CHAPTER XIII. THE QUESTION OF WAFTAGE. BUT the most energetic of powers will be useless to us, if we have not instruments for enabling it to act effectually upon the air, so as to impress upon it such motion, both as to velocity and as to direction, as may be required. We may, therefore, without further preface, state another of our requisites thus: The air-craft must be furnished with appliances for transmitting to the atmosphere the force exerted within, so as to obtain a purchase for driving the system forward, and for modifying the direction of its progress. Notwithstanding the neglect of the would-be navigators of the air to find power for the work they have taken in hand, they have been most busy in putting into varions shapes the instruments or intermediate agents of propulsion. The different means of taking the requisite hold upon the air, or of causing the forward pressure of the atmosphere upon the system to exceed the backward, may be arranged conveniently under three heads—as wings, wheels, and blasts. The first class the wings, wafts and oars-may be characterised as propellers of alternate action, and are in fact, elementary parts of some of the agents of the next class. The second or revolving instruments may be sub-divided into two sorts, the direct and the obliquely acting vane-wheels. The first is a development of the direct-action wing; the second of the oblique or bird's wing, which latter, as a simple plane acting downwards, and partly backwards, is useless for the kind of flight in which the weight is supported by gas. But in its complex or rotary form, in which the downward action on one side of the fulcrum is neutralised by the upward action on the other, the oblique waft is serviceable for direct propulsion. There is another form of revolving agent, by which the second class passes into the third. This is the fan-blast, or centrifugal wheel, which does not act by its own impact direct or oblique upon the air, but by the formation of a stream or blast, of which the mode of action will be hereafter noticed. In the third class then, or that of blasts, I shall include this form of wheel. 1 Of the wings or oars a great variety were tried by the early aeronauts, with, it would appear, just enough of success to establish the point that a balloon could be moved, and to discourage any farther attempts to make use of them. The reasons of this failure have been already pointed out; and may be briefly recapitulated thus the improper mode of application of the force; the insufficient size of the wing surfaces; and the inadequate power applied to the levers, the men not knowing how to apply their strength in 'pulling.' M. Blanchard, who had been endeavouring to fly for some years before the first balloon went up, was the first to attempt to propel the great gas-globe with little oars or wafts. The destruction of his wings by the attack of a young student just as he was preparing to make his first ascent, did not discourage him from continuing his endeavours of this sort. They were, however, very feeble. I can find no account of the size of his rowing appendages; though from the pictures of his balloon, which may be found in all the Encyclopædias, it is evident that they were far too small to be of any effect; and from the arrangement represented, it is difficult to conceive how he could have worked them. There is no more information to be had as to the extent of Lunardi's wings; but the prints of his balloon and fittings show that they were absurdly diminutive. One of the best attempts of this kind that has been made was probably that conducted by Guyton de Morveau for the Academy of Dijon, in 1784. The balloon, which was a globe 27 feet in diameter, was furnished with a pair of oars attached to a hoop encircling its equator, from which they hung, so as to act in a 1 See p. 34, above. vertical plane; they were moved by a cord led down to the car. The blade-arm of these oars was 13 feet long, of which the wing plane occupied 11 feet, being of the form of an isosceles triangle, of which the base at the lower extremity was 50 inches broad, and of which the area was 24 square feet. There were also a pair of oars attached to the car, so as to be worked in a horizontal plane. The handle-arm of each of these was 2 feet, and the outboard arm, the whole of which was occupied by the blade, 7 feet long. The blade was an elliptical plane 4 feet broad; the area of the surface being about 25 square feet. These were to be feathered by turning round their long axes during the return stroke. This is almost the only instance in which I find an account of the exact dimensions of the propelling apparatus used, being one of the very few trials of the sort that have been made by men who knew anything of the art of experimenting. Had Guyton de Morveau been living now, he, benefiting by the labours of others who have gone before us, would have framed his apparatus in a very different form. That such instruments must be utterly useless for any practical end in the propulsion of such a vessel as that to which they were fitted, requires no proof in the present day. 1 M. Salle proposed to propel the balloon by means of rectangular wing-frames or shutters of more likely dimensions; they were to be 18 feet long by 12 wide, with small panes of silk like the squares of glass in a window, each of which was to feather separately, as the shutters moved backwards to recover the stroke. He saw the necessity, not generally recognised by rowers either in the air or on the water, of counterpoising the weight of these large oar-blades; 2 but he designed to manage this in the quaintest way imaginable, by suspending each wing from a separate balloon of its own. 3 One great mistake which all the contrivers of such wings have made, is that of not learning to row a boat before they thought of pulling under a balloon. Had they taken this preliminary step, they would have learned what they had not sufficient theoretical knowledge to perceive, that to Descr. Aerost. Dijon,' pp. 141, 158, 162. 2 See a letter by Mr. M'Gregor in 'Mech. Mag.' vol. lii. p. 351. Salle, Moyen Dirig. Aérost.' (1784), pp. 24, 33. enable their oar-blade to get sufficient resistance from the water or air, it must be placed at the extremity of a very long arm, so as by increasing its arc of motion to exalt its velocity. Of course the varieties of oar-blade that have been proposed are very numerous, the chief characteristics on which the changes are rung being the open-and-shut, the feather by rotation of the axis, and the partial feather of separate small blades. Mr. Bell1 proposed an umbrella propeller,' which is nothing more than a shut-up oar-blade of the form described, caused to move in a straight line instead of in a circular arc by traversing on a guide rod. But the most eccentric fancy of the kind is one of Dr. M'Sweeney's conceptions; he proposes to have two balloons tied together by a long rope (this is his crotchet), and make one pull the other towards it, so as to pass the first by its momentum, and so on, in a game of perpetual leap-frog. The head balloon is to arrange itself so as to offer greater resistance to the air than the advancing one. The contriver seems to have about half a notion that he is here only making one balloon the wing for the other. This 'alternate warping,' says the doctor, 'will do for aerial navigation what condensing in a vessel separate from the cylinder did for the steam-engine.' 2 We next come to the system of wings or oar-blades arranged in a rotary form—as a paddle-wheel. It is quite evident at once that, unless each separate vane on the wheel is made to feather, or to change during each revolution the angle in which it lies with respect to any plane passing through the axis of the wheel, that their action, as respects the propulsion in one direction of a body attached to their axis, will be simply nothing, the forward motion on one side being counteracted by the backward motion on the other. I do not know that anyone can be convicted of actually proposing for an air-craft simple paddle-wheels such as are used by steamers, but the mistake is by no means too absurd for aerial schemers to have perpetrated. For many of them have been so far unable to see the difference between a vessel 1 Specification. See p. 63, above. 1 entirely immersed in the air and one floating upon the surface of the water, as seriously to propose to apply fixed sails to the balloon for the purpose of directing its course.' The reader will conceive that such persons may easily have missed seeing that it is only not necessary that the paddle-wheels of a steamboat should feather its vanes completely, because the resistance they meet with from the air, in the upper part of their revolution is so small compared with that which the water offers to them below, that it may be considered as practically nothing they may, therefore, have supposed that the same paddle which would answer in one case would do their work in the other. Besides, inventors are apt to make suggestions in a hurry. The following at any rate looks very like it :-'Il est à observer que les roues à palettes (ou l'hélice qui conviendra mieux pour la navigation aérienne) agissant dans un fluide 804 fois moins dense que l'eau, devront être établies de manière à avoir 804 fois plus de prise sur l'air que celles du Transatlantique n'en ont sur l'eau; ce qu'on obtiendra en augmentant simultanément la surface et la vitesse de ces palettes. Pour accroître la vitesse, il suffit d'augmenter le rayon des roues sans changer la vitesse, avec laquelle tourne l'arbre de la machine. . . . On raissonnerait de même s'il s'agissait d'une hélice au lieu de roues à palettes.' 12 However, a feathering paddle-wheel for direct action has been See, for instance, Lond. Mag.' 1784, January, p. 13, and Henin, 'Mem. sur direct. aerost.' (An. x.). 2 Mongè, Études,' p. 131. It is extremely unlikely that the steamer (the Magellan) with whose paddle-wheels (roues à palettes) the author is here comparing those of his supposed air-craft, were furnished with feathering-paddles, which till lately have very rarely been applied. He has evidently overlooked the error, though, from the way in which he mentions the screw propeller (l'hélice), he seems to have a suspicion that all is not right about the paddle-wheel for aerial propulsion. Besides, it must be remembered that the feathering necessary for a wing moving wholly in the air is a very different adjustment from that which answers the purpose required by a surface water-boat, and which is the only kind adopted in steamers. In the former case the position of the vane during its return stroke must be at right angles to that of its working stroke. In the latter case all that is ever required is that the vane should be kept at certain angles during the time it is in the water, that its stroke may be effective. |