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Aviation History
1942
1942 - 1398.PDF
16 FLIGHT JULY 2ND- IO42 KEEPING THEM FLYING How British Overseas Airways Maintain and Repair Their Aircraft and Equipment ONE of the many problems confronting those respon sible for the maintenance and repair of aircraft, air craft engines, airscrews, and ancillary equipment, is that of providing the highly specialised plant, tools and test rigs necessary for the efficient handling, processing, and testing of the many varied and sometimes complicated components which form part of the modern aircraft. At the very Outset; British Overseas Airways Corpora tion, which has to operate throughout the world a large and fast air fleet, operating at a high standard of efficiency, encountered problems of considerable difficulty in respect of first-class, easy-to-handle, servicing equipment. It can truthfully be said that the evolution of the aircraft has outpaced the development of the tools and servicing equipment which contribute in no small measure to its speedy and efficient turn-round or overhaul, and which, besides enabling the aircraft to spend a greater proportion of its life in its natural element, also add to economical operation by reducing maintenance costs The market offering of proprietary articles of plant, tools and equipment for such purposes is extremely restricted, and aircraft and aircraft engine manufacturers do not, as a rule, give much consideration to the detailed manipula tion of their products after they have left the factory mainly because the problems of production are, to a large extent, divorced itoxn those of maintenance, and more often than not it is only the operator's experience of a component under varied conditions of environment and climate which enables him to evolve special equipment needed for efficient servicing. The Service Equipment Section The Corporation, therefore, decided to form, as an ad junct to the Service Engineering Department, a Service Equipment Section, which would be entirely devoted to the design and development of special equipment for main tenance and overhaul. This Section, under the control of Mr. F. S. Saunders, commenced by turning out equipment which, due to lack of demand, could not be purchased outside. Later, the scope of its activities increased until to day it has become a\self-contained factory, comprising drawing and printing offices, stores, machine, fitting, erec tion, and construction shops. Here, apart from a large variety of finished articles, are produced rigs for testing, tools, jigs and fixtures, and other specialised equipment, some of which have been adopted by contractors controlled by the Ministry of Aircraft Production. • A number of designs, which range from a device for descaling exhaust valves, to a comprehensive test rig for automatic pilots, have been patented. Of the wide range of products of the Service Engineering Section, the following are some of the more interesting types of rigs, from the many which have been evolved: — The Universal Instrument Stand was produced to test instruments'and units not included with "the engines, such as Sperry Autopilot instruments, oil pumps, vacuum pumps, oil gauges, temperature gauges, flow meters and all the hundred and one devices employed to make the aircraft function properly. This is done by using a variable speed hydraulic unit powered by an electric motor, which drives i universal head housing the various types of pumps to be tested. Further, the rig is capable of checking gauges of all descriptions under the dead pressure testing method ; automatic pilot instruments for functioning, temperature gauges, thermal couples, flow meters and many other units. Then, the Universal Airscrew Stand was designed to receive the airscrew straight from the engine and to trans port it in a vertical position direct to the airscrew repair ,shop on its own wheels. By means of a handle and rotat ing mechanism the airscrew can be turned from the vertical to the horizontal position for stripping purposes. Assembly and blade angle checking, torque loading, etc., can also be carried out, and the airscrew can be stored on the stand in the minimum amount of floor space. An Airscrew Blade Twisting Machine for Preformed Shapes has been constructed to reset the destroyed helix angle in airscrews which have become damaged. It is a hydraulically controlled unit with two double-acting Cylin ders, each anchored to a moving head, and by the operation of a single handle and control valve the blade can be brought back once more to its correct helix angle. In con junction with this machine is a thirty-ton hydraulic press of the open mouth type, which—it may be of interest to note—was not only designed but also actually constructed in the equipment shop, owing to delay in outside deliveries of parts. Straightening Airscrew Blades During the straightening of the blade through its longi tudinal length the pitch angle is liable to be destroyed. To prevent this occurring an automatic press tool was designed to be attached to the press ram. This tool, which is operated automatically by direct contact with the object to be pressed, maintains the pitch angle under any con ditions, whether the sections be thick or thin, curved or- flat. To ensure the correct functioning of the airscrew before service, a test bed was devised. The Hydromatic or Con stant Speed Airscrew and Constant Speed Unit Test Stand is capable of constant-speeding the airscrew for pitch change whilst it is standing still, feathering and unfeather- ing, checking up on the dome assembly for proper working of valves, and pressure-testing the complete unit. It also tests the constant-speed unit for governing, accurate manual action and internal pressure, as well as for flow or volume of oil. Since the bed is fitted with complicated and numerous controls, flow meters, gauges and tach ometers, which have to be adjusted in addition to the necessary function tests, full instructions are inscribed on a cylinder with an internal drum. This cylinder is pro vided with small oblong windows, shewing only the remarks applicable to the particular test in progress. The test required is located by rotating the disc attached to the central drum against a pointer, indicating the test to be carried out, a spring-loaded ball catch locking the central drum in position. Thus, the operator is told what gauges to read, how to adjust them on each cock for pressure, whether the cock should be closed or open, the speed the tachometer should register, what flow to expect, and what should be expected of the test being performed. The speed and the power of the rig is supplied by a variable speed 6 h.p. A.C. motor, driving a gear box to which is anchored, at one end, the oil pumps, tachometer drive, etc., and at the other the constant speed control unit. Evolutions Simulated Another test bed, the Autopilot, Horizon and Gyro Rudder Test Rig is so constructed as to ensure that the instruments behave in precisely the same manner as they would, were the aircraft banking, climbing, diving or yaw ing. The tests must be extremely stringent, seeing that the instruments are called upon to perform most accurately in flight. These are also tested for recovery by the bed, which is designed to function at angles from three to fifteen degrees, and to reverse the motion each minute. The apparatus is operated by a single control. As a last example, a Plug Testing Machine and Servicing Equipment has been evolved. With this equipment aircraft engine sparking plugs can be rapidly tested for efficient Continued at joot of next page)
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