MODEL FLYING MACHINES.
Awakened popular interest--The workshop’s share--Needed
devices--Super-sensitive inventions--Unsolved problems--Tools
and materials--A model biplane--The propeller--The body--The
steering plane--The main planes--Assembling the parts--The
motive power--Flying the model--A monoplane model--Carving a
propeller--Many ideas illustrated--Clubs and competitions--Some
remarkable records.
It is related of Benjamin Franklin that when he went out with his
famous kite with the wire string, trying to collect electricity from
the thundercloud, he took a boy along to forestall the ridicule that he
knew would be meted out to him if he openly flew the kite himself.
Other scientific experimenters, notably those working upon the problem
of human flight in our own time, have encountered a similar condition
of the public mind, and have chosen to conduct their trials in secret
rather than to contend with the derision, criticism, and loss of
reputation which a sceptical world would have been quick to heap upon
them.
But such a complete revolution of thought has been experienced in these
latter days that groups of notable scientific men gravely flying kites,
or experimenting with carefully made models of flying machines, arouse
only the deepest interest, and their smallest discoveries are eagerly
seized upon by the daily press as news of the first importance.
So much remains to be learned in the field of aeronautics that no
builder and flyer of the little model aeroplanes can fail to gain
valuable information, if that is his intention. On the other hand, if
it be the sport of racing these model aeroplanes which appeals to him,
the instruction given in the pages following will be equally useful.
The earnest student of aviation is reminded that the progressive work
in this new art of flying is not being done altogether, nor even in
large part, by the daring operators who, with superb courage, are
performing such remarkable feats with the flying machines of the
present moment. Not one of them would claim that his machine is all
that could be desired. On the contrary, these intrepid men more than
any others are fully aware of the many and serious defects of the
apparatus they use for lack of better. The scientific student in his
workshop, patiently experimenting with his models, and working to
prove or disprove untested theories, is doubtless doing an invaluable
part in bringing about the sort of flying which will be more truly
profitable to humanity in general, though less spectacular.
[Illustration: A model flying machine built and flown by Louis Paulhan,
the noted aviator, at a prize contest for models in France. The design
is after Langley’s model, with tandem monoplane surfaces placed at a
dihedral angle.]
One of the greatest needs of the present machines is an automatic
balancer which shall supersede the concentrated attention which the
operator is now compelled to exercise in order to keep his machine
right side up. The discovery of the principle upon which such a
balancer must be built is undoubtedly within the reach of the builder
and flyer of models. It has been asserted by an eminent scientific
experimenter in things aeronautic that “we cannot hope to make a
sensitive apparatus quick enough to take advantage of the rising
currents of the air,” etc. With due respect to the publicly expressed
opinion of this investigator, it is well to reassure ourselves against
so pessimistic an outlook by remembering that the construction of just
such supersensitive apparatus is a task to which man has frequently
applied his intellectual powers with signal success. Witness the
photomicroscope, which records faithfully an enlarged view of
objects too minute to be even visible to the human eye; the aneroid
barometer, so sensitive that it will indicate the difference in level
between the table and the floor; the thermostat, which regulates the
temperature of the water flowing in the domestic heating system with a
delicacy impossible to the most highly constituted human organism; the
seismograph, detecting, recording, and almost locating earth tremors
originating thousands of miles away; the automatic fire sprinkler;
the safety-valve; the recording thermometer and other meteorological
instruments; and last, if not of least importance, the common
alarm-clock. And these are but a few of the contrivances with which
man does by blind mechanism that which is impossible to his sentient
determination.
Even if the nervous system could be schooled into endurance of the
wear and tear of consciously balancing an aeroplane for many hours, it
is still imperative that the task be not left to the exertion of human
wits, but controlled by self-acting devices responding instantly to
unforeseen conditions as they occur.
[Illustration: Diagram showing turbulent air currents produced when a
flat plane is forced through the air at a large angle of incidence in
the direction A-B.]
[Illustration: Diagram showing smoothly flowing air currents caused by
correctly shaped plane at proper angle of incidence.]
Some of the problems of which the model-builder may find the solution
are: whether large screws revolving slowly, or small screws revolving
rapidly, are the more effective; how many blades a propeller should
have, and their most effective shape; what is the “perfect” material
for the planes (Maxim found that with a smooth wooden plane he could
lift 2½ times the weight that could be lifted with the best made
fabric-covered plane); whether the centre of gravity of the aeroplane
should be above or below the centre of lift, or should coincide with
it; new formulas for the correct expression of the lift in terms of the
velocity, and angle of inclination--the former formulas having been
proved erroneous by actual experience; how to take the best advantage
of the “tangential force” announced by Lilienthal, and reasserted by
Hargrave; and many others. And there is always the “paradox aeroplane”
to be explained--and when explained it will be no longer a paradox, but
will doubtless open the way to the most surprising advance in the art
of flying.
It is not assumed that every reader of this chapter will become a
studious experimenter, but it is unquestionably true that every
model-builder, in his effort to produce winning machines, will be more
than likely to discover some fact of value in the progress making
toward the ultimate establishment of the commercial navigation of the
air.
The tools and materials requisite for the building of model aeroplanes
are few and inexpensive. For the tools--a small hammer; a small iron
“block” plane; a fine-cut half-round file; a pair of round-nose pliers;
three twist drills (as used for drilling metals), the largest 1/16 inch
diameter, and two smaller sizes, with an adjustable brad-awl handle
to hold them; a sharp pocket knife; and, if practicable, a small hand
vise. The vise may be dispensed with, and common brad-awls may take the
place of the drills, if necessary.
For the first-described model--the simplest--the following materials
are needed: some thin whitewood, 1/16 inch thick (as prepared for
fret-sawing); some spruce sticks, ¼ inch square (sky-rocket sticks are
good); a sheet of heavy glazed paper; a bottle of liquid glue; some of
the smallest (in diameter) brass screws, ¼ to ½ inch long; some brass
wire, 1/20 inch in diameter; 100 inches of square rubber (elastic)
“cord,” such as is used on return-balls, but 1/16 inch square; and a
few strips of draughtsman’s tracing cloth.
[Illustration:
_A_, _B_, blank from which propeller is shaped; _P_, _P_, pencil
lines at centre of bend; _C_, _D_, sections of blade at points
opposite; _E_, _G_, propeller after twisting; _H_, view of
propeller endwise, showing outward twist of tips; also shaft.]
As the propeller is the most difficult part to make, it is best
to begin with it. The flat blank is cut out of the whitewood, and
subjected to the action of steam issuing from the spout of an actively
boiling tea-kettle. The steam must be hot; mere vapor will not do the
work. When the strip has become pliable, the shaping is done by slowly
bending and twisting at the same time--perhaps “coaxing” would be the
better word, for it must be done gently and with patience--and the
steam must be playing on the wood all the time, first on one side of
the strip, then on the other, at the point where the fibres are being
bent. The utmost care should be taken to have the two blades bent
exactly alike--although, of course, with a contrary twist, the one to
the right and the other to the left, on each side of the centre. A
lead-pencil line across each blade at exactly the same distance from
the centre will serve to fix accurately the centre of the bend. If
two blocks are made with slots cut at the angle of 1 inch rise to 2¼
inches base, and nailed to the top of the work bench just far enough
apart to allow the tips of the screw to be slid into the slots, the
drying in perfect shape will be facilitated. The centre may be held to
a true upright by two other blocks, one on each side of the centre.
Some strips of whitewood may be so rigid that the steam will not make
them sufficiently supple. In this case it may be necessary to dip them
bodily into the boiling water, or even to leave them immersed for a few
minutes; afterward bending them in the hot steam. But a wetted stick
requires longer to dry and set in the screw shape. When the propeller
is thoroughly dry and set in proper form, it should be worked into the
finished shape with the half-round file, according to the several
sections shown beside the elevation for each part of the blade. The
two strengthening piece’s are then to be glued on at the centre of the
screw, and when thoroughly dry, worked down smoothly to shape. When
all is dry and hard it should be smoothed with the finest emery cloth
and given a coat of shellac varnish, which, in turn, may be rubbed to
a polish with rotten stone and oil.
It may be remarked, in passing, that this is a crude method of making a
propeller, and the result cannot be very good. It is given here because
it is the easiest way, and the propeller will work. A much better way
is described further on--and the better the propeller, the better any
model will fly. But for a novice, no time will be lost in making this
one, for the experience gained will enable the model-builder to do
better work with the second one than he could do without it.
For the aeroplane body we get out a straight spar of spruce, ¼ inch
square and 15½ inches long. At the front end of this--on the upper
side--is to be glued a small triangular piece of wood to serve as a
support for the forward or steering plane, tilting it up at the front
edge at the angle represented by a rise of 1 in 8. This block should
be shaped on its upper side to fit the curve of the under side of the
steering-plane, which will be screwed to it.
The steering-plane is cut according to plan, out of 1/16 inch
whitewood, planed down gradually to be at the ends about half that
thickness. This plane is to be steamed and bent to a curve (fore and
aft) as shown in the sectional view. The steam should play on the
_convex_ side of the bend while it is being shaped. To hold it in
proper form until it is set, blocks with curved slots may be used, or
it may be bound with thread to a moulding block of equal length formed
to the proper curve. When thoroughly dry it is to be smoothed with the
emery cloth, and a strip of tracing cloth--glossy face out--is to be
glued across each end, to prevent breaking in case of a fall. It is
then to be varnished with shellac, and polished, as directed for the
propeller. Indeed, it should be said once for all that every part of
the model should be as glossy as it is possible to make it without
adding to the weight, and that all “entering edges” (those which push
into and divide the air when in flight) should be as sharp as is
practicable with the material used.
The steering-plane is to be fastened in place by a single screw long
enough to pierce the plane and the supporting block, and enter the
spar. The hole for this screw (as for all screws used) should be
drilled carefully, to avoid the least splitting of the wood, and just
large enough to have the screw “bite” without forcing its way in. This
screw which holds the plane is to be screwed “home” but not too tight,
so that in case the flying model should strike upon it in falling,
the slender plane will swivel, and not break. It will be noticed that
while this screw passes through the centre of the plane sideways, it is
nearer to the forward edge than to the rear edge.
If the work has been accurate, the plane will balance if the spar
is supported--upon the finger, perhaps, as that is sensitive to any
tendency to tipping. If either wing is too heavy, restore the balance
by filing a little from the tip of that wing.
The main planes are next to be made. The lower deck of the biplane is
of the 1/16 inch whitewood, and the upper one is of the glazed paper
upon a skeleton framework of wood. The upright walls are of paper.
The wooden deck is to be bent into the proper curve with the aid of
steam, and when dry and set in form is to be finished and polished. The
frame for the upper deck is made of the thin whitewood, and is held
to its position by two diagonal struts of whitewood bent at the ends
with steam, and two straight upright struts or posts. It is better to
bend all cross-pieces into the curve of the plane with steam, but they
may be worked into the curve on the top side with plane and file, and
left flat on the lower side. The drawings show full details of the
construction, drawn accurately to scale.
It is best to glue all joints, and in addition to insert tiny screws,
where shown in the plans, at the time of gluing.
When all the wooden parts are in place the entire outline of the upper
plane and the upright walls is to be formed of silk thread carried
from point to point, and tied upon very small pins (such as are used
in rolls of ribbon at the stores) inserted in the wood. The glazed
paper is put on double, glossy side out. Cut the pieces twice as large
(and a trifle more) than is needed, and fold so that the smooth crease
comes to the front and the cut edges come together at the rear. The two
inner walls should be put in place first, so as to enclose the thread
front and back, and the post, between the two leaves of the folded
paper. Cutting the paper half an inch too long will give one fourth of
an inch to turn flat top and bottom to fasten to the upper and lower
decks respectively. The two outer walls and the upper deck may be cut
all in one piece, the under leaf being slit to pass on either side of
the inner walls. A bit of glue here and there will steady the parts to
their places. The cut edges at the rear of the deck and walls should
be caught together with a thin film of glue, so as to enclose the rear
threads.
[Illustration:
_A_, _B_, plan, and _C_, section, of steering plane; _H_, section
of lower main plane; _L_, wood skeleton of upper plane; _T_,
_T_, silk thread; _O_, _O_, posts; _J_, _J_, braces; _E_, rubber
strands; _D_, forward hook; _G_, shaft; _F_, thrust-block; _K_,
upper plane of paper; _M_, elevation of main planes, from the
rear.]
When the biplane is completed it is to be fastened securely to the spar
in such a position that it is accurately balanced--from side to side.
The spar may be laid on a table, and the biplane placed across it in
its approximate position. Then move the plane to one side until it tips
down, and mark the spot on the rear edge of the plane. Repeat this
operation toward the other side, and the centre between the two marks
should be accurately fastened over the centre line of the spar. Even
with the greatest care there may still be failure to balance exactly,
but a little work with a file on the heavy side, or a bit of chewing
gum stuck on the lighter side, will remedy the matter.
The body of the aeroplane being now built, it is in order to fit it
with propelling mechanism. The motive power to whirl the propeller we
have already prepared is to be the torsion, or twisting strain--in this
case the force of untwisting--of india rubber. When several strands
of pure rubber cord are twisted up tight, their elasticity tends to
untwist them with considerable force. The attachment for the rubber
strands at the front end of the spar is a sort of bracket made of the
brass wire. The ends of the wire are turned up just a little, and they
are set into little holes in the under side of the spar. Where the wire
turns downward to form the hook it is bound tightly to the spar with
silk thread. The hook-shaped tip is formed of the loop of the wire
doubled upon itself. The rear attachment of the rubber strands is a
loop upon the propeller shaft itself. As shown in the drawings, this
shaft is but a piece of the brass wire. On one end (the rear) an open
loop is formed, and into this is slipped the centre of the propeller.
The short end of the loop is then twisted around the longer shank--very
carefully, lest the wire cut into and destroy the propeller. Two turns
of the wire is enough, and then the tip of the twisted end should be
worked down flat with the file, to serve as a bearing for the propeller
against the thrust-block. This latter is made of a piece of sheet brass
(a bit of printers’ brass “rule” is just the thing) about 1/40 of an
inch thick. It should be ¼ of an inch wide except at the forward end,
where it is to be filed to a long point and bent up a trifle to enter
the wood of the spar. The rear end is bent down (not too sharply, lest
it break) to form the bearing for the propeller, a hole being drilled
through it for the propeller shaft, just large enough for the shaft to
turn freely in it. Another smaller hole is to be drilled for a little
screw to enter the rear end of the spar. Next pass the straight end
of the propeller shaft through the hole drilled for it, and with the
pliers form a round hook for the rear attachment of the rubber strands.
Screw the brass bearing into place, and for additional strength, wind
a binding of silk thread around it and the spar.
Tie the ends of the rubber cord together, divide it into ten even
strands, and pass the loops over the two hooks--and the machine is
ready for flight.
To wind up the rubber it will be necessary to turn the propeller in
the opposite direction to which it will move when the model is flying.
About 100 turns will be required. After it is wound, hold the machine
by the rear end of the spar, letting the propeller press against the
hand so it cannot unwind. Raise it slightly above the head, holding the
spar level, or inclined upward a little (as experience may dictate),
and launch the model by a gentle throw forward. If the work has been
well done it may fly from 150 to 200 feet.
Many experiments may be made with this machine. If it flies too high,
weight the front end of the spar; if too low, gliding downward from the
start, weight the rear end. A bit of chewing gum may be enough to cause
it to ride level and make a longer and prettier flight.
A very graceful model is that of the monoplane type illustrated in
the accompanying reproductions from photographs. The front view shows
the little machine just ready to take flight from a table. The view
from the rear is a snap-shot taken while it was actually flying. This
successful model was made by Harold S. Lynn, of Stamford, Conn. Before
discussing the details of construction, let us notice some peculiar
features shown by the photographs. The forward plane is arched; that
is, the tips of the plane bend slightly downward from the centre. On
the contrary, the two wings of the rear plane bend slightly upward from
the centre, making a dihedral angle, as it is called; that is, an angle
between two surfaces, as distinguished from an angle between two lines.
The toy wheels, Mr. Lynn says, are put on principally for “looks” but
they are also useful in permitting a start to be made from a table or
even from the floor, instead of the usual way of holding the model in
the hands and giving it a slight throw to get it started. However, the
wheels add to the weight, and the model will not fly quite so far with
them as without.
[Illustration: Front view of the Lynn model of the monoplane type,
about to take flight.]
The wood from which this model was made was taken from a bamboo
fish-pole, such as may be bought anywhere for a dime. The pole was
split up, and the suitable pieces whittled and planed down to the
proper sizes, as given in the plans. In putting the framework of the
planes together, it is well to notch very slightly each rib and spar
where they cross. Touch the joint with a bit of liquid glue, and wind
quickly with a few turns of sewing silk and tie tightly. This must be
done with delicacy, or the frames will be out of true. If the work is
done rapidly the glue will not set until all the ties on the plane are
finished. Another way is to touch the joinings with a drop of glue,
place the ribs in position on the spars, and lay a board carefully on
the work, leaving it there until all is dry, when the tying can be
done. It either case the joinings should be touched again with the
liquid glue and allowed to dry hard.
[Illustration: The Lynn model monoplane in flight, from below and from
the rear.]
The best material for covering these frames is the thinnest of China
silk. If this is too expensive, use the thinnest cambric. But the model
will not fly so far with the cambric covering. The material is cut
one-fourth of an inch too large on every side, and folded over, and the
fold glued down. Care should be taken that the frame is square and true
before the covering is glued on.
The motive power is produced by twisting up rubber tubing. Five and
three-quarter feet of pure rubber tubing are required. It is tied
together with silk so as to form a continuous ring. This is looped
over two screw-hooks of brass, one in the rear block and the other
constituting the shaft. This looped tubing is twisted by turning the
propeller backward about two hundred turns. As it untwists it turns the
propeller, which, in this model, is a “traction” screw, and pulls the
machine after it as it advances through the air.
[Illustration:
Details and plans of the Harold Lynn model monoplane. _W_, tail
block; _Y_, thrust-block; _S_, mounting of propeller showing
glass bead next the thrust-block, and one leather washer outside
the screw; _B_, glass bead; _C_, tin washer; _M_, _M_, tin lugs
holding axle of wheels.]
The propeller in this instance is formed from a piece of very thin
tin, such as is used for the tops of cans containing condensed milk.
Reference to the many illustrations throughout this book showing
propellers of flying machines will give one a very good idea of the
proper way to bend the blades. The mounting with the glass bead and the
two leather washers is shown in detail in the plans.
[Illustration:
Method of forming propeller of the laminated, or layer, type. The
layers of wood are glued,in the position shown and the blades
carved out according to the sections. Only one blade is shown
from the axle to the tip. This will make a right hand propeller.
]
The wheels are taken from a toy wagon, and a pair of tin ears will
serve as bearings for the axle.
The sport of flying model aeroplanes has led to the formation of many
clubs in this country as well as in Europe. Some of the mechanisms that
have been devised, and some of the contrivances to make the models
fly better and further, are illustrated in the drawings.
[Illustration:
At _A_ is shown a method of mounting the propeller with a glass
or china bead to reduce friction, and a brass corner to aid
in strengthening. _B_ shows a transmission of power by two
spur wheels and chain. _C_ is a device for using two rubber
twists acting on the two spur wheels _S_, _S_, which in turn
are connected with the propeller with a chain drive. _D_ shows
a launching apparatus for starting. _W_, the model; _V_, the
carriage; _F_, the trigger guard; _T_, trigger; _E_, elastic cord
for throwing the carriage forward to the stop _K_.]
Records have been made which seem marvellous when it is considered
that 200 feet is a very good flight for a model propelled by rubber.
For instance, at the contest of the Birmingham Aero Club (England) in
September, one of the contestants won the prize with a flight of 447
feet, lasting 48 seconds. The next best records for duration of flight
were 39 seconds and 38 seconds. A model aeroplane which is “guaranteed
to fly 1,000 feet,” according to the advertisement in an English
magazine, is offered for sale at $15.
The American record for length of flight is held by Mr. Frank Schober,
of New York, with a distance of 215 feet 6 inches. His model was of the
Langley type of tandem monoplane, and very highly finished. The problem
is largely one of adequate power without serious increase of weight.