This paper is made by clockwork
to pass over the point of the pen, and so a curved line is
made which accurately registers the speed of the ascent in
feet per minute. No longer is the ascent at the rate of a
thousand feet a minute, and the Propeller complains to the
Engine, ``I'm losing my Revs. and the Thrust. Buck up
with the Power, for the Lift is decreasing, though the Weight
remains much the same.''
Quoth the Engine: ``I strangle for Air. A certain proportion,
and that of right density, I must have to one part
of Petrol, in order to give me full power and compression,
and here at an altitude of ten thousand feet the Air is only
two-thirds as dense as at sea-level. Oh, where is he who
will invent a contrivance to keep me supplied with Air of
right density and quality? It should not be impossible
within certain limits.''
``We fully agree,'' said the dying Power and Thrust. ``Only
maintain Us and you shall be surprised at the result. For
our enemy Drift decreases in respect of distance with the increase
of altitude and rarity of air, and there is no limit to the
speed through space if only our strength remains. And
with oxygen for Pilot and Passengers and a steeper pitch[[11]]
for the Propeller we may then circle the Earth in a day!''
[[11]] A propeller screws through the air, and the distance it advances
during one revolution, supposing the air to be solid, is known as the pitch.
The pitch, which depends upon the angle of the propeller blades, must be equal
to the speed of the aeroplane, plus the slip, and if, on account of the rarity
of the air the speed of the aeroplane increases, then the angle and pitch
should be correspondingly increased.
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