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Aviation History
1925
1925 - 0099.PDF
FEBRUARY 19, 1925 INCREASING AERO-ENGINE POWER AT ALTITUDEL Bristol "Jupiter" Variable-Timing Gear HE possibility of increasing the performance of an aero be employed. By this means ground level power would be •engine at altitude by using a variable-timing gear, which can obtained up to the height at which the normal timing could .be worked by the pilot as the machine ascends, has been be employed. From this height onwards, the horse-power of IS H H 0 0 0 E 0 E 0 H 0 H El 0 E 0 0 0 H E 0 0 E 0 E E The Bristol Vari- able Timing Gear : Front of the " Jupiter " showing the simple levers by means of which the gear is operated. EBB HEBE realised for some time. Towards the end of the War, when greater performance at altitude was urgently needed, a scheme was put forward by Mr. Ricardo. He pointed out that by using a variable timing gear in conjunction with a high compression ratio and employing the simple expedient of closing the inlet valve late, so that compression would not start until well up the compression stroke when near ground level, then the timing could be gradually advanced by the pilot, until at a predetermined altitude normal timing could the engine would, of course, fall off, as with normal compression ratio engines, but there would be a considerable increase of horse-power available at all altitudes, and a marked fuel economy. This scheme for increasing the engine performance at altitude is far preferable to an over-size high-compression throttled engine, insomuch as with the former certain definite advantages are secured, such as a rising torque curve, a short compression and long expansion stroke, with no chance of pre-ignition and detonation, etc. Owing to difficulties on H0HE E E 0 0 BEE EBBEE 99
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