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Aviation History
1949
1949 - 0631.PDF
SWASHPLATE SPIDER 8ELL HOUSING OUTER GIMBAC RING used via the nbly in tht itof position, 1/ assembly. April 14th, 1949 429 9MASHPLATESPIDER Lockheed Servodyne assembly in the forward part of the engine room. The push-pull rods terminate in bell-crank connections to vertical rods pin-jointed at their upper ends to the individual control valves of the Servodyne jacks. Thus, the pilots' control motions are actually used to move the appropriate valves and so determine the direction of jack movement, the power source for actuating pitch- change of the rotor blades being provided by the hydraulic system serving the jacks. The Servodyne assembly in the engine room is divider into port and starboard halves, the former catering for collective pitch, whilst the latter accommodates cyclic pitch. The jacks are all anchored to the belly structure of the fuselage by means of their piston rods, the heads of the jack cylinders being pin-jointed to an articulated yoke linkage from which vertical connecting rods run up to the tips of three spoke-arms commonly anchored at their inner ends to the head of a vertical shaft. Approximately 40 per cent along each of the spoke arms is pin-jointed the foot of a vertical link pivoted at the head to a crank arm from the pulley around which is wrapped the cable trans- DIFFERENTIAL COLLECTIVE - PfTCH SERVODYNE FOR FRONT DFFERENTW. COLLECTIVE- PITCH SERVOCnrNE FOR PORT & STARBOARD ROTORS COMMON — COLLECTIVE - PITCH SERVODYNE mission linkage running out along the outrigger boom to the rotor hub. As the whole assembly is duplicated, it follows that there are two separate cable control runs in each of the three rotor booms, one for collective pitch and one for cyclic pitch control. The actual transmission is made up with 20-cwt Tru-lay cable around the pulleys and fairleads where change of direction occurs, the intermediate spans being made up with £in diameter bright steel tie-rod, whilst ^in pitch, 2,000 lb Renold chain inserts are incor- porated for matching with the sprockets at the heels of the control shafts in the rotor hubs. The mechanical geometry of the Servodyne assembly is such that it is more readily understandable from a drawing than from a textual description. The Servodynes are supplied with oil at 2,500 lb/sq in cut-out pressure from the Lockheed Mk. VI pumps driven from the engine and the distribution gearbox. Each pump is capable of serving both the hydraulic accumulators. Each of the latter feeds into a common junction box from which the jacks are supplied; thus the system is dupli- cated up to the junction box. The complete hydraulic system (aside from the pipe runs) is nested as a common installation in a box mounted on the starboard wall of the fuselage in the forward section of the engine room. With the powered control system in its present form, there is no feed-back to give "feel " in the pilots' controls, but a scheme is in hand for incorporating artificial " feel ". by means of spring pre-load embodying adjustment of the. null point. This refinement should permit the pilot to trim out the control stick forces to any required datum setting.. Thrust Distribution It is advisable at this point to consider the distribution of thrust function between the rotors. Regarding the three rotors respectively as A (front); B (port); and C (star- board) ; the individual rotor action for producing the four freedoms of motion is as follows : to produce roll, A remains neutral whilst a differential collective pitch is given to B. and C.; for fore and aft pitching, differential collective pitch-change is given between A, and B+C; for yawing motion A remains neutral whilst differential cyclic pitch is given between B and C; vertical motion is, of course, produced by collective pitch given commonly to A, B and C simultaneously. These can be considered as the fundamental control functions which will give attitude change about the air- craft's centre of gravity. Naturally, however, the inclina- tion of the individual thrust vectors incurred in these manoeuvres (with the exception of the last-mentioned) will secondarily result in a measure of directional progress. Reference to the detail drawings and diagrams of the con- trol transmission system should make readily understand- able the selection and sequence operation of control paths between cockpit and rotors to bring about any of the men- tioned flight manoeuvres. Here, perhaps, it will be helpful to consider the manner in which control selection is translated at the rotor hub into an appropriate blade pitch movement. Running up through the centre of each hub are two
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