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Aviation History
1928
1928 - 1185.PDF
DECEMBER 27, 1928 103 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT re^td^enS f^heTntinf "Ion" ^t T& " ^ ^T*' "* hl ^ °" ™ktln* ^tem are ****** that under the influl* oHSSe^^reaction the r^' " ? CO°lerS ^ eleCtriCal ^^ ^^ and StrainerS- rotate to a limited extent ab,,,,tT reactlOn the ucradle ™n FoT runmng-m new engines and starting-up purposes, thev shaft. Spring loaded Lc£rrl*e, T *™ % ^^ HUppIy & SpeoiaUy ^S1^ electric m<>t«r Connected o the the cradlePand cushion ftSt H ^ -°f free end of the d^am«meter shaft through a self-disengaging a (.u..luon the inequalities of torque which arise jaw clutch and having various safeguarding devices which Fig. 6. Froude Wind Tunnel Testing Plant at the Works of the Bristol Aeroplane Co., Ltd., and, on right, Fig. 7. Centrifugal Fan and Driving Motor. from the impulses of the engine. The complete cradle and engine can be racked towards or away from the open mouth of a large wind tunnel, so that in setting up and adjustment. prior to or following a test, access to the engine is unob- structed. After being mounted upon the cradle, the engine is fitted with an adapter enabling the propeller shaft to be connected through a flexible cardan shaft to a transmission shaft supported in ball bearings, which delivers the power to a "Froude" hydraulic dynamometer. I'nder running condi- tions, the entire power of the engine is absorbed and accurately measured by this machine. Running over the top of the dynamometer and thence bv easy bends towards the open orifice facing the engine, is a large wind tunnel constructed in heavy steel plate conveying air from a high speed, high pressure " Heenan " centrifugal fan designed esjteciallv to meet the exceptional requirements of test shop practice, and capable of running continuously under the heavy duties created by centrifugal force and dynamic load. A close-up view of the fan and its driving motor appears in Fig. 7. The entire construction is heavy and substantial and the freedom from vibration at all loads and speeds is extraordinary. The last-mentioned illustration shows an electric- motor of the variable speed pattern rated for 300 maximum B.H.P. and capable of giving air velocities over the engine of well over 130 m.p.h. In an adjacent test shop of the Bristol Aeroplane Co., Heenan and Froude have erected another wind tunnel driven by a variable speed motor of 550 b.h.p. and giving wind speeds past the engine well in excess of 180 m.p.h. On overload, the official test conducted shortly after starting up this plant showed wind speeds of 197 m'.p.h. It does not, of course, follow that the high wind speeds cited above are commonly used to pass out engines. Normal testing demands an expenditure of fan power in this particular wind tunnel of the order of 200 b.h.p.. but for high-perfor- mance engines and for a variety of development work, the ability to command very high wind speeds puts the Bristol Aeroplane Co. into an exceptional position and enables them to investigate features of engine design which they would otherwise be severely handicapped in doing. With their wind tunnels, Heenan and Froude supply very complete equipment and accessories, including such items as engine control levers, switches, gauges, thermometers, air speed indicators, tachometers, speed counters, etc. For fuel ' supply and measurement are included petrol tanks, strainers, 1086 protect the bearing surfaces of the engines against undue load while they are being run in. This type of wind tunnel testing plant appeals to a very wide circle of aircraft engine users owing to the enormous Fig. 8. Heenan V-type Water Cooler. range of powers and speeds and types of engines with which a single plant will deal. For instance, it is commonly possible to test engines varying in power between 80 and 1,500 b.h.p., whether they are air-cooled, water-cooled, direct drive or gear drive, and in some cases whether they run in the right- hand or left-hand direction of rotation. The convenience
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