Mechanics: The Science of Machinery

by A. Russell Bond

THREE TYPES OF DIRIGIBLES

There are three types of dirigible airships; the flexible, the semirigid, and the rigid. In the flexible type, as we have observed, the envelope must be kept tightly filled in order to hold its shape when driven against the air. The car is suspended from the gas bag. In the semirigid type a rigid frame or backbone serves as a keel for the gasbag and helps to prevent it from crumpling up. In the rigid type a casing incloses the gas or rather bags; for the gas Is contained in a number of separate bags fitted into separate compartments. The casing is composed of a framework of duralumin, which is an alloy of aluminum, with a percentage of copper and nickel. It weighs but little more than aluminum, but is five times as strong. Over the duralumin framework is stretched a sheathing of rubberized fabric. Because of the weight of this casing rigid dirigibles must be made in large size.

ACROSS THE ATLANTIC IN A DIRIGIBLE

Before the war large Zeppelins were built that were fitted with luxurious cabins and dining rooms and made regular scheduled voyages. The big British dirigibles are of the Zeppelin type. The R-34, was 672 feet long and 79 feet in diameter. It was fitted with nineteen gas bags and had a total capacity of over two million cubic feet of hydrogen. It was driven by five engines, each developing from 250 to 275 horsepower, and was capable of making from 50 to 75 miles per hour, depending upon whether or not the engines were pushed. The big dirigible left the Royal Naval Air Station, near Edinburgh, on the 2d of July, 1919, and landed at the Roosevelt Field near Mineola on the 6th, having made the trip in four days and two hours. The course covered about 3,100 sea miles, but the actual air mileage was about 6,300 miles because head winds were encountered. In aeronautic voyages it is the distance through the air that must be reckoned rather than the distance over the ground or sea. An airship may be traveling at the rate of 50 miles per hour through the air, but if there is a wind of 30 miles per hour blowing against the course of the dirigible, the latter will be making only 20 miles per hour over the ground, or if the wind is blowing with the airship it will be making 80 miles per hour over the ground. Because of the head winds the transatlantic flight of the R-34 was so much longer than had been anticipated that its stores of fuel were almost completely exhausted. And yet, when the airship started out from Edinburgh, it carried 81 tanks of gasoline, each containing nearly 70 gallons, or a total of 4,900 gallons. This fuel weighed nearly 16 tons. Almost a ton of oil and 3 tons of water added to the load and the baggage and crew amounted to 4 tons more. The total weight carried was over 24 tons and the dirigible fully loaded weighed altogether about 60 tons. When the dirigible started out it had to fly low, but as the fuel was consumed it grew lighter and rose higher. The surplus hydrogen had to be pumped into steel tanks where, owing to its compression, it was heavy and served as ballast which could at any time be fed back into the gas bags to increase the buoyancy of the airship. We can no longer think of air as having no weight when we consider that all this tonnage was supported by air.

The R-34 was by no means the largest dirigible built, but we dare not boast of the size of the airships of to-day when the aeronautics is in its in-fancy, because our present dirigibles may seem puny alongside the big aircraft that may be built to-morrow. The dimensions of the R-34 have been given because of the historic interest in this first dirigible to span the Atlantic Ocean.

HEAVIER-THAN-AIR MACHINES

Marvelous as was the achievement of the Montgolfiers and wonderful as were the aeronautic developments that followed the invention of the balloon, the dominion of the birds was not really conquered until man had learned how to fly in a machine heavier than the air. Captive aeroplanes date back to the remote ages of ancient history. Kites are really “heavier-than-air machines.” They maintain themselves in the air because they travel through the air at a considerable velocity. True, a kite may be stationary, or practically so with respect to the ground, but if we detach ourselves from the ground and view the situation from a drifting balloon, the earth will appear to be moving under us and the kite will rush past us as it is dragged by the earth to which it is tied. The idea of propelling a kite through the air, not by tying it to the earth, but by furnishing it with its own propeller and power plant, was conceived long ago, but the problem was to find a power plant light enough. The honor of being the first man to rise off the ground in an aeroplane belongs to C. Ader, who made several short flights between 1890 and 1896 in a machine driven by a twenty-horsepower steam engine. Our own S. P. Langley did some most important pioneer work in flying and built a man-lifting, steam-driven machine in 1903 which would have flown had it not been for an accident to its launching gear. In fact, this very model was flown successfully a number of years later. However, it was not until the gasoline engine was developed that the power plant problem was solved. The internal-combustion motor was made more and more powerful in proportion to its weight until now there are several types that weigh less than two pounds per horsepower.

But the power plant was only one obstacle to be overcome. The real problem was to learn how to control the machine after it rose into the air. Otto Lilienthal attempted to learn how to fly in a motorless flying machine. He provided himself with wings and, jumping off a height or running down a slope, depended upon gravity to furnish him with the necessary propulsion through the air. Unfortunately after five years of gliding experiments a fatal accident terminated his aeronautic research.

THE WRIGHT BROTHERS

In this country the Wright brothers, Orville and Wilbur, took up the work of Lilienthal and they, too, undertook to learn to fly before they built a flying machine. In all his years of experiment, Lilienthal did not have more than five hours of experience in the air. The Wright brothers determined to spend more time in the air and less in theoretical speculations at home, so they built a gliding machine that would sustain a man at a speed of eighteen miles per hour and picked out a spot on the Atlantic coast where they were assured of fairly constant winds of sixteen to twenty-five miles per hour. At first the machine was used as a kite and various experiments were made in balancing it. Then short gliding flights were made from the tops of the sand dunes. Not until the art of balancing the glider and controlling it in unsteady air currents was any attempt made at building a motor-driven flying machine. It was by these experiments that the Wright brothers discovered the system of warping the wings so as to preserve the lateral balance of the machine. After several seasons of experimental gliding, and not until they felt that they had learned how to fly, was a power machine built. This made its first flight on December 17, 1903. The first flight lasted only twelve seconds, while the fourth flight lasted fifty-nine seconds. Many months were spent in perfecting the machine and in solving the various problems of flight, and not until September, 1905, did the Wright brothers feel that they had mastered the art of flying. After that three years elapsed before the world was actually convinced of the reality of airplane flight and recognized the work of the pioneers.