SIMPLE MONOPLANE MODELS
Of the variety of aëroplanes, there seems to be no end. Nature offers
a bewildering variety of models in the innumerable birds and insects,
which may be accepted as successful monoplanes. These, in turn, may be
copied and modified indefinitely. The science of aviation is still so
young that there is ample opportunity for invention and discovery for
all, and every new trial adds something to our information, and carries
the science a step nearer perfection.
It will be found an excellent plan to build, once and for all, a
strong well proportioned motor base, and mount a powerful motor and
well modeled propeller. A variety of planes may then be tested out by
attaching them to this. The motor base will answer for practically all
monoplane forms and many biplane models as well. Such a frame should be
about three feet in length and carry one or better two motors, placed
side by side.
There is as much danger in providing too much lifting-surface in
your aëroplane as too little. This fault is well illustrated in an
exceedingly clever French model (Plate I). Although the model is well
constructed, and appears ship-shape at first glance, it nevertheless
has far too much surface and will not fly well. If the depth of the
wings were reduced fully one half, it would have a much better chance.
The best lifting-planes are those which present a broad front or
entering edge, but with comparatively little depth. The successful
flying-machines, whether monoplanes or biplanes, use these very wide
but shallow planes forward. The theory is of course that the air is
caught for an instant beneath the plane and before it has a chance to
slip off the sides, the wing has caught its very slight supporting
power and moved on to new and undisturbed air.
With this rule in mind examine the model’s front plane once more. It
will be seen that, as the air is caught under this broad surface,
it will try to escape in all directions and set up currents of air.
Instantly the broad plane loses its balance and tilts to one side or
the other. No weighting of the plane can overcome this. If the plane
were forced through the air at a very high speed a steady flight might
be possible, but it is useless to try to overcome this tendency to tip
and wabble.
The planes again are badly designed. A perfectly straight front or
entering edge gives the best results. A certain stability is gained by
curving the front plane slightly, this will be discussed later, but
there is no excuse for the semicircle described in this case. Every
inch of surface cut away from the front edge of the plane directly
reduces its lifting power. The arrow like form of the rear plane does
not matter because this is a stability plane, not a lifting plane.
In this case the rear plane is twice the size it should be.
[Illustration: PLATE I. A Clever Folding Model. The Wings Are Broader
than Need Be.]
The propeller of this model is much too small, even if the size of
the planes was correct. It is well placed however at the front of the
model where it may turn in undisturbed air. The passage of these large
planes, or any planes for that matter, is likely to cut up the air just
as a ship churns the water into a wake behind it and the propeller does
not work effectively in these eddies. The motor seems powerful and well
braced, although it might be made even longer by carrying it to the
extreme rear.
Several very useful ideas may be borrowed from the construction of the
frame of this model. It is made entirely of metal, so jointed that it
may be folded up into very compact form like an umbrella. The amateur
model builder should not attempt anything so complicated, but an old
umbrella frame may be used with good results in building a rigid frame.
Use the steel rod of the umbrella as a backbone, and cut away the ribs
you do not need. The others may be bent into various shapes to form the
front or sides of the planes, the skids or braces. Such a construction
is light and perfectly rigid.
A very effective monoplane may be made by curving the front and rear
edges of the forward plane, while keeping the rear or stability plane
rectangular in shape (Plate 2). The curve of this model may be imitated
to advantage, as well as the general proportions. Such a plane is less
likely to be deflected by air currents than a straight entering-edge
and insures longer and steadier flights. Should you be troubled by your
model twisting from side to side in flight try curving the front edge
of the forward plane.
This model is one of the easiest to make and is an excellent one for
beginners. Build the two planes separately making the larger one about
thirty inches in width and ten inches in depth, and the second one
fifteen inches in width and ten inches in depth. The curved sticks may
be worked up by using bamboo or dowel-sticks, soaking them in water
and fastening them in a bowed position while damp and leaving them to
dry. It may be found a good plan to use a heavier stick for the rear
edge of the plane to gain stability.
A single stick about one half an inch in diameter may be used for the
backbone. It will be found an excellent plan to attach the planes
lightly to the main frame so that they may be adjusted before fixing
them finally in position. Place them in the position shown in the
accompanying photograph, and move them up and down until the flights
are all that you expect, when they may be fastened for good and all.
The bracing of this model is excellent and may be safely imitated. It
enables one to tune up either plane and fix them rigidly in position.
The propeller is very properly placed forward although it appears to
be rather small. It is unnecessary to bother with any vertical rudder
for this model since the curve of the front plane insures a reasonably
straight flight.
A popular French model which may be easily imitated consists of curved
planes both front and rear (Plate 3). The curve of the planes is too
complicated to be carried out in wood, but may be readily formed by
bending a stiff wire to the desired shape. The front plane should
be about twelve inches in width and four inches in depth. The rear
should be about half this size and of the same form. The planes may be
readily mounted on a small dowel stick. A small propeller and a motor
a foot in length will answer. A small semi-circular fin should be set
below the rear plane to act as rudder. First cover the frames with a
stiff paper and after you have succeeded in adjusting it, this may be
replaced by cloth. The model will not fly far, or very steadily, but it
is interesting to practice with. The balance of the model is open to
criticism; for the center of gravity appears to be too far forward.
[Illustration: PLATE II. A Model Aëroplane Worth Imitating.]
The simplest of all models to build, and not the least interesting, is
the small paper monoplane (Plate 4). The planes which are slightly
curved are formed of a stiff card which will hold its shape when bent
into position. These may be attached to the main stick by inserting an
edge into a groove in the stick and glueing in place. It is not well to
construct these more than six inches in width over all.
One of the simplest monoplanes to construct is formed of a broad
rectangular forward plane with a fan-shaped stability-plane at the
rear (Plate 5). This is a French model which is said to have flown
long distances; that is to say, 300 feet or more. It has several
very interesting features. In the first place the combined area of
its planes is doubtless greater than that of any other model here
described. The vertical rudder which looks very shipshape and effective
is very easy to build and the frame illustrates several new principles.
The frame or motor-base may be made of heavy dowel sticks or light
lath as indicated in the photograph. It will be found simpler to
avoid tapering the frame at the rear by merely constructing a stout
rectangular base with a length two and one half times its width. The
forward plane is slightly bowed or flexed. It will be found a good
plan to construct the frame for the base and then bow a light strip at
either end against the edge. By fastening the covering to these curved
strips a smooth curved surface may be obtained.
The rear stability-plane may be stretched over a fan-shaped frame of
strips or lath which is in turn fastened to the motor-base. Another
plan is to attach the front and rear edges of the plane, the rear one
being slightly longer, and stretch the covering over these leaving the
sides free as in the photograph of the accompanying model. The vertical
rudder is very simple, consisting of a piece of dowel stick sunk in the
rear frame to which a rectangular piece of cloth is attached the front
corner being pulled taut.
The spread of the planes appears to be considerably greater than needs
be. Since the front plane is flexed it may be reduced one third or
even one half in depth without reducing its lifting quality; although
in this case it should be placed nearer the stability plane. This
reduction would, of course, make an important saving in the weight of
the craft. So large a model calls for two propellers which will prove
more effective at the front rather than the rear of the machine. It
might be well to carry the motors further back than has been done in
this model thus gaining additional power.
Since the model is expected to rise unaided from the ground the
question of the skids is very important. The design followed in the
model is excellent. The front of the frame is supported by legs
consisting of inverted triangles built of dowel sticks attached to the
frame. The axle connecting the two runs on small wheels, such as may be
borrowed from a toy automobile. The rear of the frame rests on a simple
skid made of curved reed. These supports place the model at an angle
which should enable it to rise easily without loss of power. There is
a great deal of satisfaction in working on so large a model, the parts
may be made stronger and there is less likelihood of its getting out of
order.
Now turn from these broad planes to the rather slight model (Plate 6),
and the faults of its proportion are at once obvious. The front plane
is much too far back for stability. Such a model will glide fairly
well, and, if the motor be powerful it will rise quickly, but a steady
horizontal flight is out of the question. The size of the planes seems
perilously small, and yet if they be well shaped and spaced they will
prove large enough. This is just the sort of model a beginner is likely
to make, and therefore serves a very useful purpose in pointing a
lesson.
[Illustration: PLATE III. An Ingenious French Model Made of Umbrella
Wire.]
It is not without its good points. The front plane has been carefully
flexed and attached to the motor frame at a good angle. An interesting
experiment has also been made in carrying the edges of the front
plane a trifle behind the rear edge, thus making for stability. The
vertical rudder above the rear stability-plane is well placed, although
it appears rather small. The skids upon which the model rests and the
proportion of the front to the rear elevation are excellent. It is a
first rate plan in building such a model to attach the front plane
temporarily to the motor-base, and move it back and forth in the trial
flights until the best spacing has been found.