LEARNING TO FLY.
Don't be too ambitious at the start. Go slow, and
avoid unnecessary risks. At its best there is an element
of danger in aviation which cannot be entirely eliminated, but it
may be greatly reduced and minimized by
the use of common sense.
Theoretically, the proper way to begin a glide is from
the top of an incline, facing against the wind, so that
the machine will soar until the attraction of
draws it gradually to the ground. This is the manner in
which experienced aviators operate, but it must be kept
in mind that these men are experts. They understand
air currents, know how to control the action and direction
of their machines by shifting the position of their
bodies, and by so doing avoid accidents which would be
unavoidable by a novice.
Begin on Level Ground.
Make your first flights on level ground, having a couple
of men to assist you in getting the apparatus under
headway. Take your position in the center rectangle,
back far enough to give the forward edges of the glider
an inclination to tilt upward very slightly. Now start
and run forward at a moderately rapid gait, one man at
each end of the glider assisting you. As the glider cuts
into the air the wind will catch under the uplifted edges
of the curved planes, and buoy it up so that it will rise
in the air and take you with it. This rise will not be
great, just enough to keep you well clear of the ground.
Now project your legs a little to the front so as to shift
the center of gravity a trifle and bring the edges of the
glider on an exact level with the atmosphere. This, with
the momentum acquired in the start, will keep the machine
moving forward for some distance.
Effect of Body Movements.
When the weight of the body is slightly back of the
center of gravity the edges of the advancing planes are
tilted slightly upward. The glider in this position acts
as a scoop, taking in the air which, in turn, lifts it off the
ground. When a certain altitude is reached--this varies
with the force of the wind--the tendency to a forward
movement is lost and the glider comes to the ground.
It is to prolong the forward movement as much as possible
that the operator shifts the center of gravity slightly,
bringing the apparatus on an even keel as it were by
lowering the advancing edges. This done, so long as
there is momentum enough to keep the glider moving, it
will remain afloat.
If you shift your body well forward it will bring the
front edges of the glider down, and elevate the rear ones.
In this way the air will be "spilled" out at the rear, and,
having lost the air support or buoyancy, the glider comes
down to the ground. A few flights will make any ordinary
man proficient in the control of his apparatus by his
body movements, not only as concerns the elevating and
depressing of the advancing edges, but also actual steering. You
will quickly learn, for instance, that, as the
shifting of the bodily weight backwards and forwards
affects the upward and downward trend of the planes, so
a movement sideways--to the left or the right--affects
the direction in which the glider travels.
Ascends at an Angle.
In ascending, the glider and flying machine, like the
bird, makes an angular, not a vertical flight. Just what
this angle of ascension may be is difficult to determine.
It is probable and in fact altogether likely, that it varies
with the force of the wind, weight of the rising body,
power of propulsion, etc. This, in the language of physicists,
is the angle of inclination, and, as a general thing,
under normal conditions (still air) should be put down as
about one in ten, or 5 3/4 degrees. This would be an ideal
condition, but it has not, as vet been reached. The force
of the wind affects the angle considerably, as does also
the weight and velocity of the apparatus. In general
practice the angle varies from 23 to 45 degrees. At
more than 45 degrees the supporting effort is overcome
by the resistance to forward motion.
Increasing the speed or propulsive force, tends to
lessen the angle at which the machine may be successfully
operated because it reduces the wind pressure.
Most of the modern flying machines are operated at an
angle of 23 degrees, or less.
Maintaining an Equilibrium.
Stable equilibrium is one of the main essentials to
successful flight, and this cannot be preserved in an
uncertain, gusty wind, especially by an amateur. The
novice should not attempt a glide unless the conditions
are just right. These conditions are: A clear, level
space, without obstructions, such as trees, etc., and a
steady wind of not exceeding twelve miles an hour. Always
fly against the wind.
When a reasonable amount of proficiency in the handling
of the machine on level ground has been acquired
the field of practice may be changed to some gentle
slope. In starting from a slope it will be found easier
to keep the machine afloat, but the experience at first is
likely to be very disconcerting to a man of less than iron
nerve. As the glider sails away from the top of the
slope the distance between him and the ground increases
rapidly until the aviator thinks he is up a hundred miles
in the air. If he will keep cool, manipulate his apparatus
so as to preserve its equilibrium, and "let nature take its
course," he will come down gradually and safely to the
ground at a considerable distance from the starting place.
This is one advantage of starting from an elevation--
your machine will go further.
But, if the aviator becomes "rattled"; if he loses control
of his machine, serious results, including a bad fall
with risk of death, are almost certain. And yet this
practice is just as necessary as the initial lessons on
level ground. When judgment is used, and "haste made
slowly," there is very little real danger. While experimenting
with gliders the Wrights made flights innumerable
under all sorts of conditions and never had an accident
of any kind.
Effects of Wind Currents.
The larger the machine the more difficult it will be to
control its movements in the air, and yet enlargement is
absolutely necessary as weight, in the form of motor,
rudder, etc., is added.
Air currents near the surface of the ground are diverted
by every obstruction unless the wind is blowing
hard enough to remove the obstruction entirely. Take,
for instance, the case of a tree or shrub, in a moderate
wind of from ten to twelve miles an hour. As the wind
strikes the tree it divides, part going to one side and
part going to the other, while still another part is directed
upward and goes over the top of the obstruction.
This makes the handling of a glider on an obstructed
field difficult and uncertain. To handle a glider successfully
the place of operation should be clear and the wind
moderate and steady. If it is gusty postpone your flight.
In this connection it will be well to understand the velocity
of the wind, and what it means as shown in the
Miles per hour Feet per second Pressure per sq. foot
10 14.7 .492
25 36.7 3.075
50 73.3 12.300
100 146.6 49.200
Pressure of wind increases in proportion to the square
of the velocity. Thus wind at 10 miles an hour has four
times the pressure of wind at 5 miles an hour. The
greater this pressure the large and heavier the object
which can be raised. Any boy who has had experience
in flying kites can testify to this, High winds, however,
are almost invariably gusty and uncertain as to direction,
and this makes them dangerous for aviators. It
is also a self-evident fact that, beyond a certain stage,
the harder the wind blows the more difficult it is to
make headway against it.
Launching Device for Gliders.
On page 195 will be found a diagram of the various
parts of a launcher for gliders, designed and patented
by Mr. Octave Chanute. In describing this invention
in Aeronautics, Mr. Chanute says:
"In practicing, the track, preferably portable, is
generally laid in the direction of the existing wind and
the car, preferably a light platform-car, is placed on the
track. The truck carrying the winding-drum and its motor
is placed to windward a suitable distance--say from
two hundred to one thousand feet--and is firmly blocked
or anchored in line with the portable track, which is
preferably 80 or 100 feet in length. The flying or gliding
machine to be launched with its operator is placed on
the platform-car at the leeward end of the portable track.
The line, which is preferably a flexible combination
wire-and-cord cable, is stretched between the winding-
drum on the track and detachably secured to the flying
or gliding machine, preferably by means of a trip-hoop,
or else held in the hand of the operator, so that the
operator may readily detach the same from the flying-
machine when the desired height is attained.
How Glider Is Started.
"Then upon a signal given by the operator the engineer
at the motor puts it into operation, gradually increasing
the speed until the line is wound upon the drum
at a maximum speed of, say, thirty miles an hour. The
operator of the flying-machine, whether he stands upright and
carries it on his shoulders, or whether he sits
or lies down prone upon it, adjusts the aeroplane or
carrying surfaces so that the wind shall strike them on
the top and press downward instead of upward until
the platform-car under action of the winding-drum and
line attains the required speed.
"When the operator judges that his speed is sufficient,
and this depends upon the velocity of the wind as well
as that of the car moving against the wind, he quickly
causes the front of the flying-machine to tip upward, so
that the relative wind striking on the under side of the
planes or carrying surfaces shall lift the flying machine
into the air. It then ascends like a kite to such height
as may be desired by the operator, who then trips the
hook and releases the line from the machine.
What the Operator Does.
"The operator being now free in the air has a certain
initial velocity imparted by the winding-drum and line
and also a potential energy corresponding to his height
above the ground. If the flying or gliding machine is
provided with a motor, he can utilize that in his further
flight, and if it is a simple gliding machine without
motor he can make a descending flight through the air
to such distance as corresponds to the velocity acquired
and the height gained, steering meanwhile by the devices
provided for that purpose.
"The simplest operation or maneuver is to continue
the flight straight ahead against the wind; but it is possible
to vary this course to the right or left, or even to
return in downward flight with the wind to the vicinity
of the starting-point. Upon nearing the ground the
operator tips upward his carrying-surfaces and stops his
headway upon the cushion of increased air resistance
so caused. The operator is in no way permanently
fastened to his machine, and the machine and the operator
simply rest upon the light platform-car, so that
the operator is free to rise with the machine from the
car whenever the required initial velocity is attained.
Motor For the Launcher.
"The motor may be of any suitable kind or construction,
but is preferably an electric or gasolene motor.
The winding-drum is furnished with any suitable or customary
reversing-guide to cause the line to wind smoothly
and evenly upon the drum. The line is preferably a
cable composed of flexible wire and having a cotton or
other cord core to increase its flexibility. The line
extends from the drum to the flying or gliding machine.
Its free end may, if desired, be grasped and held by the
operator until the flying-machine ascends to the desired
height, when by simply letting go of the line the operator
may continue his flight free. The line, however, is preferably
connected to the flying or gliding machine
directly by a trip-hook having a handle or trip lever
within reach of the operator, so that when he ascends
to the required height he may readily detach the line
from the flying or gliding machine."