Whether one be designing the simplest paper glider, a model or a
passenger-carrying aeroplane, the problem of stability is the same. To
keep afloat, your air craft must be supported, as a rule, by at least
two surfaces to provide longitudinal stability. To understand the
principle of longitudinal stability, picture to yourself a very
delicately-balanced board or "seesaw." The center of gravity naturally
falls between these two planes at either end, and the wings therefore
tilt up or down, or seesaw, on this invisible fulcrum. With this
principle in mind, the movement of your aeroplane, which may seem so
capricious, will be seen to follow definite laws.
When a gust of wind forces the front plane upward, the rear plane swings
down. This movement increases the angle of both planes to the
horizontal; they offer much greater resistance to the air, and the speed
of the machine is checked. As the aeroplane slows down, as a rule, it
tries to right itself, that is, to seesaw back to balance at a
horizontal position. This in turn reduces the resistance the planes
offer to the wind, and the flight is continued at its original speed.
[Illustration: An excellent piece of workmanship. Model by R. Mungokee]
[Illustration: Model with minimum plane surface. Built by A. C. Odom]
The trick, therefore, is to adjust your planes with regard to the center
of gravity so that they will always seesaw back to a horizontal
position; in other words, to secure automatic longitudinal stability.
In designing a motor base bear in mind that it must be made as long as
possible for installing the motor, and broad enough to afford stable
support for the wings, the whole being kept as light and as rigid as
possible. Since the length of the flight depends directly upon the
length of the motor, the frame of your model should be at least two feet
in length. The width of the frame may vary widely, as a glance at the
successful model aeroplanes of the year will prove. For racing model
aeroplanes, the base may be increased to four or even five feet in
length.
THE FAMOUS "ONE OUNCER."
The one-ounce models, which have been brought to such perfection in
England, are among the simplest aeroplanes to build. Fig. A models have
a record of 1,500 feet. The adjustment is delicate, however; it is a
very "tricky" affair to manage, and whether you can get the remarkable
flights made abroad is another matter. For the stick, select a piece of
straight-grained ash or some light wood three feet in length and
one-quarter of an inch square. The planes should be cut from a thin
board one-sixteenth of an inch thick. The main plane should measure
fifteen inches by three inches, and the smaller plane eight by one and a
half inches, thus giving them a high aspect ratio. They should taper
slightly towards the ends. Round off the corners of both planes and
sandpaper the edges down. If the wood will stand it, work it down, using
a sharp plane or sandpaper. The planes should be bent by steaming
slightly across the middle and set at a slight dihedral angle.
[Illustration: A — The Famous "one Ouncer." B — A Small Experimental
Model. C — A Modified Burgess Webb Model.]
The model is driven most efficiently by a six-inch propeller. If it be a
one-piece blade, prepare a propeller blank six inches by one inch, cut
from a half-inch board. Cut away to the thinnest possible blade. Use a
very simple support for your propeller shaft as well as for the motor
anchorage at the extreme forward end. The planes should be tied with
rubber strands to the stick and glued in position when properly
adjusted. Try out your model with a motor consisting of two strands of
one-eighth-inch rubber, and increase if necessary. You will need all
your ingenuity and skill and workmanship to construct a stable model
even of so simple a design which will come within one ounce. Throw it
with the wind.
A MODIFIED BLERIOT.
In improving the lines of the various self-raising models, many of the
designs have been greatly simplified. With the number of members
reduced, the construction of a successful model becomes much easier and
the chances of failure more remote. A simple rectangular frame with two
planes driven by twin propellers requires very little skill or
experience to put together. It is very easy to locate and correct the
trouble in such a model, and quickly adjust it to rise and fly for
considerable distances.
There are many forms of such planes this year which are marvels of
lightness and strength, but the beginner should try the simplest. Begin
by building a simple rectangular frame, three feet in length and ten
inches in width of half-inch or quarter-inch strips. Mortise the corners
half way through each stick and glue them in position. Increase the
steadiness of the frame by a cross piece at the center, without
mortising. Mount your motor above the frame, selecting some simple,
strong support for the axle and the anchorage.
A model which rises unassisted requires considerable power and your
propellers should have eight-inch blades and be carved from blanks one
inch thick. You may find it advisable later on to install propellers
with very broad blades. First install motors of considerable power, each
consisting of twelve or fourteen one-eighth-inch rubber strips. You will
not get more than two or three hundred turns out of them, but with a
high-pitch propeller this will give you an excellent flight, say 200
feet.
[Illustration: Model With Minimum Plane Surface.]
For the early trials use planes with a rather high aspect ratio. Make
one of the planes four by sixteen inches with square corners, and the
second, which will be carried forward, about the same size with rounded
corners. Both planes should have a slight camber.
Attach the planes to the under side of the motor base. The theory of
this adjustment is that the planes thus rest upon undisturbed air and
are more stable. The planes above the frame come in contact with air
which has been churned up more or less by the passage of the frame. A
small vertical rudder may be added below the rear frame and well back of
the center of gravity. The model should be supported at a slight
elevation by a simple skid. By adjusting the angle of the forward plane,
this model may be made to perform a number of spectacular flights. A
model very similar to this was the winner of a cup offered for the best
spectacular flights at an important New York tournament.
A SIMPLE EXPERIMENTAL MODEL.
A great deal of pleasure and profit may be had from a small experimental
model aeroplane. The beginner who is constructing his first model will
find a small machine by far the most satisfactory. The more experienced
model builder, on the other hand, will find that so simple a model will
enable him to try out new theories quickly and cheaply. A simple Bleriot
form, one foot in length, driven tail foremost is recommended. Many
successful model builders keep such a model constantly in their
workshops.
A model aeroplane of this type and size can be made to fly from the very
first. Many of the problems which appear so difficult in constructing a
three-foot model, such as balance, head resistance, and the proper
adjustment of power, practically are avoided in this miniature
aeroplane. There is a great advantage again in the fact that the small
model may be flown indoors in the average room, where the air problems
are almost negligible. Fig. B.
Let the motor base consist of a single stick one-fourth or three-eighths
of an inch square and one foot in length. At one end of the base, attach
a block of wood one inch square and of a thickness equal to that of the
stick. Glue this in position and bind it securely by wrapping with
thread touched with glue. At a point three-quarters of an inch above the
stick, drill a hole parallel to the frame for the axle of your
propeller. A hooked wire should be attached to the opposite end of the
base. One end may be run through the stick and fastened, or it may be
imbedded in a block fastened to the stick corresponding to the axle
block. A simple and effective motor anchorage may be made of metal
(described elsewhere).
Your propeller should measure four inches in diameter. A propeller cut
from a blank one by four inches and one-half of an inch thick will give
a good pitch. Either a propeller of wood or metal such as has already
been described will answer. The propeller should be mounted upon an axle
and adjusted to the bearings, and the hook after passing through the
bearings in the support turned into a hook for the rubber strands.
Select from the detailed instructions the method which appeals to you.
Be sure that the propeller spins smoothly. It should be so delicately
adjusted that it will turn literally at a breath.
Before stringing the rubber strands between the two hooks of your motor,
be sure that the hooks are bent back, so that the strands will be in a
line with the bands. The bearings should be carefully oiled. In flying
out of doors, there is danger of getting fine sand or dirt in the
bearings which, of course, greatly increases the friction. Try out your
motor with four strands of rubber one-eighth of an inch square. The
rubber sold for one-eighth inch is often a trifle under this
measurement. The propeller should, of course, be mounted with the
shorter or curved edge forward. In winding your motor, never turn it
after the second row of double knots begin to appear, and do not keep
your propeller wound a second more than is necessary before a flight.
[Illustration: An American Fleming Williams built by C. McQueen]
[Illustration: One of the earlier models built by Cecil Peoli]
For a model of this size, wooden planes are entirely practical and very
simple to construct. Much depends upon the modeling of the planes and
the smoothness of both of their surfaces. For the planes you will need
two thin boards, one eight by two inches and another four by two inches,
each one-eighth of an inch thick. Select a wood such as poplar or
spruce, which will not split easily. The ends of the planes should be
rounded in front and cut sharply away at the rear edge, as described
elsewhere. If the wood will stand reduction without breaking, plane or
sandpaper away the surfaces until they are about one-sixteenth of an
inch thick.
The planes may be flexed by steaming, but there is a still simpler
method. Paint your planes with a thin glue or varnish, and while they
are still wet and pliable, bend them to the desired shape. To shape
them, procure a strip of wood one-quarter of an inch square, tack it to
a board and bend the planes over it, and fasten them in position with
brads driven about the edges and bent over to hold it down. The stick
should be placed parallel to the entering edge and one-half an inch back
of the line. This will give you planes flexed with a dipping edge. Later
you will probably want to experiment by changing this curve, which is
very easily done by bending over a stick of different size and altering
its position.
The model is driven by the propeller with the small plane forward.
Attach the planes to the stick with the curved or entering edge forward
by tying them with a rubber band. This will hold them in position and
allow them to give when they fall. Slip the planes back and forth until
the proper position has been found. A small block of wood may be
inserted between the planes and the stick to raise the wing to the
desired elevation. Practise throwing the model as a glider until it
sails across the room on an even keel, when the motor may be installed.
Directional stability may be gained by adding a vertical rudder. It may
be made from a thin board similar to that used in the planes. Cut a
piece two inches square and round off the corners, and shave to a knife
edge. Attach this, curved edge downward, to the edge of the stick
directly beneath the rear plane, taking care that the motor does not
touch it. To complete the model, attach skids to the under surface at
the front and rear. These should be of light reed, cane or bamboo, glued
to the main frame and curved downward and backward like runners.
MODEL WITH MINIMUM PLANE SURFACE.
In the experiments in building models with very narrow planes, some
amazing results have been produced during the past year. The limit in
this reduction would seem to have been reached in the model with planes
with a ratio of eight separated by a distance equal to ten times their
width. The forward part of this amazing model is a modified biplane, and
in this respect it resembles a successful model of last season. The two
models are reproduced side by side, for the sake of comparison. The
economy of weight and resistance is instantly obvious to the most
inexperienced eye. The model rises quickly and flies for nearly three
hundred feet in a perfectly straight line.
The motor base, which has a length equal to six times its width, or
eight by forty inches, is constructed of one-quarter inch strips. A
light cross piece at the center braces the two sides. The supports for
the propeller axles extend out horizontally from the sides. This
arrangement makes it possible to mount two ten-inch propellers on an
eight-inch base. The front ends of the frame are joined by a
semicircular piece of reed which acts as a shock absorber and does away
with the weight of the cross piece. The workmanship in every detail of
this frame must be exceedingly delicate.
The planes have an aspect ratio of eight and measure two inches in depth
by sixteen in width. The outer ends of the rear plane are three inches
in their fore and aft dimensions, thus making the outer rear edge a
slight concave. The front is cut sharply away at an angle of forty-five
degrees. The upper plane lies flat upon the motor base. The lower plane
is not set directly below it as in the ordinary biplane form, but to the
rear, its front edge being on a line with the rear edge of the upper
plane, after the manner of the Valkyrie machine. The two planes are
separated by a space slightly greater than their width. Two small
rudders, elliptical in shape, are carried just behind and below the rear
plane. The model is mounted on very delicate skids built of reed, and is
inclined at a very slight angle. Six strands of one-eighth-inch rubber
are used for each motor. The unusual length of the motor makes it
possible to give six hundred turns.
THE BURGESS WEBB MODEL.
An ingenious method of lightening the front end of the motor base and at
the same time reducing the head resistance is employed in the Burgess
Webb model. A single stick frame is used with a base equal to one-fourth
its length. The cross piece is mortised to the central stick and braced
by the diagonal sticks, joining at the main frame. This cross piece is
carried out beyond the braces and pierced for the propeller shafts,
where two twin propellers are mounted. Fig. C.
The front plane is elliptical in form, with a width equal to two-thirds
the width of the base. It has an aspect ratio of two. The propeller
motors are strung on hooks attached to the outer sides of this frame.
The plane must be unusually strong to stand the pull of the motors,
which is naturally great. It is fixed to the extreme outer end of the
central stick. The main plane, which is mounted well forward in this
model, is an almost perfect semicircle. One can, of course, carry out
his own ideas in selecting the design of the planes.
A very light central stick is used which is strengthened by wires
running to a vertical strut at the center. It is claimed that the
ingenious arrangement of the forward plane cuts away from one to two
ounces in the weight of the model, and the decreased head resistance
adds both to its stability in flight and distance qualities. The
simplified form of front plane may be adopted on a variety of models.
A MODEL WITH ADJUSTABLE STABILIZERS.
A serviceable model may be built up with flat planes equipped with
ailerons both at the rear and outer ends of the planes. These tips make
it possible to control both the horizontal and vertical movement, and
permit a great many adjustments impossible with other models. The motor
base may be borrowed from some earlier model. It should be fairly heavy.
A rectangle measuring ten by forty inches built of one-half inch strips
will be found sufficiently rigid. The sides should be braced by a cross
piece at the middle. The ends and central strut may be made of some form
of truss, if desired. One of the simplest means of providing supports
for the axles of the propellers is to carry the stick at the rear, one
and a half inches beyond the side pieces, and pass the axle through a
hole drilled one-half an inch from the end.
[Illustration: A Model With Adjustable Stabilizer.]
The pull of the motors when wound is thus well distributed and, as has
been pointed out, permits of a larger propeller being used without
danger of their striking in turning. Still another advantage is that it
keeps the strands of the motor from interfering with the planes. When
the motors are strung above the planes, they have a tendency to force
the machine downward.
Construct two serviceable planes the same size, six by eighteen inches.
These should be flat and covered as smoothly as possible. Now attach to
the rear edges of each plane a series of three ailerons each two by five
inches, fastening one at either end and the third at the middle. Make
the frames of the ailerons of a very light lath strip and wire them to
the rear edge in such a way that they may be swung up or down through a
small arc. At the outer ends of each of the planes, attach semicircular
tips, each with a base of six inches and a radius of six inches. These
may be rounded off or cut away to sharp points as desired. They should
also be attached so that they may be bent up or down and will hold their
position. Mount the model on some simple arrangement of reed skids, so
that it will be elevated at a very slight angle above the horizontal.
The model complete should weigh about eight ounces. Equipped with twin
motors of fourteen strands of one-sixteenth-inch rubber each, the
propellers should be turned about four hundred times. A medium-pitch
propeller will best serve your purpose.
In flying this model, bear in mind that the flight will be directed in
an opposite direction from the angle of the ailerons, or rudders, just
as a boat answers its helm. The wing tips should be bent up or down
until the flight is stable. The complete equipment of ailerons enable
one to correct any defects in proportion which are likely to be needed
in models built by beginners.
AN EFFICIENT THREE-OUNCE MODEL.
(Record 900 Feet)
A surprising variety of designs may be carried out in models of the
three-ounce class. One of the easiest to control is a broad adaptation
of the Bleriot model, flown with its small surface forward. For a
three-foot model, first build two planes of very light material. Wire
frames are especially suited for this model. The main plane should
measure two feet in length by four in width, or with an aspect ratio of
six. The smaller plane, carried forward, should be one foot in length
with the same aspect ratio. It will be found a good plan to carry the
outer edges of this plane back, forming two inch squares at the rear
edges. A plane with a slight camber will prove the more stable.
For the frame secure two light sticks three-sixteenths of an inch square
of some fairly strong wood; a straight spruce is good. Attach the motors
to these sticks before completing the frame. Select some rigid support
for the propeller axle. Prepare two ten-inch propellers, carving the
blades from propeller blanks three-fourths of an inch thick. The motor
will probably work best when made up of six strands of rubber,
one-eighth of an inch square, although this should be finally determined
by actual test flights. Keep all parts of the motors extremely light.
To assemble the model, connect the forward ends of the sticks carrying
the motors by a piece of reed bent to a half circle, by merely binding
the ends firmly together. The sticks should diverge so that the
propellers will be about ten inches apart, giving plenty of room for the
propellers to turn without striking one another. Next fasten the larger
plane in position across the top of the sticks, and about two inches
away from the propellers, making the plane serve as a cross piece to
hold them firmly in position. The strands of the motor should preferably
be carried above the plane. This plan does away with the rear stick of
the motor base, thus saving this weight. Adjust the parts very
carefully, that the frame will be rigid enough to stand the strain of
the motor.
[Illustration: An Efficient Three-ounce Model.]
The model will require careful adjusting to be brought to an even keel.
The forward plane should be attached in such a way that it may be tilted
up or down as desired. With care, the weight of the model may be brought
within three ounces, although a fraction over will not matter. Models
built on these lines have flown in a perfectly straight line for 900
feet.
AN ALL-METAL MODEL FRAME.
In a previous paper, it was suggested that the motor base be made of
tubes of aluminum. The idea has been carried further, and attractive
frames are now constructed in which not only the main frame is
constructed of metal tubing, but the cross piece supporting the
propellers and the braces as well are of the same material. The new
metal, "magnalium," has been used successfully for this purpose. It is a
trifle heavier than aluminum, but much stronger, and almost as easy to
work. In England, the motor base is sometimes made of metal tubing one
inch in diameter, and the rubber motor is passed through the tube
itself.
[Illustration: An All-metal Model Frame.]
Such a frame may be made readily by one who has had no experience in
tinsmithing or metal work. The metal frames are sometimes constructed by
driving wooden blocks into the ends of the tubes and letting them
project one-half an inch or more. The plug may be cut off flush, and the
cross piece fastened by wire and stout nails through the cross tube into
the plug of the main tube. A convenient brace may be constructed by
cutting the tubes to the proper size, fasten the ends and pass the rivet
through both tubes at the point of intersection, and screw the nut down
firmly on the opposite side. Such a frame is practically indestructible.
There is one possible drawback, however, in the tendency of the metal to
bend if the rubber motor pulls too strongly. Once bent, it is difficult
to get back into shape. This tendency may be overcome when twin
propellers are used, by winding alternately, giving one propeller one
hundred turns and the other propeller one hundred turns, then the first
another hundred, and so on until the motor is wound up. The planes,
propellers and skids may be of any reliable design.
AN EFFICIENT SINGLE STICKER.
A very light single-stick model may be built of bamboo rods, which will
stand an immense amount of wear and tear. It consists of a single
longitudinal member with crossed pieces at either end, braced against
the central stick to withstand the pull of the motor. Select a bamboo
stick about half an inch in diameter and three feet long. An old fish
pole will answer. The cross pieces at the ends should be of some light,
strong wood, such as poplar, whitewood or ash, since they must be
mortised and drilled, and the bamboo is likely to split under the
operation. Use a three-eighth-inch strip, cutting a piece ten inches
long for the rear and another six inches in length for the front of the
base. Fasten these rigidly in position at right angles by mortising,
glueing and tying in position. Run diagonal pieces cut from quarter-inch
strips from the ends of both cross sticks to the central frame. Be
careful not to cut away the wood in mortising it, for a bad break is
likely to occur at the weakened point.
Build two serviceable planes. The larger one, which should be carried in
the rear, should measure about twenty-four inches by eight, and the
front plane twelve by four inches. Since your frame is very light and
strong, there is no need to economize weight. By carrying the braces
running from the cross sticks well out on the stick, you can provide a
broad support for the planes. Tie the wings on the motor base with
strands of rubber. In landing they will then give enough to save a bad
smash.
[Illustration: One of the best models of the year, built by John Caresi]
[Illustration: An excellent model, showing careful attention to details.
Built by L. V. Brooks]
The propellers are mounted by passing the axles through holes drilled
through the center of the rear stick about one inch from the ends. The
rubber strands may be simply passed around the front stick and tied in
position, or may be looped about a hook inserted in the stick. Use a
fairly high pitch propeller, since the base will carry a powerful motor.
Select some simple form of skid, for the model will be comparatively
light, say within ten ounces.
A ONE-PLANE MODEL.
Interesting experiments have been made this season by altering the angle
at which the main planes are set to the motor base. The theory of these
designs is, of course, that the resistance offered by an entering angle
is less than that of a straight edge. In some models, the main planes
are carried backward until the rear tips are on a line with the
propellers. The model is driven tail first by twin propellers. The
planes are besides set at a slight dihedral angle so that the angle of
incidence is greater at the ends.
A rectangular base is suggested, with a central stick. The planes, which
may be either flat or cambered, are attached to the central stick and
slightly raised by inserting strips of wood above the outer edges of the
motor base. In this way, it is possible to fix them rigidly. Wire braces
running from the outer ends to the rear of the motor base will add to
its strength. The angle of the wings to the motor base may be altered to
suit conditions. A plane of high aspect ratio works best in this
position.
THE CANNING MODEL.
There is much to be said for the model with propellers placed near the
centers of gravity and pressure. Many authorities believe that the
successful aeroplane of the future will carry propellers somewhere near
the center of the motor base. Since the thrust is exerted near the point
where the aeroplane balances, it is argued that its stability is greatly
increased, while with the propellers far removed, either to the front or
rear, the torque gains a leverage from its position which it is
difficult to control. The main difficulty with this arrangement all
along for rubber-strand motors has been that the length of the motor
must be cut down to about half, and their efficiency reduced.
In the Canning model, this difficulty has been overcome, and a motor
extending the entire length of the motor base is hitched up to twin
propellers placed near the center of gravity. A powerful motor extends
along the center of the motor base, attached to a gear wheel at the
forward end. This wheel turns two smaller gears at either side. In this
way, a motor running the entire length of the frame may be used with an
increased number of turns. A third gear wheel should be introduced to
make the propellers turn in opposite directions.
THE FLEMMING WILLIAMS MODEL.
An immense amount of curiosity has been aroused regarding the famous
Flemming Williams model. This machine has completely outdistanced all
rivals, and set a new and amazing distance record. Its builder
frequently gets flights of eighteen hundred feet with his model, and has
made the astonishing record, under favorable conditions, of one-half a
mile. In order to study this model at first hand, the writer has
imported one of the machines, built by Ding, Sayles & Company, one of
the leading model builders of England.
The distance qualities of this model will be recognized at a glance. It
is a single sticker, extremely light in all its members, combining an
extraordinarily long motor base with well-adjusted plane surfaces. The
arrangement of the wings is original. The main stability plane is set
forward in front of the center of pressure. The rear plane is formed by
filling in the space between the rear stick and the braces, thus saving
the weight of the frame usually carried in this position. The model is
driven by two seven and a half inch propellers of very high pitch. The
model is without skids and is launched from the hand.
The central member measures four feet two inches in length. The stick is
one-half by one-fourth of an inch, with the forward part tapering
gradually to one-fourth of an inch square. The base stick is eight
inches in length, cut from a strip five-eighths by one-eighth of an
inch. The diagonal pieces forming the triangle are cut from the same
material, and meet at a point eight inches from the rear, thus affording
a surface of twenty-four square inches. The wooden parts are glued and
tied together, no nails or brads being used.
The main plane is an exceedingly refined piece of workmanship. A glance
shows that it is very speedy. The frame consists of steel wire one
thirty-second of an inch in diameter. The plane measures sixteen and
one-half inches in width and four and one-half inches in depth at the
narrowest point at the center, and five and one-half inches in the
widest part at the ends. It has four cross ribs of the same wire. The
frame is covered, on the upper side, with oiled silk. The camber is
slightly higher at the sides than the middle.
The plan of fixing a rigid shaft for the propeller axle is very simple
and effective. A piece of aluminum tubing is forced over the ends of the
rear stick and glued firmly in position. A hole for the axle is then
drilled through this tube, and the wooden stick which forms its core.
The axle thus turns in what is really a metal shaft, and the friction is
reduced to a minimum. A piece of tin tubing, a putty blower, for
instance, will serve as well. In this particular machine, the propellers
are cut from a board one-sixteenth of an inch thick and bent by steaming
to the desired curve.
The shafts of the propellers are formed of a very light steel wire, less
than one thirty-second of an inch in diameter. This is passed through
the hole in the rear stick and bent into a hook in the usual way. The
motor anchorage consists of a wire passed through the central stick and
bent back, and turned into two hooks. The rubber-strand motor consists
of twenty strands of strip rubber one-eighth of an inch broad. A special
preparation resembling cosmoline is used to lubricate the rubber, thus
increasing the number of turns. The motor will take on one thousand
turns without undue strain.