North American XB-70 Valkyrie - Operational History

Operational History

The XB-70's maiden flight was on 21 September 1964. In the first flight test, one engine had to be shut down, and an undercarriage indication malfunction meant that the flight was flown with the undercarriage down, limiting speed to about half that planned. On landing, the left-side rear wheels locked, the tires ruptured, and a fire started.

The Valkyrie first became supersonic (Mach 1.1) on the third test flight on 12 October 1964, and flew above Mach 1 for 40 minutes during the following flight on 24 October. The wing tips were also lowered partially in this flight. XB-70 No. 1 surpassed Mach 3 on 14 October 1965 by reaching Mach 3.02 at 70,000 ft (21,300 m). The first aircraft was found to suffer from weaknesses in the honeycomb panels, primarily due to inexperience with fabrication and quality control of this new material. On two occasions, honeycomb panels failed and were torn off during supersonic flight, necessitating a speed limit of Mach 2.5 being placed on the aircraft.

The deficiencies discovered on AV-1 were almost completely solved on the second XB-70, which first flew on 17 July 1965. On 3 January 1966, XB-70 No. 2 attained a speed of Mach 3.05 while flying at 72,000 ft (21,900 m). AV-2 reached a top speed of Mach 3.08 and maintained it for 20 minutes on 12 April 1966. On 19 May 1966, AV-2 reached Mach 3.06 and flew at Mach 3 for 32 minutes, covering 2,400 mi (3,840 km) in 91 minutes of total flight.

XB-70 performance
Longest flight: 3:40 hours (on 6 January 1966)
Fastest speed: 2,020 mph (3,250 km/h) (on 12 January 1966)
Highest altitude: 74,000 ft (23,000 m) (on 19 March 1966)
Highest Mach number: Mach 3.08 (on 12 April 1966)
Sustained Mach 3: 32 minutes (on 19 May 1966)
Mach 3 total: 108 minutes/10 flights

A joint NASA/USAF research program was conducted from 3 November 1966 to 31 January 1967 for measuring the intensity and signature of sonic booms for the National Sonic Boom Program (NSBP). Testing was planned to cover a range of sonic boom overpressures on the ground similar but higher than the proposed American SST. In 1966, AV-2 was selected for the program and was outfitted with test sensors. It flew the first sonic boom test on 6 June 1966, obtaining a speed of Mach 3.05 at 72,000 ft (21,900 m). Two days later, AV-2 crashed following a mid-air collision with an F-104 while flying a multi-aircraft formation. Sonic boom and later testing continued with XB-70A #1.

The second flight research program (NASA NAS4-1174) investigated "control of structural dynamics" from 25 April 1967 through the XB-70's last flight in 1969. At high altitude and high speed, the XB-70A experienced unwanted changes in altitude. NASA testing from June 1968 included two small vanes on the nose of AV-1 for measuring the response of the aircraft's stability augmentation system. AV-1 flew a total of 83 flights.

The XB-70's last supersonic flight took place on 17 December 1968. On 4 February 1969, AV-1 took its final flight to Wright-Patterson Air Force Base for museum display (now the National Museum of the United States Air Force). Flight data was collected on this subsonic trip. North American Rockwell completed a four-volume report on the B-70 that was published by NASA in April 1972.