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USAF ponders T-38 air-inlet redesign

THE US AIR Force is considering, a fleet-wide adoption of a redesigned engine inlet for Northrop Grumman T-38s, after a successful NASA programme cleared an increase in the maximum take-off weight temperature limit to 39°C, from 34°C.

The NASA initiative was originally begun to improve the hot-weather take-off performance of the T-38s used by Space Shuttle astronauts to train for simulated Shuttle landings at El Paso International Airport, Texas. In summer months, when the temperature regularly exceeds 34¡C, the aircraft's fuel load, and therefore endurance, has been severely restricted.

Engineers from the Aero-sciences and Flight Mechanics division at NASA Johnson Space Center in Houston used stereo-lithography (SL) to create three-dimensional prototypes directly from computer-aided design data. Using the Center's SLA-500 SL tool, made by California-based 3D Systems, the team made a new bell-mouth design which yielded a 24% increase in thrust in static tests.

A more-practical design for flight-testing was evaluated, producing a 20% increase in static thrust and an 8% rise at 150kt (280km/h). This was enough to allow operations at maximum take-off weight at temperatures 5¡C higher than the previous limit. Using the SL system, NASA has spent around $500,000 on the programme, including flight tests. An outside contractor had offered to design, develop and test a modified inlet for $5 million.