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Aviation History
1928
1928 - 1184.PDF
102 SUPPLEMENT TO FLIGHT DECEMBER 27, 1928 THE AIRCRAFT ENGINEER Fig. 3. Froude Dynamometer testing a Rolls-Royce "Condor" Engine, and, on right, Fig. 4, testing a Napier "Lion.' testing large internal-combustion engines such as Marine Diesels of immense power. As applied to an aircraft engine, the load can be adjusted by a single handwheel while running, to very fine limits of speed and torque, and we have observed running installations showing even7 effect of engine tuning adjustment, even to the extent of 1 b.h.p. in 500. Fig. 3 shows one of these dynamo- meters testing a " Condor " engine, type IIIA at the works of Rolls Royce. Ltd.. Derby, and Fig. 4 a similar dynamo- meter testing a " Lion ' aircraft engine at the works of D. Napier & Sons. Ltd.. Acton. A problem arises, in testing air-cooled aircraft engines. connected with ventilation. It is, of course, essential that the engine should be allowed to work in a stream of air flowing, at velocities equivalent to those experienced in flight, over the heat-radiating surfaces. In the absence of adequate provision for ventilation, the engine would fail to operate satisfactorily and the brake horse-power developed would be appreciably under standard. In cases where the engines to be tested are practically all of the same kind running at substantially similar speeds, although not necessarily developing similar powers, a satis- factory dynamometer is the " Heenan-Fell " air brake, a description of which has been published elsewhere. This is shown in cross section in Fig. 5, from which it will be seen that the engine drives a centrifugal fan impeller blowing air at high velocity over the engine, which thereby provides its own ventilating blast. Power is regulated by a shutter controlled from the exterior of the casing and sliding over the periphery of the impeller, so as to vary the volume of air discharged and therefore the power consumed. The power is measured by torque reaction upon the erankcase of the engine. In many cases, however, the range of engine sizes is so considerable that a more flexible plant becomes necessary. The introduction of gearing into the design of an engine which has previously been made for direct drive, ehanges'entirely the speed and torque without necessarily altering the power. High-performance engines again require a more generous blast of cooling air than those produced for commercial purposes. Thus, the conditions of the test are directly affected and provision must be made to meet them. The Bristol Aeroplane Co. have purchased from Heenan and Froude, Ltd., specialists in engine testing plant, a number of wind tunnels, the design of which offers a satisfactory solution of these problems. An illustration of one of the wind tunnels recently set tojwork at Bristol is shown in Fig. ti. A Bristol "' Jupiter ': aero engine is mounted upon a Fig. 5. Cross-sectional Arrangement of Heenan-Fell Air Brake Dynamometer.
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