THE GLIDER.
Aerial balancing--Practice necessary--Simplicity of the glider
Materials--Construction--Gliding--Feats with the Montgomery
glider--Noted experimenters--Glider clubs.
It is a matter of record that the Wright brothers spent the better part
of three years among the sand dunes of the North Carolina sea-coast
practising with gliders. In this way they acquired that confidence
while in the air which comes from intimate acquaintance with its
peculiarities, and which cannot be gained in any other way. It is true
that the Wrights were then developing not only themselves, but also
their gliders; but the latter work was done once for all. To develop
aviators, however, means the repeating of the same process for each
individual--just as each for himself must be taught to read. And the
glider is the “First Reader” in aeronautics.
The long trail of wrecks of costly aeroplanes marking the progress in
the art of flying marks also the lack of preparatory training, which
their owners either thought unnecessary, or hoped to escape by some
royal road less wearisome than persistent personal practice. But they
all paid dearly to discover that there is no royal road. Practice, more
practice, and still more practice--that is the secret of successful
aeroplane flight.
For this purpose the glider is much superior to the power-driven
aeroplane. There are no controls to learn, no mechanism to manipulate.
One simply launches into the air, and concentrates his efforts upon
balancing himself and the apparatus; not as two distinct bodies,
however, but as a united whole. When practice has made perfect the
ability to balance the glider instinctively, nine-tenths of the art of
flying an aeroplane has been achieved. Not only this, but a new sport
has been laid under contribution; one beside which coasting upon a
snow-clad hillside is a crude form of enjoyment.
Fortunately for the multitude, a glider is easily made, and its cost is
even less than that of a bicycle. A modest degree of skill with a few
carpenter’s tools, and a little “gumption” about odd jobs in general,
is all that is required of the glider builder.
[Illustration: A gliding slope with starting platform, erected for club
use.]
The frame of the glider is of wood, and spruce is recommended, as it
is stronger and tougher for its weight than other woods. It should be
of straight grain and free from knots; and as there is considerable
difference in the weight of spruce from different trees, it is well
to go over the pile in the lumber yard and pick out the lightest
boards. Have them planed down smooth on both sides, and to the required
thickness, at the mill--it will save much toilsome hand work. The
separate parts may also be sawed out at the mill, if one desires to
avoid this labor.
The lumber needed is as follows:
4 spars 20 ft. long, 1¼ in. wide, ¾ in. thick.
12 struts 3 ft. long, 1¼ in. wide, ¾ in. thick.
2 rudder bars 8 ft. long, ¾ in. wide, ½ in. thick.
12 posts 4 ft. long, 1½ in. wide, ½ in. thick.
41 ribs 4 ft. long, ½ in. wide, ½ in. thick.
2 arm rests 4 ft. long, 2 in. wide, 1 in. thick.
For rudder frame. 24 running ft., 1 in. wide, 1 in. thick.
If it be impossible to find clear spruce lumber 20 feet in length,
the spars may be built up by splicing two 10-foot sticks together.
For this purpose, the splicing stick should be as heavy as the single
spar--1¼ inches wide, and ¾ inches thick--and at least 4 feet long, and
be bolted fast to the spar with six ⅛ inch round-head carriage bolts
with washers of large bearing surface (that is, a small hole to fit the
bolt, and a large outer diameter) at both ends of the bolt, to prevent
crushing the wood. A layer of liquid glue brushed between will help to
make the joint firmer.
[Illustration: Otto Lilienthal in his single-plane glider. The swinging
forward of his feet tends to turn the glider toward the ground, and
increase its speed.]
Wherever a bolt is put in, a hole should be bored for it with a bit of
such size that the bolt will fit snug in the hole without straining the
grain of the wood.
The corners of the finished spar are to be rounded off on a large
curvature.
The ends of the struts are to be cut down on a slight slant of about
1/16 inch in the 1¼ inches that it laps under the spar--with the idea
of tipping the top of the spar forward so that the ribs will spring
naturally from it into the proper curve.
The ribs should be bent by steaming, and allowed to dry and set in
a form, or between blocks nailed upon the floor to the line of the
correct curve. They are then nailed to the frames, the front end first:
21 to the frame of the upper plane, and 20 to that of the lower plane,
omitting one at the centre, where the arm pieces will be placed.
Some builders tack the ribs lightly into place with small brads, and
screw clamps formed from sheet brass or aluminum over them. Others
use copper nails and clinch them over washers on the under side. Both
methods are shown in the plans, but the clamps are recommended as
giving greater stiffness, an essential feature.
At the front edge of the frames the ribs are fastened flush, and being
4 feet long and the frame but 3 feet wide, they project over the rear
about 1 foot.
The arm pieces are bolted to the spars of the lower frame 6½ inches
on each side of the centre, so as to allow a free space of 13 inches
between them. This opening may be made wider to accommodate a stouter
person.
[Illustration: Plan and details of Glider. The upper plane has a rib at
the centre instead of the two arm pieces.]
The posts are then put into place and bolted to the struts and the
spars, as shown, with ⅛inch bolts.
The entire structure is then to be braced diagonally with No. 16 piano
wire. The greatest care must be taken to have these diagonals pull just
taut, so that they shall not warp the lines of the frames out of true.
A crooked frame will not fly straight, and is a source of danger when
making a landing.
The frames are now to be covered. There is a special balloon cloth
made which is best for the purpose, but if that cannot be procured,
strong cambric muslin will answer. Thirty yards of goods 1 yard wide
will be required for the planes and the rudder. From the piece cut off
7 lengths for each plane, 4 feet 6 inches long. These are to be sewed
together, selvage to selvage, so as to make a sheet about 19 feet 6
inches long and 4 feet 6 inches wide. As this is to be tacked to the
frame, the edges must be double-hemmed to make them strong enough to
resist tearing out at the tacks. Half an inch is first folded down
all around; the fold is then turned back on the goods 2½ inches and
sewed. This hem is then folded back 1 inch upon itself, and again
stitched. Strips 3 inches wide and a little over 4 feet long are
folded “three-double” into a width of 1 inch, and sewed along both
edges to the large sheet exactly over where the ribs come. These are to
strengthen the fabric where the ribs press against it. Sixteen-ounce
tacks are used, being driven through a felt washer the size of a gun
wad at intervals of four inches. If felt is not readily obtainable,
common felt gun wads will do. The tacking is best begun at the middle
of the frame, having folded the cloth there to get the centre. Then
stretch smoothly out to the four corners and tack at each. It may
then be necessary to loosen the two centre tacks and place them over
again, to get rid of wrinkles. The next tacks to drive are at the ends
of the struts; then half-way between; and so on until all are in, and
the sheet is taut and smooth. For a finer finish, brass round-head
upholsterer’s nails may be used.
The rudder, so-called, is rather a tail, for it is not movable and does
not steer the glider. It does steady the machine, however, and is very
important in preserving the equilibrium when in flight. It is formed of
two small planes intersecting each other at right angles and covered
on both sides with the cloth, the sections covering the vertical part
being cut along the centre and hemmed on to the upper and lower faces
of the horizontal part. The frame for the vertical part is fastened to
the two rudder bars which stretch out toward the rear, one from the
upper plane, and the other from the lower. The whole construction is
steadied by guys of the piano wire.
[Illustration: Lilienthal in his double-deck glider. It proved
unmanageable and fell, causing his death. The hill is an artificial one
built for his own use in experimenting.]
All wooden parts should be smoothed off with sandpaper, and given a
coat of shellac varnish.
To make a glide, the machine is taken to an elevated point on a
slope, not far up to begin with. Lift the glider, get in between the
arm rests, and raise the apparatus until the rests are snug under the
arms. Run swiftly for a few yards and leap into the air, holding the
front of the planes slightly elevated. If the weight of the body is
in the right position, and the speed sufficient, the glider will take
the air and sail with you down the slope. It may be necessary at first
to have the help of two assistants, one at each end, to run with the
glider for a good start.
[Illustration: Diagram showing differing lines of flight as controlled
by changing the position of the body. The wind must be blowing against
the direction of flight; in the illustration this would be from left to
right.]
The position of the body on the arm rests can best be learned by a few
experiments. No two gliders are quite alike in this respect, and no
rule can be given. As to the requisite speed, it must be between 15 and
20 miles an hour; and as this speed is impossible to a man running, it
is gained by gliding against the wind, and thus adding the speed of the
wind to the speed of the runner. The Wrights selected the sand dunes of
the North Carolina coast for their glider experiments because of the
steady winds that blow in from the ocean, across the land. These winds
gave them the necessary speed of air upon which to sail their gliders.
The first flights attempted should be short, and as experience is
gained longer ones may be essayed.
Balancing the glider from side to side is accomplished by swaying the
lower part of the body like a pendulum, the weight to go toward the
side which has risen. Swinging the body forward on the arm rests will
cause the machine to dip the planes and glide more swiftly down the
incline. Holding the weight of the body back in the arm rests will
cause the machine to fly on a higher path and at a slower speed. This
is objectionable because the glider is more manageable at a higher
speed, and therefore safer. The tendency at first is to place the
weight too far back, with a consequent loss of velocity, and with that
a proportionate loss of control. The proper position of the body is
slightly forward of the mechanical centre of the machine.
The landing is accomplished by shoving the body backward, thus tilting
up the front of the plane. This checks the speed, and when the feet
touch the ground a little run, while holding back, will bring the glide
to an end. Landing should be practised often with brief glides until
skill is gained, for it is the most difficult operation in gliding.
After one becomes expert, longer flights may be secured by going to
higher points for the start. From an elevation of 300 feet a glide of
1,200 feet is possible.
[Illustration: Gliding with a Chanute three-decker. A start with two
assistants.]
While it is necessary to make glides against the wind, it is not wise
to attempt flights when the wind blows harder than 10 miles an hour.
While the flight may be successful, the landing may be disastrous.
The accomplished glider operator is in line for the aeroplane, and it
is safe to say that he will not be long without one. The skilful and
practised operator of a glider makes the very best aeroplane pilot.
This chapter would not be complete without an adequate reference to the
gliders devised by Professor Montgomery of Santa Clara, California.
These machines were sent up with ordinary hot-air balloons to various
heights, reaching 4,000 feet in some instances, when they were cut
loose and allowed to descend in a long glide, guided by their pilots.
The time of the descent from the highest altitude was twenty minutes,
during which the glider travelled about eight miles. The landing was
made accurately upon a designated spot, and so gently that there was no
perceptible jar. Two of the pilots turned completely over sideways, the
machine righting itself after the somersault and continuing its regular
course. Professor Montgomery has made the assertion that he can fasten
a bag of sand weighing 150 lbs. in the driver’s seat of his glider,
and send it up tied upside down under a balloon, and that after being
cut loose, the machine will right itself and come safely to the ground
without any steering.
Lilienthal in Germany, Pilcher in England, and Chanute in the United
States are names eminent in connection with the experiments with
gliders which have been productive of discoveries of the greatest
importance to the progress of aviation. The illustration of the Chanute
glider shows its peculiarities plainly enough to enable any one to
comprehend them.
The establishment of glider clubs in several parts of the country has
created a demand for ready-made machines, so that an enthusiast who
does not wish to build his own machine may purchase it ready made.