SOME RECENT MACHINES.
Professor S. P. Langley, of the Smithsonian Institute, Washington, D.C., made a small flying model in 1896. This, however, only weighed a few pounds; but as it did actually fly and balance itself in the air, the experiment was of great importance, as it demonstrated that it was possible to make a machine with aeroplanes so adjusted as to steer itself automatically in a horizontal direction. In order to arrive at this result, an innumerable number of trials were made, and it was only after months of careful and patient work that the Professor and his assistants succeeded in making the model fly in a horizontal direction without rearing up in front, and then pitching backwards, or plunging while moving forward.
The Wright Brothers of Dayton, Ohio, U.S.A., often referred to as “the mysterious Wrights,” commenced experimental work many years ago. The first few years were devoted to making gliding machines, and it appears that they attained about the same degree of success as many others who were experimenting on the same lines at the same time; but they were not satisfied with mere gliding machines, and so turned their attention in the direction of motors. After some years of experimental work, they applied their motor to one of their large gliding machines, and it is said that with this first machine they actually succeeded in flying short distances. Later on, however, with a more perfect machine, they claim to have made many flights, amongst which I will mention three: 12 miles in 20 minutes, on September 29th, 1905; 20·75 miles in 33 minutes, on October 4th; and 24·2 miles in 38 minutes, on October 5th of the same year. As there seems to be much doubt regarding these alleged flights, we cannot refer to them as facts until the Wright Brothers condescend to show their machine and make a flight in the presence of others; nevertheless, I think we are justified in assuming that they have met with a certain degree of success which may or may not be equal to the achievements of Messrs Farman and De la Grange. It is interesting to note in this connection that all flying machines that have met with any success have been made on the same lines; all have superposed aeroplanes, all have fore and aft horizontal rudders, and all are propelled with screws; and in this respect they do not differ from the large machine that I made at Baldwyn’s Park many years ago. I have seen both the Farman and the De la Grange machines; they seem to be about the same in size and design, and what is true of one is equally true of the other; I will, therefore, only describe the one that seems to have done the best—the De la Grange. The general design of this machine is clearly shown in the illustrations ([Figs. 68] and [69]). The dimensions are as follows: The two main aeroplanes are 32·8 feet long and 4·9 feet wide; the tail or after rudder is made in the form of a Hargrave’s box kite, the top and bottom sides of the box being curved and covered with balloon fabric, thus forming aeroplanes. This box is 9·84 feet long from port to starboard, and 6·56 feet wide in a fore and aft direction. The diameter of the screw is 7·2 feet and it has a mean pitch of 5·7 feet. The screw blades are two in number and are extremely small, being only 6·3 inches wide at the outer end and 3·15 inches at the inner end, their length being 2·1 feet. The space between the fore and aft aeroplanes is 4·9 feet. The total weight is about 1,000 lbs. with one man on board. The speed of this machine through the air is not known with any degree of certainty; it is, however, estimated to be 32 to 40 miles per hour. When the screw is making 1,100 revolutions per minute, the motor is said to develop 50 H.P.
Fig. 68.—The De la Grange machine on the ground and about to make a flight.
Fig. 69.—The De la Grange machine in full flight and very near the ground.
In the following calculations, I have assumed that the machine has the higher speed—40 miles per hour. I have been quite unable to obtain any reliable data regarding the angle at which the aeroplanes are set, but it would appear that the angle is about 1 in 10. The total area of the two main aeroplanes is 321·4 square feet. A certain portion of the lower main aeroplane is cut away, but this is compensated for by the forward horizontal rudder placed in the gap thus formed. The two rear aeroplanes forming the tail of the machine have an area of 128·57 square feet. The area of all the aeroplanes is, therefore, 450 square feet. As the weight of the machine is 1,000 lbs., the lift per square foot is 2·2 lbs. Assuming that the angle of the aeroplanes is 1 in 10, the screw thrust would be 100 lbs., providing, however, that the aeroplanes were perfect and no friction of any kind was encountered. Forty miles per hour is at the rate of 3,520 feet in a minute of time, therefore, 3,520 × 10033,000 = 10·66 H.P. If we allow another 10 H.P. for atmospheric resistance due to the motor, the man, and the framework of the machine, it would require 20·66 H.P. to propel the machine through the air at the rate of 40 miles per hour. If the motor actually develops 50 H.P., 29 H.P. will be consumed in screw slip and overcoming the resistance due to the imperfect shape of the screw. The blades of the De la Grange screw propeller are extremely small, and the waste of energy is, therefore, correspondingly great—their projected area being only 1·6 square feet for both blades. Allowing 200 lbs. for screw thrust, we have the following: 2001·60 = 125 lbs. pressure per square foot on the blades. If we multiply the pitch of the screw in feet by the number of revolutions per minute, we find that if it were travelling in a solid nut it would advance over 70 miles an hour. By the Eiffel tower formula P = 0·003 V², a wind blowing at a velocity of 70 miles per hour produces a pressure of 14·7 lbs. per square foot on a normal plane; therefore, assuming that the projected area of the screw blades is 1·6, we have 1·6 × 14·7 = 23·52 lbs., which is only one-fifth part of what the pressure really is when the screws are making 1,100 turns a minute. It is interesting to note that the ends of the screw blades travel at a velocity of 414 feet per second, which is about one-half the velocity of a cannon ball fired from an old-fashioned smooth bore.
Fig. 70.—Farman’s machine in flight.
A flying machine has, of course, to be steered in two directions at the same time—the vertical and the horizontal. In the Farman and De la Grange machines, the horizontal steering is effected by a small windlass provided with a hand wheel, the same as on a steam launch, and the vertical steering is effected by a longitudinal motion of the shaft of the same windlass. As the length of the machine is not very great, it requires very close attention on the part of the man at the helm to keep it on an even keel; if one is not able to think and act quickly, disaster is certain. On one occasion, the man at the wheel pushed the shaft of the windlass forward when he should have pulled it back, and the result was a plunge and serious damage to the machine; happily no one was injured, though some of the bystanders were said to have had very narrow escapes. The remedy for this is to make all hand-steered machines of great length, which gives more time to think and act; or, still better, to make them automatic by the use of a gyroscope.
Fig. 71.—Bleriot’s machine. This machine raised itself from the ground, but as the centre of gravity was very little, if any, above the centre of lifting effect, it turned completely over in the air.
Fig. 72.—Santos Dumont’s flying machine.
Velocity and Pressure of the Wind.
The pressure varies as the square of the velocity or P ∝ V². The old formula for wind blowing against a normal plane was P = 0·005 × V². The latest or Eiffel Tower formula gives a much smaller value, being P = 0·003 × V², where V represents the velocity in miles per hour, and P the pressure in pounds per square foot.
| Velocity. | Pressure on a Sq. Foot. | Character of the Wind. | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Per Hour. | Per Minute. | Per Second. | |||||||
| Miles. | Feet. | Feet. | Lbs. | ||||||
| 1 | 88 | 1 | ·5 | ·003 | Barely observable. | ||||
| 2 | 176 | 2 | ·9 | ·012 | - | Just perceptible. | |||
| 3 | 264 | 4 | ·4 | ·027 | |||||
| 4 | 352 | 5 | ·9 | ·048 | Light breeze. | ||||
| 5 | 440 | 7 | ·3 | ·075 | - | Gentle, pleasant wind. | |||
| 6 | 528 | 8 | ·8 | ·108 | |||||
| 8 | 704 | 11 | ·7 | ·192 | |||||
| 10 | 880 | 14 | ·7 | ·3 | Fresh breeze. | ||||
| 15 | 1,320 | 22 | ·675 | Brisk breeze. | |||||
| 20 | 1,760 | 29 | ·4 | 1 | ·2 | Stiff breeze. | |||
| 25 | 2,200 | 36 | ·7 | 1 | ·875 | Very brisk breeze. | |||
| 30 | 2,640 | 44 | 2 | ·7 | - | High wind. | |||
| 35 | 3,080 | 51 | ·3 | 3 | ·675 | ||||
| 40 | 3,520 | 58 | ·7 | 4 | ·8 | Very high wind. | |||
| 45 | 3,960 | 66 | 6 | ·075 | Gale. | ||||
| 50 | 4,400 | 73 | ·4 | 7 | ·5 | Storm. | |||
| 60 | 5,280 | 88 | 10 | ·8 | - | Great storm. | |||
| 70 | 6,160 | 102 | ·7 | 14 | ·7 | ||||
| 80 | 7,040 | 117 | ·2 | 19 | ·2 | Hurricane. | |||
| 90 | 7,920 | 132 | 24 | ·3 | - | Tornado. | |||
| 100 | 8,800 | 146 | ·7 | 30 | |||||
| 110 | 9,680 | 161 | ·2 | 36 | ·3 | - | “Washoe zephyrs.”[2] | ||
| 120 | 10,560 | 176 | 43 | ·2 | |||||
| 130 | 11,440 | 191 | 50 | ·7 | |||||
| 140 | 12,320 | 205 | ·3 | 58 | ·8 | ||||
| 150 | 13,200 | 220 | 67 | ·5 | |||||
[2] With apologies to Mark Twain.
Fig. 72a.—Angles and degrees compared. It will be observed that an angle of 1 in 4 is practically 14°.
Table of Equivalent Inclinations.
| Rise. | Sine of Angle. | Angle in Degrees. | |||
|---|---|---|---|---|---|
| 1 | in | 30, | ·0333 | 1 | ·91 |
| 1 | „ | 25, | ·04 | 2 | ·29 |
| 1 | „ | 20, | ·05 | 2 | ·87 |
| 1 | „ | 18, | ·0555 | 3 | ·18 |
| 1 | „ | 16, | ·0625 | 3 | ·58 |
| 1 | „ | 14, | ·0714 | 4 | ·09 |
| 1 | „ | 12, | ·0833 | 4 | ·78 |
| 1 | „ | 10, | ·1 | 5 | ·73 |
| 1 | „ | 9, | ·1111 | 6 | ·38 |
| 1 | „ | 8, | ·125 | 7 | ·18 |
| 1 | „ | 7, | ·143 | 8 | ·22 |
| 1 | „ | 6, | ·1667 | 9 | ·6 |
| 1 | „ | 5, | ·2 | 11 | ·53 |
| 1 | „ | 4, | ·25 | 14 | ·48 |
| 1 | „ | 3, | ·3333 | 19 | ·45 |
Table of Equivalent Velocities.
| Miles per Hour. | Feet per Second. | Feet per Minute. | Metres per Minute. | Metres per Second. | |||
|---|---|---|---|---|---|---|---|
| 1, | 1 | ·5 | 88 | 26 | ·8 | ·447 | |
| 2, | 2 | ·9 | 176 | 53 | ·6 | ·894 | |
| 3, | 4 | ·4 | 264 | 80 | ·5 | 1 | ·341 |
| 4, | 5 | ·9 | 352 | 107 | ·3 | 1 | ·788 |
| 5, | 7 | ·3 | 440 | 134 | ·1 | 2 | ·235 |
| 6, | 8 | ·8 | 528 | 160 | ·9 | 2 | ·682 |
| 8, | 11 | ·7 | 704 | 214 | ·6 | 3 | ·576 |
| 10, | 14 | ·7 | 880 | 268 | ·2 | 4 | ·470 |
| 15, | 22 | 1,320 | 402 | ·3 | 6 | ·705 | |
| 20, | 29 | ·4 | 1,760 | 536 | ·4 | 8 | ·940 |
| 25, | 36 | ·7 | 2,200 | 670 | ·5 | 11 | ·176 |
| 30, | 44 | 2,640 | 804 | ·6 | 13 | ·411 | |
| 35, | 51 | ·3 | 3,080 | 938 | ·8 | 15 | ·646 |
| 40, | 58 | ·7 | 3,520 | 1,072 | ·9 | 17 | ·881 |
| 45, | 66 | 3,960 | 1,207 | 20 | ·116 | ||
| 50, | 73 | ·4 | 4,400 | 1,341 | ·1 | 22 | ·352 |
| 60, | 88 | 5,280 | 1,609 | ·2 | 26 | ·822 | |
| 70, | 102 | ·7 | 6,160 | 1,877 | ·5 | 31 | ·292 |
| 80, | 117 | ·2 | 7,040 | 2,145 | ·8 | 35 | ·763 |
| 90, | 132 | 7,920 | 2,414 | 40 | ·233 | ||
| 100, | 146 | ·7 | 8,800 | 2,682 | ·2 | 44 | ·704 |
| 110, | 161 | ·2 | 9,680 | 2,950 | ·2 | 49 | ·174 |
| 120, | 176 | 10,560 | 3,218 | ·4 | 53 | ·644 | |
| 130, | 191 | 11,440 | 3,486 | ·6 | 58 | ·115 | |
| 140, | 205 | ·3 | 12,320 | 3,755 | ·1 | 62 | ·585 |
| 150, | 220 | 13,200 | 4,023 | ·3 | 67 | ·056 | |
To convert feet per minute into
metres per second, multiply by ·00508.
Table Showing Velocity and Thrust Corresponding with Various Horse-Powers.
| Velocity in Miles per Hour. | Horse-Power. | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | ||||||||||||
| Thrust in Pounds. | ||||||||||||||||||||||
| 1, | 375 | 3,750 | 7,500 | 11,250 | 15,000 | 18,750 | 22,500 | 26,250 | 30,000 | 33,750 | 37,500 | |||||||||||
| 5, | 75 | 750 | 1,500 | 2,250 | 3,000 | 3,750 | 4,500 | 5,250 | 6,000 | 6,750 | 7,500 | |||||||||||
| 10, | 37 | ·5 | 375 | 750 | 1,125 | 1,500 | 1,875 | 2,250 | 2,625 | 3,000 | 3,375 | 3,750 | ||||||||||
| 15, | 25 | 250 | 500 | 750 | 1,000 | 1,250 | 1,500 | 1,750 | 2,000 | 2,250 | 2,500 | |||||||||||
| 20, | 18 | ·8 | 187 | ·5 | 375 | 562 | ·5 | 750 | 937 | ·5 | 1,125 | 1,312 | ·5 | 1,500 | 1,687 | ·5 | 1,875 | |||||
| 25, | 15 | 150 | 300 | 450 | 600 | 750 | 900 | 1,050 | 1,200 | 1,350 | 1,500 | |||||||||||
| 30, | 12 | ·5 | 125 | 250 | 375 | 500 | 625 | 750 | 875 | 1,000 | 1,125 | 1,250 | ||||||||||
| 35, | 10 | ·7 | 107 | ·1 | 214 | ·3 | 321 | ·4 | 428 | ·6 | 535 | ·7 | 642 | ·8 | 750 | 857 | ·1 | 964 | ·3 | 1,071 | ·4 | |
| 40, | 9 | ·4 | 93 | ·8 | 187 | ·5 | 281 | ·3 | 375 | 468 | ·8 | 562 | ·5 | 656 | ·3 | 750 | 843 | ·8 | 937 | ·5 | ||
| 45, | 8 | ·3 | 83 | ·3 | 166 | ·7 | 250 | 333 | ·3 | 416 | ·7 | 500 | 583 | ·3 | 666 | ·7 | 750 | 833 | ·3 | |||
| 50, | 7 | ·5 | 75 | 150 | 225 | 300 | 375 | 450 | 525 | 600 | 675 | 750 | ||||||||||
| 60, | 6 | ·3 | 62 | ·5 | 125 | 187 | ·5 | 250 | 312 | ·5 | 375 | 437 | ·5 | 500 | 562 | ·5 | 625 | |||||
| 70, | 5 | ·4 | 53 | ·6 | 107 | ·1 | 160 | ·7 | 214 | ·3 | 267 | ·9 | 321 | ·4 | 375 | 428 | ·6 | 482 | ·1 | 535 | ·7 | |
| 80, | 4 | ·7 | 46 | ·9 | 93 | ·8 | 140 | ·6 | 187 | ·5 | 234 | ·4 | 281 | ·3 | 328 | ·2 | 375 | 421 | ·9 | 468 | ·8 | |
| 90, | 4 | ·2 | 41 | ·7 | 83 | ·3 | 125 | 166 | ·7 | 208 | ·3 | 250 | 291 | ·7 | 333 | ·3 | 375 | 416 | ·7 | |||
| 100, | 3 | ·75 | 37 | ·5 | 75 | 112 | ·5 | 150 | 187 | ·5 | 225 | 262 | ·5 | 300 | 337 | ·5 | 375 | |||||
Fig. 72b.—When an aeroplane is driven through the air, it encounters stationary air and leaves it with a downward trend. With a thick curved aeroplane, as shown, the air follows both the top and the bottom surfaces, and the direction that the air takes is the resultant of these two streams of air. It will be seen that the air takes the same direction that it would take if the plane were flat, and raised from a to c, which would be substantially the same as shown at f, h, g. It has, however, been found by actual experiment that the curved plane is preferable, because the lifting effect is more evenly distributed, and the drift is less in proportion to the lift.
Fig. 72c.—Aeroplanes experimented with by Mr. Horatio Philipps. In the published account which is before me, the angles at which these planes were placed are not given, but, by comparing the lift with the drift, we may assume that it was about 1 in 10.
Fig. 5 seems to have been the best shape, and I find that this plane would have given a lifting effect of 2·2 lbs. per square foot at a velocity of 40 miles per hour.
Philipps’ Experiments.
| Description of Form. | Speed of Air Current. | Dimensions of Aeroplanes. | Lift. | Drift. | Lift divided by Drift. | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Feet per sec. | Miles per hour. | Whole Plane. Ozs. | Lbs. per sq. ft. | Whole Plane. Ozs. | Lbs. per sq. ft. | ||||||
| Plane surfaces, | 39 | 26·59 | 16" × 5" | 9 | 1 | ·013 | 2 | 0·225 | 4 | ·5 | |
| Fig. 1, | 60 | 40·91 | 16" × 1·25" | 9 | 4 | ·05 | 0 | ·87 | 0·392 | 10 | ·3 |
| F„g 2, | 48 | 32·73 | 16" × 3" | 9 | 1 | ·688 | 0 | ·87 | 0·163 | 10 | ·3 |
| F„g 3, | 44 | 30 | 16" × 3" | 9 | 1 | ·688 | 0 | ·87 | 0·163 | 10 | ·3 |
| F„g 4, | 44 | 30 | 16" × 5" | 9 | 1 | ·013 | 0 | ·87 | 0·098 | 10 | ·3 |
| F„g 5, | 39 | 26·59 | 16" × 5" | 9 | 1 | ·013 | 0 | ·87 | 0·098 | 10 | ·3 |
| F„g 6, | 27 | 18·41 | 16" × 5" | 9 | 1 | ·013 | 2 | ·25 | 0·253 | 4 | |
| Rook’s wing, | 39 | 26·59 | Area sq. ft. 0·5 | 8 | 1 | ·0 | 1 | ·0 | 0·125 | 8 | |
CHAPTER VIII.
BALLOONS.
As far as the actual navigation of the air is concerned, balloonists have had everything to themselves until quite recently, but we find that at the present moment, experimenters are dividing their attention about equally between balloons or machines lighter than the air, and true flying machines or machines heavier than the air. In all Nature, we do not find any bird or insect that does not fly by dynamic energy alone, and I do not believe that the time is far distant when those now advocating machines lighter than the air, will join the party advocating machines heavier than the air, and, eventually, balloons will be abandoned altogether. No matter from what standpoint we examine the subject, the balloon is unsuitable for the service, and it is not susceptible of much improvement. On the other hand, the flying machine is susceptible of a good deal of improvement; there is plenty of scope for the employment of a great deal of skill, both mechanical and scientific, for a good many years to come.
I do not know that I can express myself better now than I did when I wrote an article for the Engineering Supplement of the Times, from which I quote the following:—
“The result of recent experiments must have convinced every thinking man that the day of the balloon is past. A balloon, from the very nature of things, must be extremely bulky and fragile.
“It has always appeared to the writer that it would be absolutely impossible to make a dirigible balloon that would be of any use, even in a comparatively light wind. Experiments have shown that only a few hundred feet above the surface of the earth, the air is nearly always moving at a velocity of at least 15 miles an hour, and more than two-thirds of the time at a velocity considerably greater than this. In order to give a balloon sufficient lifting power to carry two men and a powerful engine, it is necessary that it should be of enormous bulk. Considered as a whole, including men and engine, it must have a mean density less than the surrounding air, otherwise it will not rise. Therefore, not only is a very large surface exposed to the wind, but the whole thing is so extremely light and fragile as to be completely at the mercy of wind and weather. Take that triumph of engineering skill, the ‘Nulli Secundus,’ for example. The gas-bag, which was sausage-shaped and 30 feet in diameter, was a beautiful piece of workmanship, the whole thing being built up of goldbeater’s skin. The cost of this wonderful gas-bag must have been enormous. The whole construction, including the car, the system of suspension, the engine and propellers, had been well thought out and the work beautifully executed; still, under these most favourable conditions, only a slight shower of rain was sufficient to neutralise its lifting effect completely—that is, the gas-bag and the cordage about this so-called airship absorbed about 400 lbs. of water, and this was found to be more than sufficient to neutralise completely the lifting effect. A slight squall which followed entirely wrecked the whole thing, and it was ignominiously carted back to the point of departure.
“We now learn that the War Office is soon to produce another airship similar to the ‘Nulli Secundus,’ but with a much greater capacity and a stronger engine. In the newspaper accounts it is said that the gas-bag of this new balloon would be sausage-shaped and 42 feet in diameter, that it is to be provided with an engine of 100 horse-power, which it is claimed will give to this new production a speed of 40 miles an hour through the air, so that, with a wind of 20 miles an hour, it will still be able to travel by land 20 miles an hour against the wind. Probably the writer of the article did not consider the subject from a mathematical point of view. As the mathematical equation is an extremely simple one, it is easily presented so as to be understood by any one having the least smattering of mathematical or engineering knowledge. The cylindrical portion of the gas-bag is to be 42 feet in diameter; the area of the cross-section would therefore be 1,385 feet. If we take a disc 42 feet in diameter and erect it high in the air above a level plain, and allow a wind of 40 miles an hour, which is the proposed speed of the balloon, to blow against it, we should find that the air pressure would be 11,083 lbs.—that is, a wind blowing at a velocity of 40 miles an hour would produce a pressure of 8 lbs. to every square foot of the disc.[3] Conversely, if the air were stationary, it would require a push of 11,083 lbs. to drive this disc through the air at the rate of 40 miles an hour.
[3] Haswell gives the pressure of the wind at 40 miles an hour as 8 lbs. per square foot, and this is said to have been verified by the United States Coast Survey. Molesworth makes it slightly less; but the new formula, according to most recent experiments (Dr. Stanton’s experiments at the National Physical Laboratory and M. Eiffel’s at Eiffel Tower), is P = 0·003 V², which would make the pressure only 4·8 lbs. per square foot, and which would reduce the total H.P. required from 472 to 283, where P represents pounds per square foot and V miles per hour.
“A speed of 40 miles an hour is at the rate of 3,520 feet in a minute of time. We therefore have two factors—the pounds of resistance encountered, and the distance through which the disc travels in one minute of time. By multiplying the total pounds of pressure on the complete disc by the number of feet it has to travel in one minute of time, we have the total number of foot-pounds required in a minute of time to drive a disc 42 feet in diameter through the air at a speed of 40 miles an hour. Dividing the product by the conventional horse-power 33,000, we shall have 1,181 horse-power as the energy required to propel the disc through the air. However, the end of the gas-bag is not a flat disc, but a hemisphere, and the resistance to drive a hemisphere through the air is much less than it would be with a normal plane or flat disc. In the ‘Nulli Secundus’ we may take the coefficient of resistance of the machine, considered as a whole, as 0·20—that is, that the resistance will be one-fifth as much as that of a flat disc. This, of course, includes not only the resistance of the balloon itself, but also that of the cordage, the car, the engine, and the men.
“Multiplying 1,181 by the coefficient ·20, we shall have 236; therefore, if the new balloon were attached to a long steel wire and drawn by a locomotive through the air, the amount of work or energy required would be 236 horse-power—that is, if the gas-bag would stand being driven through the air at the rate of 40 miles an hour, which is extremely doubtful. Under these conditions, the driving wheels of the locomotive would not slip, and therefore no waste of power would result, but in the dirigible balloon we have a totally different state of affairs. The propelling screws are very small in proportion to the airship, and their slip is fully 50 per cent.—that is, in order to drive the ship at the rate of 40 miles an hour, the screws would have to travel at least 80 miles an hour. Therefore, while 236 horse-power was imparted to the ship in driving it forward, an equal amount would have to be lost in slip, or, in other words, in driving the air rearwards. It would, therefore, require 472 horse-power instead of 100 to drive the proposed new balloon through the air at the rate of 40 miles an hour.
“It will be seen from this calculation that the new airship will still be at the mercy of the wind and weather. Those who pin their faith on the balloon as the only means of navigating the air may dispute my figures. However, all the factors in the equation are extremely simple and well known, and no one can dispute any of them except the assumed coefficient of resistance, which is given here as ·20. The writer feels quite sure that, after careful experiments are made, it will be found that this coefficient is nearer ·40 than ·20, especially so at high speeds when the air pressure deforms the gas-bag. Only a slight bagging in the front end of the balloon would run the coefficient up to fully ·50, and perhaps even more.”—Times, Feb. 26, 1908.
Fig. 73.—The enormous balloon, “Ville de Paris,” of the French Government. This balloon is a beautiful piece of workmanship, and is said to be the most practical balloon ever invented, not excepting the balloon of Count Zeppelin. Some idea of its size may be obtained by comparing it with the size of the men who are standing immediately underneath.
Since writing the Times article, a considerable degree of success has been attained by Count Zeppelin. According to newspaper accounts, his machine has a diameter of about 40 feet, and a length of no less than 400 feet. It appears that this balloon consists of a very light aluminium envelope, which is used in order to produce a smooth and even surface, give rigidity, and take the place of the network employed in ordinary balloons. It seems that the gas is carried in a large number of bags fitted in the interior of this aluminium envelope. However, by getting a firm and smooth exterior and by making his apparatus of very great length as relates to its diameter, he has obtained a lower coefficient of resistance than has ever been obtained before, and as his balloon is of great volume, he is able to carry powerful motors and use screw propellers of large diameter. It appears that he has made a circuit of considerable distance, and returned to the point of departure without any accident. A great deal of credit is, therefore, due to him. His two first balloons came to grief very quickly; he was not discouraged, but stuck to the job with true Teutonic grit, and has perhaps attained a higher degree of success than has ever been attained with a balloon. However, some claim that the French Government balloon, “La Patrie” is superior to the Zeppelin balloon at all points. When we take into consideration the fact that the Zeppelin machine is 400 feet long and lighter than the same volume of air, it becomes only too obvious that such a bulky and extremely delicate and fragile affair will easily be destroyed. Of course ascensions will only be made in very favourable weather, but squalls and sudden gusts of wind are liable to occur. It is always possible to start out in fine weather if one waits long enough, but if a flight of 24 hours or even 12 hours is to be attempted, the wind may be blowing very briskly when we return, and an ordinary wind will not only prevent the housing of Count Zeppelin’s balloon, but will be extremely liable to reduce it to a complete wreck in a few minutes.[4]
[4] Shortly after this was written, the Zeppelin machine was completely demolished by a gust of wind.
I am still strongly of the opinion that the ultimate mastery of the air must be accomplished by machines heavier than the air.