CHAPTER VI.

HINTS AS TO THE BUILDING OF FLYING MACHINES.

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.

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.

As before stated, great care should be taken in designing and making the framework of flying machines, and no stone should be left unturned in order to arrive at the greatest degree of lightness without diminishing the strength too much; then, again, elasticity should be considered. If we use a thin tube all the material is at the surface, far from the neutral centre, and great stiffness is obtained, but such a tube will not stand so much deflection as a piece of wood; then, again, wood is cheaper than steel, and in case of an accident, repairs are very quickly and easily made. Wood, however, cannot be obtained in long lengths absolutely free from blemishes. It therefore becomes necessary to find some way of making these long members of flying machines of such wood as may be found suitable in the following table.

+---------------------+-------------+-------------+----------+ | | Strength | Weight of a | | | | per Sq. In. | Cube Foot | Relative | | | in Lbs. | in Lbs. | Value. | +---------------------+-------------+-------------+----------+ | Alder, | ... | 50 | ... | | Apple, | ... | 49·562 | ... | | Ash, English, | 16,000 | 52·812 | 302·9 | | Ash, White, | 14,000 | 43·125 | 324·6 | | Bamboo, | 6,300 | 25 | 252 | | Beech, English, | 11,500 | 53·25 | 215·9 | | Birch, | 15,000 | 45 | 333·3 | | Box, African, | 23,000 | ... | ... | | „ France, | ... | 83 | ... | | Cedar, American, | 11,600 | 35·062 | 330·8 | | Deal, Christiania, | 12,400 | ... | ... | | Ebony, | 27,000 | 83·187 | 324·6 | | Elm, | 6,000 | 35·625 | 168·4 | | „ Rock, | 13,000 | 50 | 260 | | Fir, Norway Spruce, | ... | 32 | ... | | „ Dantzic, | ... | 36·375 | ... | | Hackmatack, | 12,000 | 37 | 324·3 | | Hickory, | 11,000 | 49·5 | 222·2 | | Ironwood, | ... | 61·875 | ... | | Juniper, | ... | 36·375 | ... | | Lance, | 23,000 | 45 | 511·1 | | Lignum-Vitæ, | 11,800 | 83·312 | 141·6 | | Lime, | ... | 50·25 | ... | | Locust, | 20,500 | 45·5 | 450·5 | | Mahogany, Honduras, | 21,000 | 35 | 600 | | „ Spanish, | 12,000 | 53·25 | 225·3 | | Maple, | ... | 46·875 | ... | | Oak, African, | 9,500 | 51·437 | 184·7 | | „ Canadian, | ... | 54·5 | ... | | „ Dantzic, | 4,200 | 47·437 | 88·5 | | „ English, | 7,571 | 53·625 | 141·2 | | „ Live, | 16,380 | 66·75 | 245·4 | | „ Pa, seasoned, | 20,333 | ... | ... | | „ White, | 16,500 | 53·75 | 306·9 | | „ Va, | 25,222 | ... | ... | | Pine, Norway, | 14,000 | 46·25 | 302·7 | | „ Pitch, | ... | 41·25 | ... | | „ Red, | 13,000 | 36·875 | 352·5 | | „ White, | 11,800 | 34·625 | 340·8 | | „ Yellow, | 13,000 | 28·812 | 451·2 | | „ Va, | 19,200 | ... | ... | | Poplar, | 7,000 | 23·937 | 292·4 | | „ White, | ... | 33·062 | ... | | Redwood, Cal, | 10,833 | ... | ... | | Spruce, | 12,400 | 31·25 | 396·8 | | Sycamore, | 13,000 | 38·937 | 333·8 | | Tamarack, | ... | 23·937 | ... | | Teak, African, | 21,000 | 61·25 | 342·8 | | „ Indian, | 15,000 | 41·062 | 365·3 | | Walnut, | ... | 41·937 | ... | | „ Black, | 16,633 | 31·25 | 532·2 | | „ Michigan, | 17,500 | ... | ... | | Willow, | 13,000 | 36·562 | 355·5 | +---------------------+-------------+-------------+----------+

The relative value of different kinds of wood is shown in this table, and it will be observed that some are much more suitable for the purpose than others. The true value of a wood to be used in flying machines is only ascertained by considering its strength in comparison with its own weight--that is, the wood which is strongest in proportion to its weight is the best. It will be seen that Honduras mahogany stands at the head of the list, but American white pine is very good for certain purposes, as it is light, strong, easily obtained, and takes the glue very well indeed. In Fig. 45, I have shown a good system of producing the long members necessary in flying machines. I will admit that it costs something to fit up and produce the kind of joints which I have shown, but when the members are once made, they are exceedingly strong and stiff. Fig. 46 shows sections of the struts, and these may be made of either straight-grained Honduras mahogany or of lance wood; either answers the purpose very well, because being very strong and straight-grained, permits the struts to be made of such a shape and size as to offer very little resistance in cutting their way through the air. The framework of the aeroplane unless carefully designed will offer great resistance to being driven through the air. Suppose that the bottom member of the truss (Fig. 47) is straight, and the top one curved in the direction shown; no matter how taut the cloth may be drawn, the pressure of the air will cause it to bag upwards between the different trusses, so as to present very nearly the correct curve which is necessary to produce the maximum lifting effect, and without offering too much resistance to the air; however, one must not forget for a single moment that the air flows over both sides of the aeroplane. When the aeroplane is made very thick in the middle and sharp at the edges (Fig. 48), with the bottom side dead level, it produces a decided lifting effect no matter which way it is being propelled through the air. This is not because the bottom side produces any lifting effect of itself, but because the air running over the top follows the surface. The aeroplane encounters air which is not moving at all. The air is first moved upwards slightly, but it also has to run down the incline to the rear edge of the aeroplane, so that, when it is discharged, it has a decided downward trend; therefore, the air passing over the top side instead of under the bottom side, produces the lifting effect, showing that the top side of an aeroplane as well as the lower side should be considered. The top side should, therefore, be free from all obstructions.

The top of the aeroplane as well as the bottom should be covered with some light material, if the very best results are to be obtained. In another chapter I have shown a form of fabric-covered aeroplane, made by myself, that was not distorted in the least by the air pressure, and produced just as good effects as it would have done if it had been carefully carved out of a piece of wood. On more than one occasion Lord Kelvin came to my place; he said that my workshop was a perfect museum of invention. At the Oxford Meeting of the British Association for the Advancement of Science, Lord Salisbury in the chair, I was much gratified when Lord Kelvin said that he had examined my work, and found that it was beautifully designed and splendidly executed. He complimented me very highly indeed. While at my place, he said that the most ingenious thing that he had seen was the way I had prevented my aeroplanes from being distorted by the air. He spoke of this several times with great admiration, and, I think, if the fabric-covered aeroplane is to be used at all, that my particular system will be found altogether the best.

Regarding the motors now being employed, I think that there is still room for a great deal of improvement in the direction of greater lightness, higher efficiency and reliability. At the present time, flying machine motors have such small cylinders, the rotation is so rapid, and the cooling appliances so imperfect, that the engine soon becomes intensely heated, and then its efficiency is said to fall off about 40 or 50 per cent., some say even 60 per cent. This is probably on account of the high temperature of the cylinder, piston, and air inlet. The heat expands the air as it enters, so that the actual weight of air in the cylinder is greatly reduced, and the engine power reduced in a corresponding degree. There is no trouble about cooling the motor, and a condenser of high efficiency may be made that will cool the water perfectly, and, at the same time, lift a good deal more than its own weight. All the conditions are favourable for using a very effective atmospheric condenser (see Figs. 30 and 31).

Water may be considered as 2400 times as efficient as air, volume for volume, in condensing steam. When a condenser is made for the purpose of using water as a cooling agent, a large number of small tubes may be closely grouped together in a box, and the water pumped in at one end of the box and discharged at the other end through relatively small openings; but when air is employed, the tubes or condensing surfaces must be widely distributed, so that a very large amount of air is encountered, and air which has struck one tube and become heated must never touch a second tube (see Figs. 30 and 31, also Appendix).

Fig. 51 shows a pneumatic buffer which I have designed, in which _a_, _a_, is a steel tube highly polished on the inside; _b_, a nozzle for connecting the air-pump, which is of the bicycle variety; _c_, a nipple to which is attached a strong india-rubber bulb; _d_, a piston which is made air-tight by a leather cup; and _f_, the connection to the lever carrying the wheels on which the machine runs. While the machine is at a state of rest on the ground, the piston-rod _d_, is run out to its full extent, and supports the weight of the machine--the pressure being about 150 lbs. to the square inch. When, however, the machine comes violently down to the earth, the piston is pushed inward, compressing the air, and by the time it has travelled, say, one-half the stroke, the air pressure will have mounted to 300 lbs. to the square inch. At this point, the rubber bulb _c_, ought to burst and allow the compressed air to escape under a high pressure. Air escaping through a relatively small hole absorbs the momentum of the descent and brings the machine to a state of rest without a destructive shock. It is, of course, necessary for the navigator to select a broad and level field for descent, and then to approach it from the leeward and slow up his machine as near the ground as possible, tilting the forward end upwards in order to arrest its forward motion, and touching the ground while still moving against the wind at a fairly high velocity. If all these points are studied, and well carried out, very little danger will result; then, again, the aeroplanes _b_, _b_, and the forward rudder _d_ (Fig. 41), should be so arranged that, in case of an accident, their outward sides may be instantly turned upwards, in such a manner as to prevent the machine from plunging, and keep it on an even keel while the engines are not running.

STEERING BY MEANS OF A GYROSCOPE.

A ship at sea has only to be steered in a horizontal direction; the water in which it is floated assures its stability in a vertical direction; but when a flying machine is once launched in the air, it has to be steered in two directions--that is, the vertical and the horizontal. Moreover, it is constantly encountering air currents that are moving with a much higher velocity than any water currents that have ever to be encountered. It is, therefore, evident that, as far as vertical steering is concerned, it should be automatic. Some have suggested shifting weights, flowing mercury, and swinging pendulums; but none of these is of the least value, on account of the swaying action which always has to be encountered. A pendulum could not be depended upon for working machinery on board a ship, and the same laws apply to an airship. We have but one means at our disposal, and that is the gyroscope. When a gyroscope is spun at a very high velocity on a vertical axis, with the point of support very much above the center of gyration, it has a tendency to maintain a vertical axis; a horizontal or swinging motion of its support will not cause it to swing like a pendulum. It therefore becomes possible by its use to maintain an airship on an even keel. In a steam steering apparatus, such as is used on shipboard, it is not sufficient to apply steam-power to move the rudders, unless some means are provided whereby the movement of the rudder closes off the steam, otherwise the rudder might continue to travel after the effect had been produced, and ultimately be broken; and so it is with steering a flying machine in a vertical direction. Whenever the fore and aft rudders respond to the action of the gyroscope and are set in motion, they must at once commence to shut off the power that works them, otherwise they would continue to travel. In the photograph (Fig. 52) I have shown an apparatus which I constructed at Baldwyn’s Park. It will be seen that the gyroscope is enclosed in a metal case; a tangent screw, just above the case, rotates a pointer around a small disc, which admits of the speed of the gyroscope being observed. Steam is admitted through a universal joint, descends through the shaft and escapes through a series of small openings placed at a tangent, so as to give rotation to the wheel after the manner of a Barker’s mill. The casing about the rotating wheel is extremely light as relates to the wheel, so that, when the gyroscope is once spun on a vertical axis, the rest of the apparatus may be tilted in any direction, while the gyroscope and its attachments maintain a vertical axis. The gyroscope and its attachments are suspended from a long steel tube, which in reality is a steam cylinder. The sleeve which supports the gyroscope moves freely in a longitudinal direction, and the whole is held in position by a triple-threaded screw on the small tube above the cylinder. The steam is admitted through a piston value operated by a species of link motion, as shown. The piston-rod extends to each end of the cylinder, and regulates the rudders by pulling a small wire rope, the travel of the piston being about 8 feet. At the end of the cylinder (not shown) the piston-rod is provided with an arm and a nut which engages the small top tube--this tube being provided with a long spiral--so that, as the piston moves, the top tube is rotated, and thereby slides the gyroscope’s support, and changes its position as relates to the piston valve. It will, therefore, be seen that the action is the same as with the common steam steering gear used on shipboard. A little adjusting screw at the right hand of the print is shown. The upward projecting arm of the bell crank lever is for the purpose of attaching the wooden handle, making it possible to move the connecting-rod instantly into a position where the steam piston will move the rudders into the position shown (Fig. 56).

I copy the following from a description which I wrote of this apparatus at the time:--

“GYROSCOPE APPARATUS FOR AUTOMATICALLY STEERING MACHINE IN A VERTICAL DIRECTION.

“This apparatus consists of a long steam cylinder which is provided with a piston, the piston-rod extending beyond the cylinder at each end; the ropes working the fore and aft rudders are attached to the ends of this piston-rod, and steam is supplied through an equilibrium valve. The gyroscope is contained in a gunmetal case, and is driven by a jet of steam entering through the trunnions. When the gyroscope is spinning at a high velocity, the casing holding it becomes very rigid and is not easily moved from its vertical position. If the machine rears or pitches, the cylinder and valve are moved with the machine while the gyroscope remains in a vertical position. This causes the steam valve to be moved so as to admit steam into the cylinder and move the piston in the proper direction to instantly bring the machine back into its normal position. As the fore and aft rudders are moved, the long tubular shaft immediately over the steam cylinder is rotated in such a manner as to move the whole gyroscope in the proper direction to close off the steam. The apparatus may be made to regulate at any angle by adjusting the screw which regulates the position of the tubular shaft. The link that suspends the end of the steam valve connecting-rod is supported by a bell crank lever, and while the machine is moving ahead, the lever occupies the position shown in the photograph (Fig. 52); but if the machinery and engine stop, the bell crank lever may be moved so as to throw the connecting-rod below the centre, when the steam will move the piston in the proper direction to throw both the rudders into the falling position, as shown in Fig. 56.”