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Aviation History
1939
1939 - 0436.PDF
/ FLIGHT. FEBRUARY I6, 1939 How the sleeve valve works— pictures from a slow-motion film. White rings represent the cylinder ports. (1) Beginning of expansion stroke. (2) Expansion stroke. (3) Opening of exhaust ports. (4-5) Exhaust stroke. (6) Opening of inlet ports. (7) T.D.C., beginning of induction stroke. (8-10) Induc tion stroke. (11) Closing of inlet ports. (12-13) Compression stroke. TABLE II. Comparative Data of Sleeve anil Poppet-Valve Cylinders. Cylinder type and valving ... Bore and stroke, in. Displacement, cu. in. Cylinder assembly weight, lb. Cooling fin area, sq. in. Sustained peak power naturally aspirated 87-octane fuel: B.m.e.p., lb./sq. in. K.p.m. B.h.p./sq. in. piston area... Mean piston speed, ft./min. Sustained power lor 100 hours octane fuel: B.m.e.p., lb./sq. in. R.p.m. B.h.p./sq. in. piston area... Mean piston speed, ft./min. 100- SLEEVE 5 X H 105.8 31.5 1,9-20 138 3,600 3.37 3,220 240 3,300 5.36 2,960 2 POPPET OVERHEAD CAMSHAFT 42 44 5x5 98.2 8 with double camshaft 2 with single camshaft 1,660 121 3,300 2.525 2,750 No development on 100 octane fuel He pointed out that it should be remembered when analys ing the above performance figures that the sleeve valve was still a relatively new device. As an indication that interesting developments might be expected, Mr. Fedden instanced a recent test designed to dis cover the limit of output of a sleeve-valve unit. The test was inconclusive because the limit proved unattainable with the supercharger available, but the results were, nevertheless, outstanding. With a boost of 14 lb./sq. in. and a cylinder of 168.8 cu. in. capacity, the b.m.e.p. obtained was 305 lb./sq. in. at 2,400 r.p.m. and 272 lb./sq. in. at 3,000 r.p.m. The corresponding powers per unit of piston area were 6.0 b.h.p./ sq. in. and 6.7 b.h.p./sq. in. respectively. If the above figures were correct for the power absorbed by the separately driven blower, the b.m.e.p. was 276 lb./sq. in. at 2,400 r.p.m. and 245 lb./sq. in. at 3,000 r.p.m., While the powers per unit of piston area were 5.4 b.h.p./sq. in. and 6.0 b.h.p./ o°2IO 3 I r X * -so to -J FUEL 1 1 CYUNOER HEAp TCMPEF CONJUM pTCN. *TURE ''J / \ \ 460 470 4SO 490 SOO 510 520 530 940 SSO S«0 BHP - Fuel consumption loop of the Perseus X at 2,400 r.p.m. sq. in. respectively. Mr. Fedden thought that the powers obtained could not be approached with a poppet-valve unit under similar conditions. He concluded from this test that the main obstacles to the immediate adoption of greatly increased ratings for sleeve- valve engines were the mechanical and lubrication difficulties in converting the gas pressure to a tangential force and the next move appeared to lie not so much with the designer as with the metallurgist and lubrication specialist. Mr. Fedden explained that the cylinder of the Bristol sleeve- valve engines has two exhaust ports in front and three inlet ports at the rear. The sleeve has only four ports, one of which uncovers alternately an exhaust and an inlet port in the cylinder. The sleeve is provided with a spherically seated bearing, which can swivel so as to remain in line with the pin of a small crank. The drive is performed by the rotation and sliding motion of the pin in the bearing and by the swivel ling motion of the latter in its housing. The small cranks are driven by a train of gears inside the front cover. Extensive research on cooling was carried out and led to satisfactory performance. The first big advance was made in 1930, when the cylinder head was provided with a fin arrangement which incorporated a baffle directing the air over the crown of the head and producing turbulent circulation around the sparking plugs. The 1930 general layout had been retained ever since and had been developed to the present form with radial finning, giving circularity under running condi tions together with cooling adequate for all power outputs attained so far. The present head was a die-casting in Y-alloy. It was interesting to note that the 1930 type of head might be regarded as the forerunner of complete pressure baffling
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