CRYSTAL PALACE EXPERIMENTS.
Having fully satisfied myself that aeroplanes flying around a circle 200 feet in circumference had their lifting effect reduced to no insignificant degree by constantly engaging air which had already had imparted to it a downward movement by a previous revolution, I determined to make some experiments where this trouble could not occur, but the opportunity did not present itself until after the large roundabout, erroneously described as “a captive flying machine,” was put up at the Crystal Palace. This presented a fine opportunity for making experiments at an extremely high velocity around a very large circle. I will only refer to a few of these experiments. To a prolongation of one of the long arms, I attached a thin steel wire rope about 60 feet above the platform; I then attached to this wire rope the little device shown ([Fig. 39]), in which a, is an aeroplane, 5 feet long and 1 foot wide, placed at an inclination of 1 in 20. Great care was used in preparing this aeroplane to see that it was free from blemish, smooth, and without any irregularities. Both edges were sharp and the curvature was about one-eighth of an inch on the underneath side. It was made relatively thick in the middle where it was attached to the bar c, and thinner at the ends. b, shows a lump of lead just heavy enough to balance the bar c, and the tail; d, was a light but strong wooden frame, all the edges being thin and sharp, and covered with a special silk that Mr. Cody had found to be best for such purposes. The wire rope e, was attached to the long arm which I referred to. The great length of the bar c, and the accuracy with which the whole was made and balanced caused the aeroplane to travel straight through the air adjusting itself to all the shifting currents. Upon starting the machine on a very calm day, this apparatus mounted as high as the point of support, sometimes going 10 or more feet higher and sometimes 8 or 10 feet lower. However, as a rule, it carried its own weight at a velocity of 80 miles an hour around a circle 1,000 feet in circumference. Under these conditions, of course, there could be no downward motion of the air as all the air affected would be removed long before it could be struck the second time by the aeroplane. I had no means of ascertaining exactly how much this plane did actually lift, because the air was always moving to some extent, and it was not an easy matter to ascertain whether it was above or below the point of support. I am sure, however, that it was as much as 36 lbs., or rather more than 7 lbs. to the square foot, and this is just what it should have lifted, providing that we consider the results obtained by smaller planes placed in an air blast of 40 miles an hour and at the same angle. When these experiments were finished, I made a very small apparatus having only about 25 square feet of lifting surface, and this carried the weight of a man, in fact several gentlemen came up from London and went round on it themselves. I saw, however, that it was a dangerous practice, because if the wind was blowing at all, the apparatus would mount very much above the point of support while travelling against the wind, only to drop much below the point of support on the other side of the circle where it was travelling with the wind; in fact, on one occasion the apparatus shown ([Fig. 39]) mounted in a high wind fully 20 feet above the point of support and came down with such a crash on the other side that it broke the wire rope. In connection with this, it is interesting to note that when I erected the first so-called “captive flying machine” on my own grounds at Thurlow Park, I intended that instead of ordinary boats such as were ultimately employed, each particular boat should be fitted with an aeroplane, that the engine should be of 200 H.P., and that the passengers should actually be running on the air, each boat being provided with a powerful electric motor in addition to the motive power that drove the shaft. Had this been carried out as was originally designed, it would have removed the apparatus altogether from the category of vulgar merry-go-rounds, but such was not to be. Unforeseen circumstances were against me. I had some of these boats fitted up with aeroplanes and running on my grounds, and two of the engineers of the London County Council came out to see the apparatus before it was put up for public use. On that occasion the wind was blowing a perfect gale of 40 miles an hour, and as the boats travelled at the rate of 35 miles an hour, they, of course, encountered a wind of 75 miles an hour when passing against the wind, and a minus velocity of 5 miles an hour when travelling with the wind on the other side of the circle. The aeroplanes, although of considerable size, were small in relation to weight. I had neglected to put any weight in the boats, and when three of us were studying the eccentric path through which the boats were travelling, suddenly one of them in passing to the windward, raised very much above the point of support and plunged down with great force on the other side; in fact, the shock was so great that it made everything rattle, but nothing was broken. Nevertheless, the engineers said at once, it would not do to run the boats with those aeroplanes; it was too dangerous. This would not, however, have occurred if the boats had been loaded, or the velocity of the wind had been less. It, however, demonstrated what a tremendous lift may be obtained from a well-made aeroplane passing at a high velocity through the wind at a sharp angle. These aeroplanes were only about 12 feet long and 5 feet wide, having, therefore, 60 square feet of surface. They were, however, strong, well-made, and perfectly smooth, both top and bottom. I would say right here that I am not a success as a showman—previous long years of rubbing up against honest men have disqualified me altogether for such a profession. I was extremely anxious to go on with my experiments. I appreciated fully that I had made a machine that lifted 2,000 lbs. more than its own weight, and I knew for a dead certainty if I took the matter up again, got rid of my boiler and water tank, and used an internal combustion engine, such as I thought I could produce, that mechanical flight would soon be a fait accompli. I had already spent more than £20,000, and was looking about for some means of making the thing self-supporting. I believed that the so-called “captive flying machine” would be very popular, and bring in a lot of money, and it would have done so, if it had been put up as originally designed. I proposed to use my share of the profits for experimental work on real flying machines. That I was not far wrong in believing that such a machine would be a success, is witnessed by the fact that just about the same time, an American inventor thought of the same thing, put up some three or four machines the first year, and the next year about 50. They were highly profitable, and there are fully 140 of them running at the present time in the U.S.A. It is a fact that nothing in the way of side-shows at exhibitions or public resorts has ever had the success of this machine in the U.S.A., and even the little machine at Earl’s Court took £325 10s. in one day and £7,500 in a season. However, this little attempt to make one hand wash the other cost me no less than £10,400, not to mention more than a year of very hard work. This sum would have been amply sufficient to have enabled me to continue my experiments until success was assured.
CHAPTER VI.
HINTS AS TO THE BUILDING OF FLYING MACHINES.
Fig. 40.—Front elevation of proposed aeroplane machine—a, a, the aeroplanes; g, g, condenser; f, the engine; q, guard for screw; k, k, support for wheels.
Fig. 41.—Side elevation of proposed superposed aeroplane machine—a, a, main aeroplanes; b, b, rear aeroplanes; c, vertical rudder; d, horizontal front rudder; e, screw; f, motor; g, condenser; h, steering gear; i and j, pneumatic buffers; k and l, wheels; m, point at which k is pivoted to the main frame; n, handle of the steering gear.
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.
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 per Sq. In. in Lbs. | Weight of a Cube Foot in Lbs. | Relative 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 | ... | ... | ||
| Bo„x,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 |
| E„m,Rock, | 13,000 | 50 | 260 | ||
| Fir, Norway Spruce, | ... | 32 | ... | ||
| F„r, 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 | ||
| Maho„any, Spanish, | 12,000 | 53 | ·25 | 225 | ·3 |
| Maple, | ... | 46 | ·875 | ... | |
| Oak, African, | 9,500 | 51 | ·437 | 184 | ·7 |
| O„k, Canadian, | ... | 54 | ·5 | ... | |
| O„k, Dantzic, | 4,200 | 47 | ·437 | 88 | ·5 |
| O„k, English, | 7,571 | 53 | ·625 | 141 | ·2 |
| O„k, Live, | 16,380 | 66 | ·75 | 245 | ·4 |
| O„k, Pa, seasoned, | 20,333 | ... | ... | ||
| O„k, White, | 16,500 | 53 | ·75 | 306 | ·9 |
| O„k, Va, | 25,222 | ... | ... | ||
| Pine, Norway, | 14,000 | 46 | ·25 | 302 | ·7 |
| Pi„e, Pitch, | ... | 41 | ·25 | ... | |
| Pi„e, Red, | 13,000 | 36 | ·875 | 352 | ·5 |
| Pi„e, White, | 11,800 | 34 | ·625 | 340 | ·8 |
| Pi„e, Yellow, | 13,000 | 28 | ·812 | 451 | ·2 |
| Pi„e, Va, | 19,200 | ... | ... | ||
| Poplar, | 7,000 | 23 | ·937 | 292 | ·4 |
| Pop„ar,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 |
| Te„k, Indian, | 15,000 | 41 | ·062 | 365 | ·3 |
| Walnut, | ... | 41 | ·937 | ... | |
| Wal„ut, Black, | 16,633 | 31 | ·25 | 532 | ·2 |
| Wal„ut, 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.
Fig. 45.—System of splicing and building up wooden members. When they have to be curved and to keep their shape, they should be bent at the curve at the time of being glued together, and joined in the middle as at d.
Fig. 46.—Cross-section of struts.
Fig. 47.—Truss suitable for use with flying machines, having aeroplanes about 6 feet to 8 feet wide.
[Fig. 47 enlarged] (30 kB)
![[Fig. 47 enlarged]](#3839971358814751280_lg47.png.id-9007035373088066657.wrap-0.html.html){kind=link}
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.
Fig. 48.—The paradox aeroplane that lifts no matter in which direction it is being driven.
Fig. 49.—The Antoinette motor.
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. 50.—Section showing the Antoinette motor, such as used in the Farman and De la Grange machines.
[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.
Fig. 51.—Pneumatic buffer—a, a, cylinder; b, attachment for pumping up; c, air outlet, covered with a rubber thimble made to burst under about 300 lbs. pressure; d, the piston.