Guy Norris/LOS ANGELES
Fight testing of the F-22 is in its busiest and most critical year, with major milestones round the corner
The US Air Force test team evaluating the Lockheed Martin/Boeing F-22 Raptor had more reason than most to celebrate the traditional US Thanksgiving holiday last November.
On the 23rd of that month, the two F-22s achieved 183 flight hours - a critical target set by the US Congress. That tally was an extra target, over and above goals already set by the Defense Acquisition Board (DAB) as a prerequisite for further funding for low-rate initial production and future survival of the F-22 programme.
The first milestone was the start of flight tests on the second F-22, Raptor 4002, which began on 29 June, last year. Other targets included the first air-to-air refuelling, the first supersonic flight, the first flight above 30,000ft (and the first flight above 18¼ angle of attack (AoA).
"We got to 26¼ AoA by the end of the year," says Boeing F-22 chief test pilot Chuck Killberg. The year also culminated in the first full-power afterburner take-offs and the achievement of a maximum altitude of 50,000ft (15,250m), reached on 1 December.
By the end of 1998, flight test hours had reached 187 and, by 10 February, the combined tally stood at almost 204h. Of this total, Raptor 4001 had amassed 98.4h and 4002 had overtaken its older sister aircraft and built 105.4h. Total flights for the two stood at 96 - most credited to the first aircraft, which spent much of its early test period making relatively short flights.
Flight tests are expected to resume later this month after a lay-up while both aircraft are modified for the next phase. These will include the full demonstration of supercruise (supersonic flight without afterburner). Although this was achieved for the first time recently, the USAF says: "We have not declared a F-22 supercruise event officially until it achieves sustained speeds of Mach 1.5." So far, maximum sustained supercruise speeds have been about M1.4. The USAF's F-22 programme office also specifies that, to qualify for its official supercruise status, the aircraft must also be at a weight similar to that of the combat configuration.
Another target for the first part of the year, taking up most of the current modification phase, is the opening of side weapons bays and deployment of stores ejectors. Full weapons tests, stores separation and jettison trials are to be undertaken by aircraft 4002. The next major milestone is scheduled for May with the expected clearance of the Pratt & Whitney F119s for full flight release, allowing full expansion of the flight envelope, says the USAF.
Contract awardsMeanwhile, aircraft 3999 (a ground test article) is to begin static tests later this month at Lockheed Martin's Marietta site in Georgia. It is due to be joined by aircraft 4000 about mid-year for the start of fatigue tests. "But the big event will be in the December timeframe, with the expected contract awards for Lot 1 production and long lead items award for Lot 2," says the USAF. This is contingent on a successful DAB review early in the fourth quarter.
A key element of the review will be the start of engine runs for aircraft 4003. The USAF says that needs to happen before the DAB can give the go-ahead for the next phase of funding. The first flight of 4003, which is provisionally earmarked for loads testing, crosswind landings, arrestor hook validation and weapons bay work, is expected before the end of this year, but may slide into 2000. With its programme targets set firmly on meeting the DAB's goals, the USAF appears to be ambivalent over flying before year end with 4003. "If we get first flight, so much the better, but it is not critical," says the service.
Tests will also continue to validate changes made to the electrical system because of earlier glitches. The first phase of flight tests revealed problems with the brake system, as well as with the software for the inertial reference system and fuel pumps. Boeing, meanwhile, has delivered the aft fuselage section of aircraft 4004, the first full-up avionics test aircraft, and in March handed over the shipset for aircraft 4005, the seventh unit and fifth production airframe, to Lockheed Martin.
Based on flight tests so far, Killberg is convinced that the F-22 test team is on to a winner. "We have the agility and manoeuvrability to absolutely dominate a close-in air battle," he says. "But I want to be further away, and that depends on the avionics, which we are only now about to test. However, based on what we have seen so far, the aircraft should be incredibly effective," he says.
Source: Flight International
