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Aviation History
1998
1998 - 0037.PDF
ent, but works well. On all approaches to the hover that I made onto the spot on the taxiway, I arrived each time over the target. If going into a confined area where maximum visibility was required, a pilot could pitch the fuselage nose-down to increase the forward vis ibility and compensate by tilting the rotors back - impossible in any other aircraft. I taxied in and Ball shut down the aircraft. Although there are safety systems in place to prevent the nacelles falling toward and doing damage, Ball took the additional precaution of pulling the already-identified circuit-breakers. The aircraft will accept fore and aft landing slopes of up to 15° quite comfortably, which is beyond the range of normal helicopters. Helicopter pilots need not worry about banging the tail rotor when landing" down-slope. Start ups, shut-downs and operations in strong winds are said to be safe.Commercial operators will want to make sure to exploit the tilt-rotor's unique capabilities and to operate city-to-city from rooftops and other similar areas within built-up areas. Excessive noise, quite rightly, would inhibit or even prevent this, so Bell Boeing has conducted extensive tests to deter mine the major noise-sources. Rotor tip-speed is one of the major produc ers, with the usual helicopter-phenomenon of each rotor passing through its own wake and making that unmistakable and loud slapping sound. Most of the noise is caused during final approach. So, the test pilots have been busy finding approach profiles to reduce it. Tip speeds in the 609 will be lower and the tip design modified from that of the XV-15. PERFORMANCE All pilots, both rotary and fixed-wing, will have* to learn new criteria, such as conversion corri dors - those areas of maximum and minimum speeds, heights, weights and configuration between which conversions should take place. Helicopter pilots will have to respect stall speeds, flap-setting limitations and the like. There are two sets of limitations to learn, one for helicopter mode, the other for that of fixed- wing configuration. Helicopter pilots will recognise the power- required curve for straight-and-level flight. It has the usual shape and bottoms out at about 6()kt, depending on the weight and altitude. Fixed-wing pilots will recognise the same curve for aircraft mode: the bottom of the curve moves to the right, giving a higher speed as die aircraft converts. The best rate of descent in helicopter auto- rotation is about 75kt. The graph in the manu al gives a rate of 2,150ft/min at 5,900kg, although the test pilots quote 4,000ft/min using the better flare-effect speed of 90kt. Man's achievements in aviation have been highlighted by the very first flight, the first heli copter flight, the first supersonic flight, and man landing on the Moon. To be able to hover, take off vertically, then fly at turboprop aircraft Pilots have to remember to increase power to maintain height during transitions to foiivard flight speeds and heights, has fired the imagination of received by Bell from more than 40 organisa tion for decades. The XV-15 does all of this, so I would now add its first flight to my list as another unique achievement, using all man's ingenuity, imagination and expertise. Deposits for firm orders have already been tions, including private owners, two offshore operators, air-taxi companies and corporate bodies. On the strength of this evaluation of the XV-15 prototype, it is time for these organisa tions to covert those orders. • •'W*;vflWiittiiHiHi';i GARETH BURGESS 97 Length overall Distance between rotor centres Rotor diameter Height overall 12.83m 9.80m 7.62m 4.67m Power (each) Max take-off weight Range (max fuel) Max speed 1.155kW(1.550shp) 6,804kg 825km (445nm) 230kt (425km/h) Powerplant 2 x Lycoming LTC1K-4K turboshaft Hover ceiling (out of ground effect) 8,650ft (2,635m) FLIGHT INTERNATIONAL 7 - 13 January 1998 35
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