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 sh.e.l.lac, will not untwist, as it is the changing character of the atmosphere which usually causes the twisted strips to change their positions.
Sh.e.l.lac 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.
RUBBER--Suitable 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-j.a.panese 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 gla.s.ses 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 ma.s.ses 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 a.s.sumed 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 a.s.sure 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 r.e.t.a.r.ding motion of the atmosphere against the missile.
The diagram Fig. 90 will aid the boy in grasping the situation. A is the airship; B the path of its flight; a the course of the bomb after it leaves the airship; and D the earth. The question is how to determine the proper movement when to release the bomb.
METHOD FOR DETERMINING MOVEMENT OF A BOMB.--Lieut. Scott, U. S. A., of the Coast Survey Artillery, suggested a method for determining these questions. It was necessary to ascertain, first, the alt.i.tude and speed. While the barometer is used to determine alt.i.tudes, it is obvious that speed is a matter much more difficult to ascertain, owing to the wind movements, which in all cases make it difficult for a flier to determine, even with instruments which have been devised for the purpose.
_Fig. 90. Course of a Bomb._
Instead, therefore, of relying on the barometer, the ship is equipped with a telescope which may be instantly set at an angle of 45 degrees, or vertically.
Thus, Fig 91 shows a ship A, on which is mounted a telescope B, at an angle of 45 degrees.
The observer first notes the object along the line of 45 degrees, and starts the time of this observation by a stop watch.
The telescope is then turned so it is vertical, as at C, and the observer watches through the telescope until the machine pa.s.ses directly over the object, when the watch is stopped, to indicate the time between the two observations.
_Fig. 91. Determining Alt.i.tude and Speed._
The height of the machine along the line D is thus equal to the line E from B to C, and the time of the flight from B to a being thus known, as well as the height of the machine, the observer consults specially-prepared tables which show just what kind of a curve the bomb will make at that height and speed.
All that is necessary now is to set the sighter of the telescope at the angle given in the tables, and when the object to be hit appears at the sight, the bomb is dropped.
THE GREAT EXTENT OF MODERN BATTLE LINES.-- The great war brought into the field such stupendous ma.s.ses of men that the battle lines have extended over an unbroken front of over 200 miles.
In the battle of Waterloo, about 140,000 men were engaged on both sides, and the battle front was less than six miles. There were, thus ma.s.sed, along the front, over 20,000 men every mile of the way, or 10,000 on each side.
In the conflict between the Allies and the Germans it is estimated that there were less than 7500 along each mile. It was predicted in the earlier stages of the war that it would be an easy matter for either side to suddenly ma.s.s such an overwhelming force at one point as to enable the attacking party to go through the opposing force like a wedge.
Such tactics were often employed by Napoleon and other great masters of war; but in every effort where it has been attempted in the present conflict, it was foiled.
The opposing force was ready to meet the attack with equal or superior numbers. The eye of the army, the aeroplane, detected the movements in every instance.
THE AEROPLANE DETECTING THE MOVEMENTS OF ARMIES.--In the early stages of the war, when the Germans drove the left of the French army towards Paris, the world expected an investment of that city. Suddenly, and for no apparent reason, the German right was forced back and commenced to retreat.
It was not known until weeks afterwards that the French had a.s.sembled a large army to the west and northwest of Paris, ready to take the Germans in flank the moment an attempt should be made to encircle the Paris forts.