ich the air
flows, and change the pterophore into an unbroken surface which
would resist the flow of air and retard the fall of the machine to a
considerable degree.'

The doctrine thus set forth might appear plausible, but it is based on
the common misconception that all the force which might be put into the
helicopter or 'pterophore' would be utilised for lifting or propelling
the vehicle through the air, just as a propeller uses all its power to
drive a ship through water. But, in applying such a propelling force
to the air, most of the force is utilised in maintaining aerodynamic
support--as a matter of fact, more force is needed to maintain this
support than the muscle of man could possibly furnish to a lifting
screw, and even if the helicopter were applied to a full-sized,
engine-driven air vehicle, the rate of ascent would depend on the amount
of surplus power that could be carried. For example, an upward lift
of 1,000 pounds from a propeller 15 feet in diameter would demand an
expenditure of 50 horse-power under the best possible conditions, and in
order to lift this load vertically through such atmospheric pressure as
exists at sea-level or thereabouts, an additional 20 horsepower would be
required to attain a rate of 11 feet per second--50 horse-power must
be continually provided for the mere support of the load, and the
additional 20 horse-power must be continually provided in order to
lift it. Although, in model form, there is nothing quite so strikingly
successful as the helicopter in the range of flying machines, yet the
essential weight increases so disproportionately to the effective area
that it is necessary to go but very little beyond model dimensions for
the helicopter to become quite ineffective.

That is not to say that the lifting screw must be totally ruled out
so far as the construction of aircraft is concerned. Much is still
empirical, so far as this branch of aeronautics is concerned, and
consideration of the structural features of a propeller goes to show
that the relations of essential weight and effective area do not
altogether apply in practice as they stand in theory. Paucton's dream,
in some modified form, may yet become reality--it is only so short
a time ago as 1896 that Lord Kelvin stated he had not the smallest
molecule of faith in aerial navigation, and since the whole history of
flight consists in proving the impossible possible, the helicopter may
yet challenge the propelled pla