DEFENCE

Upgrades will enhance F-117 capabilities BY GUY NORMS IN LOS ANGELES

The integration of a global positioning system (GPS)

and improvements to the ex­haust system could be among the upgrades to the Lockheed F-117A fleet about to be un­veiled by the US Air Force.

The upgrades will build on a succession of avionics and sys­tem improvements initiated over the past seven years. Lockheed Advanced Development Com­pany (LADC) is already deliver­ing upgraded versions of the F-117As to the USAF at the rate of one a month.

So far, 15 aircraft have been updated under the Offensive Combat Improvement Pro­

gramme (OCIP), which gives the pilot greater situational aware­ness, with a cockpit similar to that of the forthcoming F-22.

The OCIP effectively replaces the layout of the original cock­pit, mainly derived from the McDonnell Douglas F-18, with common multifunction display indicators, head-up display, fuel gauges, engine instruments, throttles and control stick.

The original sensor display, developed by Texas Instruments (TI), is derived from the North American OV-10D Bronco and the Lockheed P-3C Orion.

The new-look cockpit is sig­nificantly different, with Hon­eywell colour multifunction display indicators, a three-dimensional flight management

system, and a large moving map or digital tactical situation dis­play driven by Harris processors. Other new features include a display processor, an auto-throttle system and a pilot acti­vated recovery system. The OCIP also introduces autopilot improvements for vertical flight-path control and a new data entry panel.

Development of the OCIP was possible because of an earlier update to the weapon system computer subsystem, initiated in 1984. This replaced the F-117A's original Delco M362F computers with IBM Federal Systems AP-102 units similar to processors used by the Space Shuttle. Soft­ware was also updated.

Flight test of a new set of

Northrop shows early stealth ideas Northrop's early research into

low-observable technology, including its losing XST bid for the Defense Advanced Research Proving Agency's (DARPA) Have Blue stealth demonstrator, was critical to its beating Lockheed for the B-2 advanced-technology bomber, according to Northrop chief designer Irv Waaland.

Revealing Northrop's XST concept recently for the first time, Waaland says: "The XST designs were tailored for pene­trating a heavy defence environ­ment for attack of ground targets. Northrop and Lockheed selected highly swept planforms. Twin tails, exterior shielding of the inlet cavity and aft deck shielding of exhaust designs pro­moted external mixing of the exhaust to reduce IR [infra-red] signature. Both were based on faceting of volume to minimise radar cross-section."

Technology development of theoretical low-observable meth­ods was initiated under earlier Air Force contracts in 1965. "By 1974-5, some design studies on tailoring designs for reduced sig­nature dovetailed with DARPA's XST programme," says Waaland. "The objective of the XST pro­gramme was to determine the practical limits and system pay-

1 LOB inlet grid screen 2 Inboard canted fins 3 Boundary layer intakes forward of primary

intake (ram air for ECS possibly - as well as reduce flow separation)

4 LOB faceted external design 5 Aft deck shielding of engine exhaust 6 Central fin to promote external mixing of

exhaust 7 Trailing edge with forward sweep

© Reed Business Publishing

Northrop XST concept

offs of this approach to reduced RCS [radar cross-section]."

Northrop built and tested a full-scale RCS model of its own low-observable design in five months. In mid-1976, following the demonstrations, Lockheed was selected and built the Have Blue LO demonstrator, which led eventually to the F-117A.

Despite the blow, Northrop's low-observable expertise ma­

tured to the point where, in January 1980, it was awarded concept definition/validation of the advanced bomber concept.

Although similar in design to the F-117, the Northrop XST differed significantly in having a single engine intake positioned in the dorsal area aft of the cockpit. Boundary layer intakes, like the B-2's, are apparent for­ward of the primary intake. D

upgrades to the F-117A later this year include a new turret-mounted Infra-red Acquisition and Detection System (IRADS). The original Texas Instruments-built system was an off-the-shelf unit adapted to a twin-turret system to meet the low-observa­ble mounting requirements of the aircraft.

The new system, again by TI, is expected to double the acquisition range of the IRADS and increase the range and life of the laser.

The double-turret arrange­ment includes a forward-looking infra-red (FLIR) and downward-looking infra-red (DL1R) sys­tems. Cavities into which FLIR and DLIR are recessed are cov­ered with woven wire shrouds to handle acoustic loads and re­duce radar signature. The im­proved IRADS programme will enter flight test in mid-1992.

Navigation system upgrades form the focus for most of the work in 1992, with efforts build­ing towards replacing the out-of-production updated Boeing B-52 Offensive Avionics System-derived Honeywell inertial navi­gation system with a ring laser gyro (RLG) system.

The RLG will begin F-117 flight tests in mid-1993 to estab­lish if it is accurate enough for the F-117A's precision-attack role. Under $16 million funding, as part of the $42 million allot­ted to the F-117A upgrade in fiscal year 1992, LADC will also investigate the integration of a GPS with the RLG for even higher standards of navigation. Much of this will be dependent on the development of a low-observable antenna for the GPS.

Other upgrades being consid­ered include a mission planning system, a covert communica­tions system for attack co­ordination, a low observable demonstration of lower radar cross section (RCS) and infra­red technologies and a di­agnostic radar to verify the RCS of fleet aircraft.

The re-engining of the fleet with the General Electric F412 (developed for the cancelled A-12) is considered unlikely on cost grounds. •

24 FLIGHT INTERNATIONAL 19 - 25 February, 1992