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Aviation History
1990
1990 - 1889.PDF
[ loads and performance testing, and some weapon-separation work; AV-3 and AV-4, the first B^2s with full avionics, to low- observability and weapons testing; AV-5 to climatic and weapons testing; and AV-6 to operational test and evaluation and low- observability testing. All but one will be refurbished for delivery to Strategic Air Com mand. Deliveries begin in 1992, first to Whiteman AFB, Missouri. Preliminary flight test results released by the Air Force and Northrop suggest that B-2 handling qualities are equal to or better than those predicted by the simulator. Level- flight drag and fuel flow rates (and therefore range) are as predicted; gust response and ride quality meet projections; elevon trim is within 3° of predictions; and ground effects are less than expected (it was thought that the B-2 would "float" on landing, but appar ently it does not). The all-wing B-2 lifts off at 140kt, the speed apparently largely independent of take off weight which is likely to reach of maxi mum of around 181,500kg including a war- load of more than 18,200kg and fuel in excess of 72,500kg. Maximum speed is "high subsonic" and maximum altitude "up to 50,000ft", says Northrop. The B-2 has a large wing area, around 465m2 and more than twice that of the B-1B. Although the flying wing has a flat lift-curve slope (low change of lift with angle of attack) active gust alleviation is required to provide acceptable ride quality, using elevons and the centrebody "beaver tail". Flight controls have fast-acting actuators driven by a 280bar hydraulic system. Pilots report that the B-2 has excellent directional stability and better than expected roll performance and longitudinal stability. Although short-coupled in pitch, the aircraft is well damped with the large control sur faces accounting for about 15% of wing area. "Aerodynamically the aircraft has some prob lems," pilots acknowledge, but these are "glossed over" by the B-2's quadruplex- redundant fly-by-wire flight control system, the performance of which is described as "outstanding". FIGHTER HANDLING Extremely rigid composite primary struc tures cause the B—2 to "...handle like a fighter", says Bruce Hinds, Northrop's B-2 chief test pilot. Unlike the B-52 bomber, the wingtips of which can flex through 9.75m the stiff, 52.4m-span B-2 is described by Hinds as "crisp and responsive, even better than the simulator". Roll-responsiveness is also due in part to actuators which deflect the elevons at up to 1007s. Also described as outstanding is the B-2's stealth air data system. The B-2 has no radar-reflecting pitof tubes (unlike the F-117 stealth fighter which has four faceted air—data probes on the nose). Instead there is a network of static pressure sensors flush with the airframe (probably the rows of four discs to be seen around the nose). The air data system works by detecting differences in static pressure around the aircraft. Other flight-test highlights include suc cessful demonstration of primary and emer gency gear operation. Basic subsystems per formance is described as excellent, with few hardware discrepancies per flight and no significant fuel or hydraulic system malfunc tions (and no fuel leaks). Flights have aver aged 4h and the tenth exceeded 7h. Unrefu- elled range is greater than 11,100km (6,000nm), increasing beyond 18,500km with a single aerial refuelling. Northrop is under contract to build eight development and five initial-production B-2s. Long-lead funding for a further five A computerised design database lies at the heart of the B-2 programme has been approved and a contract is under negotiation. With B-2 unit flyaway cost at S285 million and rising, however, there is Congressional pressure to cancel, or at least mothball, the production programme. Northrop and the Air Force point out that research and development is largely paid for and that production funding is now the issue. Reducing the production rate pushes up the programme cost, they argue, each year's delay costing typically $2.5 billion. Pressed at the Palmdale briefing to justify the B-2's expense in the face of "the disinte gration of the Warsaw Pact", Brig Gen Wil liam Davitte, Special Assistant for Strategic Modernisation, pointed out that the Soviet Union has what amounts to a $400 billion air-defence system, the most extensive and lethal in world, he claimed, protecting the Soviet nuclear arsenal. The B-2 is needed to penetrate Soviet defences and threaten its nuclear assets, he declared, thus deterring a Soviet first strike. The opening of the Palmdale assembly plant served to underline the resources al ready committed to producing the B-2. Con gress, faced with promises of economies if production goes ahead and threats of escala tion if the programme is delayed, has to decide what value to place on the manufac turing technology revealed. Q FLIGHT INTERNATIONAL 4 - 10 luly 1990 27
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