PART 1

One of the commonest phases of interest in aviation is the desire to

build a flying machine. In fact, this is very frequently the first thing

the experimenter undertakes after having gone into the theory of flight

to some extent. Only too often, no effort whatever is made to get beyond

theory and the machine is an experiment in every sense of the word. An

experience of this nature is costly—far more so than is agreeable for

the student, and is likely to result in disgusting him with aviation

generally. There are hundreds of schemes and principles in the art that

have been tried again and again with the same dismal failure in the end.

Refer to the story of the Wright Brothers and note how many things they

mention having tried and rejected as worse than useless. About once in

so often someone "rediscovers" some of these things and, having no

facilities for properly investigating what patent attorneys term the

"prior art" (everything that has gone before, from the beginning of

invention, or at least patented invention) becomes possessed of the idea

that he has hit upon something entirely novel and wholly original. There

is no desire in the present work to discourage the seeker after new

principles—undoubtedly there are many yet to be discovered. The art of

flight is in its infancy and there is still a great deal to be learned

about it, but there is no more discouraged inventor than he

who-discovers a principle and, after having experimented with it at

great expense, finds that it is only one of many things that numerous

others have spent considerable money in proving fallacious, a great many

years ago.

If it be your ambition to build a flying machine and you believe that

you have discovered something new of value, it will be to your interest

to retain a responsible patent attorney to advise you as to the prior

art, before expending any money on its construction. You will find it

very much more economical in the end. There are probably not more than

half a dozen men alive in this country today who "know all the schemes

that won’t work." The average seeker after knowledge is assuredly not

likely to be one of these few, so that until he knows he is working

along new and untried lines that give promise of success, it will pay

him to stick to those that have proved successful in actual practice. In

other words, to confine his efforts in the building line to a machine

that experience has demonstrated will fly if properly constructed and,

what is of equal importance, skilfully handled. Build a machine, by all

means, if you have the opportunity. It represents the best possible

experience. But as is pointed out under the "Art of Flying," take a few

lessons from some one who knows how to fly, before risking your neck in

what is to you a totally untried element. Even properly designed and

constructed machines are not always ready to fly. An aeroplane needs

careful inspection of every part and adjustment before it is safe to

take to the air in it, and to be of any value this looking-over must be

carried out by an experienced eye.

BUILDING AEROPLANE MODELS

The student may enter upon the business of building to any extent that

his inclination or his financial resources or his desire to experiment

may lead him. The simplest stage, of course, is that of model building

and there is a great deal to be learned from the construction and flying

of experimental models. This has become quite a popular pastime in the

public schools and some very creditable examples of work have been

turned out. The apparent limitations of these rubber-band driven models

need not discourage the student, as some of the school-boy builders have

succeeded in constructing models capable of flying a quarter mile in

still air and their action in the air is wonderfully like the full-sized

machines.

*Models with Rubber-Band Motor*. The limitations of the available power

at command must be borne in mind, as the rubber-band motor is at best

but a poor power plant. It is accordingly not good practice to have the

spread of the main planes exceed 24 inches, though larger successful

models have been built. In attempting to reproduce any of the well-known

models, difficulty is often experienced in accommodating the rubber-band

motor to them, as even where the necessary space is available, its

weight throws the balance out entirely, and the result is a model that

will not fly. This has led to the production of many original creations,

but these, while excellent flyers, would not serve as models for larger

machines, as of necessity they have been designed around their power

plants. The rubber bands for this purpose may be purchased of any

aeronautic supply house. The most practical method of mounting the motor

is to attach it to the rear end of the fuselage, usually a single stick,

which is accordingly made extra long for that purpose. At the other end

it is attached to a bent wire fastened to the propeller in order to

revolve the latter. An easy way to wand up the motor is to employ an

ordinary egg beater, modified as described below, or a hand drill,

inserting a small wire yoke in the jaws in place of the usual drill, or

bit. This yoke is placed so as to engage the propeller blades, and the

latter is then turned in the opposite direction, storing energy in the

rubber band by twisting its strands tightly.

[Illustration: Fig. 1. Details of Main Frame of Rubber-Band Driven

Aeroplane Model]

For those students who do not care to undertake an original design at

the outset, or who would prefer to have the experience gained by

building from a plan that has already been tried, before attempting to

originate, the following description of a successful model is given.

This model can not only be made for less than the models sold at three

to five dollars, but is a much more efficient flyer, having frequently

flown 700 feet.

_Main Frame_. The main frame of the model monoplane consists of two

strips A of spruce, each 28 inches long, and measuring in cross section

1/4 by 3/8 of an inch. As shown in Fig. 1, the two strips are tied

together at the front with strong thread and are then glued, the glue

being spread over and between the windings of the thread, Figs. 1 and 2.

The rear ends of these strips are spread apart 4 1/4 inches to form a

stout triangular frame, and are tied together by cross bars of bamboo B

and C which are secured to the main strips A by strong thread and glue.

[Illustration: Fig. 2. Details of Forward Skids of Aeroplane Model]

_Propellers_. The propellers _D_ are two in number and are carried by

the two long strips _A_. Each propeller is 5 inches in diameter, and is

whittled out of a single block of white pine. The propellers have a

pitch of about 10 inches. After the whittling is done they are

sandpapered and coated with varnish. The thickness of the wood at the

hub _E₂_, Fig. 3, of the propeller should be about 5/8 inch. At the rear

ends of the strips _A_, bearing blocks _E₁_ are secured. These bearing

blocks are simply small pieces of wood projecting about 5/8 inch

laterally from the strips _A_. They are drilled to receive a small metal

tube _T₂_ (steel, brass, or copper), through which tube the propeller

shaft _T₁_ passes.

[Illustration: Fig. 3. Details of Propeller and Rudder of Aeroplane

Model]

The propeller shaft itself consists of a piece of steel wire passing

through the propeller hub and bent over the wood, so that it can not

turn independently of the propeller. Any other expedient for causing the

propeller to turn with the shaft may obviously be employed. Small metal

washers _T₃_, at least three in number, are slipped over the propeller

shaft so as to lie between the propeller and the bearing block.

That portion of the propeller shaft which projects forwardly through the

bearing block _E₁_ is bent to form a hook _T₄_. To the hook _T₁_ rubber

strips _T₂_ by which the propellers are driven, are secured. The rubber

strips are nearly as long as the main strips _A_. At their forward ends

they are secured to a fastening consisting of a double hook _G H_, the

hook _G_ lying in a horizontal plane, the hook _H_ in a vertical plane.

The hook holds the rubber strips, as shown in Figs. 1 and 4, while the

hook _H_ engages a hook _T_. This hook is easily made by passing a strip

of steel wire through the meeting ends of the main strips _A_, the

portions projecting from each side of the strips being bent into the

hooks _I_.

_Skids_. Three skids are provided, on which the model slides, one at the

forward end, and two near the rear end. All are made of bamboo. As shown

in Fig. 2 the front skid may be of any length that seems desirable. A

6-inch piece of bamboo will probably answer most requirements. This

piece _N_ is bent in opposite directions at the ends to form arms _Z_

and _U_, The arm _Z_ is secured to the forward ends of the two strips

_A_, constituting the main frame, by means of thread and glue. The

strips and skid are not held together by the same thread, but the skid

is attached to the two strips after they have been wound. Hence, there

are two sets of windings of thread, one for the two strips _A_

themselves, and another for the skid and the strips. Strong thread and

glue should be used, as before. In order to stiffen the skid, two bamboo

struts _W_ will be found necessary. These are bent over at the ends to

form arms _V₁_, Fig. 2. Each of the arms is secured to the under side of

a strip _A_ by strong thread and glue. The arms _X_ are superimposed and

tied to the bamboo skid _V_ with strong thread and glue.

[Illustration: Fig. 4. Details of Rear Skids on Aeroplane Model]

The two rear skids, of which one is shown in Fig. 5, consist each of two

5-inch strips of bamboo _S_, likewise bent at either end in opposite

directions to form arms _S₂_ and _S₃_, The arms _S₂_ are fastened to the

strips _A_ by strong thread and glue. To stiffen the skids a strut _C₁_

is provided for each skid. Each strut consists of a 3-inch strip of

bamboo bent over so as to form arms _C₂_. Strong thread and glue are

employed to fasten each strut in position on the strip and the skid. In

the crotch of the triangular space _B₁_, a tie bar _J_, Figs. 4 and 5,

is secured by means of thread and glue. This tie bar connects the two

skids, as shown in Figs. 1 and 4, and serves to stiffen them. The

triangular space _B₁_ is covered with paper, preferably bamboo paper. If

bamboo paper is not available, parchment or stiff light paper of some

kind may be used. It does not need to be waterproof. Thus triangular

fins are formed which act as stabilizing surfaces.

[Illustration: Fig. 5. Enlarged Details of One Rear Skid, Aeroplane

Model]

_Main Planes_. The main planes are two in number, but are different in

size. Contrary to the practice followed in large man-carrying

monoplanes, the front supporting surface is comparatively small in area

and the rear supporting surface comparatively large. These supporting

surfaces _L_ and _P_ are shown in detail in Figs. 6 and 7. It has been

found that a surface of considerable area is required at the rear of the

machine to support it, hence, the discrepancy in size. Although the two

supporting surfaces differ in size, they are made in exactly the same

manner, each consisting of a thin longitudinal piece of spruce _R_, to

which cross pieces of bamboo _Q_ are attached. In the smaller plane,

Fig. 7, all the cross pieces are of the same size. In the larger plane,

Fig. 6, the outer strips _S_ are somewhat shorter than the others. Their

length is 2 1/2 inches, whereas the length of the strips _Q_ is 3 1/2

inches. In order to allow for the more gradual tapering of the plane,

around the outer ends of the longitudinal strips _R_ and the ribs _Q_ a

strip of bamboo is tied. The frame, composed of the longitudinal strip

and cross strips, is then covered with bamboo paper, parchment paper, or

any other style light paper, which is glued in place.

[Illustration: Fig. 6. Details of Main Plane of Aeroplane Model]

[Illustration: Fig. 7. Details of Smaller Plane of Aeroplane Model]

The forward or smaller plane has a spread of 8 1/2 inches and a depth of

3 1/4 inches. The main plane has a spread of 20 inches and a depth of 3

1/2 inches at the widest portion. The author has made experiments which

lead him to believe that the tapering form given to the outer edge of

the plane improves both the stability and endurance of the machine.

The planes are slightly arched, although it will be found that flat

planes will also give good results. The rear edge of the main plane

should be placed 4 1/4 inches distant from the forward edge of the

propeller block _E₁_.

The front plane must have a slight angle of incidence, just how much

depends upon the weight of the machine, the manner in which it is made,

and various other factors. This angle of incidence is obtained by

resting the front portion of the plane on two small blocks N, Figs. 1

and 2, which are fastened to the top of the main strip _A_ by strong

thread and glue.

[Illustration: Fig. 8. Device for Winding up Rubber-Band Motors]

The height of the blocks N should be about 1/4 inch, although this will

necessarily vary with the machine. The blocks should be placed

approximately 4 inches from the forward end of the machine. The front

end of the forward plane should be elevated about 1/4 inch above the

rear end, which rests directly on the main strips.

Both the front and rear planes _L_ and _P_ are removably lashed to the

frame by means of ordinary rubber bands, which may be obtained at any

stationery store. These rubber bands are lettered _M_ in Fig. 1.

_Winding the Rubber Strips_. The rubber strips can be most conveniently

wound up by means of an egg beater, slightly changed for the purpose.

Fig. 8. The beater and the frame in which it is carried are entirely

removed, leaving only the main rod _E_, which is cut off at the lower

end so that the total length is not more than 2 or 3 inches. The two

brass strips _D_ on either side of the rod, which are attached to the

pinion _Q_ meshing with the large driving wheel _H_, are likewise

retained. A washer _F_ is soldered to the rod near its upper end, so as

to limit the motion of the small pinion and the brass strips _D_

attached to the pinion. Next a wire _B_ is bent in the form of a loop,

through which loop the central rod passes. The ends of the wire are

soldered to the side strips _D_. Lastly, a piece of wire _C_ is bent and

soldered to the lower ends of the side strips. In order to wind up a

rubber strip, the strip is detached from the forward end of the model,

and the hook _A_ slipped over the wire _C_. The opposite end of the

rubber band is held in any convenient manner. Naturally the two strips

must be wound in opposite directions, so that the two propellers will

turn in opposite directions. By stretching the rubber while it is being

wound, more revolutions can be obtained. It is not safe to have the

propeller revolve more than 700 times. The ratio of the gears of the

egg-beater winder can be figured out so that the requisite number of

twists can be given to the rubber bands for that particular number of

revolutions.

_Model with Gasoline Motor_. The next and somewhat more ambitious stage

is the building of a power-driven model, which has been made possible by

the manufacture of miniature gasoline motors and propellers for this

purpose. Motors of this kind, weighing but a few pounds and capable of

developing 1/4 horse-power or more, may be had complete with an 18-inch

aluminum propeller and accessories for about $45. As is the case with

the rubber-band driven model, the monoplane is the simplest type to

construct, and the dimensions and details of an aeroplane of this type

are given here. It will be found that a liberal-sized machine is

required to support even such a small motor. The planes, Fig. 9, have a

spread of 7 feet 8 inches from tip to tip, each wing measuring 3 1/2

feet by a chord of 15 inches. They are supported on a front and rear

wing spar of spruce, 1/2 by 3/8 inch in section, while the ribs in both

the main plane and the rear stabilizing plane measure 1/8 by 1/2 inch in

cross section. There are eight of these spruce ribs in the main plane,

and they are separately heated and curved over a Bunsen burner, or over

a gas stove, which is the same tiling. They are then nailed to the wing

spars 6 inches apart. The main spars of the fuselage are 7 feet long and

they are made of 1/2 by 3/8 inch spruce, the struts being placed 1 1/2

feet apart, measuring from the rear, with several intermediate struts to

brace the engine bed. Instead of using strut sockets for the fuselage,

which would increase the cost of construction unnecessarily, a simple

combination of a three-way wire fastener and a wire nail may be resorted

to. The shape of these fasteners is shown at _A_ in Fig. 9. They may be

cut out of old cracker boxes or tin cans (sheet iron) with a pair of

shears, the holes in the ends being made either with a small drill or by

driving a wire nail through the metal placed on a board, and filing the

burrs off smooth. A central hole must also be made for the 1 1/2 inch

wire nail which is driven through the main spar and the fastener then

slipped over it. As indicated, this nail also serves to hold the strut.

A drop of solder will serve to attach the fastener to the nail. The

front of the fuselage is 9 inches square, tapering down to 6 inches at

the rear. The height of the camber of the main planes is 1 1/2 inches

and the angle of incidence is 7 degrees, measured with relation to the

fuselage. The non-lifting tail plane at the rear which is to give the

machine longitudinal stability, measures 4 feet in span by 14 inches in

depth.

[Illustration: Fig. 9. Details of Power-Driven Aeroplane Model]

The running gear or front landing frame is made of 1/2 inch square

spruce, all joints being made with 1/16 by 1 inch bolts. Aluminum

sleeves, procurable at an aeronautic supply house, are employed for the

attachment of the rubber springs and the radius rods running down to the

wheels, which may also be purchased ready to install. Old bicycle wheels

will serve the purpose admirably. Light steel tubes 1/2 inch in diameter

are used to run these aluminum sleeves on. Two other steel tubes are

joined to the lower corner of the frame by flattening them at the ends

and drilling with a small hole for a nail. These are run diagonally up

to the fuselage and serve as buffers to take the shocks of landing. For

bracing the wings, two similar tubes are fastened to form a pyramid on

top of the main plane just back of the engine. From these, guys are run

to the wings as shown. The engine bed is made of 1/2 by 3/4-inch white

pine, and to make it solid it is carried as far back as the rear edge of

the main plane. The batteries and coil are directly attached to this

plane, care being taken in their placing to preserve the balance of the

machine. The rudder measures 14 inches square and is made of 3/8-inch

square spruce, reinforced with tin at the joints, as it is necessary to

make the frame perfectly rigid. Both sides are covered with fabric. In

this case a 1-horse-power motor furnishes the necessary energy and it is

fitted with an 18-inch aluminum propeller which it is capable of turning

at 2,400 r.p.m. The carbureter and gas tank are made integral, and the

gasoline and oil are both placed in this tank in the proportion of about

four parts to one, in order to save the weight of an extra tank for oil.

Flights of half a mile are possible with this model in calm weather, but

a great deal of measuring and testing of the fuel is necessary in order

to regulate the flight, and "grass-cutting" should be practiced by the

builder in order to properly regulate the machine. Trials have shown

that the flat non-lifting tail on the fuselage gives excellent

longitudinal stability, the machine rising nicely and making its descent

very easy angle, so that it is seldom damaged by violent collisions in

landing.

BUILDING A GLIDER

The building of hand- or power-driven models does not suffice to give

that personal experience that most students are desirous of obtaining.

The best method of securing this is to build a glider and practice with

it. Any flying machine without a motor is a glider and the latter is the

basis of the successful aeroplane. In the building of an aeroplane the

first thing constructed is the glider, _i.e._ the frame, main planes,

stabilizing planes, elevators, rudders, etc. It is only by the

installation of motive power that it becomes a flying machine. The

biplane will be found the most satisfactory type of glider as it is more

compact and therefore more easily handled, which is of great importance

for practicing in a wind. The generally accepted rule is that 152 square

feet of surface will sustain the weight of the average man, about 170

pounds, and it will be apparent that the length of the glider will have

to be greater if this surface is to be in the form of a single plane

than if the same amount is obtained by incorporating it in two

planes—the biplane. A glider with a span of 20 feet and a chord of 4

feet will have a surface of 152 square feet. So far as learning to

balance and guide the machine are concerned, this may be mastered more

readily in a small glider than in a large one, so that there is no

advantage in exceeding these dimensions—in fact, rather the reverse, as

the larger construction would be correspondingly more difficult to

handle. The materials necessary consist of a supply of spruce, linen

shoe thread, metal sockets, piano wire, turnbuckles, glue, and

closely-woven, light cotton fabric for the covering of the planes.

*Main Frame*. The main frame or box cell is made of four horizontal

beams of spruce 20 feet long and 1 1/2 by 3/4 inch in section. They must

be straight-grained and perfectly free from knots or other defects. If

it be impossible to obtain single pieces of this length, they may be

either spliced or the glider may be built in three sections, consisting

of a central section 8 feet long, and two end sections each 6 feet in

length, this form of construction also making the glider much easier to

dismantle and stow in a small space. In this case, the ends of the beams

of each end section are made to project beyond the fabric for 10 inches

and are slipped into tubes bolted to corresponding projections of the

central section. These tubes are drilled with three holes each and bolts

are passed through these holes and corresponding holes in the projecting

ends after they have been fitted into the tubes, and drawn up tightly

with two nuts on each bolt to prevent shaking loose. Ordinary 3/16-inch

stove bolts will serve very nicely for this purpose. The upper and lower

planes forming the box cell, are held apart by 12 struts, 4 feet long by

7/8 inch diameter, preferably of rounded or oval form with the small

edge forward to minimize the head resistance. It is only necessary to

space these equally, starting from both ends; this will bring the

splices of the demountable sections in the center of the square on

either side of the central section. The main ribs are 3 feet long by 1

1/4- by 1/2-inch section and their placing should coincide with the

position of the struts. Between these main ribs are placed 41 small

ribs, equally spaced and consisting of pieces 4 feet long by 1/2 inch

square. These, as well as all the other pieces, should have the sharp

edges of the square rounded off with sand paper. The ribs should have a

camber of 2 inches in their length and the simplest method of giving

them this is to take a piece of plank, draw the desired curve on it, and

then nail blocks on both sides of this curve, forming a simple mould.

The rib pieces should then be steamed, bent into this mould, and allowed

to dry, when they will be found to have permanently assumed the desired

curvature. Meanwhile, all the other pieces may be shellaced and allowed

to dry.

[Illustration: Fig 10. Wrong and Right way of Making a Wire Joint]

_Assembling the Planes_. To assemble the glider, the beams are laid out

on a floor, spaced the exact distance apart, _i.e._, 3 feet, and exactly

parallel—in the demountable plan, each section is assembled

independently. The main ribs are then glued in place and allowed to set,

after which they are strongly bound in place with the linen thread, and

the various layers of thread given a coating of hot glue as they are put

on. This method is not arbitrary, but it is simple and gives the

lightest form of construction. If desired, tie-plates, clamps, or any

other light method of fastening may be employed. This also applies to

the ribs. They are assembled by placing them flush with the front beam

and allowing them to extend back a foot beyond the rear beam, arched

side up in every case. They may be glued and bound with thread, held by

clamps, or nailed or screwed into place, care being taken to first start

a hole in the beam with an awl and to dip the nails in soft soap to

prevent splitting the wood. Twenty-one ribs, spaced one foot apart, are

used in the upper plane, and 20 in the lower, owing to the space left

for the operator in the latter. For fastening the two planes together,

whether as a whole or in sectional units, 24 aluminum sockets will be

required. These may be purchased either ready to fit, or an effective

substitute made by sawing short lengths of steel tubing, slitting them

with the hack saw an inch from the bottom, and then flattening out and

drilling the right-angle flanges thus formed to take screws for

attaching the sockets to the beams. In case these sockets are bought,

they will be provided with eye bolts for the guy wires; if homemade,

they may have extra holes drilled in the edges of the flanges for this

purpose or some simple wire fastener such as that described in

connection with the power-driven model may be used, heavier metal,

however, being employed to make them. The sockets should all be screwed

to the beams at the proper points and then the struts should be forced

into them. The next move is to "tie" the frame together with guy wires.

No. 12 piano wire being employed for this purpose. Each rectangle is

trussed by running diagonal guy wires from each corner to its opposite.

To pull these wires taut, a turnbuckle should be inserted in each and

after the wire has been pulled as tightly as possible by hand, it should

be wound upon itself to make a good strong joint, as shown at _B_, Fig.

6. A fastening as shown at _A_ will pull out under comparatively little

strain and is not safe. As is the case with most of the other fittings,

these turnbuckles may be bought or made at home, the simple bicycle type

of turnbuckle mentioned in connection with "Building a Curtiss," being

admirably adapted to this purpose. In fact, the construction of the

latter will be found to cover the requirements of the glider, except

that the ribs are simpler and lighter, as already described, and no

provision for the engine or similar details is necessary. All the guy

wires must be tightened until they are rigid, and the proper degree of

tension for them may be simply determined in the following manner:

After the entire frame is wired, place each end of it on a saw horse so

as to lift it two or three feet clear of the floor. Stand in the opening

of the central section, as if about to take a glide, and by grasping the

forward central struts, raise yourself from the floor so as to bring

your entire weight upon them. If properly put together the frame will be

rigid and unyielding, but should it sag even slightly, the guy wires

must be uniformly tightened until even the faintest perceptible tendency

to give under the weight is overcome.

_Stretching the Fabric_. The method of attaching the fabric will be

determined by whether the glider is to be one piece or sectional, and

the expense for this important item of material may be as little or as

much as the builder wishes to make it. Some employ rubberized silk,

others special aeronautic fabrics, but for the purposes of the amateur,

ordinary muslin of good quality, treated with a coat of light varnish

after it is in place, will be found to serve all purposes. The cloth

should be cut into 4-foot strips, glued to the front horizontal beams,

stretched back tightly, and tacked to both the rear horizontal beams and

to the ribs. Tacks should also supplement the glue on the forward beams

and the upholstery style should be used to prevent tearing through the

cloth. In case the glider is built in sections, the abutting edges of

the cloth will have to be reinforced by turning it over and stitching

down a strip one inch wide, and it will make this edge stronger if an

extra strip of loose fabric be inserted under the turn before sewing it

down. Eyelets must then be made along these edges and the different

sections tightly laced together when assembling the glider. It is also

desirable to place a strip of cloth or light felt along the beams under

the tacks to prevent the cloth from tearing out under the pressure.

To form a more comfortable support for the operator, two arm pieces of

spruce, 3 feet by 1 inch by 1 3/4 inches, should be bolted to the front

and rear beams about 14 inches apart over the central opening left in

the lower plane. These will be more convenient than holding on to the

struts for support, as it will not be necessary to spread the arms so

much and there will be more freedom for manipulating the weight to

control the glider in flight. In using the struts, it is customary to

grasp them with the hands, while with the arm pieces, as the name

implies, the operator places his arms over them, one of the strips

coming under each armpit. After the fabric has been given a coat of

varnish on the upper side and allowed to dry, the glider is ready for

use. The cost of the material should be about $30 to $40, depending upon

the extent to which the builder has relied upon his own ingenuity in

fashioning the necessary fittings—in any case, it will be less than the

amount required for the purchase of the engine alone for a power-driven

model.

*Glider with Rudder and Elevator*. It will be noted that this is the

simplest possible form of glider in that it is not even provided with a

rudder, but for the beginning of his gliding education the novice will

not require this, as first attempts should be confined to glides over

level ground in moderate, steady wind currents and at a modest

elevation. Some of the best gliding flights made by Herring, Chanute’s

co-worker, were in a rudderless glider. After having mastered the

rudiments of the art, the student may go as far as the dictates of his

ambition impel him in the direction of improvements in his glider, by

adding a rudder, elevator, and warping control. In fact, it is not

necessary to confine himself to the simple design of glider here

outlined at all. He may take either the Wright or Curtiss machines as a

model and build a complete glider, following the dimensions and general

methods of construction here given, though these may also be improved

upon by the man handy with tools, bearing in mind that the object to be

achieved is the minimum weight consistent with the maximum strength.

*Learning to Glide*. The first trials should be made on level ground and

the would-be aviator should be assisted by two companions to help him in

getting under way. The operator takes a position in the center

rectangle, back far enough to tilt up slightly the forward edges of the

planes. A start and run forward is made at a moderate pace, the keepers

carrying the weight of the glider and overcoming its head resistance by

running forward at the same speed. As the glider cuts into the air, the

wind caused by running will catch under the uplifted edges of the curved

planes and will buoy it up, causing it to rise in the air taking the

operator with it. This rise will be probably only sufficient to lift him

clear of the ground a foot or two. Now he projects his legs slightly

forward so as to shift the center of gravity a trifle and bring the

edges of the glider on an exact level, parallel with the ground. This,

with the momentum acquired at the start, will keep the glider moving

forward for some distance. When the weight of the operator is slightly

back of the center of gravity, the leading edges of the planes are

tilted up somewhat, increasing the angle of incidence and in consequence

the pressure under the planes, causing the glider to rise, and if the

glide is being made into a wind, as should always be the case, quite a

height may be reached as the result of this energy. Once it ceases, the

tendency to a forward and upward movement is lost, and it is to prolong

this as much as possible that the operator shifts the center of gravity

to bring the machine on an even keel, or where at a little height,

slightly below this, giving it a negative angle of incidence, which

permits him to coast down the air until sufficient speed is acquired to

reverse the angle of incidence and again rise so as to provide a "hill"

for another coast, thus prolonging the flight considerably. To put it in

the simplest language, when the operator moves backward, shifting the

center of gravity to the rear, the planes are tilted so that they catch

or "scoop up" the advancing air and rise upon it, whereas when he moves

forward and the planes tilt downward, this air is "spilled" out behind

and no longer acts as a support, and the glider coasts, either until the

ground is reached or enough momentum is gained to again mount upon the

wind. A comparatively few flights will suffice to make the student

proficient in the control of his apparatus by his body movements, not

only as concerns the elevating and depressing of the planes to ascend or

descend, corresponding to the use of the elevator on a power machine,

but also actual steering, which is accomplished by lateral movement to

the left or right.

Stable equilibrium is one of the chief essentials to successful flight

and this can not be maintained in an uncertain, gusty wind, especially

by the novice. The beginner should certainly not attempt a glide unless

the conditions are right. These are a clear, level space without

obstructions such as trees, and a steady wind not exceeding 12 miles per

hour. When a reasonable amount of proficiency has been attained in the

handling of the glider over level ground, the field of practice may be

changed to some gentle slope. In starting from this, it will be found

easier to keep the glider afloat, but the experience at first will prove

startling to the amateur, for as the glider sails away from the top of

the slope, the distance between him and the ground increases so rapidly

that he will imagine himself at a tremendous height, but by preserving

the balance and otherwise manipulating his weight in the manner taught

by the practice over the level, a nice flight of much greater distance

will be made and the machine will gradually settle down to the ground

much farther away from the starting place than was possible in the

earlier trials, this being one of the great advantages of starting from

an elevation. There is nothing that will fit the beginner so well for

the actual handling of a power machine as a thorough course of gliding

flights, and it is recommended that those who build gliders become

proficient in their use before attempting to pilot an aeroplane, whether

of their own make or not.

A further step in advance is the actual building of a full-fledged power

machine, and for those who desire a simple and comparatively inexpensive

type, requiring very little work that can not be performed in the home

workshop, a description of the construction of a Curtiss biplane is

given, while for those who are more ambitious and also have greater

financial resources, the details of the building of a Bleriot monoplane

are given.

BUILDING A CURTISS BIPLANE

Cost. First of all, the prospective builder will want to know the cost.

The best answer to this is that the machine will cost all its builder

can afford to spend upon it and probably a little more, as the man to

whom the expense is not of vital consideration will doubtless not

undertake its construction. Speaking generally, and there can be nothing

very definite about it, in view of the great difference in the

conditions, an expenditure of three to four hundred dollars will cover

the complete outlay for everything but the motor. If the builder has the

time and facilities for doing all the work himself, this amount may be

reduced very materially. On the other hand, if he finds it necessary to

purchase most of the material in form ready to assemble, it may exceed

this. But it will be a great aid to many to know that there is

practically nothing about the modern aeroplane which can not be found in

stock at one of the aeronautic supply houses. This makes it possible for

many to undertake the construction of a machine to whom it would not be

feasible, or at least not an attractive project in view of the time

involved, were it necessary to make every part at home. So far as

becoming involved in any legal difficulties is concerned owing to

existing patents, the student need not worry himself about this in

attempting the construction of a Curtiss biplane, so long as he

restricts the use of his machine to experimental purposes and does not

try to compete with the patentees in their own field—that of exhibiting

and selling machines.

[Illustration: Fig 11. Detailed Front View of Curtiss Biplane]

*General Specifications*. Just how long it will take to complete such a

machine will depend very largely upon the skill of the builder and the

extent of his resources for, as already mentioned, the expense may be

cut down by making all the necessary parts at home, but it will

naturally be at the sacrifice of a great deal of time. For instance, the

oval struts and beams may be bought already shaped from the local

planing mill, or they may be shaved down from the rough by hand.

Turnbuckles can be made from bicycle spokes and nipples and strips of

sheet steel, or they can be bought at 12 to 15 cents each. As a hundred

or more of them are needed, their cost is quite a substantial item.

[Illustration: Fig 12. Plan and Side Elevation of Curtiss Biplane]

Aeroplane construction doubtless impresses the average observer as being

something shrouded in considerable mystery—something about which there

is no little secrecy. Quite the contrary is the case in reality. Any man

who is fairly proficient as a carpenter and knows how to use the more

common machinist’s tools, such as taps and dies, drills, hacksaw, and

the like, will find no difficulty in constructing the machine of which

the details are given here. Having completed its building, he will have

to draw upon his capital to supply the motor. One capable of developing

25 to 30 horse-power at 1,000 to 1,200 r.p.m. will give the machine

considerable speed, as it will be recalled that Curtiss made a number of

his first flights with a 25-horse-power motor. As to the weight, the

lighter the better, but 400 pounds for the complete power plant will not

be excessive. The machine can sustain itself in the air with less power

than that mentioned, but with a heavy, low-power motor it will be

sluggish in action. This is an advantage for the amateur, rather than

otherwise, as it will provide him with an aeroplane that will not be apt

to get away from him during his first trials, thus making it safer to

learn on.

[Illustration: Fig 13. Details of Main and Small Ribs, Curtiss Biplane]

The Curtiss biplane has a spread of 30 feet, the main planes or wings

being divided into sections of a length equal to the distance between

struts, Figs. 11 and 12. There are five of these sections, each

measuring six feet. The struts can be taken out and the sections laid

flat on each other for storage. The framework for the front and rear

rudders can also be jointed, if desired, making it possible to store the

machine in small compass. The longest parts of the machine, when taken

apart, are the two diagonal beams running from the front wheel back to

the engine bed, and the skid. The horizontal front rudder is packed

intact. The vertical rear rudder is unhung and laid flat on the tail.

Two men can take the machine apart in a few hours, and can reassemble it

in a day. Whether these particular features of construction are covered

by patents can not be said, as Curtiss has declined to commit himself

regarding any rights he may have to them.

_Ribs_. Two distinct types of ribs are used, main ribs and small ribs,

both of the same curvature, Fig. 13. The main ribs are used between

pairs of struts, to hold apart the front and rear beams; they are heavy

enough to be quite rigid. Three to four small ribs are laid across each

section of the planes, between the pairs of main ribs, to give the cloth

the proper curvature, and to maintain it in the form desired. The main

ribs are built up of six 1/4-inch laminations of wood 7/8 inch wide and

securely glued together. The small ribs are made of three layers 1/2

inch wide.

The first part of the actual construction will be the making of these

laminated ribs, but before describing this detail, the question of

suitable material should be well considered. Both weight and strength

must be figured on and this limits the choice to a few kinds of wood. Of

these _spruce_ and _elm_ are the best available, with the occasional use

of _ash_ to give greater rigidity. Spruce is, of course, the first

choice. This wood was once considered as having no great strength, but a

series of careful tests shows this belief to be unfounded. With the

exception of the bed, or support for the motor and a few other parts,

the Wright machines are constructed wholly of spruce.

Table I gives results of tests made with spruce from Washington and

Oregon, and with elm from Michigan and Indiana. Testing scales were

employed, the pieces being supported at their ends with the load in the

center.

These tests were made with clear wood in each case, as knots naturally

decrease the strength of a piece greatly, this depending on their size

and location.

[Illustration: Fig. 14. Details of Rib Press, Curtiss Biplane]

Before proceeding with the ribs themselves, the press for giving them

the proper curvature must be made. Take a good piece of oak, ash, or

other solid wood, 8 inches wide by 5 feet long, and dressed all over. On

the side of the piece lay out the curve, the dimensions of which are

illustrated in Fig. 14. First, rule the horizontal, or chord line, on

it, marking off 4 feet 6 inches on this line, equidistant from each end.

Then divide the chord into 6-inch sections and, at the point of each

6-inch section, erect perpendiculars beginning at the rear, 3/4 inch, 1

3/8 inches, 2 inches, and so on, as indicated on the drawing. The upper

ends of these perpendiculars will form locating points for the curve.

Through them draw a smooth curve as shown, continuing it down through

the chord at each end. Take the piece with the curve thus marked on it

to the local planing, sash and blind, or sawmill—any plant equipped with

a band saw—and have it cut apart along the curve. This will cost little

or nothing—acquaintance will obtain it as a favor, and acquaintance with

any wood-working concern in the aeroplane builder’s home town will be of

great aid. Failing this aid, the operation may be carried out with a

hand saw (rip), but the job will not be as neat and will have to be

cleaned up with a draw knife and sand paper, taking care to preserve the

outline of the curve as drawn. As the rib press is really a mould or

pattern from which all the ribs are to be bent to a uniform curvature,

care must be taken in its construction.

To clamp the two halves of the press together, a dozen machine bolts

will be required; they should measure 3/4 X 15 inches. If obtainable,

eye bolts will be found more convenient as they may be turned up with

but one wrench and a bar. The steel straps are 3/8 by 1 1/2 by 10 inches

long with 3/4-inch holes drilled 9 inches apart to centers, to enclose

the 8-inch pieces.

Obtain a sufficient supply of boards of reasonably clear spruce, 1/4

inch thick, 6 to 7 inches wide, and at least 4 feet 9 inches long

(dressed both sides), to make all the ribs necessary both small and

large. This material should be purchased from the mill as it is out of

the question to attempt to cut the ribs from larger sizes by hand. Buy

several pounds of good cabinet makers’ glue and a water-jacketed

gluepot. This glue comes in sheets and in numerous grades—a good quality

should be used, costing from 40 to 50 cents a pound if bought in a large

city. Laminating the ribs in this manner and gluing them together is not

only the quickest and easiest method of giving them the proper curve,

being much superior to steam bending, but is also stronger when well

done, as the quality of the material can be watched more closely.

Start with the making of the small ribs; apply the glue thin and piping

hot in a generous layer to three boards with a good-sized flat paint or

varnish brush. Omit on the upper surface of third board and apply

between three others, Fig. 13. This will give two series of three each

in the press. Tighten up the end bolts first, as the upper part of the

press near the top of the curve is likely to be weak unless liberally

proportioned. Then turn down the nuts on the other bolts. Do not attempt

to turn any one of them as far as it will go the first time, but tighten

each one a little at a time, thus gradually making the compression over

the whole surface as nearly uniform as possible. This should be

continued until the glue will no longer ooze out from between the

boards, indicating that they are in close contact. Twenty-four hours

should be allowed for drying, and when taken out the cracks between the

boards should be almost invisible in the finished ribs.

Have the laminated boards cut by a power rip saw at the planing mill, to

the dimensions shown in the drawing, making an allowance of 1/4 inch for

the width of the saw blade at each cut in calculating the number of ribs

which can be cut from each board. In addition, a margin should be

allowed at each side, as it is impractical to get all the thin boards

squarely in line. For the main ribs, apply the glue between all six

boards, clamp and dry in the same manner. Thirty small ribs will be

required, if three are used in each section, and forty if four are

specified, while twelve main ribs will be needed for standard

construction, and sixteen if the quick-demountable plan referred to is

followed. It is advisable to make several extra ribs of each kind in

addition. If the builder has not sufficient faith in spruce alone,

despite the figures given in Table I, one of the laminations, preferably

the center, or if two be employed, the outer ones, may be of ash, though

this will add considerably to the weight.

To prevent the ribs from splitting open at the ends, they are protected

by light steel ferrules, shown in Fig. 15. When received in the

rough-sawed condition from the mill, the ribs must be tapered at the

ends with a plane or spoke shave to fit these ferrules, and the sharp

edges should be rounded off. In doing this, it must be remembered that

the upper surface of the small ribs gives the curvature to the cloth

surface, so that any tapering must be done on the lower side. The main

ribs may be tapered from both sides, as it is the center line, or crack

between the third and fourth laminations, that determines the curve.

Every inch along this line A-inch holes are to be drilled for the

lacing, Fig. 15.

The ferrules for the front ends of the small ribs are light 1/2-inch

seamless steel tubing; they may be flattened to the proper shape in a

vise without heating and are drilled with a 1/8-inch hole. They are

driven tight on to the tapered ends of the ribs and fastened in place

with a small screw. The rear-end ferrules are 1/2-inch lengths of

3/8-inch tubing, driven on and drilled with a 1/32-inch hole for the

rear-edge wire. The rear ferrules of the main ribs may be the same

1/2-inch tubing used for the front of the small ribs; they should be cut

off so that their ends will come in the same line as the holes in the

ends of the small ribs. If the quick-demountable plan be followed, the

second main rib from each end may be left long and drilled with a hole

like the small ribs. The front ferrules of the main ribs should be

3/4-inch tubing of heavier gauge, drilled with a 1/4-inch hole. The

finished ribs are sandpapered smooth and shellaced or coated with spar

varnish. The latter is much more expensive and slower in drying but has

the great advantage of being weather-proof and will protect the glue

cracks from moisture. The ferrules may be painted with black enamel.

[Illustration: Fig. 15. Details of Ribs and Struts, Curtiss Biplane]

_Struts_. Before going into the detail of the construction of the

remainder of the _main cell_ and its attached framing, a brief

description of its parts and their relation to one another will make

matters clearer. The upright struts, Fig. 15, which hold the two planes

apart, fit at each end into sockets, which are simply metal cups with

bolts projecting through their ends. Fig. 16. Those at the bottom of the

front row of struts pass through the eyes of the turnbuckles and

connections for the wire trussing, then through the flattened ferrules

of the main ribs, and finally through the beam, all being clamped

together with a nut. Those at the top go through the turnbuckles first,

then through the beam, and finally the rib ferrule. The bolts at the

back row of struts must go through the full thickness of the main ribs,

and so must be longer. The drawings. Figs. 15 and 16, show the method of

attachment of both the main and the small ribs and illustrate a neat

method of attaching the turnbuckles—instead of being strung on the

socket bolt one after another, they are riveted to the corners of a

steel plate which alone is clamped under the socket.

[Illustration: Fig. 16. Details of Metal Parts of Curtiss Biplane]

_Beams_. The beams are jointed at each strut connection, the ends being

cut square and united by a sheet-steel sleeve, a pattern of which is

shown in Fig. 16, clamped on by two small bolts. The hole for the socket

bolt is drilled half in each of the two abutting beams. As it is very

difficult to obtain long pieces of wood sufficiently straight grained

and free from knots for the purpose, this jointed system considerably

cheapens the construction. Both beams and struts are of spruce, but to

give additional strength, the beams of the middle section may be ash.

Special aero cloth, rubberized fabrics, or light, closely-woven duck

(racing yacht sail cloth of fine quality, this being employed at first

by the Wright Brothers in their machines) forms the surfaces of the

wings. The front edge of each section of the surface is tacked to the

beam and the rear edge is laced over the rear wire already referred to,

this wire being stretched taut through the holes in the rear tips of the

ribs, both main and small. After the cloth is stretched tight, it is

tacked to the small ribs, a strip of tape being laid under the tack

heads to prevent the cloth from pulling away from under them. If the

aeroplane is intended to be taken apart very often, the standard design

as shown by the large drawings, Figs. 11 and 12, may be modified so as

to make it unnecessary to unlace the cloth each time. This is arranged

by regarding the two outer sections at each end of the plane as one, and

never separating them. Additional main ribs are then provided at the

inner ends of these sections, and are attached directly to the beams,

instead of being clamped under the strut sockets. In taking the machine

apart, the struts are pulled from the sockets, leaving the latter in

place. It will then be an advantage to shorten the main planes somewhat,

say 3 inches on each section, so that the outer double sections will

come under the "12-foot rule" of the Express Companies.

_Running Gear_. Three wheels are provided—one in front under the

outrigger and two under the main cell for starting and landing. Two

beams extend from the front wheel to the engine bed and serve to carry

the pilot’s seat, as will be seen from the elevator, Fig. 12. A third

beam runs back horizontally from the front wheel and on rough ground

acts as a skid. The rest of the running gear is made of steel tubing,

the pieces being joined simply by flattening the ends, drilling and

clamping with bolts; no sockets or special connections of any kind are

necessary here. If desired, the wheels may be carried in bicycle forks

and may be fitted with shock absorbers, some idea of the various

expedients adopted by different builders for this purpose being

obtainable from the sketches. Fig. 40 in "Types of Aeroplanes." Two

separate tubes, one on each side of the wheel make a simple construction

and will probably serve just as well. The details of the running gear

will be given later.

_Outrigging and Rudders_. For the outriggers and the frames carrying the

front horizontal or elevating rudder and the rear vertical rudder and

tail, or horizontal keel, either spruce or bamboo may be employed.

Bamboo will be found on machines turned out by the Curtiss factory, and

while it is the lighter of the two, it is not generally favored, as

spruce is easier to obtain in good quality and is far easier to work. At

their ends, these outriggers are fitted with ferrules of steel tubing,

flattened and drilled through. The outriggers are attached to the main

framework of the machine by slipping the ferrules over the socket bolts

of the middle section struts, above and below the beams. It is

preferable, however, to attach the rear outriggers to extra bolts

running through the beams, so that when the machine is to be housed the

tail and rudder can be unshipped and the triangular frames swung around

against the main frame, considerably reducing the space required.

The tail, horizontal and vertical rudders, and the ailerons are light

frames of wood, covered on both sides with the same kind of cloth as the

main planes or wings. These frames are braced with piano wire in such a

manner that no twisting strains can be put on them. The front horizontal

rudder, which is of biplane construction like the main cell, is built up

with struts in the same way. Instead of being fitted with sockets,

however, the struts are held by long screws run through the planes and

into their ends, passing through the eyes of the turnbuckles.

DETAILS OF CONSTRUCTION

*Main Planes and Struts*. It is preferable to begin with the

construction of the main planes and their struts and truss wires, the

ribs already described being the first step.

The main beams offer no special difficulties. They are ovals 1 1/4 by 1

5/8 inches, all 6 feet long except the eight end ones, which are 6 feet

2 inches. The beams of the central section should be of ash, or should

be thicker than the others. In the latter case, they must be tapered at

the ends so that the clamping sleeves will fit and the additional wood

must be all on the lower side, so that the rib will not be thrown out of

alignment. The spruce used for the other beams should be reasonably

clear and straight grained, but a small knot or two does not matter,

provided it does not come near the ends of the beam. The beams may be

cut to the oval shape by the sawmill or planed down by hand.

"Fish-shaped" or "stream-line" section, as it is more commonly termed,

is used for the struts, Fig. 15. It is questionable whether this makes

any material difference in the wind resistance, but it is common

practice to follow it in order to minimize this factor. It is more

important that the struts be larger at their centers than at the ends,

as this strengthens them considerably. At their ends the struts have

ferrules of the 1-inch brass or steel tubing, and fit into the sockets

which clamp the ribs and beams together. The material is spruce but the

four central struts which carry the engine bed should either be ash or

of larger size, say 1 1/4 by 3 inches.

_Care Necessary to Get Planes Parallel_. The front struts must be longer

than the rear ones by the thickness of a main rib at the point where the

rear strut bolt passes through it, less the thickness of the rib ferrule

through which the bolt of the front strut must pass. However, the first

distance is not really the actual thickness of the rib, but the distance

between the top of the rear beam and the bottom of the strut socket. In

the drawings the difference in length between the front and rear struts

is given as 2 inches, but it is preferable for the builder to leave the

rear struts rather long and then measure the actual distance when

assembling, cutting the struts to fit. The ends of the struts should

also be countersunk enough to clear the head of the socket bolt.

One of the items which the builder can not well escape buying in

finished form is the strut sockets. These are cup-shaped affairs of

pressed steel which sell at 20 cents each. Sixteen of them will be

required for the main frame, and a dozen more can advantageously be used

in the front and rear controls, though for this purpose they are not

absolutely necessary. They can also be obtained in a larger oval size

suitable for the four central struts that carry the engine bed, as well

as in the standard 1-inch size. The bolts which project through the

bottom of the sockets are ordinary 1/4-inch stove bolts, with their

heads brazed to the sockets.

For the rear struts, where the bolt must pass through the slanting main

rib, it is advisable to make angle washers to put under the socket and

also between the beam and rib. These washers are made by sawing up a

piece of heavy brass tubing, or a bar with a 1/4-inch hole drilled in

its center, the saw cuts being taken alternately at right angles and at

60 degrees to the axis of the tube.

The sleeves which clamp together the ends of the beams are made of sheet

steel of about 20 gauge. The steel is cut out on the pattern given in

the drawing, Fig. 16, and the 3/16-inch bolt holes drilled in the

flanges. The flanges are bent over by clamping the sheet in a vise along

the bending line and then beating down with a hammer. Then the sleeves

can be bent into shape around a stray end of the beam wood. The holes

for the strut socket bolts should not be drilled until ready to

assemble. Ordinarily, 3/16-inch stove bolts will do to clamp the flanges

together.

Having reached this stage, the amateur builder must now supply himself

with turnbuckles. As already mentioned, these may either be purchased or

made by hand. It is permissible to use either one or two turnbuckles on

each wire. One is really sufficient, but two—one at each end—add but

little weight and give greater leeway in making adjustments. As there

are about 115 wires in the machine which need turnbuckles, the number

required will be either 115 or 230, depending upon the plan which is

followed. Those of the turnbuckles to be used on the front and rear

controls and the ailerons, about one-fifth of the total number, may be

of lighter stock than those employed on wires which carry part of the

weight of the machine.

*Making Turnbuckles for the Truss Wires*. On the supposition that the

builder will make his own turnbuckles, a simple form is described here.

As will be seen from Fig. 16, the turnbuckles are simply bicycle spokes,

with the nipple caught in a loop of sheet steel and the end of the spoke

itself twisted into an eye to which the truss wire can be attached. The

sheet steel used should be 18 or 16 gauge, and may be cut to pattern

with a heavy pair of tin snips. The spokes should be 3/32 inch over the

threaded portion. The eye should be twisted up tight and brazed so that

it can not come apart. The hole in the middle of each strip is, of

course, drilled the same size as the spoke nipple. The holes in the ends

are 3/16 inch.

In the original Curtiss machines, the turnbuckles were strung on the

socket bolts one after another, sometimes making a pack of them half an

inch thick. A much neater construction is shown in the drawings, in

which the bolt pierces a single plate with lugs to which to make the

turnbuckles fast by riveting. The plates are of different shapes, with

two, three, or four lugs, according to the places where they are to be

used. They are cut from steel stock 3/32 inch thick, with 1/4-inch holes

for the socket bolts and 3/16 inch, or other convenient size, for the

rivets that fasten on the turnbuckles.

The relative merits of cable and piano wire for trussing have not been

thoroughly threshed out. Each has its advantages and disadvantages. Most

of the well-known builders use cable; yet if the difference between

1,000 feet of cable at 2 1/4 cents per foot (the price for 500-foot

spools), and 8 pounds of piano wire at 70 cents a pound, looks

considerable to the amateur builder, let him by all means use the wire.

The cable, if used, should be the 3/32-inch size, which will stand a

load of 800 pounds; piano wire should be 24 gauge, tested to 745 pounds.

It should be noted that there is a special series of gauges for piano

wire, known as the music wire gauge, in which the size of the wire

increases with the gauge numbers, instead of the contrary, as is usual

with machinery wire gauges.

One by no means unimportant advantage of the piano wire is that it is

much easier to fasten into the turnbuckles. A small sleeve or ferrule, a

1/4-inch length of 1/8-inch tubing, is first strung on the wire. The end

of the wire is then passed through the turnbuckle eye, bent up, thrust

through the sleeve, and again bent down. When the machine is taken

apart, the wire is not disconnected from the eye, but instead the

turnbuckle spoke is unscrewed from the nipple. The shape of the

sheet-steel loop should be such as to hold the latter in place. Cable,

on the other hand, must be cut with about 2 inches to spare. After being

threaded through the turnbuckle eye, the end is wound back tightly on

itself and then soldered, to make certain that it can not loosen.

With a supply of turnbuckles and cable or piano wire at hand, the

builder may go ahead with the main box-like structure or cell, which

should be completed except for the cloth covering, and in proper

alignment, before taking up the construction of the running gear and

controls.

*Running Gear*. The running gear of the machine is built of seamless

steel tubing, those parts which carry the weight of the machine direct

being of 3/4-inch outside diameter, 16-gauge tubing, while the others

are 5/8-inch outside diameter, either 18 or 20 gauge. About 25 feet of

the heavy and 45 feet of the light tubing will be required, in lengths

as follows: Heavy, four 3-foot, three 4-foot; light, one 6-foot, two

4-foot 6-inch, and seven 4-foot pieces. Referring to Fig. 17, two

diagonal braces from the rear beam to the engine bed, the V-shaped piece

under the front engine bed struts and all of the rear frame except the

horizontal piece from wheel to wheel, are of heavy tubing. The

horizontal in the rear frame, diagonals from the rear wheels and the

rear end of the skid to the front beam, the two horizontals between the

front and rear beam, and the forward V are of light tubing.

[Illustration: Fig. 17. Details of Curtiss Running Gear]

Three ash beams are used in the running gear. Two of these run

diagonally from the rear end of the engine bed to the front wheel. These

are about 10 feet long and 1 by 1 3/4 inches section. The third, which

on rough ground acts as a skid, is 8 1/2 feet long and about 2 inches

square. Between the joints where the tubing frames are attached to it,

the upper corners may be beveled off with a spoke shave an inch or more

down each side. The beams are attached to the front wheel with strips of

steel stock 1 1/2 inches wide and 1/8 inch thick. The engine bed beams

are also ash about 1 by 1 3/4 inches section. Their rear ends are bolted

to the middle of the rear engine bed struts and the front ends may be

1/2 inch higher.

[Illustration: SCENE AT AVIATION MEET AT ROUEN, FRANCE, SHOWING AN

ANTOINETTE MONOPLANE MAKING A TURN

_This Photograph Protected By International Copyright_]

[Illustration: A FRENCH MONOPLANE TRAVELLING SIXTY-FIVE MILES AN HOUR

_This Photograph Protected By International Copyright_]

The wheels are usually 20 by 2 inches, and of the bicycle type, but

heavier and wider in the hub; the tires are single tube. These wheels,

complete with tires, cost about $10 each. This size is used on the

standard Curtiss machines, but novice operators, whose landings are not

quite as gentle as they might be, find them easily broken. Therefore, it

may be more economical in the end to pay a little more and get heavier

tires—at least to start with.

For working the tubing into shape, a plumber’s blow torch is almost

indispensable—most automobilists will already possess one of these. The

oval, flat variety, holding about one pint, is very handy and packs away

easily, but on steady work requires filling somewhat too frequently.

With a dozen bricks a shield can be built in front of the torch to

protect the flame and concentrate the heat. Whenever it is to be

flattened and bent, the tubing should be brought to a bright red or

yellow heat. Screwing the vise down on it will then flatten it quickly

without hammer marks. Where the bend is to be made in the middle of the

piece, however, it may be necessary to resort to the hammer and anvil.

It is convenient to start with the framework under the rear beam. This

may be drawn accurately to full size on the workshop floor, and the

tubes bent to fit the drawing. With this framework once in place, a

definite starting point for the remainder of the running gear is

established. Here and in all other places, when boring through wood, the

holes should be drilled out full, and larger washers should be placed

under the bolt head and nut. All nuts should be provided with some sort

of locking device The perspective drawing. Fig. 17, should show the

general arrangement clearly enough to enable the builder to finish the

running gear.

*Outriggers*. Both the front and rear control members, or "outriggers"

as they are termed, Fig. 12, may be conveniently built up on the central

section of the main frame, which, it is assumed, has now been fitted

with the running gear.

The horizontal rudder, or "elevator," is a biplane structure like the

main cell of the machine, but with fewer struts; it is carried in front

of the main planes on two *A*-shaped frames. The vertical rudder, at the

rear, is split along the middle and straddles a fixed horizontal plane,

or _tail_. This also is carried on two *A*-shaped frames. Lateral

stability is controlled by two auxiliary planes or ailerons, one at each

side of the machine and carried on the two outer front struts. These

three control units—_elevator_, _tail_ and _rudder_, and _ailerons_—will

now be taken up separately and their construction, location on the

machine, and operation will be described.

[Illustration: Fig. 18. Details of Rudders and Ailerons, Curtiss

Biplane]

_Horizonal Rudder or Elevator_. The two planes of the elevator are 2

feet wide by 5 feet 8 inches long and are spaced 2 feet apart, being

held in this position by ten struts. The frames of the planes are built

of spruce sticks 1/2 by 1 inch, each plane having two sticks the full

length and five evenly spaced crosspieces or ribs. These are joined

together with squares of X-sheet tin, as shown in the detailed drawing,

Fig. 18. With a little experimenting, paper patterns can be made from

which the tin pieces can be cut out. The sticks are then nailed through

the tin with 3/4-inch brads.

It is convenient to draw the frames out accurately on a smooth wood

floor and then work over this drawing. The first few brads will hold the

sticks in place. When all the brads have been driven, a little drop of

solder should be run in around the head of each one. This is a tedious

job. One must be careful to use no more solder than necessary as it

increases the weight very rapidly. Two pounds of wire solder should be

sufficient for all the control members which are built in this way. When

the top side is soldered, pry the frame loose from the floor with a

screwdriver and turn it over. Then the projecting points of the brads

must be clinched and the soldering repeated.

At this stage, the two frames should be covered on both sides with the

prepared cloth used for covering the main planes. The method of

preparing this cloth is detailed a little farther along.

The struts, so-called, to continue the analogy with the main planes, are

turned sticks of spruce 3/8 inch in diameter. They are fitted at each

end with ferrules of thin 3/8-inch brass, or steel tubing, driven on

tight. Instead of using sockets, the struts are held at each end, simply

by a long wood screw driven through the tin and wood of the plane frame

and into the strut. These screws also hold the turnbuckles for the truss

wires. For trussing purposes, the elevator is regarded as consisting of

two sections only, the intermediate struts being disregarded.

The turnbuckles and wire used here and in the other control members may

well be of lighter stock than those used in the main planes. Piano wire,

No. 18, or 1/16-inch cable is amply strong. The sheet steel may be about

22 gauge, instead of 16, and the bicycle spokes smaller in proportion.

No turnbuckle plates are necessary. The screws running into the struts

may be passed directly through the eyes of the turnbuckles, where they

would have been attached to the turnbuckle plate. In order to secure a

square and neat structure, those struts which have turnbuckles at their

ends should be made a trifle shorter than the others.

At each end, the elevator has an *X*-shaped frame of 1/4-inch steel

tubing; at the intersection of the *X*’s are pivots on which the

elevator is supported. Each *X* is made of two tubes, bent into a y and

flattened and brazed together at the points. The ends of the *X*’s are

flattened and bent over so that the screws which hold the struts in

place may pass through them.

[Illustration: Fig. 19. Curtiss Biplane Ready for Flight]

To the front middle strut is attached an extension which acts as a lever

for operating the elevator. This is a stick of spruce 3/4 inch in

diameter and 3 feet 3 inches long. At its upper end it has a ferrule of

steel tubing, flattened at the end. The lower part of the stick may be

fastened to the strut by wrapping the tube with friction tape, or by

improvising a couple of sheet steel clamps. The upper end of the stick

is braced by a 1/4-inch steel tube, extending to the top of the rear

middle strut, and held by the same screw as the strut. This extension

lever is connected to the steering column by a bamboo rod, 1 inch in

diameter and about 10 feet long, provided with flattened ferrules of

steel tubing at each end. Each ferrule should be held on by a 1/8-inch

stove bolt passing through it.

_Front and Rear Outrigger Frames_. Both the front elevator and the tail

and rudder at the rear, are carried, as mentioned above, each on a pair

of *A*-shaped frames, similar to one another, except that those in the

rear are longer than those in the front. Both are made of spruce of

about the same section as used for the struts of the main frame. These

pieces may either be full length, or they may be jointed at the

intersection of the crosspieces, the ends being clamped in a sheet-steel

sleeve, just like that used on the beams of the main frame. In this

case, it is advisable to run a 1/8-inch stove bolt through each of the

ends.

[Illustration: Fig. 20. Details of Outriggers and Front Elevating Planes

as Seen from Driver’s Seat]

The crosspieces of the *A*-frames are spruce of the same section, or a

little smaller. At their ends may be used strut sockets like those of

the main frame; or, if it is desired to save this expense, they may be

fastened by strips of 1/16-inch steel stock with through bolts.

The front outrigger has, besides the two A-frames, a rather complicated

arrangement of struts designed to brace the front wheel against the

shocks of landing. This arrangement does not appear very plain in a plan

or elevation, and may best be understood by reference to the photograph,

Fig. 19, and the perspective drawing, Fig. 20. Fig. 20 is a view from

the driver’s seat. The elevator is seen in front, the *A*-frames at each

side, and at the bottom the two diagonal beams to the engine bed and the

skid.

Reference to this drawing will show the two diagonals run from the front

wheel up and back to the top of the main frame, and two more from the

wheel forward to the short crosspieces near the apexes of the *A*-frame:

there is also a vertical strut which intersects two horizontal pieces

running between the ends of the longer crosspieces of the *A*-frames.

Altogether, there are five attachments on each side of the front wheel,

through which the axle bolt must pass, viz, the connections to the skid,

to one of the diagonals to the engine bed, to one of the rear diagonals,

to one of the front diagonals, and to one side of the fork carrying the

vertical strut. Of these the skid attachments should be on the inside

closest to the wheel, and the engine bed diagonals next.

The four additional diagonals running to the front wheel may be spruce

of the same section used in the *A*-frames, or turned one inch round. At

each end they have flattened ferrules of steel tubing. The beams of the

*A*-frames have similar ferrules at the ends where they attach to the

main frames. These attachments should be made on the socket bolts of the

struts on either side of the middle 6-foot section and on the outer side

of the main beams—not between the beam and the socket itself.

It is possible, of course, to make all the *A*-frames and diagonal

braces of bamboo, if desired, the qualities of this material already

having been referred to. Bamboo rods for this purpose should be between

1 and 1 1/4 inches in diameter. Where ferrules are fitted on the ends,

the hole of the bamboo should be plugged with wood glued in place.

Generally, in the construction of the outrigger frames, the builder can

use his own discretion to a considerable extent. There tire innumerable

details which can be varied—far too many to consider even a part of the

possibilities in this connection. If the builder runs across any detail

which he does not see mentioned here, he may safely assume that any

workmanlike job will suffice. Often, the method may be adapted to the

materials on hand. The diagonal wires from the crosspieces of the

A-frames to the struts should be crossed.

_Rudder and Tail Construction_. The frame for the rudder and tail are

constructed in much the same way as those for the elevator, Fig. 18.

Spruce sticks 1 by 1/2 inch are used throughout, except for the piece at

the back edge of the rudder and the long middle piece across the tail;

these should be 1 1/2 by 1/2 inch. This long middle piece of the tail is

laid across on top of the rest of the framework. When the cloth is put

on, this makes the upper surface slightly convex while the lower surface

remains flat. The ends of this piece should be reinforced with sheet

steel, fairly heavy and drilled for 1/4-inch bolts, attaching the tail

to the *A*-frames.

The rudder is hung from two posts extending above and below the tail.

These posts may be set in cast aluminum sockets, such as may be obtained

from any supply house for 20 cents apiece. The posts need not be more

than 3/4 inch in diameter. At their outer ends, they should have

ferrules of steel tubing, and the turnbuckles or other attachments for

the truss wires should be attached by a wood screw running into the end

of each. From these posts the rudder may be hung on any light hinges the

builder may find convenient, or on hinges improvised from screw eyes or

eye bolts, with a bolt passing through the eyes of each.

In steering, the rudder is controlled by a steering wheel carried on a

hinged post in front of the pilot. This post should be ash about 1 by 1

1/4 inches. It hinges at the bottom on a steel tube of 1/2-inch diameter

which passes through it and is supported at the ends on diagonal beams

to the engine bed. Two diagonals of lighter tubing may be put in to hold

the posts centered between the two beams.

The post is, of course, upright, and the hub of the wheel is horizontal.

The wheel may be conveniently mounted on a piece of tubing of the same

size as the hub hole, run through the post and held by a comparatively

small bolt, which passes through it and has a big washer on either end.

The wheel is preferably of the motor-boat variety with a groove around

the rim for the steering cable.

The rear edge of the tail should be about 1 inch lower than the front.

To make the rudder post stand approximately vertical, wedge-shaped

pieces of wood may be set under the sockets.

The steering connections should be of flexible cables of steel such as

are made for this purpose. There should be a double pulley on the post

just under the wheel, and the cables should be led off the post just at

the hinge at the bottom, so that swinging the post will not affect them.

The cable is then carried under the lower main plane and out the lower

beams of the *A*-frames. It is attached to the rudder at the back edge;

snap hooks should be used for easy disconnection in packing. Perhaps the

best way of guiding the cable, instead of using pulleys, is to run it

through short pieces of tubing lashed to the beams with friction tape.

The tubing can be bent without flattening by first filling it with

melted lead, which, after the bending, can be melted out again.

*Ailerons for Lateral Stability*. The framework of the ailerons is made

in the same way as that for the elevator, tail, and rudder, Fig. 18. The

pieces around the edges should be 1 1/2 by 1/2 inch, as also the long

strip laid over the top of the ribs. The ribs should be 1/2 by 3/4 inch.

Each aileron has two holes, one for the strut to pass through, and the

other for the diagonal truss wires at their intersection. The back edge

also has a notch in it to clear the fore and aft wires. Each aileron is

hung on four strips of soft steel about 1/2 by 3/16 inch, twisted so

that one end is at right angles to the other. These are arranged one on

each side of the strut which passes through the aileron, and one at each

end. Bolts through the struts carry three of them and the outer one is

trussed by wires to each end of the outer strut.

A frame of 1/4-inch steel tubing fits around the aviator’s shoulders and

is hinged to the seat, so that he can move it by leaning from one side

to the other. This is connected by flexible cable to the rear edges of

the ailerons, so that when the aviator leans to the left, he will raise

the left and lower the right aileron. The upper edges of the ailerons

are directly connected to each other by a cable running along the upper

front beam, so that they must always move together.

*Covering of the Planes*. Mention has already been made of the fact, in

the general description of the machine, that light sail cloth, as

employed on the Wright machines, may be used for the planes or wings. As

a matter of fact, many different materials may be successfully employed,

the selection depending upon the builder himself and his financial

resources. About 55 square yards of material will be required, and in

comparing prices always compare the width as this may vary from 28 to 55

inches. Rubberized silk which is used on the standard Curtiss machines

is the most expensive covering, its cost running up to something like

two hundred dollars. There are also several good aero fabrics on the

market which sell at 60 cents a square yard, as well as a number of

brands of varnish for the cloth—most of them, however, quite expensive.

The most economical method is to employ a strong linen cloth coated with

shellac, which will be found very satisfactory.

The covering of the frames with the cloth may well be postponed until

after the engine has been installed and tested, thus avoiding the

splashing of oil and dirt which the fabric is apt to receive during this

operation. The wire to which the cloth is laced, must be strung along

the rear ends of the ribs of each plane. The wires pass through holes in

the ends of the small ribs and are attached to the main ribs with

turnbuckles. At the ends of the planes the main ribs must be braced

against the pull of the wire by a piece of 1/4-inch tubing running from

the end of the rib diagonally up to the rear beam. Both turnbuckles and

tube are fastened with one wood screw running into the end of the rib.

The cloth should be cut to fit the panels between the main ribs and

hemmed up, allowing at least an inch in each direction for stretch.

Small eyelets should be put along the sides and rear edges an inch apart

for the lacing. At the front edge, the cloth is tacked directly to the

beam, the edge being taken well under and around to the back. Strong

fish line is good material for the lacing.

After the cloth is laced on, it must be tacked down to the small ribs.

For this purpose, use upholstery tacks as they have big cup-shaped heads

which grip the cloth and do not tear out. As an extra precaution a strip

of heavy tape must be run over each rib under the tack heads. All the

control members are covered on both sides, the edges being folded under

and held by tacks.

*Making the Propeller*. If the completed biplane is to fly properly and

also have sufficient speed to make it safe, considerable care must be

devoted to the design and making of the propeller. Every aeroplane has a

safe speed, usually referred to in technical parlance as its _critical

speed_. In the case of the Curtiss biplane under consideration, this

speed is about 40 miles an hour. By speeding up the motor considerably,

it may be able to make 42 to 43 miles an hour in a calm, such a

condition representing the only true measure of an aeroplane’s ability

in this direction, while on the other hand, it would not be safe to let

its speed with relation to the wind (not to the ground) fall much below

35 miles an hour. At any slower rate of travel, its dynamic stability

would be precarious and the machine would be likely to dive to the

ground unexpectedly. The reasons for this have been explained more in

detail under the heading of "The Internal Work of the Wind."

The necessity of making the propeller need not discourage the ambitious

builder—if he can spare the time to do it right, it will be excellent

experience. If not, propellers designed for driving a machine of this

size can be purchased ready to mount from any one of quite a number of

manufacturers. But as the outlay required will be at least $50,

doubtless most experimenters will prefer to undertake this part of the

work as well as that of building the framework and main cell,

particularly as more than 90 per cent of the sum mentioned is

represented by labor. The cost of the material required is insignificant

by comparison.

_True-Screw Design_. First it will be necessary to design the propeller

to meet the requirements of the biplane itself. As this is a matter that

has already been gone into in considerable detail under the appropriate

heading, no further explanation of propeller characteristics or of the

technical terms employed, should be needed here. We will assume that the

biplane is to have a speed of 40 miles per hour in still air with the

motor running at 1,200 r.p.m. With this data, it will not be difficult

to calculate the correct pitch of the propeller to give that result.

Thus

40 X 5,280 X 100 / 60 X 1,200 X 85 = 3.45

or in round numbers a pitch of 3 1/2 feet. 40 (the speed in miles per

hour) times 5,280 (feet per mile) divided by 00 (minutes in an hour)

gives the speed of the aeroplane in feet per minute. Dividing this by

1,200 (revolutions per minute) gives the number of feet the aeroplane is

to advance per revolution of the propeller. The "100/85" part of the

equation represents the efficiency of the propeller which can safely be

figured on, _i.e._, 85 per cent, or an allowance for slip of 15 per

cent. Forty miles an hour is the maximum speed to be expected, while the

r.p.m. rate of the engine should be that at which it operates to the

best advantage.

The merits of the _true-screw_ and _variable-pitch_ propellers have

already been dwelt upon. The former is not only more simple to build,

but experience has shown that, as generally employed, it gives better

efficiency. Hence, the propeller under consideration will, be of the

true-screw type. Its pitch has already been calculated as 3 1/2 feet.

For a machine of this size and power, it should be 6 feet in diameter.

Having worked out the pitch and decided upon the diameter, the next and

most important thing is to calculate the pitch angle. It will be evident

that no two points on the blade will travel through the air at the same

speed. Obviously, a point near the tip of the propeller moves faster

than one near the hub, just as in rounding a curve, the outer wheel of

an automobile has to travel faster than the inner, because it has to

travel farther to cover the same ground. For instance, taking the

dimensions of the propeller in question it will be seen that its tips

will be traveling through the air at close to 4.3 miles per minute, that

is,

6 X π X 1200 / 5,280 = 4.28

in which 6, the diameter of the propeller in feet, times π gives the

circumference of the circle which is traveled by the blade tips 1,200

times per minute; this divided by the number of feet per mile gives the

miles per minute covered. On the other hand, a point on the blade but 6

inches from the hub will turn at only approximately 3,500 feet per

minute. Therefore, if every part of the blade is to advance through the

air equally, the inner part must be set at a greater angle than the

outer part. Each part of the blade must be set at such an angle that at

each revolution it will move forward through the air a distance equal to

the pitch. This is known as the pitch angle. The pitch divided by the

circumference of the circle described by any part of the blade, will

give a quantity known as the tangent of an angle for that particular

part. The angle corresponding to that tangent may most easily be found

by referring to a book of trigonometric tables.

For example, take that part of the blade of a 3 1/2-foot pitch propeller

which is 6 inches from the center of the hub. Then

3.5 X 12 / 6 X 2 π = 1.1141 tangent of 48 degrees 5 minutes

in which 3.5 X 12 reduces the pitch to inches, while 6 X 2π is the

circumference of the circle described by the point 6 inches from the

hub. However, in order to give the propeller blade a proper hold on the

air, it must be set at a greater angle than these figures would

indicate. That is, it must be given an angle of incidence similar to

that given to every one of the supporting planes of the machine. This

additional angle ranges from 2 degrees 30 minutes, to 4 degrees,

depending upon the speed at which the particular part of the blade

travels; the greater the speed, the less the angle. This does not apply

to that part of the blade near the hub as the latter is depended upon

solely for strength and is not expected to add to the effective thrust

of the propeller.

Table II shows the complete set of figures for a blade of 3 1/2-foot

pitch, the angles being worked out for sections of the blade 3 inches

apart.

These angles are employed in Fig. 21, which shows one blade of the

propeller and its cross sections.

It should be understood that these calculations apply only to the type

of propeller known as the _true screw_, as distinguished from the

_variable pitch_. The design of the latter is a matter of personal skill

and experience in its making which is hardly capable of expression in

any mathematical formula. There are said to be only about three men in

this country who know how to make a proper variable-pitch propeller, and

it naturally is without advantage when made otherwise.

[Illustration: Fig. 21. Details of Propeller Construction, Curtiss

Biplane]

_Shaping the Blades_. Like the ribs, the propeller is made up of a

number of laminations of boards finished true and securely glued,

afterward being cut to the proper shape, though this process, of course,

involves far more skill than in the former case. Spruce is the strongest

wood for its weight, but it is soft and cracks easily. Maple, on the

other hand, is tough and hard, so that it will be an advantage to

alternate the layers of these woods with an extra maple board, in order

to make both outside strips of the harder wood, so as to form a good

backing for the steel flanges at the hub, the rear layer extending the

full length of the thin rear edges of the blades. Other woods may be

employed and frequently are used by propeller manufacturers, such as

mahogany (not the grained wood used for furniture, but a cheaper grade

which is much stronger), walnut, alternate spruce and whitewood, and

others.

The boards should be selected with the greatest care so as to insure

their being perfectly clear, _i.e._, absolutely free of knots,

cross-grained streaks, or similar flaws, which would impair their

strength and render them difficult to work smoothly. They should measure

6 inches wide by 6 feet 1 inch in length. Their surfaces must be

finished perfectly true, so that they will come together uniformly all

over the area on which they bear on one another, and the various pieces

must be glued together with the most painstaking care. Have the glue

hot, so that it will spread evenly, and see that it is of a uniform

consistency, in order that it may be smoothly applied to every bit of

the surface. They must then be clamped together under as much pressure

as it is possible to apply to them with the means at hand, the rib press

already described in detail forming an excellent tool for this purpose.

Tighten up the nuts evenly a little at a time, avoiding the application

of excessive or uneven pressure at one point, continuing the gradual

tightening up process until it can not be carried any farther. This is

to prevent the boards from assuming a curve in drying fast. Allow at

least twenty-four hours for drying, during which period the laminated

block should be kept in a cool, dry place at as even a temperature as

possible.

Before undertaking the remainder of the work, all of which must be

carried out by hand, with the exception of cutting the block to the

outline of the propeller, which may be done with a band saw, a set of

templates or gauges should be made from the drawings. These will be

necessary as guides for finishing the propeller accurately. Draw the

sections out full size on sheets of cardboard or tin and cut out along

the curves, finally dividing each sheet into two parts, one for the

upper side and one for the lower. Care must be taken to get the sides of

the template square, and when they are used, the propeller should be

laid on a perfectly true and flat block. Each template should be marked

as it is finished, to indicate what part of the blade it is a gauge for.

The work of cutting the laminated block down to the lines represented by

the templates is carried out with the aid of the plane, spoke shave, and

gouge. After the first _roughing out_ to approximate the curvature of

the finished propeller is completed, the cuts taken should be very fine,

as it will be an easy matter to go too deep, thus spoiling the block and

necessitating a new start with fresh material. For finishing, pieces of

broken glass are employed to scrape the wood to a smooth surface,

followed by coarse and finally by fine sandpaper.

_Mounting_. The hub should be of the same diameter as the flange on the

engine crank shaft to which the flywheel was bolted, and should have its

bolt holes drilled to correspond. To strengthen the hub, light steel

plates of the same diameter are screwed to it, front and back, and the

bolt holes drilled right through the metal and wood. This method of

fastening is recommended where it is possible to substitute the

propeller for the flywheel formerly on the engine, it being common

practice to omit the use of the flywheel altogether. The writer does not

recommend this, however, as the advantages of smoother running and more

reliable operation gained by the use of a flywheel in addition to the

propeller far more than offset any disadvantage represented by its

weight. It will be noted that the Wright motors have always been

equipped with a flywheel of ample size and weight and this is

undoubtedly responsible, in some measure at least, for the fact that the

Wright biplanes fly with considerably less power than is ordinarily

employed for machines of the same size. If the motor selected be

equipped with an unusually heavy flywheel, and particularly where the

wheel is of comparatively small diameter, making it less effective as a

balancer, it may be replaced with one of lighter weight and larger

diameter. It may be possible to attach it by keying to the forward end

of the crank shaft, thus leaving the flange from which the flywheel was

taken free for mounting the propeller. An ordinary belt pulley will

serve excellently as the new flywheel, as most of its weight is centered

in its rim, but as the common cast-iron belt pulley of commerce is

seldom intended to run at any such speed as that of an automobile motor,

it should be examined carefully for flaws. Otherwise, there will be

danger of its blunting with disastrous results under the influence of

centrifugal force. Its diameter should not exceed 16 inches in order to

keep its peripheral speed within reasonable limits. Where the mounting

of the motor permits of its use, a wood pulley 18 to 20 inches in

diameter with a steel band about 1/8 to 1/4-inch thick, shrunk on its

periphery, may be employed. Most builders will ridicule the idea of a

flywheel other than the propeller itself. "You do not need it; so why

carry the extra weight?" will be their query. It is not absolutely

necessary, but it is an advantage.

In case the flywheel of the engine selected is keyed to the crank shaft,

or in case it is not possible to mount both the flywheel and the

propeller on different ends of the crank shaft, some other expedient

rather than that of bolting to the flange must be adopted. In such a

case, the original flywheel, where practical to retain it, may be

drilled and tapped and the propeller attached directly to it. Where the

flywheel can not be kept, it will usually be found practical to cut off

its rim and bolt the propeller either to the web or spokes, or to the

flywheel hub, if it be cut down to the latter.

The drawing. Fig. 21, shows the rear or concave side of the propeller.

From the viewpoint of a man standing in its wind and facing forward, it

turns to the left, or anti-clockwise. On many of the propellers now on

the market, the curved edge is designed to go first. This type may have

greater advantages over that described, but the straight front edge

propeller is easier for the amateur to make.

*Mounting the Engine*. Having completed the propeller, the next step is

the mounting of the engine. Reference to the types available to the

amateur aeroplane builder has already been made. There are a number of

motors now on the market that have been designed specially for this

purpose and not a few of them are of considerable merit. Their cost

ranges from about $250 up to $2,500, but it may be possible to pick up a

comparatively light-weight automobile motor second hand which will serve

all purposes and which will cost far less than the cheapest aeronautic

motor on the market. It must be capable of developing 30 actual

horse-power at 1,000 to 1,200 r.p.m. and must not exceed 400 pounds

complete with all accessories, such as the radiator and piping, magneto,

water, oil, etc. Considerable weight may be saved on an automobile motor

by removing the exhaust manifold and substituting a lighter flywheel for

the one originally on the engine—or omitting it altogether, as just

mentioned. A light-weight aeronautic radiator should be used in

preference to the usual automobile radiator.

When placing the engine in position on the ash beams forming its bed or

support, it must be borne in mind that the complete machine, with the

operator in the aviator’s seat, is designed to balance on a point about

1 1/2 feet back of the front edge of the main planes. As the operator

and the motor represent much the larger part of the total weight, the

balance may easily be regulated by moving them slightly forward or

backward, as may be required. It will be necessary, of course, to place

the engine far enough back in any case to permit the propeller blades to

clear the planes. The actual installation of the engine itself will be

an easy matter for anyone who has had any experience in either

automobile or marine gasoline motor work. It is designed to be bolted to

the two engine beams in the same manner as on the side members of the

frame of an automobile, or the engine bed in a boat. Just in front of

the engine is the best place for the gasoline tank, which should be

cylindrical with tapering ends, to cut down its wind resistance. If the

designer is not anxious to carry out points as fine as this, a light

copper cylindrical tank may be purchased from stock. It should hold at

least ten gallons of gasoline. In front of the tank is the radiator.

*Controls*. The controls may be located to conform to the builder’s own

ideas of accessibility and convenience. Usually the switch is placed on

the steering column, and it may be of the ordinary _knife_ variety, or

one of the special switches made for this purpose, as taste may dictate.

The throttle control and spark advance may either be in the form of

pedals, working against springs, or of small levers working on a notched

sector, at the side of the seat. The complete control, levers, and

sector may be purchased ready to mount whenever desired, as they are

made in this form for both automobile and marine work. This likewise

applies to the wheel, which it would not pay the amateur to attempt to

make.

Another pedal should work a brake on the front wheel, the brake shoe

consisting of a strip of sheet steel, fastened at one end to the fore

part of the skid and pressed against the wheel by a bamboo rod directly

connected with the brake pedal. An emergency brake can also be made by

loosely bolting a stout bar of steel on the skid near its rear end; one

end of this bar is connected to a lever near the seat, so that when this

lever is pulled back the other end of the bar tends to dig into the

ground. As making a landing is one of the most difficult feats for the

amateur aviator to master and sufficient space for a long run after

alighting is not always available, these brakes will be found a very

important feature of the machine.

[Illustration: Fig. 22. Method of Starting the Engine of an Aeroplane]

The engine is started by swinging the propeller, and this is an

operation requiring far more caution than cranking an automobile motor.

Both hands should be placed on the same blade. Fig. 22, and the latter

should always be pulled downward—never upward. With the switch off,

first turn the propeller over several times to fill the cylinders with

gas, leaving it just ahead of dead center of one of the cylinders, and

with one blade extending upward and to the left at a 45-degree angle.

After closing the switch, take the left blade with both hands and swing

it downward sharply, getting out of the way of the following blade as

quickly as possible.

*Tests*. The first thing to be done after the propeller is finished and

mounted on the engine is to test the combination, or power plant of the

biplane, for speed and thrust, or pulling power. From these two

quantities it will be easy to figure the power that the engine is

delivering. The only instruments necessary are a spring balance reading

to 300 pounds or over; a revolution counter, such as may be procured at

any machinist’s supply house for a dollar or two; and a watch. One end

of the spring balance is fastened to the front end of the skid and the

other to a heavy stake firmly driven in the ground a few feet back. The

wheels of the biplane should be set on smooth boards so that they will

not offer any resistance to the forward thrust. When the engine is

started the spring balance will give a direct reading of the pull of the

propeller.

With one observer noting the thrust, another should check the number of

revolutions the engine is turning per minute. To do this, a small hole

should previously have been countersunk in the hub of the propeller to

receive the conical rubber tip of the revolution counter. The observer

stands behind the propeller, watch in one hand and revolution counter in

the other. At the beginning of the minute period, the counter is pressed

firmly against the hub, and quickly withdrawn at the end of the minute.

A stop watch is naturally an advantage for the purpose. The horse-power

is figured as follows, assuming, for example, a thrust of 250 pounds at

1,200 r.p.m.

250 X 1200 X 3.5 X 100 / 33.000 X 85 = 37 h. p.

As before, the "100/85" allows for the slip and represents the

efficiency of the propeller; 33,000 is the number of foot pounds per

minute or the equivalent of one horse-power, and 3.5 is the pitch of the

propeller.

*Assembling the Biplane*. Assembling the machine complete requires more

space than is available in the average workshop. However, it is possible

to assemble the sections of the planes in a comparatively small room,

carrying the work far enough to make sure that everything will go

together properly when the time comes for complete assembly at the

testing ground. In this case, it is preferable to assemble the end

sections first, standing them away when complete to make room for the

central section, on which the running gear and outriggers are to be

built up.

The builder will have decided by this time whether he will make his

machine on the regular plan, with one main rib between each section, or

on the quick-detachable plan, which has two main ribs on either side of

the central section, as previously explained.

It is desirable to be able to assemble two sections at once and this

should be possible anywhere as it requires a space only about 6 by 13

feet. Two wood 2X4’s, about 12 feet long, should be nailed down on the

blocks on the floor; make these level and parallel to each other at a

distance of 3 feet 6 inches on centers, one being 3 inches higher than

the other. Strips of wood should be nailed on them, so as to hold the

main beams of the frame in place while assembling.

The two front and two rear beam sections are laid in place and joined

with the sheet-steel sleeves, the flanges of the sleeves on the inner

side of the beams. Then through the sleeves in the front beams, which

are, of course, those on the higher bed, drill the holes for the strut

socket bolts (1/4 inch). The holes for the outer ones go through the

projecting ends of the beams; those for the inner ones are half in each

of the two abutting beams. At the end where the central section joins

on, a short length of wood of the same section may be inserted in the

sleeve while drilling the hole. An assistant should hold the beams

firmly together while the holes are being drilled.

Now lay in place the three main ribs belonging to the two sections under

construction and fasten them at the front ends by putting in place the

strut sockets for which the holes have been drilled, with a turnbuckle

plate under each socket, Fig. 16. The strut socket bolt passes through

the main rib and the beam. The bed on which the assembling is being

done, should be cut when sufficiently under the joints to leave room for

the projecting bolt ends. Set the ribs square with the front beams, then

arrange the rear beams so that their joints come exactly under the ribs;

clamp the ribs down and drill a true, vertical hole through the rib

beam, holding the two sections of the beam together as before. Then put

the rear strut sockets in place, using the angle washers previously

described, above and below the rib.

When the quick-detachable plan is followed, the ribs at the inner ends

of the double section, where they join the central section, should be

bolted on an inch from the ends of the beam, using 1/4-inch stove bolts

instead of the socket bolts. The sleeves should be slotted, so that they

can slide off without removing these bolts, as the sleeves and ribs

which occupy the position over the joints of the beams, belong to the

central section.

The sections should now be strung up with the diagonal truss wires which

will make them rigid enough to stand handling. The wires are attached at

each end to the flange bolts of the sleeves. Either one or two

turnbuckles may be used on each wire, as already explained; if but one

turnbuckle be used, the other end of the wire may be conveniently

attached to a strip of sheet steel bent double and drilled for the bolt,

like the sheet-steel slip of a turnbuckle. The attachment, of whatever

nature, should be put between the end and the flange of the sleeve, not

between the two flanges.

Three or four ribs can be used on each section; four are preferable on

sections of full 6-foot length. They are, of course, evenly spaced on

centers. At the front ends, they are attached to the beam by wood screws

through their flattened ferrules. The attachment to the rear beam is

made with a slip of sheet steel measuring 1/2 by 3 inches, bent over the

rib and fastened to the beam at each side with a wood screw. A long wire

nail is driven through the rib itself on the beam.

Four double sections should be built up in this manner, the right and

left upper and the right and left lower sections. Uppers and lowers are

alike except for the inversion of the sockets in the upper sections.

Rights and lefts differ in that the outer beams are long enough to fill

up the sleeves, not leaving room for another beam to join on.

Inserting the struts in their sockets between the upper and lower

sections of the same side will now form either of the two sides of the

machine complete. Care should be taken to get the rear struts the proper

length with respect to the front ones to bring the upper and lower

planes parallel. The distance from the top of the lower front beam to

the top of the upper front beam should be the same as the distance

between the rows of bracing holes in the upper and lower main ribs just

above and below the rear struts—about 4 feet 6 inches. It should hardly

be necessary to mention that the thick edges of the struts come to the

front—they are fish-shaped and a fish is thicker at the head than at the

tail.

The truss wires may now be strung on in each square of the struts,

beams, and main ribs, using turnbuckles as previously described. The

wires should be taut enough to sing a low note when plucked between the

thumb and forefinger. If the construction is carried out properly, the

framework will stand square and true with an even tension on all the

wires. It is permissible for the struts to slant backward a little as

seen from the side, but all should be perfectly in line.

For adjusting the turnbuckles, the builder should make for himself a

handy little tool usually termed a nipple wrench. It is simply a strip

of steel 1 1/2 by 1/2 by 3/32 inches, with a notch cut in the middle of

the long sides to fit the flattened ends of the turnbuckle nipples. This

is much handier than the pliers and does not burr up the nipples.

It has been assumed in this description of the assembling that the

builder is working in a limited space; if, on the contrary, he has room

enough to set up the whole frame at once, the work will be much simpler.

In this case, the construction bed should be 30 feet long. First build

up the upper plane complete, standing it against the wall when finished;

then build the lower plane, put the struts in their sockets, and lay on

the upper plane complete.

Returning to the plan of assembly by sections, after the side sections

or wings of the machine have been completed, the struts may be taken out

and the sections laid aside. The middle section, to which the running

gear and outriggers will be attached, is now to be built up in the same

way. If the builder is following the plan in which there is one main rib

between each section, it will be necessary to take off the four inner

main ribs from the sections already completed, to be used at the ends of

the central section. The plan drawing of the complete machine shows that

the ribs of the central section are cut off just back of the rear beam

to make room for the propeller. This is necessary in order to set the

motor far enough forward to balance the machine properly. The small ribs

in this section have the same curve but are cut off 10 inches shorter at

their rear ends, and the stumps are smoothed down for ferrules like

those for the other small ribs. In the plan which has one main rib

between each section, the main rib on each side of the central section

must be left full length. In the quick-detachable plan with two main

ribs on each side of the central section, the inner ones, which really

belong to this section, are cut off short like the small ribs.

In the drawing of the complete machine, the distance between the struts

which carry the engine bed is shown as 2 feet. This is only approximate,

as the distance must be varied to suit the motor employed. By this time,

the builder will have decided what engine he is going to use—or can

get—and should drill the holes for the sockets of these struts with due

respect to the width of the engine’s supporting feet or lugs,

remembering that the engine bed beams go on the inside of the struts. In

the drawing of the running gear. Fig. 17, the distance between the

engine-bed struts has been designated _A_. The distances, _B_, on each

side are, of course, approximately (6’— 2*A*), whatever _A_ may be.

[Illustration: VIEW OF THE FRENCH AVIATION GROUNDS SHOWING THE HANGARS

RANGED ALONG THE EDGES OF THE FIELD

_This Photograph Protected By International Copyright_]

EXAMINATION PAPER

BUILDING AND FLYING AN

AEROPLANE

*PART I*

*Read Carefully*: Place your name and full address at the head of the

paper. Any cheap, light paper like the sample previously sent you may be

used. Do not crowd your work, but arrange it neatly and legibly. _Do not

copy the answers from the Instruction Paper; use your own words so that

we may be sure that you understand the subject_.

1. What type of machine, biplane or monoplane, makes the best glider

and why?

2. Give the dimensions of a glider which will support a man’s weight.

3. In a glider which has no rudder, how is the machine controlled?

4. Give carefully the details of the start in making a glide.

5. In what direction relative to the wind should a glide be made?

Justify your answer.

6. How must the stability and balance of a glider in flight be

controlled?

7. State the proper conditions for a successful glide.

8. Give the essential characteristics of a Curtiss aeroplane,

defining the various parts.

9. Describe briefly the details of construction of the main

supporting surfaces of a Curtiss.

10. Draw a diagram of the assembled planes showing how the struts and

cross wires are placed to give the required rigidity.

11. Give the details of the running gear of the Curtiss.

12. What is the office of the Curtiss ailerons and how are they

controlled from the operator’s seat? Draw sketch.

13. Describe the details of the front and rear outriggers.

14. What type of propeller is advised for the Curtiss? Give the

details of its construction.

15. Describe carefully the manner in which a propeller should move

through the air in order to give the maximum propulsion.

16. What determines the exact location of the motor in the aeroplane?

17. Give correct method of starting the motor when ready for a flight.

18. What tests should be conducted before a flight is undertaken?

*After completing the work, add and sign the following statement:*

I hereby certify that the above work is entirely my own.

(Signed)