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Aviation History
1937
1937 - 0419.PDF
FEBRUARY I8, 1937- FLIGHT. 161 tion to the freedom provided by the two sets of hinges the blades have a third degree of freedom, i.e., to alter their pitch angle. The last-mentioned freedom is, how ever restricted or damped, as will be explained later. The inner end of each blade carries a crank arm on a vertical hinge, the hinge being incorporated in order to leave the blades free to "catch up" or lag behind one another. A so-called '' spider'' is mounted centrally above the rotor head, and also carries three arms mounted on vertical hinges. The free ends of the blade cranks are connected (by a cup and ball joint) to the free ends of the spider cranks. When the spider is raised, by means of a separate control in the cockpit, its three crank arms rise with it and carry with them the free ends of the blade cranks, thereby increasing the pitch angles of all three blades (the spider rotates with the rotor head, of course), and when the spider is lowered the pitch angles are re duced This control might be termed the lift control, as it varies the amount of lift given by the blades, and is used for steep take-off and for checking sinking when landing. The flying control has the effect of shifting the centre of lift of the whole rotor system by causing the blades to assume an increased pitch angle at one point of their travel around the circle and a decreased pitch angle at )R CONTROL other points. This is effected quite simply by tilting the spider. Obviously, if the spider is tilted back the blades will assume a low-pitch angle when passing through their rearmost position and a larger-pitch angle when passing through the foremost position, thus shifting the centre of lift ahead of the rotor pivot and thereby causing the machine to climb. If the spider is tilted to the lett tn« pitch angle will be large on the right-hand side and small on the left-hand side, and the machine will bank and turn to the left. Flying controls on the A.R.III gyroplane also include a trimming tailplane and a pedal-operated rudder of orthodox type. Details of the actual mechanical application of the funda mental principles outlined above are illustrated in the sketches. The rotor blades have single steel-tube spars of small diameter but heavy gauge. No attempt has been made at saving weight on the rotor blades ; in fact, weight has deliberately been kept fairly high in order to obtain a good flywheel effect to assist take-off and to ease the machine down gently through the last couple of feet of the landing. In this connection it may be pointed out that the mass of the blade per unit of frontal area is important. In the A.R.III, Mark II, which is the machine now flying at Han- worth, this value reaches a high figure and has much to do with the good energy-assisted take-off and the shock- less landing without preliminary glide which are features of this machine. At its outer end the blade spar has screwed into it a SPIDER RIGID ARM HINGED ARMS INTERLAPPING YOKES FRICTION DAMPER View from above of the Hafner rotor hub, showing the "spider" with its °ne rigid and two hinged amis, the incidence cranks on the blade roots, and the internal piston which carries the bearings for the sP>der spindle and the joystick. JOYSTICK
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