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Aviation History
1998
1998 - 0033.PDF
power in die experimental XV-15 - in the 609 they will be. START UP AND GO The aircraft is the only experimental tilt-rotor which Bell Boeing has, so we had to be careful with it. The engine starts were slow and benign, as one would expect from T53s. The two rotors are interconnected by a shaft which runs along the span of the wing with a (slight) direction- changing gearbox in die middle, so that, as soon as the first engine was started, both prop-rotors turned. This same shaft will allow both rotors to be driven by one engine only in the event of a single engine failure. In the event of a double-engine failure, bodi rotors will autorotate at the same speed. Equal speed is not as critical as in, say, a Boeing Chinook or Kaman K-Max, where the rotors intermesh. Out-of-synch rotors can produce problems, however, because of the inequality of the lift being produced. The XV-15 pilot has a left/right switch to fine-tune individual rotor- torques to overcome poor synchronisation. It was a fine, clear day widi only 6kt (11 km/h) of wind. I would have preferred something stronger to test the out-of-wind characteristics. We were at 200ft (60m) pressure altitude, but with slightly less density. We had full fuel, which, with all the test equipment on board (there is no room in the cabin for a passenger) gave us a weight of 6,080kg, compared with a maximum permissible of 6,800kg. The 609 will have a further 500kg available. HOVER TAXI One of the several differences that helicopter pilots will have to address is dieir use of the pow erful lift forces generated by the rotors. Many oP die manoeuvres usually performed by moving the cyclic stick are now done by tilting the nacelles, which can go from 0° (ie, horizontal) for fixed-wing mode, to 90° for helicopter mode or anywhere in between, and even to 95° to fly/taxi backwards, slow down quickly, or main tain a level attitude when hovering downwind. With 1,155kWavailable from each engine, the slightest tilt makes a significant difference. The 609 will have even more engine power (l,380kWfrom each Pratt & Whitney Canada PT6C-67A) and an extra 600mm of diameter on the prop-rotors. I beeped the rotor RPM'up to 98% for heli copter mode, applied just a bit more than 20% torque to enter the RPM-governed range and give good rotor control and, keeping die cyclic- stick neutral, tilted the rotors 1 ° forward and we taxied towards Bell's flight-test runway at Arlington, Texas. A dab on die brakes revealed the usual characteristic of helicopter brakes: not so powerful as to tip the aircraft on to its nose, yet powerful enough when used differentially to turn the aircraft. This is required because the rudder power is weak at this stage. It is to be hoped that die 609 will have nosewheel steer ing. There is a light and audio warning to Gray (right) learns the ropes from Ball: ejection seats are unusual in a rotary-wing aircraft inform the pilots that the undercarriage is up and a light also to warn that the brakes are on. The cabin door on the experimental model is in the same position as it will be on the civil version - on the right-hand side where the pilot can see die winch when on a rescue mis sion and far enough behind the engine prop- rotor plane to be out of harm's way. The experimental and commercial versions are both designed for single-pilot operation, even to instrument-flight-rules conditions. The other overriding impression is that, although an extremely complex aircraft lurks under the skin, the management of the systems is straightforward and die handling benign. Rockwell-Collins will provide a glass cockpit for the 609.1 had die preliminary, early version at my side: a large liquid-crystal display • XV-15 has just one liquid-crystal display: the 609 will have a full "glass cockpit" FLIGHT INTERNATIONAL 7 - 13 January 1998 31
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