It is only a matter of fairness to state that, under favorable conditions, some very creditable records have been made with modern balloons, viz:
November 23d, 1907, the French dirigible Patrie, travelled 187 miles in 6 hours and 45 minutes against a light wind. This was a little over 28 miles an hour.
The Clement-Bayard, another French machine, sold to the Russian government, made a trip of 125 miles at a rate of 27 miles an hour.
Zeppelin No. 3, carrying eight pa.s.sengers, and having a total lifting capacity of 5,500 pounds of ballast in addition to pa.s.sengers, weight of equipment, etc., was tested in October, 1906, and made 67 miles in 2 hours and 17 minutes, about 30 miles an hour.
These are the best balloon trips on record, and show forcefully the limitations of speed, the greatest being not over 30 miles an hour.
Speed of Flying Machines.
Opposed to the balloon performances we have flying machine trips (of authentic records) as follows:
Bleriot--monoplane--in 1908--52 miles an hour.
Delagrange--June 22, 1908--10 1/2 miles in 16 minutes, approximately 42 miles an hour.
Wrights--October, 1905--the machine was then in its infancy--24 miles in 38 minutes, approximately 44 miles an hour. On December 31, 1908, the Wrights made 77 miles in 2 hours and 20 minutes.
Lambert, a pupil of the Wrights, and using a Wright biplane, on October 18, 1909, covered 29.82 miles in 49 minutes and 39 seconds, being at the rate of 36 miles an hour. This flight was made at a height of 1,312 feet.
Latham--October 21, 1909--made a short flight, about 11 minutes, in the teeth of a 40 mile gale, at Blackpool, Eng. He used an Antoniette monoplane, and the official report says: "This exhibition of nerve, daring and ability is unparalled in the history of aviation."
Farman--October 20, 1909--was in the air for 1 hour, 32 min., 16 seconds, travelling 47 miles, 1,184 yards, a duration record for England.
Paulhan--January 18, 1901--47 1/2 miles at the rate of 45 miles an hour, maintaining an alt.i.tude of from 1,000 to 2,000 feet.
Expense of Producing Gas.
Gas is indispensable in the operation of dirigible balloons, and gas is expensive. Besides this it is not always possible to obtain it in sufficient quant.i.ties even in large cities, as the supply on hand is generally needed for regular customers. Such as can be had is either water or coal gas, neither of which is as efficient in lifting power as hydrogen.
Hydrogen is the lightest and consequently the most buoyant of all known gases. It is secured commercially by treating zinc or iron with dilute sulphuric or hydrochloric acid. The average cost may be safely placed at $10 per 1,000 feet so that, to inflate a balloon of the size of the Zeppelin, holding 460,000 cubic feet, would cost $4,600.
Proportions of Materials Required.
In making hydrogen gas it is customary to allow 20 per cent for loss between the generation and the introduction of the gas into the balloon.
Thus, while the formula calls for iron 28 times heavier than the weight of the hydrogen required, and acid 49 times heavier, the real quant.i.ties are 20 per cent greater. Hydrogen weighs about 0.09 ounce to the cubic foot. Consequently if we need say 450,000 cubic feet of gas we must have 2,531.25 pounds in weight. To produce this, allowing for the 20 percent loss, we must have 35 times its weight in iron, or over 44 tons. Of acid it would take 60 times the weight of the gas, or nearly 76 tons.
In Time of Emergency.
These figures are appalling, and under ordinary conditions would be prohibitive, but there are times when the balloon operator, unable to obtain water or coal gas, must foot the bills. In military maneuvers, where the field of operation is fixed, it is possible to furnish supplies of hydrogen gas in portable cylinders, but on long trips where sudden leakage or other cause makes descent in an unexpected spot unavoidable, it becomes a question of making your own hydrogen gas or deserting the balloon. And when this occurs the balloonist is up against another serious proposition--can he find the necessary zinc or iron? Can he get the acid?
Balloons for Commercial Use.
Despite all this the balloon has its uses. If there is to be such a thing as aerial navigation in a commercial way--the carrying of freight and pa.s.sengers--it will come through the employment of such monster balloons as Count Zeppelin is building. But even then the carrying capacity must of necessity be limited. The latest Zeppelin creation, a monster in size, is 450 feet long, and 42 1/2 feet in diameter. The dimensions are such as to make all other balloons look like pigmies; even many ocean-going steamers are much smaller, and yet its pa.s.senger capacity is very small. On its 36-hour flight in May, 1909, the Zeppelin, carried only eight pa.s.sengers. The speed, however, was quite respectable, 850 miles being covered in the 36 hours, a trifle over 23 miles an hour. The reserve buoyancy, that is the total lifting capacity aside from the weight of the airship and its equipment, is estimated at three tons.
CHAPTER XXII. PROBLEMS OF AERIAL FLIGHT.
In a lecture before the Royal Society of Arts, reported in Engineering, F. W. Lanchester took the position that practical flight was not the abstract question which some apparently considered it to be, but a problem in locomotive engineering. The flying machine was a locomotive appliance, designed not merely to lift a weight, but to transport it elsewhere, a fact which should be sufficiently obvious. Nevertheless one of the leading scientific men of the day advocated a type in which this, the main function of the flying machine, was overlooked. When the machine was considered as a method of transport, the vertical screw type, or helicopter, became at once ridiculous. It had, nevertheless, many advocates who had some vague and ill-defined notion of subsequent motion through the air after the weight was raised.
Helicopter Type Useless.
When efficiency of transport was demanded, the helicopter type was entirely out of court. Almost all of its advocates neglected the effect of the motion of the machine through the air on the efficiency of the vertical screws. They either a.s.sumed that the motion was so slow as not to matter, or that a patch of still air accompanied the machine in its flight. Only one form of this type had any possibility of success. In this there were two screws running on inclined axles--one on each side of the weight to be lifted. The action of such inclined screw was curious, and in a previous lecture he had pointed out that it was almost exactly the same as that of a bird"s wing. In high-speed racing craft such inclined screws were of necessity often used, but it was at a sacrifice of their efficiency. In any case the efficiency of the inclined-screw helicopter could not compare with that of an aeroplane, and that type might be dismissed from consideration so soon as efficiency became the ruling factor of the design.
Must Compete With Locomotive.
To justify itself the aeroplane must compete, in some regard or other, with other locomotive appliances, performing one or more of the purposes of locomotion more efficiently than existing systems. It would be no use unless able to stem air currents, so that its velocity must be greater than that of the worst winds liable to be encountered. To ill.u.s.trate the limitations imposed on the motion of an aeroplane by wind velocity, Mr.
Lanchester gave the diagrams shown in Figs. 1 to 4. The circle in each case was, he said, described with a radius equal to the speed of the aeroplane in still air, from a center placed "down-wind" from the aeroplane by an amount equal to the velocity of the wind.
Fig. 1 therefore represented the case in which the air was still, and in this case the aeroplane represented by _A_ had perfect liberty of movement in any direction
In Fig. 2 the velocity of the wind was half that of the aeroplane, and the latter could still navigate in any direction, but its speed against the wind was only one-third of its speed with the wind.
In Fig. 3 the velocity of the wind was equal to that of the aeroplane, and then motion against the wind was impossible; but it could move to any point of the circle, but not to any point lying to the left of the tangent _A_ _B_. Finally, when the wind had a greater speed than the aeroplane, as in Fig. 4, the machine could move only in directions limited by the tangents _A_ _C_ and _A_ _D_.
Matter of Fuel Consumption.
Taking the case in which the wind had a speed equal to half that of the aeroplane, Mr. Lanchester said that for a given journey out and home, down wind and back, the aeroplane would require 30 per cent more fuel than if the trip were made in still air; while if the journey was made at right angles to the direction of the wind the fuel needed would be 15 per cent more than in a calm. This 30 per cent extra was quite a heavy enough addition to the fuel; and to secure even this figure it was necessary that the aeroplane should have a speed of twice that of the maximum wind in which it was desired to operate the machine. Again, as stated in the last lecture, to insure the automatic stability of the machine it was necessary that the aeroplane speed should be largely in excess of that of the gusts of wind liable to be encountered.
Eccentricities of the Wind.
There was, Mr. Lanchester said, a loose connection between the average velocity of the wind and the maximum speed of the gusts. When the average speed of the wind was 40 miles per hour, that of the gusts might be equal or more. At one moment there might be a calm or the direction of the wind even reversed, followed, the next moment, by a violent gust.
About the same minimum speed was desirable for security against gusts as was demanded by other considerations. Sixty miles an hour was the least figure desirable in an aeroplane, and this should be exceeded as much as possible. Actually, the Wright machine had a speed of 38 miles per hour, while Farman"s Voisin machine flew at 45 miles per hour.
Both machines were extremely sensitive to high winds, and the speaker, in spite of newspaper reports to the contrary, had never seen either flown in more than a gentle breeze. The damping out of the oscillations of the flight path, discussed in the last lecture, increased with the fourth power of the natural velocity of flight, and rapid damping formed the easiest, and sometimes the only, defense against dangerous oscillations. A machine just stable at 35 miles per hour would have reasonably rapid damping if its speed were increased to 60 miles per hour.
Thinks Use Is Limited.
It was, the lecturer proceeded, inconceivable that any very extended use should be made of the aeroplane unless the speed was much greater than that of the motor car. It might in special cases be of service, apart from this increase of speed, as in the exploration of countries dest.i.tute of roads, but it would have no general utility. With an automobile averaging 25 to 35 miles per hour, almost any part of Europe, Russia excepted, was attainable in a day"s journey. A flying machine of but equal speed would have no advantages, but if the speed could be raised to 90 or 100 miles per hour, the whole continent of Europe would become a playground, every part being within a daylight flight of Berlin. Further, some marine craft now had speeds of 40 miles per hour, and efficiently to follow up and report movements of such vessels an aeroplane should travel at 60 miles per hour at least. Hence from all points of view appeared the imperative desirability of very high velocities of flight. The difficulties of achievement were, however, great.
Weight of Lightest Motors.
As shown in the first lecture of his course, the resistance to motion was nearly independent of the velocity, so that the total work done in transporting a given weight was nearly constant. Hence the question of fuel economy was not a bar to high velocities of flight, though should these become excessive, the body resistance might const.i.tute a large proportion of the total. The horsepower required varied as the velocity, so the factor governing the maximum velocity of flight was the horsepower that could be developed on a given weight. At present the weight per horsepower of feather-weight motors appeared to range from 2 1/4 pounds up to 7 pounds per brake horsepower, some actual figures being as follows:
Antoinette........ 5 lbs.
Fiat.............. 3 lbs.
Gnome....... Under 3 lbs.
Metallurgic....... 8 lbs.
Renault........... 7 lbs.
Wright.............6 lbs.
Automobile engines, on the other hand, commonly weighed 12 pounds to 13 pounds per brake horsepower.
For short flights fuel economy was of less importance than a saving in the weight of the engine. For long flights, however, the case was different. Thus, if the gasolene consumption was 1/2 pound per horsepower hour, and the engine weighed 3 pounds per brake horsepower, the fuel needed for a six-hour flight would weigh as much as the engine, but for half an hour"s flight its weight would be unimportant.
Best Means of Propulsion.