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into vapours。 These vapours are sent through a series of pipes surrounded
with cold water； where they are cooled and become liquid again。 Petrol is
a mixture of these lighter products of the oil。
If petrol be placed in the air it readily turns into a vapour； and this
vapour is extremely inflammable。 For this reason petrol is always kept in
sealed tins； and very large quantities are not allowed to be stored near
large towns。 The greatest care has to be exercised in the use of this
〃unsafe〃 spirit。 For example； it is most dangerous to smoke when filling a
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tank with petrol； or to use the spirit near a naked light。 Many motor…cars
have been set on fire through the petrol leaking out of the tank in which it
is carried。
The tank which contains the petrol is placed under one of the seats of
the motor…car； or at the rear； if in use on a motor…cycle it is arranged along
the top bar of the frame； just in front of the driver。 This tank is connected
to the 〃carburettor〃； a little vessel having a small nozzle projecting
upwards in its centre。 The petrol trickles from the tank into the carburettor；
and is kept at a constant level by means of a float which acts in a very
similar way to the ballcock of a water cistern。
The carburettor is connected to the cylinder of the engine by another
pipe； and there is valve which is opened by the engine itself and is closed
by a spring。 By an ingenious contrivance the valve is opened when the
piston moves out of the cylinder； and a vacuum is created behind it and in
the carburettor。 This carries a fine spray of petrol to be sucked up through
the nozzle。 Air is also sucked into the carburettor； and the mixture of air
and petrol spray produces an inflammable vapour which is drawn straight
into the cylinder of the engine。
As soon as the piston moves back； the inlet valve is automatically
closed and the vapour is compressed into the top of the cylinder。 This is
exploded by an electric spatk； which is passed between two points inside
the cylinder； and the force of the explosion drives the piston outwards
again。 On its return the 〃exhaust〃 or burnt gases are driven out through
another valve； known as the 〃exhaust〃 valve。
Whether the engine has two； four； or six cylinders； the car is propelled
in a similar way for all the pistons assist in turning one shaft； called the
engine shaft； which runs along the centre of the car to the back axle。
The rapid explosions in the cylinder produce great heat； and the
cylinders are kept cool by circulating water round them。 When the water
has become very hot it passes through a number of pipes； called the
〃radiator〃； placed in front of the car； the cold air rushing between the coils
cools the water； so that it can be used over and over again。
No water is needed for the engine of a motor cycle。 You will notice
that the cylinders are enclosed by wide rings of metal； and these rings are
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THE MASTERY OF THE AIR
quite sufficient to radiate the heat as quickly as it is generated。
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CHAPTER XXII The Aeroplane Engine
We have seen that a very important part of the internal…combustion
engine； as used on the motor…car； is the radiator； which prevents the engine
from becoming overheated and thus ceasing to work。 The higher the speed
at which the engine runs the hotter does it become； and the greater the
necessity for an efficient cooling apparatus。
But the motor on an aeroplane has to do much harder work than the
motor used for driving the motor…car； while it maintains a much higher
speed。 Thus there is an even greater tendency for it to become overheated；
and the great problem which inventors of aeroplane engines have had to
face is the construction of a light but powerful engine equipped with some
apparatus for keeping it cool。
Many different forms of aeroplane engines have been invented during
the last few years。 Some inventors preferred the radiator system of cooling
the engine； but the tank containing the water； and the radiator itself； added
considerably to the weight of the motor； and this； of course； was a serious
drawback to its employment。
But in 1909 there appeared a most ingeniously…constructed engine
which was destined to take a very prominent part in the progress of
aviation。 This was the famous 〃Gnome〃 engine； by means of which races
almost innumerable have been won； and amazing records established。
We have already referred to the engine shaft of the motor…car； which is
revolved by the pistons of the various fixed cylinders。 In all aeroplane
engines which had appeared before the Gnome the same principle of
construction had been adopted； that is to say； the cylinders were fixed； and
the engine shaft revolved。
But in the Gnome engine the reverse order of things takes place； the
shaft is fixed； and the cylinders fly round it at a tremendous speed。 Thus
the rapid whirl in the air keeps the engine cool； and cumbersome tanks and
unwieldy radiators can be dispensed with。 This arrangement enabled the
engine to be made very light and yet be of greater horse…power than that
attained by previously…existing engines。
A further very important characteristic of the rotary…cylinder engine is
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that no flywheel is used； in a stationary engine it has been found necessary
to have a fly…wheel in addition to the propeller。 The rotary…cylinder engine
acts as its own fly…wheel； thus again saving considerable weight。
The new engine astonished experts when they first examined it； and all
sorts of disasters to it were predicted。 It was of such revolutionary design
that wiseacres shook their heads and said that any pilot who used it would
be constantly in trouble with it。 But during the last few years it has passed
from one triumph to another； commencing with a long…distance record
established by Henri Farman at Rheims； in 1909。 It has since been used
with success by aviators all the world over。 That in the Aerial Derby of
1913which was flown over a course Of 94 miles around Londonsix of
the eleven machines which took part in the race were fitted with Gnome
engines； and victory was achieved by Mr。 Gustav Hamel； who drove an
80…horse…power Gnome； is conclusive evidence of the high value of this
engine in aviation。
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CHAPTER XXIII A Famous British Inventor of
Aviation Engines
In the general design and beauty of workmanship involved in the
construction of aeroplanes； Britain is now quite the equal of her foreign
rivals； even in engines we are making extremely rapid progress； and the
well…known Green Engine Company； profiting by the result of nine years'
experience； are able to turn out aeroplane engines as reliable； efficient； and
as light in pounds weight per horse…power as any aero engine in existence。
In the early days of aviation larger and better engines of British make
specially suited for aeroplanes were our most urgent need。
The story of the invention of the 〃Green〃 engine is a record of triumph
over great difficulties。
Early in 1909the memorable year when M。 Bleriot was firing the
enthusiasm of most engineers by his cross…Channel flight； when records
were being established at Rheims； and when M。 Paulhan won the great
prize of L10；000 for the London to Manchester flight Mr。 Green
conceived a number of ingenious ideas for an aero engine。
One of Mr。 Green's requirements was that the cylinders should be
made of cast…steel； and that they should come from a British foundry。 The
company that took the work in hand； the Aster Company； had confidence
in the inventor's idea