyrie 62-0001 at Wright-Patterson Air Force Base, Ohio. (U.S. Air Force)
North American Aviation XB-70A-1-NA Valkyrie 62-0001 at Wright-Patterson Air Force Base, Ohio. (U.S. Air Force)
 North American Aviation XB-70A-1-NA Valkyrie 62-0001 at Wright-Patterson Air Force Base, Ohio. This photograph shows the twelve elevons that act as elevators, flaps and ailerons, the swiveling action of the vertical fins, open drag chute doors and the variable exhaust outlets. (U.S. Air Force).
North American Aviation XB-70A-1-NA Valkyrie 62-0001 at Wright-Patterson Air Force Base, Ohio. This photograph shows the twelve elevons that act as elevators, flaps and ailerons, the swiveling action of the vertical fins, open drag chute doors and the variable exhaust outlets. (U.S. Air Force).

© 2019, Bryan R. Swopes

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27 September 1956

Captain Milburn G. Apt, U.S. Air Force, with a Bell X-2. (U.S. Air Force)
Captain Milburn Grant Apt, United States Air Force, with a Bell X-2. (U. S. Air Force)

27 September 1956: Captain Milburn G. (“Mel”) Apt, United States Air Force, was an experimental test pilot assigned to the Air Force Flight Test Center at Edwards Air Force Base, California. After Frank Everest and Iven Kincheloe had made twelve powered flights in the Bell X-2 supersonic research aircraft, Mel Apt was the next test pilot to fly it.

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).

Bell X-2 46-675 on its transportation dolly at Edwards Air Force Base, California, 1952. (NASA)
The second of two Bell X-2 supersonic research rocketplanes, 46-675, on its transportation dolly at Edwards Air Force Base, California, 1952. On 12 May 1953 this X-2 exploded during a captive test flight, killing Bell’s test pilot Jean L. “Skip” Ziegler. (NASA)

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.

Bell X-2 46-674 after drop from Boeing EB-50D Superfortress 48-096. (U.S. Air Force)
Bell X-2 46-674 after drop from Boeing EB-50D Superfortress 48-096. (U.S. Air Force)

With Mel Apt in the cockpit on his first rocketplane flight, the B-50 carried the X-2 to 31,800 feet (9,693 meters). After it was dropped from the bomber, Apt ignited the rocket engine and began to accelerate. He passed Mach 1 at 44,000 feet (13,411 meters) and continued to climb. Apt flew an “extraordinarily precise profile” to reach 72,200 feet (22,007 meters) where he put the X-2 into a dive. The rocket engine burned 12.5 seconds longer than planned, and at 65,589 feet (19,992 meters) the X-2 reached Mach 3.196 (2,094 miles per hour, 3,377 kilometers per hour).

Milburn Apt was the first pilot to exceed Mach 3. He was The Fastest Man Alive.

Bell X-2 46-674 in flight over Southern California, 1955–56. Note the supersonic diamond-shaped shock waves in the rocket engine's exhaust. (Bell aircraft Corporation)
Bell X-2 46-674 in flight over Southern California, 1955–56. Note the supersonic diamond-shaped shock waves in the rocket engine’s exhaust. (Bell Aircraft Corporation)

It was known that the X-2 could be unstable in high speed maneuvers. The flight plan called for Apt to slow to Mach 2.4 before beginning a gradual turn back toward Rogers Dry Lake where he was to land, but he began the turn while still at Mach 3. Twenty seconds after engine burn out, the X-2 began to oscillate in all axes and departed controlled flight. His last radio transmission was, “There she goes.” ¹

Mel Apt was subjected to acceleration forces of ± 6 Gs. It is believed that he was momentarily unconscious. Out of control, the X-2 fell through 40,000 feet (12,192 meters) in an inverted spin. Apt initiated the escape capsule separation, in which the entire nose of the X-2 was released from the airframe. It pitched down violently and Mel Apt was knocked unconscious again. He regained consciousness a second time and tried to parachute from the escape capsule, but was still inside when it hit the desert floor at several hundred miles per hour. Mel Apt was killed instantly.

Since 1950, Milburn G. Apt was the thirteenth test pilot killed at Edwards Air Force Base.

Wreckage of the Bell X-2, 46-674. (U.S. Air Force)
Wreckage of the Bell X-2, 46-674, in the Kramer Hills, east of Edwards Air Force Base. (U.S. Air Force)
Wreckage of the Bell X-2, 46-674. (NASM 9A08208)

Milburn Grant Apt was born at Buffalo, Kansas, 8 April 1924. He was the third child of Oley Glen Apt, a farmer, and Ada Willoughby Apt.

“Mel” Apt enlisted as a private in the Air Corps Enlisted Reserve, United States Army, 9 November 1942. On 23 June 1943, Private Apt was appointed an Aviation Cadet. After completing flight training, Cadet Apt was commissioned a Second Lieutenant, Army of the United States (A.U.S.). He was promoted to First Lieutenant, A.U.S., 4 September 1945. Apt was released from active duty on 11 August 1946. On 10 October 1947, he was reclassified as a Second Lieutenant, Air Corps, United States Army, with date of rank 8 April 1945.

In February 1950, Lieutenant Apt, then stationed at Williams Air Force Base, Arizona, married Miss Faye Lorrie Baker of Phoenix. They would have two children.

Mel Apt earned a Bachelor of Science degree from the University of Kansas, Lawrence, Kansas, in 1951, and a second bachelor’s degree in aeronautical engineering from the Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio. He then attended the U.S. Air Force Experimental Test Pilot School at Edwards Air Force Base, California, graduating in September 1954. Apt was assigned to the Fighter Operations Branch, Air Force Flight Test Center, as a test pilot.

On 22 December 1954, Captain Apt was flying a chase plane during a test at Edwards. The test aircraft crash-landed on the dry lake and caught fire with its pilot trapped inside. Mel Apt, with his bare hands, rescued the other test pilot, saving his life. For this courageous act, he was awarded the Soldier’s Medal.

Captain Apt was posthumously awarded the Distinguished Flying Cross for his flight in the X-2. The medal was presented to his widow in a ceremony at Edwards in March 1957.

Captain Milburn Grant Apt, United States Air Force, was 32 years old at the time of his death. His remains were buried at the Buffalo Cemetery, Buffalo, Kansas.

Captain Iven Carl Kincheloe and Captain Milburn Grant Apt (seated in cockpit) with the Bell X-2 at Edwards Air Force Base, 1956. (Jet Pilot Overseas)

¹ Recommended: Coupling Dynamics in Aircraft: A Historical Perspective, by Richard E. Day, Dryden Flight Research Center, Edwards AFB, California NASA Special Publications 532, 1997.

© 2018, Bryan R. Swopes

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