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Aviation History
1986
1986 - 3544.PDF
Fastest blades in the world Last August a modified Westland Lynx broke the world helicopter speed record by a handsome margin. A speed of just over 216kt was reached, which meant that the advancing tips of its composite blades were near-sonic at Mach 0-97. Harry Hopkins reports. The world speed record set by G-LYNX was no mere publicity stunt. It demonstrated that West- land's designers have successfully applied the "Berp" (British Experimental Rotor Programme) blade design, which is capable both of flying at extreme subsonic Mach numbers, and of delaying retreating-blade stall. Westland is confident that G-LYNX could also have taken the rate-of-climb record, and expects the speed-record performance to be translated into prac tical applications on future light- attack/anti-tank helicopters. The "Berp-tip" blade (see Flight, August 31, 1985) allows faster flight with the same blade loading, and it allows high incidence (up to between 20° and 22°) on retreating blades without stall because of strong vortex action at the tip. It also acts as an aerodynamic damper, opposing flutter growth at a local stall point, while the "nick" between the straight leading edge and the tip works as a fence. The concept was first tried out in 1984, on a Puma at RAE Bedford, and the speed record was the culmination of trials begun in August 1985 on a military Lynx. To obtain the high speed necessary to prove the concept on G-LYNX, consider able preparatory work was necessary. In early trials, rotor loadings were taken up to the equivalent of 18,0001b at sea 24 level—an increase of 39 per cent over the standard Lynx—by carrying 12,0001b to 12,000ft altitude. The trials took the heli copter up to 170kt at lower rotor loadings in level flight and to 180kt in a dive, with 110 per cent rotor speed (NR). But engine temperature limitations, fuselage drag, and tail-rotor stall kept speed below the potential of the new blade design. To stretch the machine's performance toward the rotor capability, the tailplane was lowered to the position it occupies in the Lynx 3 and W.30. Tip fins were offset 8°, to help offload the tail rotor. Rolls-Royce Gem 60 engines, as used on the W.30-100 and Lynx 3, were installed, along with water methanol injection and a modified gearbox so that transmission margins were available to meet 5 per cent extra output. The required rotor power left surplus engine output, which was diverted to the tailpipe, now configured for more thrust. "We wanted to use the thermodynamics that we couldn't get our hands on any other way," says Westland. Rolls-Royce gave guidance on the power FLIGHT INTERNATIONAL, 27 December 1986
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