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As inventors frequently propose the construction of a vacuum balloon, to secure buoyancy without the use of gas, it may be desirable to estimate the strength of material required to resist crushing, say in a spherical balloon.

The unit stress in the wall of a thin, hollow, spherical balloon subject to uniform hydrostatic pressure, which is prevented from buckling, is given by equating the total stress on a diametral section of the shell to the total hydrostatic pressure across a diametral section of the sphere, thus:

in which S may be the stress in pounds per square inch, p the resultant hydrostatic pressure in pounds per square inch, r the radius of the sphere, t the wall thickness.

The greatest allowable mass of the shell is found by equating it to the mass of the displaced air, thus:

in which ?₁ is the density of the wall material, ?₂ the density of the atmosphere outside.

Now, assuming p = 15, ?₁/?₂ = 6,000, for steel and air, the equations give:

per square inch as the stress in a steel vacuum balloon.

For aluminum ?₁ is less, but the permissible value of S is also less in about the same proportion.

The last equation shows that for a given material and atmospheric environment, the stress in the shell or wall of the spherical balloon is independent of the radius of the surface. It is also well known that the stress is less for the sphere than for any other surface. Hence, no surface can be constructed in which S will be less than 3p?₁/2?₂. The argument is easily seen to apply to a partial vacuum balloon, since a balloon of one nth vacuum will float a cover of but one nth the mass and strength.

The above result was obtained on the assumption that the shell was prevented from buckling. As a matter of fact, it would buckle long before the crushing stress could be attained. We must conclude, therefore, that while a vacuum balloon has alluring features, the materials of engineering are not strong enough to favor such a structure. Perhaps it is nearer the truth to say that such a project is visionary, with the materials now available.

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A like argument applies to the balloon reservoir in which it has been proposed to compress the surplus gas taken from a balloon hull on expansion of its contents by change of level or temperature. If a given mass of gas obeying Boyle’s law be pumped into a receiver of given shape and mass, the resultant stress in the receiver wall will be independent of the size. Hence the material of the proposed reservoir, if expanded to the size of the hull itself, will weigh the same, and suffer the same increment of unit stress, for a given mass increment of gas. Hence, instead of pumping the above-mentioned gas surplus from the hull into the reservoir, this latter may be discarded and its mass of material spread over the hull itself. This argument applies only if the shapes of hull and reservoir be equally effective, as, for example, if both be cylindrical.

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On Wednesday, the 27th instant, the new aËrostatic Experiment, invented by Messrs. Montgolfier of Annonay, was repeated by M. Charles, Professor of experimental Philosophy at Paris.

A hollow Globe 12 feet Diameter was formed of what is called in England Oiled Silk, here Taffetas gommÉ, the Silk being impregnated with a Solution of Gum elastic in Linseed Oil, as he said. The Parts were sewed together while wet with the Gum, and some of it was afterwards passed over the Seam, to render it as tight as possible.

It was afterwards filled with inflammable Air that is produced by pouring Oil of Vitriol upon Filings of Iron, when it was found to have a tendency upwards so strong as to be capable of lifting a Weight of 39 Pounds, exclusive of its own Weight which was 25 lbs and the Weight of the Air contain’d.

It was brought early in the morning to the Champ de Mars, a Field in which Reviews are sometimes made, lying between the military School and the River. There it was held down by a Cord till 5 in the afternoon, when it was to let loose. Care was taken before the Hour to replace what Portion had been lost, of the inflammable Air, or of its Force, by injecting more.

It is supposed that not less than 50,000 People were assembled to see the Experiment, The Champ de Mars being surrounded by multitudes, and vast Numbers on the opposite Side of the River.

At 5 O’clock Notice was given to the Spectators by the Firing of two Cannon, that the Cord was about to be cut. And presently the Globe was seen to rise, and that as fast as a Body of 12 feet Diameter, with a force only of 39 Pounds, could be suppos’d to remove the resisting Air out of its Way. There was some Wind, but not very strong. A little Rain had wet it, so that it shone, and made an agreeable appearance. It diminished in Apparent Magnitude as it rose, till it enter’d the Clouds, when it seem’d to me scarce bigger than an Orange, and soon after became invisible, the Clouds concealing it.

The multitude separated, all well satisfied and delighted with the Success of the Experiment, and amusing one another with discourses of the various uses it may possibly be apply’d to, among which many were very extravagant. But possibly it may pave the Way to some Discoveries in Natural Philosophy of which at present we have no conception.

A Note secur’d from the Weather had been affix’d to the Globe, signifying the Time & Place of its Departure, and praying those who might happen to find it, to send an account of its state to certain Persons at Paris. No News was learned of it till the next Day, when information was received that it fell a little after 6 o’clock, at Gonesse, a Place about four Leagues Distance, and that it was rent open, and some say had ice in it. It is suppos’d to have burst by the Elasticity of the contain’d Air when no longer compress’d by so heavy an Atmosphere.

One of 38 feet Diameter is preparing by Mr. Montgolfier himself, at the Expence of the Academy, which is to go up in a few days. I am told it is constructed of Linen & Paper, and is to be filled with different Air, not yet made public, but cheaper than that produc’d by the Oil of Vitriol, of which 200 Paris Pints were consum’d in filling the other.

It is said that for some Days after its being fill’d the Ball was found to lose an eighth Part of its Force of Levity in 24 Hours; Whether this was from Imperfection in the Tightness of the Ball, or a Change in the Nature of the Air, Experiments may easily discover....

M. Montgolfier’s Air to fill the Globe has hitherto been kept secret; some suppose it to be only common Air heated by passing thro’ the Flame of burning Straw, and thereby extreamly rarefied. If so, its Levity will soon be deminish’d by Condensation, when it comes into the cooler Region above....

P. S. I just now learned that some observers say, the Ball was 150 Seconds in rising, from the cutting of the Cord till hid in the Clouds; that its height was then about 500 Toises, but, being moved out of the Perpendicular by the Wind, it had made a Slant so as to form a Triangle, whose base on the Earth was about 200 Toises. It is said the Country People who saw it fall were frightened, conceiv’d from its bounding a little, when it touched the Ground, that there was some living Animal in it, and attack’d with Stones and Knives, so that it was much mangled; but it is now brought to Town and will be repair’d.

The great one of M. Montgolfier is to go up, as is said, from Versailles, in about 8 or 10 days. It is not a Globe but of a different Form, more convenient for penetrating the Air.

It contains 50,000 cubic Feet, and is supposed to have Force of Levity equal to 1,500 pounds weight. A Philosopher here, M. PilÂtre du Rozier, has seriously apply’d to the Academy for leave to go up with it, in order to make some experiments. He was complimented on his Zeal and Courage for the Promotion of Science, but advis’d to wait till the management of these Balls was made by Experience more certain & safe. They say the filling of it in Montgolfier’s Way will not cost more than half a Crown. One is talk’d of to be 110 feet Diameter. Several gentlemen have ordered small ones to be made for their Amusement. One has ordered four of 15 feet Diameter each; I know not with what Purpose; but such is the present Enthusiasm for promoting and improving this Discovery, that probably we shall soon make considerable Progress in the art of constructing and using the Machines.

Among the Pleasanteries Conversation produces on this subject, some suppose Flying to be now invented, and that since Men may be supported in the Air, nothing is wanted but some light handy instrument to give and direct Motion. Some think Progressive Motion on the Earth may be advanc’d by it, and that a Running Footman or a Horse slung and suspended under such a Globe so as to have no more of Weight pressing the Earth with their Feet, then Perhaps 8 or 10 pounds, might with a fair Wind run in a straight Line across Countries as fast as that Wind, and over Hedges, Ditches & even Waters. It has been even fancied that in time People will keep such Globes anchored in the Air, to which by Pullies they may draw up Game to be preserved in the Cool & Water to be frozen when Ice is wanted. And that to get Money, it will be contriv’d to give People an extensive View of the Country, by running them up in an Elbow Chair a Mile high for a Guinea, &c., &c.

B. Franklin.
Passy, Nov. 22d, 1783.

... Enclosed is a copy of the Proces verbal taken of the Experiment yesterday in the Garden of the Queen’s Palace la Muette, where the Dauphin now resides, which being near my House I was present. This Paper was drawn up hastily, and may in some Places appear to you obscure; therefore I shall add a few explanatory Observations.

This Balloon was larger than that which went up from Versailles and carried the Sheep, &c. Its bottom was open, and in the middle of the Opening was fixed a kind of Basket Grate, in which Faggots and Sheaves of Straw were burnt. The Air rarefied in passing thro’ this Flame rose in the Balloon, swell’d out its sides, and Fill’d it.

The Persons who were plac’d in the Gallery made of Wicker, and attached to the Outside near the Bottom, had each of them a Port thro’ which they could pass Sheaves of Straw into the Grate to keep up the Flame, & thereby keep the Balloon full. When it went over our Heads, we could see the Fire which was very considerable. As the Flame slackens, the rarefied Air cools and condenses, the Bulk of the Balloon diminishes and it begins to descend. If those in the Gallery see it likely to descend in an improper Place, they can by throwing on more Straw, & renewing the Flame, make it rise again, and the Wind carries it farther.

One of these courageous Philosophers, the Marquis d’Arlandes, did me the honour to call upon me in the Evening after the Experiment, with Mr. Montgolfier, the very ingenious Inventor. I was happy to see him safe. He informed me that they lit gently, without the least Shock, and the Balloon was very little damaged.

This method of filling the Balloon with hot Air is cheap and expeditious, and it is supposed may be sufficient for certain purposes, such as elevating an Engineer to take a view of an Enemy’s Army, Works, &c., conveying Intelligence into, or out of a besieged Town, giving Signals to distant places, or the like.

The other method of filling a Balloon with permanently elastic inflammable Air, and then closing it is a tedious Operation, and very expensive; Yet we are to have one of that kind sent up in a few days. It is a Globe of 26 feet diameter. The Gores that compose it are red and white Silk, so that it makes a beautiful appearance. A very handsome triumphal Car will be suspended to it, in which Messrs. Roberts, two Brothers, very ingenious Men, who have made it in concert with Mr. Charles, propose to go up. There is room in this Car for a little Table to be placed between them, on which they can write and keep their journal, that is, take Notes of everything they observe, the State of their Thermometer, Barometer, Hygrometer, &c., which they will have more leisure to do than the others, having no fire to take care of. They say they have a contrivance which will enable them to descend at Pleasure. I know not what it is. But the Expence of this machine, Filling included, will exceed, it is said, 10,000 Livres.

This Balloon of only 26 feet diameter, being filled with Air ten times lighter than common Air, will carry up a greater Weight than the other, which tho’ vastly bigger, was filled with an Air that could scarcely be more than twice as light. Thus the great Bulk of one of these Machines, with the short duration of its Power, & the great Expence of filling the other will prevent the Inventions being of so much Use as some may expect, till Chemistry can invent a cheaper light Air producible with more Expedition.

But the Emulation between the two Parties running high, the Improvement in the Construction and Management of the Balloons had already made a rapid Progress; and one cannot say how far it may go. A few Months since the idea of Witches riding thro’ the Air upon a Broomstick, and that of Philosophers upon a Bag of Smoke, would have appeared equally impossible and ridiculous.

These Machines must always be subject to be driven by the Winds. Perhaps Mechanic Art may find easy means to give them progressive Motion in a Calm, and to slant them a little in the Wind.

I am sorry this Experiment is totally neglected in England, where mechanic Genius is so strong. I wish I could see the same Emulation between the two Nations as I see between the two Parties here. Your Philosophy seems to be too bashful. In this Country we are not so much afraid of being laught at. If we do a foolish thing, we are the first to laugh at it ourselves, and are almost as much pleased with a Bon Mot or a Chanson, that ridicules well the Disappointment of a Project, as we might have been with its Success. It does not seem to me a good reason to decline prosecuting a new Experiment which apparently increases the power of a Man over Matter, till we can see to what use that power can be applied. When we have learnt to manage it, we may hope some time or other to find Uses for it, as men have done for Magnetism and Electricity, of which the first Experiments were mere Matters of Amusement.

This Experience is by no means a trifling one. It may be attended with important Consequences that no one can foresee. We should not suffer Pride to prevent our progress in Science.

Beings of a Rank and Nature far superior to ours have not disdained to amuse themselves with making and launching Balloons, otherwise we should never have enjoyed the Light of those glorious objects that rule our Day & Night, nor have had the Pleasure of riding round the Sun ourselves upon the Balloon we now inhabit.

B. Franklin.
Passy, Dec. 1, 1783.

In mine of yesterday I promised to give you an account of Messrs. Charles & Roberts’ Experiment, which was to have been made this Day, and at which I intended to be present. Being a little indispos’d, & the Air cool, and the Ground damp, I declin’d going into the Garden of the Tuilleries where the Balloon was plac’d, not knowing how long I might be oblig’d to wait there before it was ready to depart; and chose to stay in my Carriage near the Statue of Louis XV, from whence I could well see it rise, & have an extensive View of the Region of Air thro’ which, as the Wind sat, it was likely to pass. The Morning was foggy, but about one o’clock the Air became tolerably clear; to the great satisfaction of spectators, who were infinite. Notice having been given of the intended Experiment several days before in the Papers, so that all Paris was out, either about the Tuilleries, on the Quays & Bridges, in the Fields, the Streets, at the Windows, or on the Tops of Houses, besides the inhabitants of all the Towns & Villages of the Environs. Never before was a philosophical Experiment so magnificently attended. Some Guns were fired to give Notice that the departure of the great Balloon was near, and a small one was discharg’d which went to an amazing height, there being but little Wind to make it deviate from its perpendicular Course, and at length the Sight of it was lost. Means were used, I am told, to prevent the great Balloon’s rising so high as might endanger its Bursting. Several Bags of Sand were taken on board before the Cord that held it down was cut, and the whole Weight being then too much to be lifted, such a Quantity was discharg’d as to permit its Rising slowly. Thus it would sooner arrive at that Region where it would be in equilibrio with the surrounding Air, and by discharging more Sand afterwards, it might go higher if desired. Between One & Two o’Clock, all Eyes were gratified with seeing it rise majestically from among the Trees and ascend gradually above the Buildings, a most beautiful Spectacle! When it was about 200 feet high, the brave Adventurers held out and wav’d a little white Pennant, on both sides their Car, to salute the Spectators, who return’d loud Claps of Applause. The Wind was very little, so that the Object, tho’ moving to the Northward, continued long in View; and it was a great while before the admiring People began to disperse. The persons embark’d were Mr. Charles, Professor of Experimental Philosophy, & zealous Promotor of that Science; and one of the Messieurs Robert, the very ingenious Constructors of the Machine. When it arrived at its height, which I suppose might be 3 or 400 Toises, it appeared to have only horizontal Motion. I had a Pocket Glass, with which I follow’d it, till I lost Sight first of the Men, then of the Car, and when I last saw the Balloon, it appear’d no bigger than a Walnut. I write this at 7 in the evening. What became of them is not yet known here. I hope they descended by Day-light, so as to see and avoid falling among Trees or on Houses, and that the Experience was completed without any mischievous Accident, which the Novelty of it & the want of Experience might well occasion. I am the more anxious for the Event, because I am not well informed of the Means provided for letting themselves gently down, and the Loss of these very ingenious Men would not only be a Discouragement to the Progress of the Art, but be a sensible Loss to Science and Society.

Tuesday Morning, December 2,—I am reliev’d from my Anxiety by hearing that the Adventurers descended well near l’Isle Adam, before Sunset. This Place is near 7 Leagues from Paris. Had the Wind blown fresh, they might have gone much farther.

P.S. Tuesday Evening ... I hear farther that the Travellers had perfect Command of the Carriage, descending as they pleas’d by letting some of the inflammable Air escape, and rising again by discharging some Sand; that they descended over a Field so low as to talk with Labourers in passing and mounted again to pass a Hill. The little Balloon falling at Vincennes shows that mounting higher it met with a Current of Air in a contrary Direction; an Observation that may be of use to future aËrial Voyagers.

B. Franklin.

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The ClÉment-Bayard II may be classed among the airships usually called “flexible.” The shape of its hull is preserved not by any rigid framing, but by internal gas pressure maintained by ballonets fed by ventilating fans. Moreover, the suspension which binds envelope and car together as one solid is composed wholly of flexible elements, without any rigid intermediary structure.

The general plan, then, of the craft comprises three prominent features, well marked and distinct in character:

(a) The fish-shaped envelope with major section well forward, a form favorable to both speed and stability.

(b) The trussed girderlike car whose length allows the load to be distributed over the hull, thus preserving its nicety of outline. The most minute and technical and mechanical details were studied for eighteen months by M. ClÉment and his devoted collaborator, the engineer Sabathier. The girder car, as will be seen presently, is particularly well designed to serve as car, sustainer and stiffener. No stabilizing device is attached to the envelope; all are fixed to the car, on which is mounted also the complete propulsion plant.

(c) The suspension which binds the buoyant envelope to the car serves no other purpose. Note also the ingenious arrangement of two motors and two propellers, forming two independent systems, yet unitable under certain conditions. The placement of the propellers, rudders and stabilizing surfaces well above the bottom of the car, insures them against dangerous contact on landing, or while maneuvering near the ground.

The envelope is of rubberized Continental cloth. Its volume is 7,000 cubic meters, length 76.5 meters and major diameter 13.22 meters, or an elongation of 5.76 diameters. Inside the gas envelope is an air bag of 2,200 cubic meters. It is divided into two compartments, Q and Q´, which can be filled with air together or separately through the air duct, Q, joined to a blower, P, run by the two motors, or by hand when so desired. The balloon proper comprises two gas valves, R. Each compartment of the ballonet has one air valve, S. The valves of the type ClÉment-Bayard-ChauviÈre are automatic. Their construction is so perfect that for the first time in France, at least on a balloon of so large bulk, the blower runs continuously in constant communication with the ballonet, the pressure in the envelope remaining invariable, due to the regular play of the valves, which yield at the pressure for which they are set. They may also be Worked by hand from the pilot’s bridge in case of emergency. The envelope has on its upper side three ripping seams, one in the middle, the others toward either end. These rip panels can be worked together or separately, and permit the rapid deflation of the balloon.

The long car is attached to the hull by hempen duck feet fastened to a bolt rope running along the envelope below the equator; these duck feet terminate below in steel suspension cables fixed to the car. Below the principal bolt rope are others to which are fastened the duck feet of the oblique cords, which assure the perfect solidarity of the envelope and car. The steel cable sustainers have an ingenious patented regulating windlass. The girder car consists of a latticed girder, built of steel tubes united with cast-iron joints and steel-tie wires. Its whole length is 45 meters, of which 14.5 meters constitute the car proper. It is divided into segments which are easily demountable, thus rendering it easily transportable by truck or railway. The forward segment, A, tapers toward the front to a sharp point and is of triangular cross-section. The mid segment, B, constituting the car, has a quadrangular section of variable size. The rear segment, D, is of triangular section, diminishing progressively toward the rear, which rises to a sort of tail supporting the empennage and the direction rudders. The entire girder car when resting on the ground is supported by two pneumatic shock absorbers, U, U, projecting from its floor.

The car proper comprises three parts: in front, the motor and machine room, 2.5 meters wide; in the middle, the elevated bridge, N, for the pilot and his aide; in the rear, the passenger cabin, 8 meters long, 1.3 meters wide and 2 meters high for the observers and wireless telegraphy plant. The two reservoirs of essence, M, m, are placed above the passenger about the center of pressure. The blower P, for the ballonets, and the guide ropes T, are placed above the pilot’s bridge.

In the motor room are symmetrically arranged two Bayard-ClÉment engines, G G, separated enough to allow free passage between them. Each motor is elastically supported to obviate vibrations, and connects with the transmission shaft by a variable speed gear. The engines can be run separately or together by a connecting sprocket chain, and develop 100 to 130 horse-power each. The cooling of each motor is effected by an aluminum radiator, L L, of large surface.

The ChauviÈre propellers, K K, six feet in diameter, are driven by shafting and gear wheels at a normal speed of 250 rotations per minute. A special recording device serves to show their thrust at each instant, as also the torque of the motors.

The pilot, standing on the bridge where he enjoys a clear view, has immediate charge of the vessel’s movements. Before him are the various controls which he must operate, and the divers indicators which he must consult. These are the direction wheel, the manometers, the aneroid and registering barometers, the clinometer, the blower control to regulate the amount and distribution of pressure, the elevating-rudder wheel, the spark control, the ripping cord, the release string of the guide-rope, and the system of transmitting orders to the mechanicians whereby he can control the engines and the blowers which furnish air to the radiator and ballonet.

The direction and poise of the vessel in flight are controlled by the rudders and empennage at the rear, and its altitude from minute to minute is governed by the elevating biplane E´, of 30 square meters above the car in the mid region of the vessel.

The Patrie[81]

The Patrie, the third of its type, was first operated in 1906. The gas bag of the first balloon was built by Surcouf at Billancourt, Paris. The mechanical part was built at the Lebaudy Sugar Refinery. Since then the gas bags have been built at the Lebaudy balloon shed at Moisson, near Paris, under the direction of their aËronaut, Juchmes. The gas bag of the Patrie was 197 feet long with a maximum diameter of 33 feet, 9 inches, situated about 2/5 of the length from the front; volume 111,250 cubic feet; length approximately six diameters. This relation, together with the cigar shape, is in accordance with the plans of Colonel Renard’s dirigible, built and operated in France in 1884; the same general shape and proportions being found in the Ville de Paris.

The first Lebaudy was pointed at the rear, which is generally admitted to be the proper shape for the least resistance, but to maintain stability it was found necessary to put a horizontal and vertical plane there, so that it had to be made an ellipsoid of revolution to give attachment for these planes.

The ballonet for air had a capacity of 22,958 cubic feet or about 1/5 of the total volume. This is calculated to permit reaching a height of about one mile and to be able to return to the earth, keeping the gas bag always rigid. To descend from a height of one mile, gas would be released by the valve, then air pumped into the ballonet to keep the gas bag rigid, these two operations being carried on alternately. On reaching the ground from the height of one mile, the air would be at the middle of the lower part of the gas bag and would not entirely fill the ballonet. To prevent the air from rolling from one end to the other when the air ship pitches, thus producing instability, the ballonet was divided into three compartments by impermeable cloth partitions. Numerous small holes were pierced in these partitions, through which the air finally reached the two end compartments.

In September, 1907, the Patrie was enlarged by 17,660 cubic feet by the addition of a cylindrical section at the maximum diameter, increasing the length but not the maximum diameter.

The Gas Bag.—The gas bag is cut in panels; the material is a rubber cloth made by the Continental Tire Company at Hanover, Germany. It consists of four layers arranged as follows:

	Weight oz. per square yard.
a. Outer layer of cotton cloth covered with lead chromate	2.5
b. Layer of vulcanized rubber	2.5
c. Layer of cotton cloth	2.5
d. Inner layer of vulcanized rubber	2.21
	———
Total weight	9.71

A strip of this cloth one foot wide tears at a tension of about 934 pounds. A pressure of about one inch of water can be maintained in the gas bag without danger. The lead chromate on the outside is to prevent the entrance of the actinic rays of the sun, which would cause the rubber to deteriorate. The heavy layer of rubber is to prevent the leaking of the gas. The inner layer of rubber is merely to prevent deterioration of the cloth by impurities in the gas. This material has the warp of the two layers of cotton cloth running in the same direction and is called straight thread. The material in the ballonet weighs only about 7¾ ounces per square yard, and has a strength of about 336 pounds per running foot. When the Patrie was enlarged in September, 1907, the specifications of the material allowed a maximum weight of 10 ounces per square yard, a minimum strength of 907 pounds per running foot, and a loss of 5.1 cubic inches of hydrogen per square yard in twenty-four hours at a pressure of 1.18 inches of water. Bands of cloth are pasted over the seams inside and out with a solution of rubber to prevent leaking through the stitches.

Suspension.—One of the characteristics of the Patrie is the “short” suspension. The weight of the car is distributed over only about 70 feet of the length of the gas bag. To do this, an elliptical-shaped frame of nickel-steel tubes is attached to the bottom of the gas bag; steel cables run from this down to the car. A small hemp net is attached to the gas bag by means of short wooden cross-pieces, or toggles, which are let into holes in a strong canvas band which is sewed directly on the gas bag. The metal frame, or platform, is attached to this net by means of toggles, so that it can be quickly removed in dismounting the air ship for transportation. The frame can also be taken apart, 28 steel cables about 0.2 inches in diameter run from the frame down to the car, and are arranged in triangles. Due to the impossibility of deforming a triangle, rigidity is maintained between the car and gas bag.

The objection to the “short” suspension of the Patrie is the deformation of the gas bag. A distinct curve can be seen in the middle.

The Car.—The car is made of nickel-steel tubes (12 per cent nickel). This metal gives the greatest strength for minimum weight. The car is boat-shaped, about 16 feet long, about 5 feet wide and 2½ feet high. About 11 feet separate the car from the gas bag. To prevent any chance of the fire from the engine communicating with the hydrogen, the steel framework under the gas bag is covered with a noncombustible material.

The pilot stands at the front of the car, the engine is in the middle, the engineer at the rear. Provision is made for mounting a telephotographic apparatus, and for a 100-candle-power acetylene searchlight. A strong pyramidal structure of steel is built under the car, pointing downward. In landing the point comes to the ground first and this protects the car, and especially the propellers, from being damaged. The car is covered to reduce air resistance. It is so low, however, that part of the equipment and most of the bodies of those inside are exposed, so that the total resistance of the car is large.

The Motor.—The first Lebaudy had a 40-horse-power Daimler-Mercedes benzine motor. The Patrie was driven by a 60 to 70-horse-power 4-cylinder Panhard and Levassor benzine motor, making 1,000 r. p. m.

The Propellers.—There are two steel propellers 8½ feet in diameter (two blades each) placed at each side of the engine, this giving the shortest and most economical transmission. To avoid any tendency to twist the car, the propellers turn in opposite directions. They are “high speed,” making 1,000 to 1,200 r. p. m.

The gasoline tank is placed under the car inside the pyramidal frame. The gasoline is forced up to the motor by air compression. The exhaust is under the rear of the car pointing down and is covered with a metal gauze to prevent flames coming out. The fan which drives the air into the ballonet is run by the motor, but a dynamo is also provided so that the fan can always be kept running even if the motor stops. This is very essential as the pressure must be maintained inside the gas bag so that the latter will remain rigid and keep its form. There are five valves in all, part automatic and part both automatic and also controlled from the car with cords. The valves in the ballonet open automatically at less pressure than the gas valves, so that when the gas expands all the air is driven out of the ballonet before there is any loss of gas. The ballonet valves open at a pressure of about O.78 inches of water, the gas valves at about 2 inches.

Stability.—Vertical stability is maintained by means of fixed horizontal planes. One having a surface of 150 square feet is attached at the rear of the gas bag and due to its distance from the center of gravity is very efficient. The elliptical frame attached under the gas bag has an area of 1,055 square feet, but due to its proximity to the center of gravity, has little effect on the stability. Just behind the elliptical frame is an arrangement similar to the feathering of an arrow. It consists of a horizontal plane of 150 square feet, and a vertical plane of 113 square feet. To maintain horizontal stability, that is, to enable the air ship to move forward in a straight line without veering to the sides, fixed vertical planes are used. One runs from the center to the rear of the elliptical frame and has an area of 108 square feet.

In addition to the vertical surface of 113 square feet at the rear of the elliptical frame, there is a fixed plane of 150 square feet at the rear of the gas bag. To fasten the two perpendicular planes at the rear of this gas bag, cloth flaps are sewed directly on the gas bag. Nickel-steel tubes are placed in the flaps, which are then laced over the tubes. With these tubes as a base, a light tube and wire framework is attached and waterproof cloth laced on this framework. Additional braces run from one surface to the other and from each surface to the gas bag. The rudder is at the rear under the gas bag. It has about 150 square feet and is balanced.

A movable horizontal plane near the center of gravity, above the car, is used to produce rising or descending motion, or to prevent an involuntary rising or falling of the air ship due to expansion or contraction of the gas or to other causes. After the adoption of this movable horizontal plane, the loss of gas and ballast was reduced to a minimum. Ballast is carried in 10- and 20-pound sandbags. A pipe runs through the bottom of the car from which the ballast is thrown.

There are two long guide-ropes, one attached at the front of the elliptical frame and the other on the car. On landing, the one in front is seized first so as to hold the air ship with the head to the wind. The motor may then be stopped and the descent made by pulling down on both guide-ropes. A heavy rope 22 feet long, weighing 110 pounds, is attached at the end of a 164-foot guide-rope. This can be dropped out on landing to prevent coming to the ground too rapidly. The equipment of the car includes a “siren” speaking trumpet, carrier pigeons, iron pins and a rope for anchoring the air ship, reserve supply of fuel and water, and fire extinguisher.

After being enlarged in September, 1907, the Patrie made a number of long trips at an altitude of 2,500 to 3,000 feet. In November, 1907, she went from Paris to Verdun, near the German frontier, a distance of about 175 miles, in about 7 hours, carrying four persons. This trip was made in a light wind blowing from the northeast. Her course was east, so that the wind was unfavorable. On Friday, November 20, 1907, during a flight near Verdun, the motor stopped due to difficulty with the carburetor. The air ship drifted with the wind to a village about 10 miles away, where she was safely landed. The carburetor was repaired on the 20th. Soon after, a strong wind came up and tore loose some of the iron pickets with which it was anchored. This allowed the air ship to swing broadside to the wind; it then tilted over on the side far enough to let some of the ballast bags fall out. The 150 or 200 soldiers who were holding the ropes were pulled along the ground until directed by the officer in charge to let go. After being released, it rose and was carried by the wind across the north of France, the English Channel and into the north of Ireland. It struck the earth there, breaking off one of the propellers, and then drifted to sea.

The RÉpublique

This is the latest of the French military dirigible balloons, and differs but slightly from its predecessor, the Patrie. The volume has been increased by about 2,000 cubic feet. The length has been reduced to 200 feet and the maximum diameter increased to 35½ feet. The shape of the gas bag accounts for the 2,000 additional cubic feet of volume. The motor and propeller are as in the Patrie. The total lifting capacity is 9,000 pounds, of which 2,700 pounds are available for passengers, fuel, ballast, instruments, etc. Its best performance was a 125-mile flight made in 6½ hours against an unfavorable wind.

The material for the gas bag of the new air ship was furnished by the Continental Tire Company. It is made up as follows:

	Weight oz. per square yard.
Outer yellow cotton layer	3.25
Layer of vulcanized rubber	3.25
Layer of cotton cloth	3.25
Inner layer of rubber	0.73
	———
Total weight	10.48

It is interesting to note the changes which this type has undergone since the first one was built. The Jaune, constructed in 1902–3, was pointed at the rear and had no stability plane there; later it was rounded off at the rear and a fixed horizontal plane attached. Finally a fixed vertical plane was added. The gas bag has been increased in capacity from 80,670 cubic feet to about 131,000 cubic feet. The manufacturers have been able to increase the strength of the material of which the gas bag is made, without materially increasing the weight. The rudder has been altered somewhat in form. It was first pivoted on its front edge, but later on a vertical axis, somewhat to the rear of this edge. With the increase in size, has come an increase in carrying capacity and, consequently, a greater speed and more widely extended field of action.

Ville de Paris

This air ship was constructed for Mr. Deutsch de la Meurthe, of Paris, who has done a great deal to encourage aËrial navigation. The first Ville de Paris was built in 1902, on plans drawn by Tatin, a French aËronautical engineer. It was not a success. Its successor was built in 1906, on plans of Surcouf, an aËronautical engineer and balloon builder. The gas bag was built at his works in Billancourt, the mechanical part at the Voisin shop, also in Billancourt. The plans are based on those of Colonel Renard’s air ship, the France, built in 1884, and the Ville de Paris resembles the older air ship in many particulars. In September, 1907, Mr. Deutsch offered the use of his air ship to the French Government. The offer was accepted, but delivery was not to be made except in case of war or emergency. When the Patrie was lost in November, 1907, the military authorities immediately took over the Deutsch air ship.

Gas Bag.—The gas bag is 200 feet long for a maximum diameter of 34½ feet, giving a length of about 6 diameters, as in the France and the Patrie. Volume, 112,847 cubic feet; maximum diameter at about ? of the distance from the front, approximately, as in the Patrie. The middle section is cylindrical with conical sections in front and rear. At the extreme rear is a cylindrical section with eight smaller cylinders attached to it. The ballonet has a volume of 21,192 cubic feet or about ? of the volume, the same proportion found in the Patrie. The ballonet is divided into three compartments from front to rear. The division walls are of permeable cloth, and are not fastened to the bottom so that when the middle compartment fills with air, and the ballonet rises, the division walls are lifted up from the bottom of the gas bag, and there is free communication between the three compartments. The gas bag is made up of a series of strips of perpendicular to a meridian line. These strips run around the bag, their ends meeting on the under meridian. This is known as the “barchistode” method of cutting out the material, and has the advantage of bringing the seams parallel to the line of greatest tension. They are therefore more likely to remain tight and not allow the escape of gas. The disadvantage lies in the fact that there is a loss of 33? per cent of material in cutting. The material was furnished by the Continental Tire Company, and has approximately the same tensile strength and weight as that used in the Patrie. It differs from the other in one important feature—it is diagonal thread, that is, the warp of the outer layer of cotton cloth makes an angle of 45 degrees with the warp of the inner layer of cotton cloth. The result is to localize a rip or tear in the material. A tear in the straight thread material will continue along the warp, or the weave, until it reaches a seam.

Valves.—There are five in all, made of steel, about fourteen inches in diameter; one on the top connected to the car by a cord, operated by hand only; two near the rear underneath. These are automatic but can be operated by hand from the car. Two ballonet valves directly under the middle are automatic and are also operated from the car by hand. The ballonet valves open automatically at a pressure of 2/3 inches of water; the gas valves open at a higher pressure.

Suspension.—This air ship has the “long” suspension. That is, the weight is distributed along practically the entire length of the gas bag. A doubled band of heavy canvas is sewn with six rows of stitches along the side of the gas bag. Hemp ropes running into steel cables transmit most of the weight of the car to these two canvas bands and thus to the gas bag. On both sides and below these first bands are two more. Lines run from these to points half way between the gas bag and the car, then radiate from these points to different points of attachment on the car. This gives the triangular or nondeformable system of suspension, which is necessary in order to have the car and gas bag rigidly attached to each other. With this “long” suspension, the Ville de Paris does not have the deformation so noticeable in the gas bag of the Patrie.

The Car.—This is in the form of a trestle. It is built of wood with aluminum joints and O.12 inch wire tension members. It is 115 feet long, nearly 7 feet high at the middle and a little over 5½ feet wide at the middle. It weighs 660 pounds and is considered unnecessarily large and heavy. The engine and engineer are well to the front, the aËronaut with steering wheels is about at the center of gravity.

Motor.—The motor is a 70 to 75-horse-power Argus, and is exceptionally heavy.

Propeller.—The propeller is placed at the front end of the car. It thus has the advantage of working in undisturbed air; the disadvantage is the long transmission and difficulty in attaching the propeller rigidly. It has two blades and is 19.68 feet long with a pitch of 26.24 feet. The blades are of cedar with a steel arm. The propeller makes a maximum of 250 turns per minute when the engine is making 900 revolutions. Its great diameter and width compensate for its small speed.

Stability.—This is maintained entirely by the cylinders at the rear. Counting the larger one to which the smaller ones are attached, there are five, arranged side by side corresponding to the horizontal planes of the Patrie, and five vertical ones corresponding to the Patrie’s vertical planes. The volume of the small cylinders is so calculated that the gas in them is just sufficient to lift their weight, so they neither increase nor decrease the ascensional force of the whole. The horizontal projection of these cylinders is 1,076 square feet. The center of this projection is 72 feet from the center of gravity of the gas. The great objection to this method of obtaining stability, is the air resistance due to these cylinders, and consequent loss of speed. The stability of the Ville de Paris in a vertical plane is said to be superior to that of the Patrie, due to the fact that the stability planes of the latter do not always remain rigid. The independent velocity of the Ville de Paris probably never exceeded 25 miles an hour.

The Rudder.—The rudder has a double surface of 150 square feet placed at the rear end of the car, 72 feet from the center of gravity. It is not balanced, but is inclined slightly to the rear so that its weight would make it point directly to the rear if the steering gear should break. Two pairs of movable horizontal planes, one at the rear of the car having 43 square feet, and one at the center of gravity (as on the Patrie) having 86 square feet, serve to drive the air ship up or down without losing gas or ballast.

Guide-Ropes.—A 400-foot guide-rope is attached at the front end of the car. A 230-foot guide-rope is attached to the car at the center of gravity.

About thirty men are required to maneuver the Ville de Paris on the ground. The pilot has three steering wheels, one for the rudder and two for the movable horizontal planes. The instruments used are an aneroid barometer, a registering barometer giving heights up to 1,600 feet, and an ordinary dynamometer, which can be connected either with the gas bag or ballonet by turning a valve. A double column of water is also connected to the tube to act as a check on the dynamometer. Due to the vibration of the car caused by the motor, these instruments are suspended by rubber attachments. Even with this arrangement, it is necessary to steady the aneroid barometer with the hand in order to read it. The vibration prevents the use of the statoscope.

Germany

Three different types of air ships are being developed in Germany. The Gross is the design of Major Von Gross, who commands the Balloon Battalion at Tegel near Berlin. The Parseval is being developed by Major Von Parseval, a retired German officer, and the Zeppelin is the design of Count Zeppelin, also a retired officer of the German Army.

The Gross

The first air ship of this type made its first ascension on July 23, 1907. The mechanical part was built at Siemen’s Electrical Works in Berlin; the gas bag by the Riedinger firm in Augsburg.

Gas Bag.—The gas bag is made of rubber cloth furnished by the Continental Tire Company similar to that used in the Ville de Paris. It is diagonal-thread, but there is no inner layer of rubber, as they do not fear damage from impurities in the hydrogen gas. Length, 131¼ feet; maximum diameter about 39? feet; volume, 63,576 cubic feet; the elongation is about 3?. The form is cylindrical with spherical cones at the ends, the whole being symmetrical.

Suspension.—The suspension is practically the same as that of the Patrie. A steel and aluminum frame is attached to the lower part of the gas bag, and the car is suspended on this by steel cables. The objection to this system is even more apparent in the Gross than in the Patrie. A marked dip along the upper meridian of the gas bag shows plainly the deformation.

The Car.—The car is boat-shaped like that of the Patrie. It is suspended thirteen feet below the gas bag.

Motor.—The motor is a 20- to 24-horse-power, 4-cylinder Daimler-Mercedes.

Propellers.—There are two propellers 8³/10 foot in diameter, each having two blades. They are placed one on each side, but well up under the gas bag near the center of resistance. The transmission is by belt. The propellers make 800 r. p. m.

Stability.—The same system, with planes, is used in the Gross as in the Patrie, but it is not nearly so well developed. At the rear of the rigid frame, attached to the gas bag, are two fixed horizontal planes, one on each side. A fixed vertical plane runs down from between these horizontal planes, and is terminated at the rear by the rudder. A fixed horizontal plane is attached on the rear of the bags as in the Patrie. The method of attachment is the same, but the plane is put on before inflation in the Gross air ship, afterwards in the Patrie. The stability of the Gross air ship in a vertical plane is reported to be very good, but it is said to veer considerably in attempting to steer a straight course.

The many points of resemblance between this dirigible and the Lebaudy type are worthy of notice. The suspension or means of maintaining stability, and the disposition for driving are in general the same. As first built, the Gross had a volume of 14,128 cubic feet less than at present, and there was no horizontal plane at the rear of the gas bag. Its maximum speed is probably fifteen miles per hour. As a result of his experiments of 1907, Major Von Gross has this year produced a perfected air ship, built on the same lines as his first, but with greatly increased volume and dimensions. The latest one has a volume of 176,000 cubic feet, is driven by two 75-horse-power Daimler motors, and has a speed of 27 miles per hour.

On September 11th of this year, the Gross air ship left Berlin at 10.25 p.m., carrying four passengers, and returned the next day at 11.30 a.m., having covered 176 miles in the period of a little over 13 hours. This is the longest trip, both in point of time and distance, ever made by any air ship returning to the starting point.

The Parseval

The Parseval air ship is owned and controlled by the Society for the Study of Motor Balloons. This organization, composed of capitalists, was formed practically at the command of the emperor, who is very much interested in aËrial navigation. The society has a capital of 1,000,000 marks, owns the Parseval patents and is ready to construct air ships of the Von Parseval type. The present air ship was constructed by the Riedinger firm at Augsburg, and is operated from the balloon house of this society at Tegel, adjoining the military balloon house.

The gas bag is similar in construction to that of the Drachen balloon, used by the army for captive work. Volume, 113,000 cubic feet; length, 190 feet; maximum diameter, 30½ feet. It is cylindrical in shape, rounded at the front and pointed at the rear. The material was furnished by the Continental Tire Company. It is diagonal-thread, weighing about 11³/10 ounces per square yard and having a strength of about 940 pounds per running foot. Its inner surface is covered with a layer of rubber.

Ballonets.—There are two ballonets, one at each end, each having a capacity of 10,596 cubic feet. The material in the ballonet weighs about 8¼ ounces per square yard, the cotton layers being lighter than in the material for the gas bag. Air is pumped into the rear ballonet before leaving the ground, so that the air ship operates with the front end inclined upward. The air striking underneath exerts an upward pressure, as on an aËroplane, and thus adds to its lifting capacity. Air is pumped into the ballonets from a fan operated by the motor. A complex valve, just under the middle of the gas bag, enables the engineer to drive air into either, or both ballonets. The valves also act automatically and release air from the ballonets at a pressure of about 0.9 inches of water.

In the middle of the top of the gas bag is a valve for releasing the gas. It can be operated from the car, and open automatically at a pressure of about 2 inches of water. Near the two ends and on opposite sides are two rip strips controlled from the car by the cords.

Suspension.—The suspension is one of the characteristics of the air ships, and is protected by patents. The car has four trolleys, two on each side, which run on two steel cables. The car can run backwards and forwards on these cables, thus changing its position with relation to the gas bag. This is called “loose” suspension. Its object is to allow the car to take up, automatically, variations in thrust due to the motor, and variations in resistance due to the air. Ramifications of hemp rope from these steel cables are sewed onto a canvas strip, which in turn is sewed onto the gas bag. This part of the suspension is the same as in the Drachen balloon. The weight is distributed over the entire length of the gas bag.

The Car.—The car is 16.4 feet long and is built of steel tubes and wire. It is large enough to hold the motor and three men, though four or five may be taken.

Motor.—The motor is a 110-horse-power Daimler-Mercedes. Sufficient gasoline is carried for a run of twelve hours.

Propeller.—The propeller, like the suspension, is peculiar to this air ship and is protected by patents. It has four cloth blades which hang limp when not turning. When the motor is running, these blades, which are carefully weighed with lead at certain points, assume the proper position due to the various forces acting. The diameter is 13¾ feet. The propeller is placed above the rear of the car near the center of resistance. Shaft transmission is used. The propeller makes 500 r. p. m. to 1,000 of the motor. There is a space of 6½ feet from the propeller blades to the gas bag, the bottom of the car being about 30 feet from the gas bag. This propeller has the advantage of being very light. Its position, so far from the engine, necessarily incurs a great loss of power in transmission.

The steering wheel at the front of the car has a spring device for locking it in any position.

The 1908 model No. 1 of this air ship was constructed for the purpose of selling it to the government. Among other requirements is a 12-hour flight without landing, and a sufficient speed to maneuver against a 22-mile wind. A third and larger air ship of this type is now under construction.

United States

Signal Corps Dirigible No. 1

Due to the lack of funds, the United States Government has not been able to undertake the construction of an air ship sufficiently large and powerful to compete with those of European nations. However, specifications were sent out last January for an air ship not over 120 feet long and capable of making 20 miles per hour. Contract was awarded to Capt. Thomas S. Baldwin, who delivered an air ship last August to the Signal Corps, the description of which follows:

Gas Bag.—The gas bag is spindle shaped, 96 feet long, maximum diameter, 19 feet 6 inches, with a volume of 20,000 cubic feet. A ballonet for air is provided inside the gas bag, and has a volume of 2,800 cubic feet. The material for the gas bag is made of two layers of Japanese silk, with a layer of vulcanized rubber between.

Car.—The car is made of spruce, and is 66 feet long, 2½ feet wide and 2½ feet high.

Motor.—The motor is a 20-horse-power water-cooled Curtiss make.

Propeller.—The propeller is at the front end of the car, and is connected to the engine by a steel shaft. It is built of spruce, has a diameter of 10 feet, 8 inches, with a pitch of 11 feet, and turns at the rate of 450 r. p. m. A fixed vertical surface is provided at the rear end of the car to minimize veering, and a horizontal surface attached to the vertical rudder at the rear tends to minimize pitching. A double horizontal surface controlled by a lever and attached to the car in front of the engine, serves to control the vertical motion and also to minimize pitching.

The position of the car very near to the gas bag, is one of the features of the Government dirigible. This reduces the length and consequently the resistance of the suspension, and places the propeller thrust near the center of resistance.

The total lifting power of the air ship is 1,350 pounds of which 500 pounds are available for passengers, ballast, fuel, etc. At its official trials a speed of 19.61 miles per hour was attained over a measured course and an endurance run lasting two hours, during which seventy per cent of the maximum speed was maintained.

Dirigible No. 1, as this air ship has been named, has already served a very important purpose in initiating officers of the Signal Corps in the construction and operation of a dirigible balloon. With the experience now acquired, the United States Government is in a position to proceed with the construction and operation of an air ship worthy of comparison with any now in existence, but any efforts in this direction must await the action of Congress in providing the necessary funds.

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The flyer of 1903 carried a four-cylinder gasoline motor of four-inch bore and four-inch stroke. Complete with magneto, radiators, tanks, water, fuel, etc., the motor weighed a little over 200 pounds, and at 1,200 revolutions per minute developed 16 horse power for the first 15 seconds after starting. After a minute or two the power did not exceed 13 or 14 horse power. At 1,020 revolutions per minute—the speed of the motor in the flights at Kitty Hawk on the 17th of December, 1903—it developed about 12 horse power.

The flyer of 1904 was equipped with a motor similar to the first, but of 1/8-inch larger bore. This engine at 1,500 revolutions per minute developed 24 horse power for the first 15 seconds, but only 16 to 17 horse power after a few minutes run. Complete with water, fuel and other accessories, it weighed 240 pounds.

The same engine with a few modifications in the oiling device and the carburetor, was used in all the flights of 1905. A test of its power made soon after the flights of October, 1905, revealed a gain of 3 horse power over tests made just before mounting it on the flyer in 1904. This gain is attributed to the increased smoothness of the cylinders and pistons produced by wear. The small output of these engines was due to lack of experience in building gasoline motors.

During the past year further improvements have been made, and our latest engines of four-inch bore and four-inch stroke produce about 25 horse power continuously. The improvement in the reliability of the motor has been even more marked, so that now flights of long distances can be attempted without danger of failure on account of the stopping of the motor.

A comparison of the flyers of 1903, 1904 and 1905 show some interesting facts. The flyer of 1903 weighed, complete with operator, 745 pounds. Its longest flight was of 59 seconds duration, with a speed of 30 miles an hour and an expenditure of 12 horse power. The flyer of 1904 weighed about 900 pounds, including a load of 70 pounds in iron bars. A speed of more than 34 miles an hour was maintained for a distance of three miles with an expenditure of 17 horse power. The flyer of 1905 weighed, including load, 925 pounds. With an expenditure of 19 to 20 horse power it traveled over 24 miles at a speed of more than 38 miles an hour. The flights of 1904 and 1905 would have been slightly faster had they been made in a straight line, as were those of 1903.

In 1903, 62 pounds per horse power were carried at a speed of 30 miles an hour; in 1904, 53 pounds, at 34 miles an hour; and in 1905, 46 pounds at 38 miles an hour. It will be noted that the weight carried per horse power is almost exactly in inverse ratio to the speed, as theory demands—the higher the speed, the smaller the weight carried per horse power.

Since flyers can be built with approximately the same dynamic efficiency for all speeds up to 60 miles an hour, a flyer designed to carry a total weight of 745 pounds at 20 miles an hour would require only 8 horse power or two thirds of the power necessary for 30 miles an hour. At 60 miles 24 horse power would be necessary—twice that required to carry the same weight at 30 miles an hour. At 120 miles an hour 60 to 75 horse power would probably be necessary, and the weight carried per horse power would be only 10 or 12 pounds. At such high speed the resistance of the operator’s body and the engine is a formidable factor, consuming 64 times as much horse power as at 30 miles an hour. At speeds below 60 miles an hour this resistance is almost negligible.

It is evident that the limits of speed have not as yet been closely approached in the flyers already built, and that in the matter of distance, the possibilities are even more encouraging. Even in the existing state of the art it is easy to design a practical and durable flyer that will carry an operator and supplies of fuel for a flight of over 500 miles at a speed of 50 miles an hour.

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During the past two years Glenn H. Curtiss, who, more than any other experimenter, has been given to developing the aËroplane for various uses, has experimented with floats for his biplane that would enable it to rise from the surface of the water. Something over a year ago he succeeded in developing a speed of about twenty miles an hour on the water, but this was insufficient to rise from the surface.

At the beginning of the new year Mr. Curtiss moved to the Pacific Coast and set about endeavoring to develop suitable floats which would make it possible for his machine to rise from the surface of the water. These experiments have been carried on at San Diego, where Mr. Curtiss is instructing several naval and military officers in the art of flying.

In his first experiments on the Pacific Coast Mr. Curtiss followed the successful experiments of this sort made by M. Henri Fabre at Marseilles, France, about a year ago, as far as the design of his floats was concerned. He constructed one large float six feet wide, five feet from front to rear, and one foot thick at its central point, and placed this under the center of the machine. The bottom of this float was perfectly flat and arranged at an incline of ten or twelve degrees. Some distance forward of the main float, at about the position of the front wheel in the land machine, another float six feet wide, by one foot from front to rear, and six inches deep, was placed; while at the extreme front end of the machine, on a special outrigger, was mounted a small elevating hydroplane six feet wide by eight inches in a fore-and-aft direction, and one and one-half inches thick. This hydroplane was fixed at an angle of about twenty-five degrees and was intended to lift the front part of the machine. A spray shield was fitted back of it, as shown in the diagram, page 333.

The first experiments were made with these new floats on January 26th last; and although they made a considerable disturbance in the water, especially at low speed, the aviator was enabled to get up a speed on the surface of about forty-five miles an hour. He found that at as low a rate as ten miles the hydroplanes (which normally were submerged) rose to the surface, while as the speed increased only the rear edges of the two main planes were required to support the machine. The aËroplane readily attained sufficient speed to rise in the air, for as the speed increased and the floats emerged from the water, the head resistance of the floats diminished and there was only the skin friction of the water on a few inches of the rear edge of these floats, plus the air resistance, to be overcome.

At the first try-out, while traveling over the water at high speed, Mr. Curtiss found himself suddenly nearing the shore, and to avoid running aground he turned his horizontal rudder sharply upward, with the result that the machine rose from the water with perfect ease. He soon alighted again, and in the second flight he made a circle and remained in the air a minute and twenty-one seconds. Two other experimental flights were made the first day, and on January 27th he made a three-and-one-half-minute flight and stated, upon alighting, that he found no difficulty in remaining aloft as long as he pleased. The machine showed a speed of fifty miles an hour in the air as against forty-five miles an hour when skimming over the surface of the water.

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Not satisfied with the several floats with which he had attained his first success in rising from the water, Mr. Curtiss immediately constructed a single float twelve feet long by two feet in width and twelve inches deep. This float is built of wood and resembles a flat-bottomed boat or scow, the top being covered with canvas to keep the water from getting in. Three feet from the front end the bottom is curved upward forming a bow the full width of the float, while at the same distance from the rear the float slants downward in a similar manner.

This single float is placed under the aËroplane in such a position that the main weight of the machine and aviator is slightly to the rear of the center of the float, which causes the latter to incline upward slightly and thus gives the necessary angle for hydroplaning on the surface of the water. The weight of this new float is but fifty pounds, or less than half as much as that of the two floats that were used before.

The paint was barely dry on the new float before Mr. Curtiss had it fitted to his machine and gave it a trial. This was done on February 1st and the trial was thoroughly successful. The machine ran over the surface of the water with very much less disturbance than before and rose in the air readily. A glance at the photographs showing the new and the old floats in action will give one an excellent idea of the much less commotion caused by the single scow-shaped float. Besides being much more compact and creating less disturbance, this float or scow can be used for carrying articles or a passenger.

In order to keep the aËroplane from tilting to one side or the other, an inclined stick four feet long and three inches wide, to which is attached on its upper side an inflated rubber tube, is fastened to the front edge of the lower plane at each end. By the use of these props the aËroplane does not tip readily when skimming along the surface, even though the scow-shaped float used is but two feet in width.

After meeting with success with his new float, Mr. Curtiss, on February 17th, made more flights with the motor and propeller placed at the front of his biplane and with his seat placed at the rear of the main planes. The chief of these flights was one which he made from North Island, where he is experimenting, over San Diego harbor to the cruiser Pennsylvania. He alighted upon the surface close beside the cruiser and his aËroplane was hauled up beside the warship and placed on her deck.

After a short visit on the cruiser the aviator was again lowered to the surface in his machine. A sailor started the engine, and Mr. Curtiss flew back to his starting point in short order. The naval authorities were greatly pleased with his demonstration and it is probable that the Navy Department will purchase one of these machines in the near future and continue the instruction of its officers.

After increasing the surface of his biplane Mr. Curtiss, on February 24th, took up one of his naval pupils, Lieutenant T. G. Ellyson, as a passenger. He made a flight of one and one-half miles, rising to a height of one hundred feet and flying as slowly as twenty-five miles an hour, or as fast as fifty miles an hour, at will. Lieutenant Ellyson was seated on the pontoon below the aËroplane. He could look down in the water and see bottom at a depth of twenty-five feet, and he believes submarines can be easily located by flying over the water. The slow speed at which it is possible to fly will make the biplane especially useful for bomb dropping. As we go to press Mr. Curtiss is about to try his machine fitted with wheels and floats as well.

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ass="pginternal">85, 92.

Parseval type of, 138, 139, 140–143, 473–476.

Patrie, 115, 118, 119.

Porter’s, 86, 87.

practical development of nonrigid, 115 et seq.

practical speed of, 101.

Renard and Krebs’, 93–97.

Republique, 115, 118, 119, 466.

Robert’s, 81, 82, 83.

Russie, 120.

Santos-Dumont’s, 102–114.

Schwartz’s, 99, 100.

steam, 87, 89.

successful military, 456.

two systems of, 101.

types of, 122.

U. S. Military I, 138, 476, 477.

Ville de Nancy, 124, 125.

Ville de Paris, 120–123, 467–471.

voyage of across English channel, 132, 136, 137.

in Zeppelin, 153–156.

Zeppelin IV, explosion, 157, 158.

Zeppelin passenger service, 167–169.

Zeppelin type of, 145–169.

Zodiac type of, 127, 128, 129.

passive:

cabinet for lofty ascents in, 71, 72.

Charles’ passenger, 42, 43.

cruise of, from London to Weilburg, 54.

dragon fire-inflated, 20.

earliest conceptions of, 18, 29.

earliest experiments with, 30, 31, 32.

early history of, 29 et seq.

first coal gas, 54.

first human passengers in, 38.

first hydrogen, 35.

first passengers in, 92, 93.

Demoiselle monoplanes, 324.

DÉperdussin, 339.

Deutsche de la Meurthe, 120 259.

Dew point, 358.

Dientsbach, Carl, vii, 164.

Distance records, 311–314.

Doldrums, 381.

Doubleday, Page & Co., 478.

Drift, defined, 186.

Dubonnet, 312.

Du Cros, Arthur, 131.

Dutrieu, Helene, 321.

Dynamic flyers, 174.

Endurance records, 311–314.

Engine, Daimler, 99, 150, 163.

Gnome, 312.

KÖrting, 139.

Mercedes, 140.

Panhard-Levassor, 136.

RÉnault, 311.

Vivinus, 129.

Engineering News, 435.

English Channel flights, 50–53, 56, 137, 289–292.

English military dirigibles, 130–137.

Eole, 223.

Equator of balloon, 76.

Equilibrium, of angels, 7, 8.

Esnault-PÉlterie, Robert, 304, 314, 337, 340.

EspaÑa, the, 124, 126, 127.

Espy, 419, 420.

Etrich, Igo, 335, 336.

Fabre, 332–335.

Farman, Henri, 259–264, 298, 303, 305, 321.

Maurice, 305, 311.

Federation AËronautique International, 322, 323.

Fequant, Lieutenant, 312.

Ferber, Captain, 256.

Ferrel, W., 356, 376–379, 397, 413, 436.

Fin, 229.

Flesselle, the, 48, 49, 293.

Munn & Co., 481.

Muscular flight, 3–7.

Nadar’s balloon, the Geant, 60.

Nassau, Great Balloon of, 55.

Nature, 217, 427.

Nieuport, 339.

Northcliffe, Lord, 305.

Olieslaegers, Jan, 311.

Orthopters, 174.

Ovid, 3.

Panhard-Levassor, 136.

Parachutes, 176–81.

Parseval dirigibles, 138, 140–143.

Parseval, Major von, 77, 138.

Passive fliers, 174.

Patrie, the, 115, 118, 119, 459–465.

Paulhan, Louis, 284, 293–296, 305, 311, 315, 316, 317, 324, 325.

Peltier, H., 456.

PÉnaud, A., 188.

Pendular stability, 233.

Philadelphia Ledger, the, 313.

Phillips, Horatio, 191, 192, 199.

Picardie military maneuvers, 131.

Pilcher, 216–218, 246.

Polignac, Marquis de, 301.

Porter, Rufus, 86, 87.

Post, Augustus, 6, 75.

Power expended in flight, 6, 7.

Power flyers, 174.

Pressure, critical, 351.

atmospheric, 370–374.

Preussen, the, 70.

Projectile stability, 232.

Propeller, ChauviÈre, 125, 136.

Puy de Dome, 314.

Pylons, 292.

Rayleigh, Lord, 6, 427.

Records, aËroplane,

altitude, 307–309.

cross-country, 311–314.

distance, 311.

duration, 311–314.

load, 311–314.

speed, 314.

Wellman, Walter, 25, 75, 383.

Wenham, 185, 186, 245.

Weyman, 314, 331.

White Wing, the, 266.

Wilkins, 10.

Winans, Ross, 320.

Wind gusts, distribution of, 425, 426.

energy of, 435, 436.

instrumental study of, 427–459.

nature of, 425 et seq.

soaring value of, 426, 427, 439.

sustaining force of, 426.

Winds, ascending trend of, 211.

cause of periodic, 383.

cyclonic, 394 et seq.

diurnal, 392–393.

dry whirl, 420, 421.

fluctuations of, 427–439.

general cause of, 363, 364.

kinds of permanent, 380.

kinds of periodic, 383.

monsoon, 385, 391.

nonperiodic, 394 et seq.

nonvortical, 422 et seq.

permanent and periodic, 376 et seq.

prevailing westerlies, 380, 382, 383.

trade-winds and antitrade, 380, 381.

useful for voyages, 381, 383.

in soaring, 303, 393, 403, 421, 425–439.

Wise, John, 73, 74, 383, 415, 416.

WÖlfert, 99.

World, the New York, 313, 316.

Wright brothers, 245–251, 270–282, 309, 324, 326, 329, 338, [1] With apologies to the California professor who will ride on wings worked by muscular force alone.