By Geoffrey Rodliffe
Richard Pearse constructed several internal combustion engines: three of these are still in existence, the earliest one probably being the most interesting. It is also suggested that he built one multi-cylinderi- engine for farm use, but no trace of this now remains. In addition his motorcycle, with a single cylinder engine built from scrap parts, is on exhibition at the Museum of Transport and Technology.
Construction of the First Engine (1898 / 1903)
The only practical examples available to Pearse were hot bulb oil and traction engines. He made use of the double action principle, which was a feature of traction engines, and combined this with the design of internal combustion engines about which he had read. The result was an aero engine of completely original design. The 1906 patent specification mentions a two cylinder engine and describes one similar to that recovered by Mr Ogilvie during 1971. This engine is obviously the one used during the 1900/05 period. Until this was found it was assumed that the first serious engine Pearse had built was the four cylinder motor now exhibited at M.0.T.A.T. His first engine was obviously constructed from the most suitable scrap metals to be found in the locality of his home. We are told that for the cylinders he used cast iron soil drainpipe with an internal diameter of 4", which was being imported for land drainage. It is interesting to note that present day cylinder liners are still being made of cast iron.
By using both ends of a cylinder to provide power strokes, twice the power could be obtained from one cylinder and the weight halved. Pearse used two cylinders about a foot apart, with a crosshead fitted in a frame-work between them. His early engine did not have a crankcase, the reciprocating parts all being exposed. The carburettors, like those on a later engine, could well have been of a wick type. The inlet valves were enclosed in the induction pipes, were spring loaded in the closed position and opened automatically on the induction stroke.
It is probable that the oil mentioned by Pearse in his patent application was paraffin. This was supplied to a tin can carburettor system of his own devising through vapourising pipes running around the cylinders. It is also probable that the motor ran at one fixed r.p.m. and was started up on full power. He did not provide water cooling but mentioned air blast from the propeller helping to cool the cylinders. Exhaust valves were mechanically operated by means of pushrods and toggles, the drive being taken from the crankshaft by means of one large and one small bicycle sprocket which gave two to one reduction. Little is known about the ignition system. Pearse is known to have had considerable help from a local engineer, who assisted him in the manufacture of spark plugs and most probably with other aspects of the ignition system.
The engine and propeller were tested mounted on a framework and fitted with a spring balance. This enabled him to judge the varying thrust developed by adjustments of the propeller blade angles. The two cylinder engine was first examined by an expert in the aviation world, who estimated that Pearse could have obtained at least 15 horse power. This was calculated on a conservative basis. As we have no record of the engine r.p.m. which Pearse obtained, possibly he did not have the means of checking this and could himself only make a guess.
It is obvious that his first engine would not have been capable of running for more than a few minutes at a time, due to lack of cooling and lubrication. However, the short bursts of power obtained were of sufficient duration to get the plane airborne for brief periods. Once having reached this stage, it must have been very frustrating for him to envisage the further work and finance required even to develop his engine to the stage where he could fly to a neighboring farm and return maybe with a sack of potatoes!