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Aviation History
1935
1935 - 0338.PDF
i68 FLIGHT. FEBRUARY 14, Kjjr against a stop and.prevents the wheel fork from being forced back. When the wheel is fully raised the collar is in the farthest forward position, as shown in one of the drawings. A visual indicator or pointer informs the pilot at any time of the position of the undercarriage, while with the wheels fully up an electrical contact is made which, in conjunction with the throttle, sounds a warning note when the throttle is closed beyond the position corresponding to cruising speed. Several British aircraft, both military and civil, now " on the stocks " or undergoing tests have retractile land ing gears. These include the Blackburn H.S.T.io, Avro 652, the large Armstrong Whitworth monoplane with four " Tiger " engines, the Bristol commercial monoplane, and the Bristol F.7/30 single-seater fighter. For new com mercial types the longitudinally retracting gear seems favoured. The Bristol single-seater has fairings below its cantilever wings, into which the wheels retract. Turning to America, in the new " Electra " the Lock heed Company has used an undercarriage in which the wheels retract into the engine nacelles, leaving a small portion of their tyres exposed. The undercarriage is operated electrically by means of gears and torque shafts. One motor operates both wheels. The operation is auto matic in that, when the switch in the cockpit is thrown, the gear moves; then, when the wheels are up or down, as the case may be, the motor stops without further action by the pilot. An auxiliary hand mechanism is pro vided for emergencies. One of the first retracting mechan isms to be developed in the U.S.A., the Boeing gear is operated elec trically, but provision is made for auxiliary manual control. The wheels fold backwards into recesses in the under portion of the wing, leaving about half their effective diameter extending beneath the lower surface. Retraction can be effected in forty seconds, and thirty seconds are required to extend the wheels, which are of the large low- pressure type. There are three devices installed in the pilot's cock pit to give warning of the position of the gear—a dial, a red " bull's- eye " light oh the instrument board, and a Klaxon horn behind the pilot's seat Developed originally for use on am phibians (as shown in this diagram matic sketch), the American Grumman gear is now being fitted to landplanes. It is operated by cables. The sturdy American Boeing gear for twin- engined aeroplanes. A portion of the wheel still protrudes below the wing when the undercarriage is retracted. Douglas D.C.2 monoplane. This is made in two inde pendent units which retract upward and forward into the engine nacelles. Each wheel is carried in a fork formed by two shock-absorber struts. A hydraulic pump, ac cessible to. either the pilot or his assistant, raises the wheels in twenty-five seconds and lowers them in twenty seconds. A counter balanced mechanism facilitates hand pumping, and the complications of electric drive are eliminated. The brake operation remains positive with the wheels retracted. When the gear is in the "up" position the axles come up against pillow blocks built into the nacelle structure. The wheels protrude ap proximately nine inches, and the machine may be landed with the undercarriage up with only the air screw tips suffering damage. In fact, since the wheels when retracted are even farther forward of the centre of gravity than when ex tended, there is no tendency to nose over during such a landing. The first of the standard British retractile undercarriages to fold laterally was that fitted to the British Klemm '' Eagle '' cantilever monoplane. Another excellent American gear is that fitted to the In this undercarriage the Dunlop medium-pressure wheels, cr-J WINDING HANDLE BEVEL GEAR "fe^ite^ First of the standard British gears to retract laterally, that of the British Klemm "Eagle" (illustrated in detail on the left) embodies the neat locking device shown in the small sketch above.
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