The _aviplane_, _ornithoptère_ or _orthopter_ is a flying machine with
bird-like flapping wings, which has received occasional attention
from time to time, as the result of a too blind adherence to Nature's
analogies. Every mechanical principle is in favor of the screw as
compared with any reciprocating method of propulsion. There have been
few actual examples of this type: a model was exhibited at the Grand
Central Palace in New York in January of this year.
The mechanism of an orthopter would be relatively complex, and the
flapping wings would have to "feather" on their return stroke. The
flapping speed would have to be very high or the surface area very
great. This last requirement would lead to structural difficulties.
Propulsion would not be uniform, unless additional complications were
introduced. The machine would be the most difficult of any type to
balance. The motion of a bird's wing is extremely complicated in its
details--one that it would be as difficult to imitate in a mechanical
device as it would be for us to obtain the structural strength of an
eagle's wing in fabric and metal, with anything like the same extent of
surface and limit of weight. According to Pettigrew, the efficiency of
bird and insect flight depends largely upon the elasticity of the wing.
Chatley gives the ratio of area to weight as varying from fifty (gnat)
to one-half (Australian crane) square feet per pound. The usual ratio
in aeroplanes is from one-third to one-half.
About the only advantages perceptible with the orthopter type of
machine would be, first, the ability "to start from rest without
a preliminary surface glide"; and second, more independence of
irregularity in air currents, since the propulsive force is exerted
over a greater extent than is that of a screw propeller.