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.
Ah, Reader, smile not unbelievingly, as you smiled but
a few years past. There may be greater wonders yet. Consider
that as the speed increases, so does the momentum
or stored-up force in the mass of the aeroplane become
terrific. And, bearing that in mind, remember that with
altitude gravity decreases. There may yet be literally other
worlds to conquer.[[12]]
[[12]] 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.
Now at fifteen thousand feet the conditions are chilly
and rare, and the Pilot, with thoughts of breakfast far below,
exclaims, ``High enough! I had better get on with the
Test.'' And then, as he depresses the Elevator, the Aeroplane
with relief assumes its normal horizontal position.
Then, almost closing the Throttle, the Thrust dies away.
Now, the nose of the Aeroplane should sink of its own volition,
and the craft glide downward at flying speed, which is in
this case a hundred miles an hour. That is what should
happen if the Designer has carefully calculated the weight
of every part and arranged for the centre of gravity to be just
the right distance in front of the centre of lift.
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