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Aviation History
2003
2003 - 2527.PDF
TECHNOLOGY PROPULSION GRAHAM WARWICK / WASHINGTON DC Boeing seeks cash to pursue pulsejet VTOL experiment Light Aerial Multipurpose Vehicle will be powered by ultra-efficient turbofans in the cruise Boeing Phantom Works is seeking funding to develop a novel aircraft that uses simple pulsejets for verti cal take-off and landing (VTOL). The Light Aerial Multipurpose Vehicle (LAMV) uses pulsed-ejector thrust augmentor (PETA) engines for only 90s on take-off and land ing. Small ultra-efficient turbofans are used in the cruise. In the PETA concept, multiple pulsejets are mounted vertically in augmentor ducts running along the sides of the LAMV's fuselage. The ducts entrain freestream air, which augments the thrust of the pulsejets. The unsteady exhaust produced by a pulsejet draws in more air than the steady exhaust of a conventional jet, increasing the augmentation ratio. "We can get augmentation of 1.6:1 with steady flow, but 2-plus with unsteady flow. We can double the thrust of the pulsejet, which is the pump for the ejector," says John Skorupa, senior manager strategic development, advanced airlift and tankers. Because it is essentially a simple tube, the thrust-to-weight ratio of a pulsejet is already high, at around 10:1. The Phantom Works has studied several sizes of pulsejet, ranging from one producing 501b thrust (0.2kN) at 150Hz, to one producing 1,0001b thrust at 60Hz. The smaller pulsejet is 0.9m (3ft) long and 25mm (lin) in diameter, while the larger is 3m long and 200mm in diameter. Higher thrust - and therefore longer - pulsejets could be accommodated in a fuselage by "bending" them, Skorupa says. Boeing has shown two concepts. One has a 700kg (1,5401b) payload, removable wing and empennage and the other is a more conven tional aircraft with a 1,600kg pay- load, 260kt (482km/h) cruise speed and a 2,000km (l,080nm) range. Skorupa says the exhaust veloc ity of the pulsed-ejector thrust aug- mentors would be similar to the rotor downwash of a helicopter, and temperatures would be low, compared to other jet-lift VTOL designs, at around 80°C (175°F). Boeing's Phantom Works has studied several sizes of vehicle ORBITAL BOOST MICHAEL PHELAN / LONDON NASA plans space tether trials NASA is hoping to use electrody- namic space tethers (EDT) to adjust the orbit altitudes of spacecraft, with a trial planned for next year. The propulsive small expendable deployer system (ProSEDS) experi ment will be launched from an expendable rocket, and will deploy an ultra-thin 15km (9.3m)-long tether, part of which will be a bare- wire conductor (Flight International, 19-26 February 2002). The experi ment is designed to use EDT tech nology to drag the Delta rocket stage from which it is deployed back into the Earth's atmosphere to burn up. Space tethers have long been proposed as methods of changing the orbital height of satellites by exchanging momentum between two masses, such as two satellites at different orbital heights. In the past, conducting tethers have also been flown which can generate electrical current as they pass through the Earth's magnetic field. The ProSEDS experiment is dif ferent in that it relies on momen tum exchange resulting from the flow of current through the tether. Converting some of the satellite's kinetic energy into electrical power causes the satellite to slow down gradually, decaying its orbit to the point where it re-enters the Earth's atmosphere. NASA says such a sys tem could be used to remove "space junk", such as a satellite at the end of its useful life. NASA believes the principle could work equally well in reverse. By forcing a current through the tether in the other direction, energy is added to the orbit of the tether which boosts it - and the attached satellite - into a higher orbit. The current could be drawn from solar panels on the satellite. NASA says such a tether could be used to continually reboost the orbit of the International Space Station, countering the effect of atmospheric drag without requir ing additional propellant. RECORD Solo non-stop global flight attempt set for next year Adventurer Steve Fossett is to attempt the first solo non-stop round-the-world unrefuelled flight next year, using a Burt Rutan-designed aircraft capable of staying aloft for 80h. Virgin Group chairman Sir Richard Branson will be the reserve pilot for the Virgin Atl antic Airways-sponsored attempt scheduled for either April or October next year, dep ending on weather. The 11.8m (38.7ff)-long jet- powered GlobalFlyer is due to be completed at Rutan's Scaled Composites facility in Mojave, California, in December. With a maximum take-off weight of 10,000kg (22,000lb), it will carry almost 8,200kg of fuel, the highest fuel-weight proportion of any aircraft to date, according to Branson. The GlobalFlyer features a single composite structure high- aspect ratio unswept wing with a span of 34.8m and an area of 37m2 (400ft2). The wing will bend upwards significantly for the early portion of the flight, returning to a more conventional shape as the fuel load lightens. Twin tail booms serve as addi tional fuel tanks and mounts for the retractable landing gear. With an empty weight of only 1,090kg, the aircraft has a small 2.1m pressurised cockpit located in the centre fuselage, above which is mounted a single 2,300lb (10.2kN) Williams FJ44- 3 ATW turbofan. Although resembling Rutan's piston-powered Voyager, which achieved the f rst non-stop round-the-world flight in 1986, the GlobalFlyer should complete the challenge in about one-third the time of the 216h two-person Voyager flight, and its high cruise altitude will allow it to avoid much of the adverse weather encoun tered by the original mission. The GlobalFlyer will cruise at about 250kt(460km/h) at 45,000-52,000ft. www.fliqhtinternational.com FLIGHT INTERNATIONAL 4-10 NOVEMBER 2003 31
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