ur. The reserve buoyancy, that is the total lifting capacity
aside from the weight of the airship and its equipment, is estimated at
three tons.

CHAPTER XXII. PROBLEMS OF AERIAL FLIGHT.

In a lecture before the Royal Society of Arts, reported in Engineering,
F. W. Lanchester took the position that practical flight was not the
abstract question which some apparently considered it to be, but a
problem in locomotive engineering. The flying machine was a locomotive
appliance, designed not merely to lift a weight, but to transport it
elsewhere, a fact which should be sufficiently obvious. Nevertheless one
of the leading scientific men of the day advocated a type in which
this, the main function of the flying machine, was overlooked. When
the machine was considered as a method of transport, the vertical screw
type, or helicopter, became at once ridiculous. It had, nevertheless,
many advocates who had some vague and ill-defined notion of subsequent
motion through the air after the weight was raised.

Helicopter Type Useless.

When efficiency of transport was demanded, the helicopter type was
entirely out of court. Almost all of its advocates neglected the effect
of the motion of the machine through the air on the efficiency of the
vertical screws. They either assumed that the motion was so slow as not
to matter, or that a patch of still air accompanied the machine in its
flight. Only one form of this type had any possibility of success. In
this there were two screws running on inclined axles--one on each
side of the weight to be lifted. The action of such inclined screw was
curious, and in a previous lecture he had pointed out that it was almost
exactly the same as that of a bird's wing. In high-speed racing craft
such inclined screws were of necessity often used, but it was at
a sacrifice of their efficiency. In any case the efficiency of the
inclined-screw helicopter could not compare with that of an aeroplane,
and that type might be dismissed from consideration so soon as
efficiency became the ruling factor of the design.

Must Compete With Locomotive.

To justify itself the aeroplane must compete, in some regard or other,
with other locomotive appliances, performing one or more of the purposes
of locomotion more efficiently than existing systems. It would be no use
unless able to stem air currents, so that its velocity must be greater
than that of the worst winds liable to be encountered. To illustrate the
limi