Guy Norris/ST LOUIS
THE REQUEST FOR proposals for the Joint Advanced Strike Technology (JAST) concept-demonstration phase was released on 22 March, after Lockheed Martin withdrew a protest which threatened to delay the programme (Flight International, 27 March-2 April).
The protest was withdrawn after the return of cost data inadvertently faxed by the JAST programme office to competitors Boeing and McDonnell Douglas (MDC).
The MDC/Northrop Grumman/British Aerospace team, meanwhile, is testing a revised lift-engine exhaust designed to eliminate a hot-gas ground-environment issue uncovered during rig tests of its JAST contender.
"We have designed a solution to that and we're testing it," says John Steurer, MDC JAST programme general manager. The revised design "...deflects exhaust from the lift jet at idle...and there is no melting asphalt", he says, quashing rumours about the severity of the problem.
Exhaust from the GEA-FXL lift engine, being developed by General Electric, Allison Engines and Rolls-Royce, exits through louvred vanes. In the hover, the louvres split to direct gases fore and aft.
"We're looking for ways to minimise the ground environment," says Steurer. For the transition to forward flight, the vanes vector- thrust up to 45¡ aft. A 5¡ forward-vectored braking capability is now being tested.
The team remains confident that the 75-80kN (17,000-18,000lb)-thrust lift engine will be powerful enough to propel the aircraft in the event of a main lift/cruise-engine failure. "We think we can fly on the lift engine alone. The tunnel data says you can," he says.
Despite the lift-engine's proximity to the main-engine inlets, MDC says that hot-gas ingestion is not a threat. "We have not seen that problem at all and we do not even need LIDS [lift-improvement devices]," says Steurer. LIDS running along either side of the belly in the initial design, to offset anticipated suck-down effects, have been eliminated, reducing weight and complexity.
The team is under pressure to solve the ground-environment issue before June, so that data from up to 6,000h of wind tunnel tests can be used in its concept-demonstration bid. Results from the initial 3,000h test phase, plus the current tests, confirm that "...flying qualities are excellent and drag-prediction test results, are confirming our analytical predictions".
Source: Flight International
