aeroplanes-第21章
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be advantageously used as a model aeroplane； but
in that case the broad end should be foremost。
_Fig。 86。 The Deltoid Racer。_
Fig。 86 shows the deltoid glider； or aeroplane；
with three cross braces； A； B； C； in the two forward
braces of which are journaled the propeller
shaft D； so that the propeller E is at the broad
end of the glider。
A short stem F through the rear brace C； provided
with a crank； has its inner end connected
with the rear end of the shaft D by a rubber band
G； by which the propeller is driven。
A tail may be attached to the rear end； or at
the apex of the planes； so it can be set for the
purpose of directing the angle of flight； but it will
be found that this form has remarkable stability
in flight； and will move forwardly in a straight
line； always making a graceful downward movement
when the power is exhausted。
It seems to be a form which has equal stabilizing
powers whether at slow or at high speeds；
thus differing essentially from many forms which
require a certain speed in order to get the best
results。
RACING MODELS。Here and in England many
racing models have been made； generally of the
A…shaped type； which will be explained hereinafter。
Such models are also strong； and able to
withstand the torsional strain required by the
rubber which is used for exerting the power。
It is unfortunate that there is not some type of
cheap motor which is light； and adapted to run
for several minutes； which would be of great value
in work of this kind； but in the absence of such
mechanism rubber bands are found to be most
serviceable； giving better results than springs or
bows； since the latter are both too heavy to be
available； in proportion to the amount of power
developed。
Unlike the large aeroplanes； the supporting
surfaces； in the models； are at the rear end of
the frames； the pointed ends being in front。
_Fig。 87。 A…Shaped Racing Glider。_
Fig。 87 shows the general design of the A…
shaped gliding plane or aeroplane。 This is composed
of main frame pieces A； A； running fore
and aft； joined at their rear ends by a cross bar
B； the ends of which project out slightly beyond
their juncture with the side bars A； A。 These
projecting ends have holes drilled therein to receive
the shafts a； a； of the propeller D； D。
A main plane E is mounted transversely across
this frame at its rear end； while at its forward
end is a small plane； called the elevator。 The
pointed end of the frame has on each side a turnbuckle
G； for the purpose of winding up the shaft；
and thus twisting the propeller； although this is
usually dispensed with； and the propeller itself
is turned to give sufficient twist to the rubber for
this purpose。
THE POWER FOR MODEL AEROPLANES。One end
of the rubber is attached to the hook of the shaft
C； and the other end to the hook or to the turnbuckle
G； if it should be so equipped。
The rubbers are twisted in opposite directions；
to correspond with the twist of the propeller
blades； and when the propellers are permitted to
turn； their grip on the air will cause the model to
shoot forwardly； until the rubbers are untwisted；
when the machine will gradually glide to the
ground。
MAKING THE PROPELLER。These should have
the pitch uniform on both ends； and a simple
little device can be made to hold the twisted blade
after it has been steamed and bent。 Birch and
holly are good woods for the blades。 The strips
should be made thin and then boiled； or； what is
better still； should be placed in a deep pan； and
held on a grid above the water； so they will be
thoroughly steamed。
They are then taken out and bent by hand； or
secured between a form specially prepared for
the purpose。 The device shown in Fig。 88 shows
a base board which has in the center a pair of
parallel pins A； A； slightly separated from each
other。
_Fig。 88。 Making the Propeller。_
At each end of the base board is a pair of holes
C； D； drilled in at an angle； the angles being the
pitch desired for the ends of the propeller。 In
one of these holes a pin E is placed； so the pins
at the opposite ends project in different directions；
and the tips of the propeller are held
against the ends of these pins； while the middle
of the propeller is held between the parallel pins
A； A。
The two holes； at the two angles at the ends of
the board； are for the purpose of making right
and left hand propellers； as it is desirable to use
two propellers with the A…shaped model。 Two
propellers with the deltoid model are not so necessary。
After the twist is made and the blade properly
secured in position it should be allowed to thoroughly
dry； and afterwards； if it is coated with
shellac； will not untwist； as it is the changing
character of the atmosphere which usually causes
the twisted strips to change their positions。
Shellac prevents the moist atmosphere from affecting
them。
MATERIAL FOR PROPELLERS。Very light propellers
can also be made of thin； annealed aluminum
sheets； and the pins in that case will serve as
guides to enable you to get the desired pitch。
Fiber board may also be used； but this is more
difficult to handle。
Another good material is celluloid sheets；
which； when cut into proper strips； is dipped in
hot water； for bending purposes； and it readily
retains its shape when cooled。
RUBBERSuitable rubber for the strips are
readily obtainable in the market。 Experiment
will soon show what size and lengths are best
adapted for the particular type of propellers
which you succeed in making。
PROPELLER SHAPE AND SIZE。A good proportion
of propeller is shown in Fig。 89。 This also
shows the form and manner of connecting the
shaft。 The latter A has a hook B on one end to
which the rubber may be attached； and its other
end is flattened； as at C； and secured to the blade
by two…pointed brads D； clinched on the other
side。
_Fig。 89。 Shape and Size。_
The collar E is soldered on the shaft； and in
practice the shaft is placed through the bearing
hole at the end of the frame before the hook is
bent。
SUPPORTING SURFACES。The supporting surfaces
may be made perfectly flat； although in this
particular it would be well to observe the rules
with respect to the camber of large machines。
CHAPTER XV
THE AEROPLANE IN THE GREAT WAR
DURING the civil war the Federal forces used
captive balloons for the purpose of discovering
the positions of the enemy。 They were of great
service at that time； although they were stationed
far within the lines to prevent hostile guns from
reaching them。
BALLOON OBSERVATIONS。Necessarily； observations
from balloons were and are imperfect。 It
was found to be very unsatisfactory during the
Russian…Japanese war； because the angle of vision
is very low； and； furthermore； at such distances the
movements； or even the location of troops is not
observable； except under the most favorable conditions。
Balloon observation during the progress of a
battle is absolutely useless； because the smoke
from the firing line is； necessarily； between the
balloon and the enemy； so that the aerial scout
has no opportunity to make any observations； even
in detached portions of the fighting zone； which
are of any value to the commanders。
CHANGED CONDITIONS OF WARFARE。Since our
great war； conditions pertaining to guns have been
revolutionized。 Now the ranges are so great that
captive balloons would have to be located far in
the rear； and at such a great distance from the
firing line that even the best field glasses would
be useless。
The science of war has also evolved another
condition。 Soldiers are no longer exposed during
artillery attacks。 Uniforms are made to imitate
natural objects。 The khaki suits were designed
to imitate the yellow veldts of South Africa；
the gray…green garments of the German
forces are designed to simulate the green fields
of the north。
THE EFFORT TO CONCEAL COMBATANTS。The
French have discarded the historic red trousers；
and the elimination of lace； white gloves； and
other telltale insignias of the officers； have been
dispensed with by special orders。
In the great European war armies have burrowed
in the earth along battle lines hundreds of
miles in length； made covered trenches； prepared
artificial groves to conceal batteries； and in many
ingenious ways endeavored to make the battlefield
an imitation field of nature。
SMOKELESS POWDER。While smokeless powder
has been utilized to still further hide a fighting
force； it has； in a measure； uncovered itself； as
the battlefield is not now； as in olden times； overspread
with masses of rolling smoke。
Nevertheless； over every battlefield there is a
haze which can be penetrated only from above；
hence the possibilities of utilizing the aeroplane
in war became the most important study with all
nations； as soon as flying became an accomplished
fact。
INVENTIONS TO ATTACK AERIAL CRAFT。Before
any nation had the opportunity to make an actual
test on the battlefield； inventors were at work to
devise a means whereby an aerial foe could be
met。 In a measure the aerial gun has been successful；
but months of war has shown that the
aeroplane is one of the strongest arms of the
service in actual warfare。
It was assumed prior to the European war that
the chief function of the aeroplane would be the
dropping of bombs；that is for service in attacking
a foe。 Actual practice has not justified
this theory。 In some places the appearance of
the aeroplane has caused terror； but it has been
found the great value is its scouting advantages。
FUNCTION OF THE AEROPLANE IN WAR。While
bomb throwing may in the future be perfected；
it is not at all an easy problem for an aviator to
do work which is commensurate with the risk
involved。 The range is generally too great； the
necessity of swift movement in the machine too
speedy to assure accuracy； and to attack a foe at
haphazard points can never be effectual。 Even
the slowly…moving gas fields； like the Zeppelin；
cannot deliver bombs with any degree of precision
or accuracy。
BOMB…THROWING TESTS。It is interesting； however；
to understand how an aviator knows where
or when to drop the bomb from a swiftly…moving
machine。 Several things must be taken into consideration；
such as the height of the machine from
the earth； its speed； and the parabolic curve that
the bomb will take on its flight to the earth。
When an object is released from a moving machine
it will follow the machine from which it is
dropped； gradually receding from it； as it descends；
so that the machine is actually beyond
the place where the bomb strikes the earth； due
to the retarding motion of the atmosphere agains
