CONSTRUCTING A GLIDING MACHINE.
First decide upon the kind of a machine you want--
monoplane, biplane, or triplane. For a novice the biplane
will, as a rule, be found the most satisfactory as
it is more compact and therefore the more easily handled.
This will be easily understood when we realize that the
surface of a flying machine should be laid out in proportion
to the amount of weight it will have to sustain.
The generally accepted ru
e is that 152 square feet of
surface will sustain the weight of an average-sized man,
say 170 pounds. Now it follows that if these 152 square
feet of surface are used in one plane, as in the monoplane,
the length and width of this plane must be greater
than if the same amount of surface is secured by using
two planes--the biplane. This results in the biplane
being more compact and therefore more readily manipulated
than the monoplane, which is an important item
for a novice.
Glider the Basis of Success.
Flying machines without motors are called gliders. In
making a flying machine you first construct the glider.
If you use it in this form it remains a glider. If you
install a motor it becomes a flying machine. You must
have a good glider as the basis of a successful flying
It will be well for the novice, the man who has never
had any experience as an aviator, to begin with a glider
and master its construction and operation before he
essays the more pretentious task of handling a fully-
equipped flying machine. In fact, it is essential that he
should do so.
Plans for Handy Glider.
A glider with a spread (advancing edge) of 20 feet, and
a breadth or depth of 4 feet, will be about right to begin
with. Two planes of this size will give the 152 square
yards of surface necessary to sustain a man's weight.
Remember that in referring to flying machine measurements
"spread" takes the place of what would ordinarily
be called "length," and invariably applies to the long
or advancing edge of the machine which cuts into the air.
Thus, a glider is spoken of as being 20 feet spread, and
4 feet in depth. So far as mastering the control of the
machine is concerned, learning to balance one's self in
the air, guiding the machine in any desired direction by
changing the position of the body, etc., all this may be
learned just as readily, and perhaps more so, with a 20-
foot glider than with a larger apparatus.
Kind of Material Required.
There are three all-important features in flying machine
construction, viz.: lightness, strength and extreme
rigidity. Spruce is the wood generally used for glider
frames. Oak, ash and hickory are all stronger, but they
are also considerably heavier, and where the saving of
weight is essential, the difference is largely in favor of
spruce. This will be seen in the following table:
Weight Tensile Compressive
per cubic ft. Strength Strength
Wood in lbs. lbs. per sq. in. lbs. per sq in.
Hickory 53 12,000 8,500
Oak 50 12,000 9,000
Ash 38 12,000 6,000
Walnut 38 8,000 6,000
Spruce 25 8,000 5,000
Pine 25 5,000 4,500
Considering the marked saving in weight spruce has
a greater percentage of tensile strength than any of the
other woods. It is also easier to find in long, straight-
grained pieces free from knots, and it is this kind only
that should be used in flying machine construction.
You will next need some spools or hanks of No. 6
linen shoe thread, metal sockets, a supply of strong
piano wire, a quantity of closely-woven silk or cotton
cloth, glue, turnbuckles, varnish, etc.
Names of the Various Parts.
The long strips, four in number, which form the front
and rear edges of the upper and lower frames, are called
the horizontal beams. These are each 20 feet in length.
These horizontal beams are connected by upright strips,
4 feet long, called stanchions. There are usually 12 of
these, six on the front edge, and six on the rear. They
serve to hold the upper plane away from the lower one.
Next comes the ribs. These are 4 feet in length (projecting
for a foot over the rear beam), and while intended
principally as a support to the cloth covering of
the planes, also tend to hold the frame together in a
horizontal position just as the stanchions do in the vertical.
There are forty-one of these ribs, twenty-one on
the upper and twenty on the lower plane. Then come
the struts, the main pieces which join the horizontal
beams. All of these parts are shown in the illustrations,
reference to which will make the meaning of the
various names clear.
Quantity and Cost of Material.
For the horizontal beams four pieces of spruce, 20 feet
long, 1 1/2 inches wide and 3/4 inch thick are necessary.
These pieces must be straight-grain, and absolutely free
from knots. If it is impossible to obtain clear pieces
of this length, shorter ones may be spliced, but this is
not advised as it adds materially to the weight. The
twelve stanchions should be 4 feet long and 7/8 inch in
diameter and rounded in form so as to offer as little
resistance as possible to the wind. The struts, there
are twelve of them, are 3 feet long by 11/4 x 1/2 inch. For
a 20-foot biplane about 20 yards of stout silk or unbleached
muslin, of standard one yard width, will be
needed. The forty-one ribs are each 4 feet long, and
1/2 inch square. A roll of No. 12 piano wire, twenty-four
sockets, a package of small copper tacks, a pot of glue,
and similar accessories will be required. The entire
cost of this material should not exceed $20. The wood
and cloth will be the two largest items, and these should
not cost more than $10. This leaves $10 for the varnish,
wire, tacks, glue, and other incidentals. This estimate
is made for cost of materials only, it being taken for
granted that the experimenter will construct his own
glider. Should the services of a carpenter be required
the total cost will probably approximate $60 or $70.
Application of the Rudders.
The figures given also include the expense of rudders,
but the details of these have not been included as the
glider is really complete without them. Some of the best
flights the writer ever saw were made by Mr. A. M. Herring in a
glider without a rudder, and yet there can
be no doubt that a rudder, properly proportioned and
placed, especially a rear rudder, is of great value to the
aviator as it keeps the machine with its head to the
wind, which is the only safe position for a novice. For
initial educational purposes, however, a rudder is not
essential as the glides will, or should, be made on level
ground, in moderate, steady wind currents, and at a
modest elevation. The addition of a rudder, therefore,
may well be left until the aviator has become reasonably
expert in the management of his machine.
Putting the Machine Together.
Having obtained the necessary material, the first move
is to have the rib pieces steamed and curved. This curve
may be slight, about 2 inches for the 4 feet. While
this is being done the other parts should be carefully
rounded so the square edges will be taken off. This
may be done with sand paper. Next apply a coat of
shellac, and when dry rub it down thoroughly with fine
sand paper. When the ribs are curved treat them in
the same way.
Lay two of the long horizontal frame pieces on the
floor 3 feet apart. Between these place six of the strut
pieces. Put one at each end, and each 4 1/2 feet put
another, leaving a 2-foot space in the center. This will
give you four struts 4 1/2 feet apart, and two in the center
2 feet apart, as shown in the illustration. This makes
five rectangles. Be sure that the points of contact are
perfect, and that the struts are exactly at right angles
with the horizontal frames. This is a most important
feature because if your frame "skews" or twists you
cannot keep it straight in the air. Now glue the ends
of the struts to the frame pieces, using plenty of glue,
and nail on strips that will hold the frame in place while
the glue is drying. The next day lash the joints together
firmly with the shoe thread, winding it as you would to
mend a broken gun stock, and over each layer put a
coating of glue. This done, the other frame pieces and
struts may be treated in the same way, and you will thus
get the foundations for the two planes.
Another Way of Placing Struts.
In the machines built for professional use a stronger
and more certain form of construction is desired. This
is secured by the placing the struts for the lower plane
under the frame piece, and those for the upper plane
over it, allowing them in each instance to come out flush
with the outer edges of the frame pieces. They are then
securely fastened with a tie plate or clamp which passes
over the end of the strut and is bound firmly against
the surface of the frame piece by the eye bolts of the
Placing the Rib Pieces.
Take one of the frames and place on it the ribs, with
the arched side up, letting one end of the ribs come
flush with the front edge of the forward frame, and the
other end projecting about a foot beyond the rear frame.
The manner of fastening the ribs to the frame pieces is
optional. In some cases they are lashed with shoe
thread, and in others clamped with a metal clamp fastened
with 1/2-inch wood screws. Where clamps and
screws are used care should be taken to make slight
holes in the wood with an awl before starting the screws
so as to lessen any tendency to split the wood. On the
top frame, twenty-one ribs placed one foot apart will be
required. On the lower frame, because of the opening
left for the operator's body, you will need only twenty.
Joining the Two Frames.
The two frames must now be joined together. For this
you will need twenty-four aluminum or iron sockets
which may be purchased at a foundry or hardware shop.
These sockets, as the name implies, provide a receptacle
in which the end of a stanchion is firmly held, and have
flanges with holes for eye-bolts which hold them firmly
to the frame pieces, and also serve to hold the guy wires.
In addition to these eye-bolt holes there are two others
through which screws are fastened into the frame pieces.
On the front frame piece of the bottom plane place six
sockets, beginning at the end of the frame, and locating
them exactly opposite the struts. Screw the sockets into
position with wood screws, and then put the eye-bolts in
place. Repeat the operation on the rear frame. Next
put the sockets for the upper plane frame in place.
You are now ready to bring the two planes together.
Begin by inserting the stanchions in the sockets in the
lower plane. The ends may need a little rubbing with
sandpaper to get them into the sockets, but care must
be taken to have them fit snugly. When all the stanchions
are in place on the lower plane, lift the upper
plane into position, and fit the sockets over the upper
ends of the stanchions.
Trussing with Guy Wires.
The next move is to "tie" the frame together rigidly
by the aid of guy wires. This is where the No. 12 piano
wire comes in. Each rectangle formed by the struts and
stanchions with the exception of the small center one,
is to be wired separately as shown in the illustration.
At each of the eight corners forming the rectangle the
ring of one of the eye-bolts will be found. There are
two ways of doing this "tieing," or trussing. One is to
run the wires diagonally from eye-bolt to eye-bolt, depending
upon main strength to pull them taut enough,
and then twist the ends so as to hold. The other is to
first make a loop of wire at each eye-bolt, and connect
these loops to the main wires with turn-buckles. This
latter method is the best, as it admits of the tension being
regulated by simply turning the buckle so as to draw
the ends of the wire closer together. A glance at the
illustration will make this plain, and also show how the
wires are to be placed. The proper degree of tension
may be determined in the following manner:
After the frame is wired place each end on a saw-horse
so as to lift the entire frame clear of the work-shop
floor. Get under it, in the center rectangle and, grasping
the center struts, one in each hand, put your entire
weight on the structure. If it is properly put together
it will remain rigid and unyielding. Should it sag ever
so slightly the tension of the wires must be increased
until any tendency to sag, no matter how slight it may
be, is overcome.
Putting on the Cloth.
We are now ready to put on the cloth covering which
holds the air and makes the machine buoyant. The kind
of material employed is of small account so long as it is
light, strong, and wind-proof, or nearly so. Some aviators
use what is called rubberized silk, others prefer
balloon cloth. Ordinary muslin of good quality, treated
with a coat of light varnish after it is in place, will answer
all the purposes of the amateur.
Cut the cloth into strips a little over 4 feet in length.
As you have 20 feet in width to cover, and the cloth is
one yard wide, you will need seven strips for each plane,
so as to allow for laps, etc. This will give you fourteen
strips. Glue the end of each strip around the front
horizontal beams of the planes, and draw each strip back,
over the ribs, tacking the edges to the ribs as you go
along, with small copper or brass tacks. In doing this
keep the cloth smooth and stretched tight. Tacks should
also be used in addition to the glue, to hold the cloth to
the horizontal beams.
Next, give the cloth a coat of varnish on the clear, or
upper side, and when this is dry your glider will be
ready for use.
Reinforcing the Cloth.
While not absolutely necessary for amateur purposes,
reinforcement of the cloth, so as to avoid any tendency
to split or tear out from wind-pressure, is desirable. One
way of doing this is to tack narrow strips of some
heavier material, like felt, over the cloth where it laps
on the ribs. Another is to sew slips or pockets in the
cloth itself and let the ribs run through them. Still another
method is to sew 2-inch strips (of the same material
as the cover) on the cloth, placing them about one
yard apart, but having them come in the center of each
piece of covering, and not on the laps where the various
pieces are joined.
Use of Armpieces.
Should armpieces be desired, aside from those afforded
by the center struts, take two pieces of spruce, 3 feet
long, by 1 x 1 3/4 inches, and bolt them to the front and
rear beams of the lower plane about 14 inches apart.
These will be more comfortable than using the struts,
as the operator will not have to spread his arms so
much. In using the struts the operator, as a rule, takes
hold of them with his hands, while with the armpieces,
as the name implies, he places his arms over them, one
of the strips coming under each armpit.
Frequently somebody asks why the ribs should be
curved. The answer is easy. The curvature tends to
direct the air downward toward the rear and, as the air
is thus forced downward, there is more or less of an impact
which assists in propelling the aeroplane upwards.