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Aviation History
1929
1929 - 0015.PDF
JANUARY 3, 1929 THE POBJOY P.I. LIGHT PLANE ENGINE AT the time of the 1926 Light 'Plane Competition at Lympne brief reference was made to the Pobjoy engine, which was designed by Capt. D. R. Pobjoy for the Cranwell C.L.A.4 Jight 'plan*. Since that time considerable development work has been carried out with this engine, and just recently one has successfully passed the Air Ministry Type Test for Civil Engines. This week we are able to give some brief particulars, together with illustrations of Pobjoy P.I., a 60-h.p. 7-cyl. ;iir-cooled radial of robust construction, small size, and light weight. A high power is obtained by running the engine at 3,000 r.p.m. and driving the air screw through a simple reduction gear. Its seven small pistons running at comparatively high revolutions permit the engine to operate with complete absence of vibration, and produce a very smooth reaction on the mounting. In spite of its speed of revolution, the engine shows a high degree of reliability and durability, as a result of careful attention to bearing and detail design. The Type Test engine had previously done about 120 hours full speed running before being submitted for the type test ; very little wear, however, has taken place. The official report on the strip inspection will be published in due course. New piston rings were fitted some time previous to commencing the Type Test. It appears that they were scarcely run in, as the final power curve shows that the engine de- veloped 1J h.p. more at the end of the tests, than at the commencement. The oil consumption also steadily diminished and the average for the last 20 hours was 1 J pints per hour. The exhaust valves, as viewed through the exhaust ports, remained black throughout the tests ; their seats are in excellent condition. Starting by hand from cold is easy, no priming being required ; this is due to the design of induction system, the -.mail bulk of the engine and to the fact that the magnetos run much quicker than the airscrew. A hand starter to be operated from the aeroplane cockpit has )>eon designed for the engine, but has not yet been fitted. General Design and Construction The aluminium crankcase is in four parts, as will be seen from the installation drawing. The two central portions carry the crankshaft on roller bearings. The front cover houses the reduction gear and the front plain bearing of the crankshaft. The rear cover carries the cam gear, the mag- netos and the induction spider and carburettor. The crankshaft is in two parts and the crankpin is case hardened. On the latter runs the big-end floating bush of plain bronze, which in turn runs in the hardened ring of the master-rod. The six auxiliary connecting rods are linked to this ringby floating case-hardened wrist pins. The aluminium pistons are of the slipper type and providedwith two rings ; the hardened gudgeon pin floats in its rod and its piston. The cylinder barrels are of steel, and are screwed into the cast aluminium heads. There are two valves per cylinder. A front view of the Pobjoy P.I. light 'plane engine. -O- "O- O O The PobjojvP.I. : A 5- c yl. air- cooled radial engine of 60 h.p. for light 'planes, which recently passed its Air Ministry Type Test. •o- -<>- o- -o- -o- D2
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