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!
|