4. X-35 testing progresses, manufacturing of parts begins

Wind tunnel model of the lift-fan exhaust nozzle for Lockheed Martin's STOVL JSF variant. It was mounted horizontally for testing.

The X-35 Joint Strike Fighter (JSF) program, led by Lockheed Martin Tactical Aircraft Systems (www.lockheedmartin.com), is progressing through the testing phases of development. Since government approval of its initial design review in June, several tests have been conducted on airframe and propulsion systems. The initial engineering drawings have also been released and production of parts has begun at the Skunk Works. The first series of test flights for the X-35 is scheduled for early 1999.

Recently, Lockheed Martin has completed testing of several major propulsion system components. The first series of tests conducted on the high-speed inlet/forebody model has yielded favorable results. These tests were conducted in a 16-ft transonic wind tunnel located at the Arnold Engineering Development Center in Tennessee. "The test results indicated that the measured performance levels met or exceeded predicted levels and that the X-35 inlet design is quite effective in providing high-quality airflow to the engine throughout the planned flight test envelope," said Fran Ketter, propulsion system integration manager for Lockheed Martin's JSF program.

Testing on low-speed inlet/forebody models has also been completed. These tests were conducted in a 9 x 15 ft subsonic wind tunnel and a 8 x 6 ft supersonic wind tunnel located at the NASA Lewis Research Center in Ohio. Resulting from these tests was the modeling of the full range of short takeoff/vertical landing (STOVL) operating conditions. This model verifies that the engine and inlet design are compatible and yields favorable results in engine performance.

Other testing was conducted by the manufacturer of the X-35 STOVL aircraft's lift fan system, Allison Engine Company. Results from its tests substantiated computational fluid dynamics calculations of exhaust nozzle performance. BF Goodrich, a subcontractor of Allison Engine Company, conducted tests on its lift fan clutch. "Testing has already demonstrated high-speed clutch engagements representative of X-35 STOVL operating conditions, and we're seeing a very favorable clutch plate wear rate, which translates into a clutch plate life of over four times the X-35 flight demonstration requirement," explained Ketter.

Wind tunnel model of the three-bearing swivel duct assembly and exhaust nozzle for Lockheed Martin's STOVL JSF. Testing was conducted by Pratt & Whitney and Rolls Royce.

Other subcontractors of the X-35 propulsion system are Pratt & Whitney (www.pratt-whitney.com) and Rolls-Royce. They performed scale model testing of the three-bearing swivel duct and nozzle assembly. The assembly was derived from the F119 engine's design. Testing was conducted at NASA's Langley facility in Virginia. This nozzle assembly will augment the lift fan, giving the X-35 STOVL capability. This will be accomplished through directing engine thrust in support of lift fan thrust.

The structural and aerodynamic properties of the lift fan system were validated through 200 hours of vertical lift propulsion testing conducted by Lockheed Martin. This testing was performed using a 91% scale model. This patented lift fan system generates a cool downward thrust in conjunction with the thrust vectoring nozzle of the engine to give the X-35 STOVL capability. Lockheed Martin was awarded this $1.1 billion JSF contract on November 16, 1996.

The X-35 program was developed for the U.S. Air Force, Navy, and Marine Corps, and for the U.K. Royal Navy. Upon completion of a 31 x 48 ft steel assembly fixture, large-scale production will begin at Skunk Works in January 1998.