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Aviation History
1926
1926 - 0144.PDF
MARCH 4, 1926 are operated by short rockers, while the exhaust valves are operated directly from the overhead camshaft. The valve stems have been considerably lengthened so as to give room for longer valve springs, the lift of the valves being rather greater than in the " Puma." Aluminium alloy pistons of new design are employed, and although they are of larger bore, they are actually lighter than the original. This also applies to other reciprocating directly to the induction manifold, which is cast integral with the cylinder head block, and it was found that in cold weather some slight trouble was experienced with freezing. This was overcome, in the first engines as fitted in a D.H.9, by a sheet aluminium cowling, but in all subsequent " Nimbus" engines the carburettor will be bolted direct to a water- jacketed inlet cast integral with the jacket, and then the need for a special cowling will disappear. THE A.D.C. " NIMBUS " AERO ENGINE : These photographs show—Above, inlet and exhaust sides of a cylinder head block. On the left, a view inside a cylinder head block, showing the large water spaces surrounding the valves. On the right, an inlet valve with its springs, washers, etc. The photograph in the lower left-hand corner shows a water-jacket block, with its cylinder head block. In future engines the water-jacket casting will have cast with it a water-jacketed inlet. On the right, a steel cylinder liner and its aluminium piston. parts which, in spite of the greater power developed, are lighter than those of the original engine. The overhead valve gear remains substantially the same as that of the " Puma," as does also the crankshaft. The connecting-rods are of the same type as those of the original engine, but are of slightly different dimensions. The induction system is a particularly simple one, with two carburettors feeding three cylinders each. In the first "Nimbus" engines built, the carburettors did not bolt At the moment of writing, the " Nimbus " has not been subjected to the actual Air Ministry type tests, but in the course of the makers' own tests, two of these engines have been thoroughly tried out, the runs including two non-stop runs of 10 hours each under Air Ministry supervision. What with tests on the Heenan and Froude brake, the calibrated airscrew, and in actual flight on board a D.H.9, the first two engines have between them completed something like 150 hours' funning, 124
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