A careful consideration of the salient features leading to
maximum efficiency in aeroplanes--particularly in regard to
speed and climb, which were the two most important military
requirements--showed that a vital feature was the reduction in
the amount of weight lifted per horse-power employed; which in
1914 averaged from 20 to 25 lbs. This was effected both by
gradual increase in the power and size of the engines used and
by great improvement in their detailed design (by increasing
compression ratio and saving weight whenever possible); with the
result that the motive power of single-seater aeroplanes rose
from 80 and 100 horse-power in 1914 to an average of 200 to 300
horse-power, while the actual weight of the engine fell from 3
1/2-4 lbs. per horse-power to an average of 2 1/2 lbs. per
horse-power. This meant that while a pre-war engine of 100
horse-power would weigh some 400 lbs., the 1918 engine developing
three times the power would have less than double the weight.
The result of this improvement was that a scout aeroplane at the
time of the Armistice would have 1 horse-power for every 8 lbs.
of weight lifted, compared with the 20 or 25 lbs. of its 1914
predecessors. This produced a considerable increase in the rate
of climb, a good postwar machine being able to reach 10,000 feet
in about 5 minutes and 20,000 feet in under half an hour. The
loading per square foot was also considerably increased; this
being rendered possible both by improvement in the design of wing
sections and by more scientific construction giving increased
strength. It will be remembered that in the machine of the very
early period each square foot of surface had only to lift a
weight of some 1 1/2 to 2 lbs., which by 1914 had been increased
to about 4 lbs. By 1918 aeroplanes habitually had a loading of 8