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Aviation History
1952
1952 - 1842.PDF
The construction of the co//ective- pitch lever, which carried a twist- grip fine-adjustment for engine power. ABOUT BRISTOL HELICOPTERS . . . customary on the first flight of the day to take off and then hover a few feet off the ground to check controls and instruments. The helicopter is also trimmed as soon as it leaves the ground. During the waiming-up or running-up period prior to flight it is usual also to check the tilting of the rotor-tip path in relation to control- column movements and to check the functioning of the cyclic- pitch indicator. During my brief flight experience in the 171 I took the controls for a few minutes, and, as mentioned earlier, found them lighter and more responsive than I had been led to believe. I was told that pilots accustomed to earlier types of helicopters usually tend to over-correct when they first fly the 171. Another feature which I noted was the wide range of r.p.m. available in flight. The normal limits for flying are marked as a colour sector on the indicator, and, Simplified diagram indicating the linkage for control of cyclic pitch. FLIGHT, 4 July 1952 while the pilot would usually select approxi- mately250 r.p.m. for flight, he can with safety allow the rotor speed to fall to as low as 200 r.p.m. in auto- rotation (or 245 with power on) or increase it to 287. A synchroscope is provi ded so that he may check the relationship between rotor and engine r.p.m. The Bristol 171 can be described as neutrally stable for normal flight; by this it is meant that, with the aid of the trimmers working on the principle of spring-loading and very sensitive in operation) and after having been set in steady flight, the aircraft will maintain its condition for 20 or 30 seconds, hands and feet off. The linkage between the control column and the rotor head is reversible, so that if any out- of-balance forces should develop they can be felt at once by the pilot through the control column. The collective-pitch lever, however, does have an irreversible mechanism, and once the lever is set for steady flight it can be left alone. To resume the flight where we left off—hovering at a few feet off the ground—Mr. Hosegood began a climb parallel with the long runway at Filton, maintaining his rotor speed at about 270 with boost at 29in and a forward speed of about 45 kt. The aircraft is, in fact, capable of climbing at a maximum rate of about 800 ft/min up to 4,000ft. On levelling out, the boost was reduced and the rotor revs brought back to 240. The aircraft then cruised quite happily at 82 kt indicated. The flight was very smooth and, although the stick was inclined to shake, if left with hands off, this was purely a matter of its anchorage and nothing directly to do with the rotor head or the flight of the aircraft. It is not until higher speeds are approached, say, 95 or more knots, that there is any appreciable shake. Incidentally, although the 171, in common with most heli copters, readily flies sideways or backwards, it is recommended that in such circumstances the speed should be very low. In normal cross-country flight, when the power and collective- pitch setting has been chosen, the stick becomes, in effect, the speed control; in transverse movement the response is as with The non-standard cockpit ofG-ALSX meets the pilot's requirements for a simple blind-flying panel ahead of him, uninterrupted forward and downward view, and grouped controls between the seats. Although the instrument layout is rather different from that illustrated in the photograph, the sketch serves to indicate the standard layout of the Service Sycamore cockpit and to indicate the various controls and instruments provided. "Flight" photograph and Drawing 13 15 17 19 114 16 18 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. Oil temp, and pressure. Boost pressure. Tachometer. D.R. compass repeater. Artificial horizon. Cross-level. A.S.!. Rate of climb. Clock. Altimeter. Cyl. temperature. Vacuum gauge. Gearbox oil temp. Fuel contents. Fuel pressure. Air pressure. Ammeter. Lane identification. Deccometers. 20. 21. 22. 23. 24. 2S. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. Cyclic-pitch control. Throttle and collective pitch. | Engine starter button. \ Clutch warning lamp.- Tail rotor pitch pedals. ' Cyclic-pitch indicator. Ignition switches. Rotor-pitch indicator. Landing-lamp lever. Clutch-pump pedal. Hand-brake. Longitudinal bias wheel. Pitch lever release button. Fuel cock. Lateral bias wheel. STR.12 or STR.9X. Decca receiver. Decca control boxes. Power unit. \
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