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This engine is on conditional loan from
The National Museum of Naval Aviation - Pensacola, Florida.

     The J79 was produced in twelve different variants with numerous sub-variants. This particular engine would have been used on the Northrop X-21 Laminar Flow Control Testbed.

     The Northrop X-21A was an experimental aircraft designed to test wings with laminar flow control. It was based on the Douglas WB-66D airframe, with the wing-mounted engines moved to the rear fuselage and making space for air compressors. The aircraft first flew on 18 April 1963 with NASA test pilot Jack Wells at the controls.Although useful testing was  accomplished, the extensive maintenance of the intricate laminar-flow  system caused the end of the program.

Laminar-flow control is a technology that offers the potential for significant improvement in drag coefficient which  would provide improvements in aircraft fuel usage, range or endurance that far exceed any known single aeronautical technology. In principle,  if 80% of wing is laminar, then overall drag could be reduced by 25%.  The frictional force between the air and the aircraft surface, known as viscous drag, is much larger in a turbulent boundary layer than in a laminar one. The principal type of active laminar-flow control is  removal of a small amount of the boundary-layer air by suction through  porous materials, multiple narrow surface slots, or small perforations.

Two major modifications were required, the first involving the standard underwing podded J71 engines being removed and replaced by a pair of 9490 lb.s.t General Electric XJ79-GE-13 non-afterburning turbojets mounted in pods attached to the rear of the  fuselage sides. Bleed air from the J79 engines was fed into a pair of underwing fairings, each of which housed a "bleed-burn" turbine which  sucked the boundary layer air out through the wing slots.

The X-21A test vehicles (55-0408 and 55-0410) also incorporated sophisticated laminar flow control systems built into a completely new wing of increased span and area,  with a sweep reduced from 35 ° to 30 °. The wing had a multiple series of span-wise slots (800,000 in total) through which turbulent  boundary-layer was "sucked in," resulting in a smoother laminar flow.  Theoretically, reduced drag, better fuel economy and longer range could be achieved.

The forward cockpit carried a pilot and two flight engineers while two additional flight test engineers were housed in a  central fuselage bay underneath the wing.

In initial testing there were significant problems with the porous materials and surface slots getting plugged with debris, bugs, even rain. In certain conditions, ice crystals would form due to the rapid cooling of air over those laminar surfaces abruptly disrupting laminar flow, causing rapid melting and rapid transition back to laminar flow. Maximum achievement was 95% laminar flow over those areas desired. However, the design effort was cancelled due to the plugging problems.

Nevertheless, pioneering data were obtained in the X-21 flight program, including the effects of surface irregularities, boundary-layer turbulence induced by three-dimensional spanwise flow effects in the boundary layer (referred to as spanwise contamination)  and degrading environmental effects such as ice crystals in the  atmosphere.

     The General Electric J79 is an axial-flow turbojet engine built for use in a variety of fighter and bomber aircraft. Produced by General Electric Aircraft Engines and under license by other companies worldwide, it was one of the first US-designed engines to outperform designs from the United Kingdom, which had previously led in the jet field.

     The J79 was developed in the 1950s as an outgrowth of the General Electric J73 engine program, originally called J73-GE-X24A, intended for reliable Mach 2 performance.

     The first flight of the engine was on 20 May 1955 where the engine was placed in the bomb bay of a J47-powered B-45C (48-009). The J79 was lowered from the bomb bay and the four J47s were shut down leaving the B-45 flying on the single J79. The first flight after testing was on 17 February 1956, powering the first pre-production Lockheed YF-104A Starfighter. While the engine proved highly successful from an operational standpoint, the Vietnam War experience showed the disadvantages of its highly visible, smoky exhaust when used to power military aircraft. It enjoyed a production run of more than 30 years. Over 17,000 J79s were built in the United States, and under license in Belgium, Canada, Germany, Israel, Italy, and Japan.

     The second prototype XF4D-1 Skyray was loaned to General Electric in 1956 for further testing of the J79, with this engine fitted the Skyray could exceed Mach 1 in level flight where the standard aircraft remained subsonic. Grumman's F11F-1 Tiger was also fitted with the engine. The aircraft was designated F11F-1F Super Tiger, but did not enter production.

     The J79 was used on the F-104 Starfighter, B-58 Hustler, F-4 Phantom II, A-5 Vigilante, and the IAI Kfir. A downgraded version of the F-16 Fighting Falcon with a J79 was proposed as a low-cost fighter for export, and though a prototype aircraft was flown, it found no customers.

     The J79 was replaced by the late 1960s in new fighter designs by afterburning turbofans such as the Pratt & Whitney TF30 used in the F-111 and F-14, and newer generation turbofans with the Pratt & Whitney F100 used in the F-15 Eagle which offer better cruise fuel efficiency by moving unburned air around the core of the engine.