KRONFELD ON GLIDING AND SOARING.pdf - Lakes Gliding Club

THE FUTURE OF SOARING FLIGHT 315
isolated gusts for the gaining of height, but we do not yet
know the best methods of doing this.
Again and again we are stimulated to further inquiries
in this direction by our observation of soaring birds, such as
the albatross. On the occasion of a recent journey round the
world, Professor Prandtl, the director of the Aerodynamic
Research Institute of Gottingen, studied the flight of these
birds, which are the best soarers of the feathered world.
While many observers believe that ocean birds only fly
in the up-currents produced by the crests of the waves,
Prandtl has another explanation of their long and wide
journeys over the billows. On the voyage from Yokohama
to Honolulu he was able to gain a clear idea of their method
of flight.
They utilize the difference between the wind velocity
immediately above the surface of the water over which
they have chosen to fly and that higher up. They rise
against the wind by means of the energy which is freed
when they climb suddenly from a slowly moving layer
into a more rapid one. Having risen, they turn and fly
down again with the increased speed they have gained ;
in the lower layer they repeat the manoeuvre. The amount
of energy which can be acquired in this way can be calculated
mathematically ; hence it follows that we ought to be
able to hover above the sea for as long and as far as we
desire, provided that there is a wind of sorts. This axiom
is applicable everywhere where different atmospheric
velocities are to be encountered.
It has also been shown theoretically and by experiments
in wind tunnels that climbing is feasible in variable winds
which blow in gusts from different directions on our level
or from above or below us.
All these problems—most particularly that of the general
nature of wind gusts—have not been sufficiently exploited,
and we cannot say what future investigations of their nature
will be possible. It is futile to deny the possibility of
solving any technical problem, for which reason it should
be possible to imitate the flight of the albatross with a
small machine that could easily be manoeuvred. There
is a crying need for " wind feelers,"—instruments that