Graham Warwick/ATLANTA
EARLY IN THE US Joint Strike Fighter (JSF) programme, key technologies were identified which offered high pay-offs, but involved high risks, for all the teams competing. The result was a programme to mature critical technologies and reduce associated risks, while sharing the results between the competing teams, ready for the transition from JSF concept-demonstration to engineering and manufacturing development in 2001.
One critical technology identified was the integration of subsystems, which promised to reduce aircraft size, weight and cost significantly. The 52-month, $118 million Joint/Integrated Subsystems Technology (J/IST) programme now under way is intended to demonstrate those benefits and includes ground and flight tests of electric actuation.
Traditional federated subsystems include separate auxiliary power-unit (APU), emergency power-unit (EPU), air-turbine states (ATS), environmental-control system (ECS) and electrical-generation, hydraulic and heat-transfer systems. Integration will eliminate seven of 13 subsystems, says the JSF programme office, combining the APU, EPU, ATS and ECS into a thermal/energy-management module (T/EMM). Hydraulics will be replaced by power-by-wire.
The J/IST programme will demonstrate the T/EMM, switched-reluctance starter/generators, electro-hydrostatic actuators (EHA) and fan-duct heat-exchanger technology. Projected benefits include cost reductions of 3-5% in procurement, 3-4% in life-cycle, up to 5.5% in take-off gross weight and up to 9.1% in size - and a range increase of up to 20%.
The T/EMM has an APU at one end and an electrically driven ECS cooling-turbine at the other. The T/EMM is used to start the engine electrically, an APU-mounted starter/generator driving a similar unit on the engine. The engine-mounted starter/ generator then drives the ECS fan, eliminating the need for engine bleed-air. Bleeding engine air reduces thrust, which is critical in the short-take-off/vertical-landing variant of the JSF.
McDonnell Douglas (MDC), leading one JSF team, has subcontracted T/EMM development to AlliedSignal. MDC will conduct a "mini-T/EMM" demonstration in 1999, followed in late 1999 by a T/EMM/engine-integration demonstration at Pratt & Whitney. The latter will involve the P&W F119 engine and AlliedSignal T/EMM, both with starter/ generators, and a Hamilton Standard high-temperature heat exchanger in the F119 fan duct.
The fan-duct heat exchanger will eliminate the need for ram-air inlets, reducing radar signature and drag, while dumping the T/EMM exhaust into the engine will reduce infra-red signature, the JSF programme office says.
A switched-reluctance starter/generator has no windings, just a laminated rotor and computer-controlled stator, which allows it to be switched between starter and generator modes. The J/IST demonstration will use a 200kW starter/generator, measuring just 480 x 355mm and weighing 80kg, producing two channels of unconditioned electrical power and with two independent inverter/controllers.
The Sundstrand starter/generators will be also used in 270V DC electric-actuation flight-tests planned by Lockheed Martin for mid-1999 using the F-16 Advanced Fighter Technology Integration (AFTI) test-bed. The AFTI/F-16 will be modified with Parker EHAs on the flaperons, elevators and rudder, controlled by Lear vehicle-management-system (VMS) computers and powered from four electrical sources - engine- and EPU-driven starter/generators and batteries.
Northrop Grumman will conduct a more extensive electric-actuation ground test, using an MDC F-18 iron-bird test rig. This will involve Moog 37kW (50hp) EHAs and engine- and T/EMM-mounted starter/ generators and will simulate avionics power demands while running the large, high-horsepower electric actuators, to test failure modes.
The Moog and Parker EHAs both have dual DC electric motors powering hydraulic pumps, which drive dual tandem actuator rams. They differ in the control-redundancy scheme, Parker using a quadruplex VMS unit while Moog uses triplex. The JSF programme office says that the weight of EHAs has been reduced, from 15.9kg to 7.3kg, while their power has increased, from 27kW to 37kW, as the technology has advanced.
Source: Flight International
