Fig. 42.—Plan of proposed aeroplane machine, in which a, a are the proposed superposed main aeroplanes; b, b, the after superposed aeroplanes; c, c, the forward horizontal rudder; d, platform; e, screw; h, h, and i, i, pulleys used in communicating motion from the steering gear, f, to the rudder, j; g, lever attached to the aeroplane or rudder, c, c, and connected to the steering gear, f.
For those who really wish to build a flying machine that will actually fly with very little experimental work, I have given an outline sketch sufficiently explicit to enable a skilful draughtsman to make a working drawing in which [Fig. 40] is a front elevation, [Fig. 41] a side elevation, and [Fig. 42] a plan. [Fig. 41], a, a, shows the two forward or main aeroplanes; b, b, the two after aeroplanes, which are smaller and shorter; c, the rudder; d, the forward horizontal rudder; e, the screw; f, the motor; g, the condenser or cooler; h, the steering gear; i, and j, atmospheric buffers; k and l, wheels attached to a lever pivoted to the body of the machine; q, a shield for protecting the screw. It will be observed that the framework is extremely long, and, consequently, the distance between the aeroplanes is very great; but it should be borne in mind that the longer the machine, the less any change of center of lifting effect, as relates to the center of gravity, will be felt. Moreover, it is much easier to manœuvre a machine of great length than one which is very short, because it gives one more time to think and act. If the length was infinitely great the tendency to pitch would be infinitely small. I have shown a steering gear consisting of a lever with a handle n, arranged in such a manner that it moves both the vertical rudder c, and the horizontal rudder d, so that the man who steers the machine has nothing to think of except to point the lever n, p, in the direction that he wishes the machine to go. This lever is mounted on a universal joint at h, and is connected with suitable wires to the two rudders. In order to prevent shock when the machine alights, it is necessary to provide something that is strong and, at the same time, yielding, and able to travel through a considerable distance before the machine comes to a state of rest. In the machines which I have seen on the Continent, a very elaborate apparatus is employed, which is not only very heavy, but also offers a considerable resistance to the forward motion of the machine through the air. It consists of many tubes, very long levers and heavy spiral springs, etc. In the device which I am recommending, all this is dispensed with, and something very much simpler, cheaper, and lighter is substituted. Moreover, with my proposed apparatus a certain amount of lifting effect is produced. The levers k, k, to which the wheels are attached, should be of thin wood, light and strong, and say about a foot wide, strongly pivoted to the frame and held in position by an atmospheric buffer made of strong and thin steel tubing, shown in section ([Fig. 51]). These pneumatic cylinders may be pumped up to any degree, so as to support the weight of the machine, and then, as it comes down, the compression and escape of air arrest its motion. The condenser g, is placed in such a position that it will act even while the machine is on the ground and the propellers working. In Continental machines, very small screw propellers are used. These screws have probably been made small because the experimenters have found that they encounter a good deal of friction in the atmosphere, but this is caused by imperfect shape and the rib of steel at the back of the blades. In order to use a small screw, experimenters have been forced to use a very quick-running engine which makes it necessary to have the cylinders very short, so, in order to get the necessary power, they are obliged to use no less than eight cylinders. However, by increasing the diameter of the screw and making it of such a form that very little or no atmospheric skin friction is encountered, a much better and cheaper engine of a totally different type may be employed. There is no reason why more than four cylinders should be used, but the stroke of the piston and diameter of the cylinder should be increased. Doubtless Continental experimenters have an idea that, as the engine cannot be provided with a flywheel, it must have a very large number of cylinders in order to give a steady pull completely around the circle, and thus avoid so-called “dead centers”; but, when we consider the enormously high velocity of the periphery of the screw, and also take into consideration that the momentum is in proportion to the square of the velocity, it is quite obvious that there can be no slowing up between strokes even if only one cylinder should be employed working on the four-cycle principle, in which work is only done one stroke in four. Then, again, I find that the weight of these Continental engines can be greatly reduced, providing that they are made with the same degree of refinement that I employed in building my steam engines.
Recently there has been a great deal of discussion in Engineering and other journals regarding the comparative merits of the aeroplane system and the hélicoptère. Some condemn both systems and pin their faith to flapping wings. It has been contended that the screw propeller is extremely wasteful in energy, and that in all Nature neither fish nor bird propels itself by means of a screw. As we do not find a screw in Nature, why then should we employ it in a machine for performing artificial flight?
Why not stick to Nature? In reply to this, I would say that even Nature has her limits, beyond which she cannot go. When a boy was told that everything was possible with God, he asked; “Could God make a two-year old calf in five minutes?” He was told that God certainly could. “But,” said the boy, “would the calf be two years old?” It appears to me that there is nothing in Nature which is more efficient, or gets a better grip on the water than a well-made screw propeller, and no doubt there would have been fish with screw propellers, providing that Dame Nature could have made an animal in two pieces. It is very evident that no living creature could be made in two pieces, and two pieces are necessary if one part is stationary and the other revolves; however, the tails and fins very often approximate to the action of the propeller blades; they turn first to the right and then to the left, producing a sculling effect which is practically the same. This argument might also be used against locomotives. In all Nature, we do not find an animal travelling on wheels, but it is quite possible that a locomotive might be made that would walk on legs at the rate of two or three miles an hour. But locomotives with wheels are able to travel at least three times as fast as the fleetest animal with legs, and to continue doing so for many hours at a time, even when attached to a very heavy load. In order to build a flying machine with flapping wings, to exactly imitate birds, a very complicated system of levers, cams, cranks, etc., would have to be employed, and these of themselves would weigh more than the wings would be able to lift. However, it is quite possible to approach very closely to the motion of a bird’s wings with no reciprocating or vibrating parts, and without flapping at all.
Fig. 43.—Plan of a hélicoptère machine showing position of the screws. Owing to the tilting of the shaft forward, the blades present no angle when at d, d, but 10° at c, c, while at f, f their angle above the horizontal is 5°. The horizontal arrows show the direction of the wind against the machine.
Fig. 44.—Shows the position of the blades of a hélicoptère as they pass around a circle, when the angle of the shaft and the angle of the blades are the same.
In [Fig. 43], I have shown a plan of a hélicoptère machine in which two screws are employed rotating in opposite directions, a, a, being the port screw; b, b, the starboard screw; and d, d, the platform for the machinery and operator. The screws should be 20 feet in diameter and made of wood. Suppose now that the pitch of these screws is such that the extremities of the blades have an angle of 5°; if now we tilt the shaft forward in the direction of flight to the extent of 5°, we shall completely wipe out the angle of inclination of the blades when at b ([Fig. 44]), whereas it will be observed that the pitch as regards the horizontal will be increased to 10° at a, on the outer side, and remain unchanged at c, and d. If the peripheral velocity of the blades is, say, four times the velocity at which the machine is expected to travel, the blades will get a good grip on the air at c, d, but when they travel forward and encounter air which is travelling at a high velocity in the opposite direction, they assume the position shown at b. If the pitch of the screw blades was a little more than the angle of the shaft, the blades at b would also produce a lifting effect, and as the velocity with which they pass through the air is extremely high, a very strong lifting effect would be produced even if the angle was not more than 1 in 40. By tracing the path and noting the position of the ends of the blades as they pass completely around the circle as shown ([Fig. 44]), it will be observed that they very closely resemble the motion of a bird’s wing. I have no doubt that a properly made machine on this plan would be highly satisfactory, but one should not lose sight of the fact that even with a machine of this type, well designed and sufficiently light to sustain itself in the air while flying, it would still be necessary for it to move along rapidly when starting in order to get the necessary grip on the air. Upon starting the engine, in a machine of this kind, a very strong downward draught of air would be produced, and the whole power of the engines would be used in maintaining this downward blast, but if the machine should at the same time be given a rapid forward motion sufficiently great to bring the blades into contact with new air, the inertia of which had not been disturbed, and which was not moving downwards, the lifting effect would be increased sufficiently to lift the machine off the ground. It would, therefore, work very much like an aeroplane machine. It would also be possible to provide a third screw of less dimensions and running at a less velocity, to push the machine forward, so as not to render it necessary to give such a decided tilt to the shafts.