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Aviation History
1958
1958 - 0353.PDF
Helicopters of the World A "FLIGHT" SURVEY OF CURRENT AND PROJECTED TYPES GREAT BRITAIN Bristol Aircraft Ltd. Filton, Bristol. Sycamore Over 150 Sycamores havebeen delivered, and production is at the rate of approximately four aircraft permonth. All parts of the airframe have overhaul periods of 800 hours or more,and the Alvis Leonides engine overhaul period (a Leonides is invariably fitted) isat present 400 hours. The basic Sycamore is a five-seater. Inaddition to the main cabin, which has a volume of 100 cu ft, it has a luggage com-partment of 20 cu ft and is provided with all the fixed fittings needed to convert itto any of six major roles, viz., search and rescue, air ambulance, passenger trans-port, freight transport, aerial crane and dual instruction. In addition to theseprimary capabilities, the Sycamore is suited to a variety of special tasks, and toequip it for any one of these, or to change it from one to another, is a simple opera-tion. For all roles the aircraft is normally equipped with three folding canvas seatsfor passengers and one seat beside the pilot which can be turned to face rearwards. The main rotor blades are attached tothe sleeves on the rotor head by a light, strong root-fitting formed by interleavingsteel plates with the spar laminations. Tie- rods take the centrifugal force directly intension, but are flexible in torsion. The blade levers are connected by balljoints to the arms of a control spider carried by taper roller bearings on a control axlemounted in a control cone. The cone is moved up and down by the collective pitchcontrol lever, the axle and spider moving with it and changing the pitch of all bladescollectively; an irreversible mechanism prevents blade loads coming back to thecontrol stick. When the control axle is tilted about its cup-and-ball joint by thecyclic pitch control, however, the pitch is changed cyclically, minimum pitch beingwhere the spider arms are lowest and maximum pitch diametrically opposite.Inter-blade and drag-hinge dampers neu- tralize rotor vibration. The blades aresupported when at rest or turning slowly by droop stops which ensure the necessary INDEX: PAGE 402 clearance between the blades and the fuse-lage for starting and stopping in high or gusty winds. When the rotor speed ex-ceeds approximately 100 r.p.m., these stops are withdrawn, leaving the full free-dom of movement which is essential for flight. These stops ensure that the mini-mum clearance between the main rotor Above and below, Bristol Sycamore.
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