itted
to their first practicable flying machine the engine which made the
historic first aeroplane flight; this engine developed 30 horse-power,
and weighed only about 7 lbs. per horse-power developed, its design and
workmanship being far ahead of any previous design in this respect, with
the exception of the remarkable engine, designed by Manly, installed in
Langley's ill-fated aeroplane--or 'aerodrome,' as he preferred to call
it--tried in 1903.

The light weight of the Wright brothers' engine did not necessitate a
high number of revolutions per minute to get the requisite power; the
speed was only 1,300 revolutions per minute, which, with a piston
stroke of 3.94 inches, was quite moderate. Four cylinders were used,
the cylinder diameter being 4.42 inches; the engine was of the
vertical type, arranged to drive two propellers at a rate of about 350
revolutions per minute, gearing being accomplished by means of chain
drive from crank-shaft end to propeller spindle.

The methods adopted by the Wrights for obtaining a light-weight engine
were of considerable interest, in view of the fact that the honour
of first achieving flight by means of the driven plane belongs to
them--unless Ader actually flew as he claimed. The cylinders of this
first Wright engine were separate castings of steel, and only the
barrels were jacketed, this being done by fixing loose, thin aluminium
covers round the outside of each cylinder. The combustion head and valve
pockets were cast together with the cylinder barrel, and were not water
cooled. The inlet valves were of the automatic type, arranged on the
tops of the cylinders, while the exhaust valves were also overhead,
operated by rockers and push-rods. The pistons and piston rings were
of the ordinary type, made of cast-iron, and the connecting rods were
circular in form, with a hole drilled down the middle of each to reduce
the weight.

Necessity for increasing power and ever lighter weight in relation to
the power produced has led to the evolution of a number of different
designs of internal combustion engines. It was quickly realised that
increasing the number of cylinders on an engine was a better way of
getting more power than that of increasing the cylinder diameter, as the
greater number of cylinders gives better torque-even turning effect--as
well as keeping down the weight--this latter because the bigger
cylinders must be more stoutly constructed than the small sizes; this
fact ha