After these general remarks, we may proceed to a practical description
of manufacture, which will apply to kites of all dimensions. It will be
prudent to begin on small models, as requiring small outlay.
Having decided on the size of your kite, cut out two pieces of material
as wide as a box is to be deep, and as long as the circumference of the
box plus an inch and a half to spare. Machine stitch 5/8 inch tapes
along each edge, using two rows of stitching about 1/8 inch from the
edges of the tape. Then double the piece over, tapes inside, and
machine stitch the ends together, three quarters of an inch from the
edge. Note.—All thread ends should be tied together to prevent
unravelling, and ends of stitching should be hand-sewn through the
tape, as the greatest strain falls on these points.
The most convenient shape for the rods is square, as fitting the
corners and taking tacks most easily. The sectional size of the rods is
governed by the dimensions of the kite, and to a certain extent by the
number of stretchers used. If four stretchers are employed in each box,
two near the top and two near the bottom, the rods need not be so stout
as in a case where only a single pair of central stretchers is
preferred.
Lay the two boxes flat on the floor, in line with one another, and the
joins at the same end. Pass two rods through, and arrange the boxes so
that the outer edges are 1/2 inch from the ends of the rods. (These
projections protect the fabric when the kite strikes the ground).
Lay the rods on one corner, so that the sides make an angle of 45
degrees with the floor, pull the boxes taut—be careful that they are
square to the rods—and drive three or four tacks through each end of
the box into the rods. Then turn them over and tack the other sides
similarly. Repeat the process with the other rods after measuring to
get the distances correct.
The length of the stretchers is found approximately by a simple
arithmetical sum, being the square root of the sum of the squares of
the lengths of two adjacent sides of the box. For example, if each box
is 20 by 15 inches, the diagonal is the square root of (20 squared
plus 15 squared) = square root of 625 = 25 inches. The space occupied
by the vertical rods will about offset the stretch of the material, but
to be on the safe side and to allow for the notches, add another
half-inch for small kites and more proportionately for large ones. It
is advisable to test one pair of stretchers before cutting another, to
reduce the effect of miscalculations.
The stretcher notches should be deep enough to grip the rods well and
prevent them twisting, and one must take care to have those on the same
stretcher exactly in line, otherwise one or other cannot possibly “bed”
properly. A square file is useful for shaping the notches.
Ordinarily stretchers do not tend to fall out, as the wind pressure
puts extra strain on them and keeps them up tight. But to prevent
definitely any movement one may insert screw eyes into the rods near
the points at which the stretchers press on them, and other eyes near
the ends of the stretchers to take string fastenings. These attachments
will be found useful for getting the first pair of stretchers into
position, and for preventing the stretchers getting lost when the kite
is rolled up.
The bridle is attached to four eyes screwed into the rods near the tops
of the boxes. (See Fig. 118.) The top and bottom elements of the bridle
must be paired off to the correct length; the top being considerably
shorter than the bottom. All four parts may be attached to a brass
ring, and all should be taut when the ring is pulled on. The exact
adjustment must be found by experiment. In a very high wind it is
advisable to shorten the top of the bridle if you have any doubt as to
the strength of your string, to flatten the angle made by the kite with
the wind.
[Illustration: FIG. 115.—Details of stretcher attachment for
diamond-shaped box kites.]
Diamond Box Kites.—In another type of box kite the boxes have four
equal sides, but the boxes are rhombus-shaped, as in Fig. 116, the long
diagonal being square to the wind, and the bridle attached at the front
corner.
For particulars of design and construction I am much indebted to Mr. W.
H. Dines, F.R.S., who has used the diamond box kite for his
meteorological experiments to carry registering meteorographs several
thousands of feet into the air.
The longitudinal sticks used at the corners have the section shown in
Fig. 115. They are about four times as wide at the front edge, which
presses against the fabric, as at the back, and their depth is about
twice the greater width. This shape makes it easy to attach the shorter
stretchers, which have their ends notched and bound to prevent
splitting.
[Illustration: FIG. 116.—Plan of diamond box kite, showing arrangement
of stretchers.]
Fig. 117 is a perspective diagram of a kite. The sail of each box
measures from top to bottom one-sixth the total circumference of the
box, or, to express the matter differently, each face of the box is
half as long again as its depth. The distance separating the boxes is
equal to the depth of a box.
The sides of a box make angles of 60 degrees and 120 degrees with one
another, the depth of the space enclosed from front to back being the
same as the length of a side. With these angles the effective area of
the sails is about six-sevenths of the total area. Therefore a kite of
the dimensions given in Fig. 117 will have an effective area of some
thirty square feet.
[Illustration: FIG. 117.—Diamond box kite in perspective. Ties are
indicated by fine dotted lines.]
The long stretchers pass through holes in the fabric close to the
sticks, and are connected with the sticks by stout twine. Between
stretcher and stick is interposed a wedge-shaped piece of wood (A in
Fig. 115), which prevents the stick being drawn out of line. This
method of attachment enables the boxes to be kept tight should the
fabric stretch at all—as generally happens after some use; also it does
away with the necessity for calculating the length of the stretchers
exactly.
The stretchers are tied together at the crossing points to give support
to the longer of the pair.
The dotted lines AB, AC, AD, EM, and EN in Fig. 117 indicate ties made
with wire or doubled and hemmed strips of the fabric used for the
wings. AB, running from the top of the front stick to the bottom of the
back stick, should be of such a length that, when the kite is stood on
a level surface, the front and back sticks make right angles with that
surface, being two sides of a rectangle whereof the other two sides are
imaginary lines joining the tops and bottoms of the sticks. This tie
prevents the back of the kite drooping under pressure of the wind, and
increases the angle of flight. The other four ties prevent the back
sails turning over at the edges and spilling the wind, and also keep
them flatter. This method of support should be applied to the type of
kite described in the first section of this chapter.
String Attachment.—A box kite will fly very well if the string is
attached to the top box only. The tail box is then free to tilt up and
trim the kite to varying pressures independently of the ascent of the
kite as a whole. When the bottom box also is connected to the string it
is a somewhat risky business sending a kite up in a high wind, as in
the earlier part of the ascent the kite is held by the double bridle
fairly square to the wind. If any doubt is entertained as to the
ability of the string to stand the pressure, the one-box attachment is
preferable, though possibly it does not send the kite to as great a
height as might be attained under similar conditions by the two-box
bridle.
[Illustration: FIG. 118.—Box kite with rear wings.]
When one has to attach a string or wire to a large kite at a single
point, the ordinary method of using an eye screwed into the front stick
is attended by obvious risks. Mr. Dines employs for his kites (which
measure up to nine feet in height) an attachment which is independent
of the front stick. Two sticks, equal in length to the width of the
sail, are tacked on to the inner side of the sail close to the front
stick. Rings are secured to the middle of the sticks and connected by a
loop of cord, to which the wire (in this case) used for flying the kite
is made fast.
A Box Kite with Wings.—The type of kite shown in Fig. 118 is an
excellent flyer, very easy, to make and very portable. The two boxes
give good longitudinal stability, the sides of the boxes prevent quick
lateral movements, and the two wings projecting backwards from the rear
corners afford the “dihedral angle” effect which tends to keep the kite
steadily facing the wind. The “lift,” or vertical upward pull, obtained
with the type is high, and this, combined with its steadiness, makes
the kite useful for aerial photography, and, on a much larger scale,
for man-lifting.
The materials required for the comparatively small example with which
the reader may content himself in the first instance are:
8 wooden rods or bamboos, 4 feet long and 1/2 inch in diameter. 4 yards
of lawn or other light, strong material, 30 inches wide. 12 yards of
unbleached tape, 5/8 inch wide. 8 brass rings, 1 inch diameter.
The Boxes.—Cut off 2 yards 8 inches of material quite squarely, fold
down the middle, crease, and cut along the crease. This gives two
pieces 80 by 15 inches.
Double-stitch tape along the edges of each piece.
Lay the ends of a piece together, tapes inside, and stitch them
together half an inch from the edge. Bring a rod up against the
stitching on the inside, and calculate where to run a second row of
stitching parallel to the first, to form a pocket into which the rod
will slip easily but not loosely. (See Fig. 119, a.)
Remove the rod and stitch the row.
Now repeat the process at the other end of the folded piece. The
positions of the other two rod pockets must be found by measuring off
15 inches from the inner stitching of those already made. (Be careful
to measure in the right direction in each case, so that the short and
long sides of the box shall be opposite.) Fold the material beyond the
15-inch lines to allow for the pockets and the 1/2-inch “spare,” and
make the two rows of stitching.
[Illustration: FIG. 119.—Plan of box kite with rear wings.]
Repeat these operations with the second strip of material, and you will
have prepared your two boxes, each measuring, inside the pockets, 15 by
about 20 inches. (See Fig. 119.) Now cut out the wings in accordance
with the dimensions given in Fig. 120. Each is 47-1/2 inches long and
15 inches across at the broadest point. It is advisable to cut a
pattern out of brown paper, and to mark off the material from this, so
arranging the pattern that the long 47-1/2-inch side lies on a
selvedge. [The edge of a fabric that is woven so that it will not fray
or ravel.]
[Illustration: FIG. 120.—Wing for box kite.]
Double stitch tapes along the three shorter sides of each wing,
finishing off the threads carefully. Then sew the wings to what will be
the back corners of the boxes when the kite is in the air—to the
“spares” outside the rod pockets of a long side.
Take your needle and some strong thread, and make all corners at the
ends of pockets quite secure. This will prevent troublesome splitting
when the kite is pulling hard.
Sew a brass ring to each of the four wing angles, AA, BB, at the back,
and as many on the front of the spares of the rod pockets diagonally
opposite to those to which the wings are attached, halfway up the
boxes. These rings are to take the two stretchers in each box.
Slip four rods, after rounding off their ends slightly, through the
pockets of both boxes, and secure them by sewing the ends of the
pockets and by the insertion of a few small tacks. These rods will not
need to be removed.
The cutting and arrangement of the stretchers and the holes for the
same require some thought. Each stretcher lies behind its wing, passes
in front of the rod nearest to it, and behind that at the corner
diagonally opposite. (See Fig. 119.) The slits through which it is
thrust should be strengthened with patches to prevent ripping of the
material.
Two persons should hold a box out as squarely as possible while a
stretcher is measured. Cut a nick 3/8 inch deep in one end of the
stretcher, and pass the end through the fabric slits to the ring not on
the wing. Pull the wing out, holding it by its ring, and cut the
stretcher off 1 inch from the nearest point of the ring. The extra
length will allow for the second nick and the tensioning of the
material. Now measure off the second stretcher by the first, nick it,
and place it in position. If the tension seems excessive, shorten the
rods slightly, but do not forget that the fabric will stretch somewhat
in use.
[Illustration: FIG. 121.—Box kite with front and back wings.]
Make the stretchers for the second box, and place them in position. The
wings ought to be pretty taut if the adjustments are correct, but
should they show a tendency to looseness, a third pair of stretchers of
light bamboo may be inserted between the other two, being held up to
the rods by loops of tape. In order to be able to take up any
slackness, the wing end of each stretcher may be allowed to project a
couple of inches, and be attached by string to the near ring, as
described on p. 271. The bridle to which the flying string is attached
is made up of four parts, two long, two short, paired exactly as
regards length. These are attached to eyes screwed into the front rods
three inches below the tops of the boxes. Adjustment is made very easy
if a small slider is used at the kite end of each part. These sliders
should be of bone or some tough wood, and measure 1 inch by 3/8 inch.
The forward ends of the bridle are attached to a brass ring from which
runs the flying string.
It is advisable to bind the stretchers with strong thread just behind
the notches to prevent splitting, and to loosen the stretchers when the
kite is not in use, to allow the fabric to retain as much as possible
of its elasticity.
The area of the kite affected by wind is about 14 square feet; the
total weight, 1-1/2 lb. The cost of material is about 2s.
The experience gained from making the kite described may be used in the
construction of a larger kite, six or more feet high, with boxes 30 by
22 by 22 inches, and wings 24 inches wide at the broadest point. If a
big lift is required, or it is desired to have a kite usable in very
light breezes, a second pair of wings slightly narrower than those at
the back may be attached permanently to the front of the boxes, or be
fitted with hooks and eyes for use on occasion only. (Fig. 121.) In the
second case two sets of stretchers will be needed.
[Illustration: FIG. 122.—Simple string winder for kite.]
Note.—If all free edges of boxes and wings are cut on the curve, they
will be less likely to turn over and flap in the wind; but as the
curvature gives extra trouble in cutting out and stitching, the
illustrations have been drawn to represent a straight-edged kite.
Kite Winders.—The plain stick which small children flying small kites
on short strings find sufficient for winding their twine on is far too
primitive a contrivance for dealing with some hundreds of yards, may
be, of string. In such circumstances one needs a quick-winding
apparatus. A very fairly effective form of winder, suitable for small
pulls, is illustrated in Fig. 122.
Select a sound piece of wood, 3/8-inch thick, 5 inches wide, and about
1 foot long. In each end cut a deep V, the sides of which must be
carefully smoothed and rounded with chisel and sandpaper. Nail a wooden
rod, 15 inches long and slightly flattened where it makes contact,
across the centre of the board, taking care not to split the rod, and
clinch the ends of the nails securely. The projecting ends of the rods
are held in the hands while the string runs out. The projecting piece,
A, which must also be well secured, is for winding in. The winding hand
must be held somewhat obliquely to the board to clear the spindle.
Winding is much less irksome if a piece of tubing is interposed between
the spindle and the other hand, which can then maintain a firm grip
without exercising a braking effect.
This kind of winder is unsuited for reeling in a string on which there
is a heavy pull, as the hands are working at a great disadvantage at
certain points of a revolution.
[Illustration: FIG. 123.—Plan of string-winding drum, frame, and
brake.]
A far better type is shown in Figs. 123 and 124. Select a canister at
least 6 inches in diameter, and not more than 6 inches long, with an
overlapping lid. Get a turner to make for you a couple of wooden discs,
3/8 inch thick, and having a diameter 2 inches greater than that of the
tin. Holes at least 3/8 inch across should be bored in the centre of
each. Cut holes 1 inch across in the centre of the lid and the bottom
of the canister, and nail the lid concentrically to one disc, the
canister itself to the other. Then push the lid on the tin and solder
them together. This gives you a large reel. For the spindle you will
require a piece of brass tubing or steel bar 1 foot long and large
enough to make a hard driving fit with the holes in the wood. Before
driving it in, make a framework of 3/4-inch strip iron (Fig. 123), 3/32
or 1/8 inch thick, for the reel to turn in. The width of this framework
is 1 inch greater than the length of the reel; its length is twice the
diameter of the canister. Rivet or solder the ends together. Halfway
along the sides bore holes to fit the spindle.
Make a mark 1 inch from one end of the spindle, a second l/8 inch
farther away from the first than the length of the reel. Drill
3/16-inch holes at the marks. Select two wire nails which fit the
holes, and remove their heads. Next cut two 1/4-inch pieces off a tube
which fits the spindle. The reel, spindle, and framework are now
assembled as follows:
[Illustration: FIG. 124.—End view of string winder, showing brake and
lever.]
Push the end of the spindle which has a hole nearest to it through one
of the framework holes, slip on one of the pieces of tubing, drive the
spindle through the reel until half an inch projects; put on the second
piece of tubing, and continue driving the spindle till the hole bored
in it shows. Then push the nails half-way through the holes in the
spindle, and fix them to the ends of the reel by small staples. A crank
is made out of 1/2-inch wood (oak by preference) bored to fit the
spindle, to which it must be pinned. A small wooden handle is attached
at a suitable distance away. If there is any fear of the wood splitting
near the spindle, it should be bound with fine wire. An alternative
method is to file the end of the spindle square, and to solder to it a
piece of iron strip in which a square hole has been made to fit the
spindle. The crank should be as light as is consistent with sufficient
strength, and be balanced so that there shall not be unpleasant
vibration when the string runs out fast, and of course it must be
attached very securely to the spindle.
What will be the front of the framework must be rounded off on the top
edge, which has a wire guide running parallel to it (Fig. 123) to
direct the string on to the reel; and into the back are riveted a
couple of eyes, to which are attached the ends of a cord passing round
the body, or some stationary object.
[Illustration: FIG. 125.—String winder in operation.]
A pin should be provided to push into a hole at one end of the reel and
lock the reel by striking the framework, and it will be found a great
convenience to have a brake for controlling the reel when the kite is
rising. Such a brake is easily fitted to the side of the frame, to act
on the left end of the reel when a lever is depressed by the fingers.
There should be a spring to keep it off the reel when it is not
required. The diagrams show where the brake and brake lever are
situated.
Note.—To obtain great elevations a fine wire (piano wire 1/32 inch in
diameter) is generally used, but to protect the user against electric
shocks the wire must be connected with an “earthed” terminal, on the
principle of the lightning conductor.
XXIV.
PAPER GLIDERS.
In this chapter are brought to your notice some patterns of paper
gliders which, if made and handled carefully, prove very satisfactory.
Gliders are sensitive and “moody” things, so that first experiments may
be attended by failure; but a little persistence will bring its reward,
and at the end of a few hours you will, unless very unlucky, be the
possessor of a good specimen or two.
The three distinguishing features of a good glider are stability,
straightness of flight, and a small gliding angle. If the last is as
low as 1 in 10, so that the model falls but 1 foot vertically while
progressing 10 feet horizontally, the glider is one to be proud of.
Materials.—The materials needed for the gliders to be described are
moderately stout paper—cream-laid notepaper is somewhat heavy for the
purpose—and a little sealing wax or thin sheet metal for weighting.
[Illustration: FIG. 126.—Paper glider: Model “A.”]
[Illustration: FIG. 127.—How to launch Model “A.”]
Model “A.”—Double a piece of paper 8 inches long and 2-1/2 inches wide,
and cut out, through both folds, the shape shown in Fig. 126. Flatten
the piece and fold the “head” inwards four times on the side away from
the direction in which the paper was folded before being cut out.
Flatten the folds and fix to the centre a little clip formed by
doubling a piece of thin metal 3/16 by 1/2 inch. Make certain that the
wings are quite flat, and then, holding the glider between thumb and
first finger, as shown in Fig. 127, push it off gently. If the balance
is right, it will fly quite a long way with an undulating motion. If
too heavy in front, it will dive; if too light, it will rise suddenly
and slip backwards to the ground. The clip or the amount of paper in
the head must be modified accordingly. This type is extraordinarily
efficient if the dimensions, weighting, and shape are correct, and one
of the easiest possible to make.
Model “B.”—The next model (Fig. 128), suggesting by its shape the
Langley steam-driven aeroplane, has two sets of wings tandem. Double a
piece of paper and cut out of both folds simultaneously a figure of the
shape indicated by the solid lines in the diagram. The portion A is
square, and forms the head weight; B indicates the front planes, C the
rear planes. Bend the upper fold of each pair into the positions B1,
C1, marked by dotted lines. Their front edges make less than a right
angle with the keel, to ensure the wings slanting slightly upwards
towards the front when expanded.
The model is now turned over, and the other wings are folded exactly on
top of their respective fellows. Then the halves of the head are folded
twice inwards, to bring the paper into as compact a form as possible.
It remains to open out the wings at right angles to the keel, and then
raise their tips slightly so that the two planes of a pair shall make
what is called a “dihedral” angle with one another.
[Illustration: FIG. 128.—Details of paper gliders: Model “B” above,
Model “C” below.]
Before launching, look at your model endways and make sure that the
rear planes are exactly in line with those in front. It is essential
that they should be so for straight flight. Then grip the keel at its
centre between finger and thumb and launch gently. Mark how your glider
behaves. If it plunges persistently, trim off a very little of the
head. If, on the contrary, it settles almost vertically, weight must be
added in front. The position of the weight is soon found by sliding a
metal clip along the keel until a good result is obtained.
Note that if the leading edges of the front wings are bent slightly
downwards the glider may fly much better than before.
A good specimen of this type is so stable that if launched upside down
it will right itself immediately and make a normal flight.
Model “C.”—This is cut out of doubled paper according to the solid
lines of Fig. 128. The three sets of planes are bent back in the manner
already described, but the front planes are given a somewhat steeper
angle than the others. This type is very stable and very fairly
efficient.
General Remarks.—Always pick up a glider by the keel or middle, not by
one of the wings, as a very little distortion will give trouble.
The merits of a glider depend on length, and on straightness of flight;
so in competition the launching height should be limited by a string
stretched across the room, say 6 feet above the floor. If the room be
too short for a glider to finish its flight, the elevation at which it
strikes the wall is the measure of its efficiency.
Out-of-door flights are impracticable with these very frail models when
there is the slightest breeze blowing. On a perfectly calm day,
however, much better fun can be got out of doors than in, owing to the
greater space available. A good glider launched from a second-floor
window facing a large lawn should travel many yards before coming to
grass.
Large gliders of the types detailed above can be made of very stout
paper stiffened with slips of cane or bamboo; but the time they demand
in construction might perhaps be more profitably spent on a
power-driven aeroplane such as forms the subject of the next chapter.
XXV.
A SELF-LAUNCHING MODEL AEROPLANE.
By V. E. Johnson, M.A.
This article deals not with a scale model—a small copy of some
full-sized machine—but with one designed for actual flight; with one
not specially intended to create records either of length or duration,
but which, although small details must perforce be omitted, does along
its main lines approximate to the “real thing.”
Partly for this reason, and partly because it proves a far more
interesting machine, we choose a model able to rise from the ground
under its own power and make a good flight after rising, assuming the
instructions which we give to have been carefully carried out. It is
perhaps hardly necessary to add that such a machine can always be
launched by hand when desired.
Before entering into special details we may note some broad principles
which must be taken into account if success is to attend our efforts.
Important Points.—It is absolutely essential that the weight be kept
down as much as possible. It is quite a mistake to suppose that weight
necessarily means strength. On the contrary, it may actually be a cause
of weakness if employed in the wrong place and in the wrong way. The
heavier the machine, the more serious the damage done in the event of a
bad landing. One of the best and easiest ways of ensuring lightness is
to let the model be of very simple construction. Such a model is easier
to build and more efficient when constructed than one of more
complicated design. Weigh every part of your model as you construct it,
and do not be content until all symmetrically arranged parts which
should weigh the same not only look alike but do actually balance one
another. (Note.—The writer always works out the various parts of his
models in grammes, not ounces.) If a sufficiently strong propeller
bearing weighing only half a gramme can be employed, so much the
better, as you have more margin left for some other part of the model
in which it would be inadvisable to cut down the weight to a very fine
limit.
Details.—To pass now to details, we have four distinct parts to deal
with:—