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

machine.



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

stanchion sockets.



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.