NB-58A Testbed for General Electric J93

Last revised July 5, 2001

Another little-known role for the B-58A was that of flying testbed for the General Electric J93 turbojet

The General Electric J93 turbojet engine was designed as the powerplant for both the North American XB-70A Valkyrie bomber and the North American XF-108 Rapier interceptor. The J93 was a single-shaft axial-flow turbojet with a variable-stator compressor and a fully-variable convergent/divergent exhaust nozzle. The maximum sea-level thrust was 31,500 pounds.

The J93 engine was ready before either the XB-70A or the XF-108 were, so the Air Force concluded that the engine should be initially flight tested in an existing aircraft. B-58A serial number 55-662 was selected for the project, and on July 1, 1959, Convair began the modification of the aircraft so that it could accept the installation of a J93 engine in a specially-modified underfuselage pod. Following the completion of the Convair modifications, the aircraft was delivered to General Electric's Edwards AFB operation as a NB-58A. While there, a J93-GE-3 engine was installed in a special underfuselage pod.

Unfortunately, the F-108 interceptor was cancelled outright and the B-70 project was reoriented to a research project only. A few NB-58A ground runs were made with the J93 engine in place, but the day before the first flight was scheduled to take place, the funding for the NB-58A project was cancelled. Consequently, the NB-58A/J93 combination never took to the air. The special pod was removed from the NB-58 testbed, and the NB-58A itself was converted to a TB-58A and later flew chase missions for the XB-70A at Edwards AFB. It was consigned to storage at MASDC in 1970, and eventually scrapped in 1977.


  1. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

  2. Post World War II Bombers, Marcelle Size Knaack, Office of Air Force History, 1988.

  3. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.

  4. Convair B-58 Hustler: The World's First Supersonic Bomber, Jay Miller, Aerofax, 1997.

  5. E-mail from Jennifer Raabe, with information and confirmation that NB-58A flight tests with J93 engine never actually took place.