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Aviation History
1937
1937 - 2136.PDF
130 FLIGHT. JULY 29, 1937. THE ASPIN ENGINE in DETAIL Full Description of an Uncon ventional Flat-four Aero Unit for Which Remarkable Per formance Figures are Claimed DETAILS of the Aspin engine which have already appeared in Flight have indicated that this unit was of more than passing interest, and that it embodied prin ciples of construction which appeared to overcome many of the difficulties associated with internal combustion engines as at present accepted. The claims made for the engine suggested that very high volumetric and thermal efficiencies had been attained, while mechanical efficiency and reliability appeared to be vouched for by the fact that exceedingly high rates of revolution were possible, and, indeed, were a feature of the normal perform ance. In deference to the wishes of F. M. Aspin, Ltd., Egyptian Mills, Elton, Bury, Lanes, no more than brief general remarks on the performance and some external photographs were pub lished. At the same time, a Flight representative has been allowed to study the drawings and the components of test and experimental engines as development proceeded, and the con clusion was reached that the somewhat startling claims were by no means exaggerated, and that the Aspin engine did in fact break new ground. Moreover, it did not appear to be in the freak category, but was evolved on sound and logical lines. It is now possible to give a full description of the aero engine, together with detail drawings which reveal not only the unusual design, but the remarkable simplicity of construc tion. At first glance it might be said to be a rotary-valve engine, but this would not be by any means an adequate description, for the rotary valve arrangement is rather incidental to the use of a rotary combustion chamber, upon which most of the thermal efficiency hinges. This rotary combustion chamber is in the form of a cup or cell set eccentrically in a cone, the base of which is the top of the cylinder. The cone is rotated by gearing and a port in its side sweeps over the inlet and exhaust ports in the cylinder head, putting them in communi cation with the combustion chamber. The sparking plug is This rear view of tha Aspin flat-four aero engine shows the mag netos and induction system (with Claudel Hobson carburettor and a mixing fan). fitted into the cylinder head, and therefore is not directly in connection with the combustion chamber except when the port in the cone is opposite the plug hole. Here, again, is a key feature of tne engine. One of the claims made was that even with compression ratios of the order of 10 to i and higher the engine would run indefinitely at 8,000 r.p.m. on a " pot "- insulator touring plug, and this masking of the plug from the combustion chamber, except at the moment of ignition, pro vides the explanation. So much for the general arrangement of the cylinder head. Mechanical efficiency and reliability are factors largely dependent upon the arrangement above described; there are no heavy spring loads to deal with, nor have the reciprocating masses of poppet valves to be considered. The rotary chamber is merely an addition to " flywheel weight " and calls for very little power to drive, since the cone is carried by roller bearings and does not make frictional contact with the cylinder head. Thermal efficiency depends upon the shape and location of (Left) The Aspin engine partially dismantled. The small gear wheel is driven by the horizontal shaft which can be seen emerg ing from the rear of the cylinders. The two other gear wheels drive the rotating combustion heads. (Above) The head, with one rotary member in place and the other removed, revealing the ports. Note the oil groove running up the conical face.
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