The New York herald., 1922-10-29
Flight Without Motors
Practical and Scientific Aspects Of the Rapidly
Developing Art of Gliding.

axes" This means that when there Is
steady wind we get the actual motion
Of the glider as seen from the earth by
adding the velocity OF the wind to the
motion of the glider In still air in other
words. to an observer travelling with the
wind the motion OF the glider would not
reveal any effects that can be attributed
to the steady wind.
In horizontal steady wind. there
fore. real flight Is no more possible with
out an engine than In absolutely wind
less air. Any argument that leads to =
contrary conclusion must have fallacy
somewhere, II we are to have any conf
dence In the principles upon which all
our mechanics are based. 1t Is true
that a steady horizontal wind can be
used as an aid in gliding. Thus. by
pointing his machine into the wind the
pilot can get off the ground with less
initial speed than In still air. Further.
when the machine is already in the air
the pilot can, by pointing 1t with the
wind increase the horizontal distance
Travelled before reaching the ground
again. But q steady horizontal wind
cannot make the machine stay at the
same level In the air for any length Of
time, or climb. For these purposes the
wind must be upward or variable.
If the wind is steady but has an up
ward component 1t helps in the attain
ment Of real flight, which we can call
wind flight. Given a steady wind with
sufficient upward vertical component a
glider can perform real flights and MAKE
evolutions similar to those Of ordinary
airplane flight
It Is not necessary, however, to postu-
late steady upward wind. If the wind is
variable, and this Is, of course, usually
the case, energy can be derived from
the wind even If it is horizontal or
downward. This can be seen by little
analysis based on the ordinary equations
of motion of the glider. Thus. suppose
that the wind Is in a straight line but OF
varying speed. If we write the accel-
erations In these equations In terms OF
the motion relative to the air we readily
find that the motion Of the glider rela-
tive to the air is the same as II the air
were at rest and a force per unit mass
were given to the glider In a direction
opposite to that of the wind and proper
Ional to the acceleration Of the wind.
II. then, the machine is pointed into
he rising wind and the wind varies
uickly enough flying becomes possible.
If the wind Is being retarded similar
propulsive effect is obtained by pointing
the machine with the wind It follows
that in a fairly sudden gust, which can
be taken to consist of a-quickly incfeas-
ing wind followed by quickly decreas
Ing wind, the pilot can take advantage
Of both phases by pointing the machine
into the rising wind and with the falling
wind. Quick maneuvering Is Of course
essential as we'll as an intimate ac-
quaintance with the movements that are
always taking place in the air.
With more complicated variations in
the wind more complex results are OBJ
tanned. 1t is now clear. however, that
the future of wind flight Is associated
with three main lines of study:
(1) The motions that are continually
taking place in the atmosphere need to
be studied. not only the meteorological
wind phenomena as ordinarily under
stood but particularly the detailed air
motions. the internal structure Of the
wind"
(2) Motorless flight presents prob.
lens Of design that are different from
those Of ordinary airplanes. This IL
because the glider Is a much lighter ma
chine than the airplane. Stability II
but easy control Is q sine
qua non, since so much depends upon
taking as full advantage as possible Of
any temporary and often unanticipated
motion In the air.
(3) The rigid dynamics Of wind flight
is also an important factor In the prog
ress OF the art, Only in very excep-
tional circumstances can the motion OF
q glider be steady. Upward steady
winds or uniformly varying winds are
only of rare occurrence and brief dura-
ton. and In trying to perform real flight
in an engineless machine the pilot must
make use Of any stray wind that comes
to his aid. The motion In wind night
must consequently be very variable. In
this respect wind flight must generally
differ In essence from engine fiight. In
the latter steady flight IL the rule, In the
former steady flight Is bound to be q
rarity. The pilot must
therefore learn from experiences and
from calculation to know what to ex-
pect from his machine under different
conditions The dynamics OF wind flight
should be q fruitful subject Of study
both for the aviator and the mathama-
kiciau