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Aviation History
1937
1937 - 0395.PDF
FEBRUARY II, 1937. FLIGHT. »55 AERONAUTICAL HYDRAULICS Capabilities and Possibilities of Lockheed Hydraulic Actua tion : The "Air- draulic " Strut y s POOT OUTH PETB.OL COCK "* PORT LANDiNC V LIGHT T^^ftL. I 1 / R'JDDES, T21MWER- c A project for the hydraulic operation of a large number of items on a hypothetical twin- engined bomber. / STA09 0 At LANDING /' LIGHT // f~ THE continued encroachment of mechanical devices into even the remotest portions of large modern aircraft seems inevitable. In smaller machines, too, the "gadget merchant' is leaving his mark. The extra convenience ofiered bv these new contrivances is necessarily accompanied by complication, and it devolves upon the designers of accessor-,' gear to limit that complication as much as is humanly possible without sacrificing dependability or demanding anv great phvsical or mental effort. The Automotive products Co., Ltd., of Leamington Spa, Warwickshire, are applying their experience in the manufacture ot Lockheed hydraulic brakes to the production of remote controls for aircraft use, and have developed a series of pumps, jacks, indicators, etc.. with some interesting features. The employment of a simple hydraulic jack in conjunction with a power-driven pump confers simplicity, any desired speed ratio (depending on the proportioning of the hydraulic units) and, through the application of valves, the ability to make the mechanism reversible or irreversible. It is possible to install the Lockheed undercarriage jacks at any angle and, thanks to flexible connections, to swing them through any arc. One type has a mechanical locking device at the inner extremity of its stroke, while a second provides a lock at each end. "The mechanical lock, it is claimed, en ables an end load to be carried directly by the structure of the jacP, ensuring that anv rupturing" of the fluid system that may occur as the result of aa accident shall not afiect the safety of the aircraft. The jacks may be used as part of an electric circuit which is completed by operating units (a hand pump, connection with a hydraulic flap control, or an engine-driven pump), there being appropriate indicating instru ments in the pilot's cockpit. In the Lockheed flap control system the jack or jacks are attached directly to the flap. Where the hinge movement of • flap is sufficiently large as to require considerable effort on the part of the pilot the flap gear can be operated by the Lockheed engine driven pump. The alternative means of operation is through a hand pump unit, the handle grip of which controls the flap. To lower the flap the handle must be twisted, and pumped, and to return it, twisied in the opposite direction and pumped again. The Lockheed engine-driven pump has no crankshaft, con necting rods, swash-plates or kindred mechanism. This pump, or the stand-by hand-operated unit, may be connected at will with any of the hydraulically operated units (undercarriage jack, tail wheel jack, flap jack, etc.) by a selector valve under the control of the pilot. A device giving both visual and audible signals constitutes a safeguard against human forgetfulness in raising or lower ing the unden arriage. When the landing gear is down a green light is shown, when in course of retraction an orange light appears, and when up a red .light in addition to the orange light is flashed. Furthermore, a control box in con nection with the A S.l ensures that when the air speed drops to approximately that of the machine when about to land a bell will ring should the under carriage be retracted. Apart from gear suitable for the operation of undercarriages, flaps, etc., which require to be moved from one extreme position to an other, Lockheeds are offering a range of controls suitable for use with devices calling for adjust ment within close limits, e.g., trimming tabs, radiator shutters, cooling flaps, etc. Essentially ths system employed consists ol a master hydraulic transmitter de signed so that according to the direction in which the hand wheel is rotated fluid is pumped in One direction or the other. The slave units used in conjunction with this transmitter are simple piston- cylinder units giving positive actuation in both directions. A special automatic mechanical lock ing device is incorporated which is freed automatically upon the application of pressure. A selector valve ia employed so that the transmitter may be used with ;i number of slave units. Electrical The simplicity of the Lockheed "Airdraulic" leg can bs gathered from this sketch.
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