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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. Propellers with a pitch capable of being varied by the pilot are the dream of propeller designers. For explanation of "slip" see Chapter IV. on propellers.
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Getting out of my depth? Invading the realms of fancy? Well, perhaps so, but at any rate it is possible that extraordinary speed through space may be secured if means are found to maintain the impulse of the engine and the thrust-drift efficiency of the propeller at great altitude.
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Box-kite. The first crude form of biplane.
PART IV
'CROSS COUNTRY
The Aeroplane had been designed and built, and tested in the air, and now it stood on the Aerodrome ready for its first 'cross-country flight.
It had run the gauntlet of pseudo-designers, crank inventors, press "experts," and politicians; of manufacturers keen on cheap work and large profits; of poor pilots who had funked it, and good pilots who had expected too much of it. Thousands of pounds had been wasted on it, many had gone bankrupt over it, and others it had provided with safe fat jobs.