hanic and pilot, 85 gallons of petrol, and 12
gallons of lubricating oil. Compulsory landings were made every 63
miles, and the engine was stopped. In spite of these trying conditions,
the engine ran, from start to finish, nearly nine hours without the
slightest trouble.

Sufficient has been said to prove conclusively that the thought and
labour expended in the perfecting of the Green engine have not been
fruitless.

CHAPTER XXIV. The Wright Biplane (Camber of Planes)

Now that the internal-combustion engine had arrived, the Wrights at
once commenced the construction of an aeroplane which could be driven
by mechanical power. Hitherto, as we have seen, they had made numerous
tests with motorless gliders; but though these tests gave them much
valuable information concerning the best methods of keeping their craft
on an even keel while in the air, they could never hope to make much
progress in practical flight until they adopted motor power which would
propel the machine through the air.

We may assume that the two brothers had closely studied the engines
patented by Daimler and Levassor, and, being of a mechanical turn of
mind themselves, they were able to build their own motor, with which
they could make experiments in power-driven flight.

Before we study the gradual progress of these experiments it would be
well to describe the Wright biplane. The illustration facing p. 96 shows
a typical biplane, and though there are certain modifications in most
modern machines, the principles upon which it was built apply to all
aeroplanes.

The two main supporting planes, A, B, are made of canvas stretched
tightly across a light frame, and are slightly curved, or arched, from
front to back. This curve is technically known as the CAMBER, and upon
the camber depend the strength and speed of the machine.

If you turn back to Chapter XVII you will see that the plane is modelled
after the wing of a bird. It has been found that the lifting power of a
plane gradually dwindles from the front edge--or ENTERING EDGE, as it
is called--backwards. For this reason it is necessary to equip a machine
with a very long, narrow plane, rather than with a comparatively broad
but short plane.

Perhaps a little example will make this clear. Suppose we had two
machines, one of which was fitted with planes 144 feet long and 1
foot wide, and the other with planes 12 feet square. In the former the
entering edge of the plane would be twelve time