An Encyclopedia of the History of Technology part 65 potx

PART THREE: TRANSPORT 622 Lilienthal’s activities inspired the American railway engineer Octave Chanute to make a number of hang-gliders in 1896. Chanute was an enthusiast who had collected a great deal of information on earlier theories and experiments, which he summarized in a seminal work, Progress in Flying Machines, published in 1894; his practical experiments were therefore founded on a firm basis of knowledge and engineering experience. The most significant machine was a biplane hang- glider with a cruciform stabilizing tail unit, which was successfully and regularly flown on the shores of Lake Michigan by Chanute’s assistant A. M.Herring. Herring attempted to develop a power unit for a version of this machine, and claimed to have made two short hops (with an engine driven from a compressed gas supply sufficient for 15 seconds’ running) in October 1898. THE WRIGHT BROTHERS Wilbur and Orville Wright of Dayton, Ohio, were directly inspired by reading about Lilienthal’s gliding activities. They were the first seriously to consider the problem of controlling a flying machine. Earlier experimenters had, explicitly or implicitly, considered the flying machine as a stable vehicle to be steered in the desired direction. The Wrights recognized that a machine moving in three dimensions in a turbulent atmosphere would need more dynamic control by its pilot. Their solution was a biplane wing structure with a wire-braced truss structure. The central part was rigid, but the outer parts could be twisted under the pilot’s control. The tip section on one side was inclined at a greater angle to the airflow, thus lifting that wing; the other tip was twisted in opposition to lower it; and the wing thereby banked. This inclined the lift vector and thus turned the aircraft. At first they used a fixed vertical fin at the rear of the aircraft like the flights of an arrow to stabilize the aircraft; then converted this into a rudder act ing simultaneously with the wing twist; and finally separated the two controls to allow the pilot freedom to sideslip if he wished. For control in pitch, the Wrights used an auxiliary aerofoil ahead of the wings, directly operated by the pilot. (They followed their predecessors in assuming that control about the pitching axis—vertical motion of the aircraft — was essentially independent of the control about the rolling and yawing axes — horizontal motion. The theoretical explanation of this fact was given by the Welsh mathematician G.H.Bryan in 1904, but it is doubtful that any of the pioneer aviators were aware of this until several years later, by which time it was recognized as an empirical truth.) The Wrights started experimenting with gliders in 1899, and applied for a patent in March 1903 on their configuration and on the basic concept of twisting (or warping) the wing for control in roll, which was granted in 1906. They also built their first powered machine, using a light four-cylinder petrol engine which AERONAUTICS 623 they designed and constructed themselves (having failed to find a commercial supplier able to meet their requirements). The engine drove a pair of rear- mounted wooden propellers: not the least of their practical achievements was to design more efficient propellers than any previously used, by a combination of inspired theoretical assumptions and experimental research. The first ‘Flyer’, as they called it, was flown successfully on 17 December 1903 (Figure 12.4). The four flights made that day are now recognized as the first controlled powered man-carrying flights in history—although the longest lasted less than a minute. The first Flyer was wrecked by a gust of wind shortly after its fourth landing, and the events of that day are important only because the Wrights went on to perfect their design in 1904 and 1905. Their second and third Flyers retained the same configuration, but by altering the location and relative sizes of the control surfaces they improved the controllability. The first machine was so unstable in pitch that it was almost uncontrollable, but by October 1905, after about 120 experimental flights (mainly very short), they were able to fly for over half an hour under perfect control. They still eschewed stability, believing that they could only maintain adequate control in turbulent air by deliberately aiming for an unstable aircraft; in this they were undoubtedly influenced by their experience as bicycle riders and manufacturers. The Wrights’ successful development of a practical flying machine was, surprisingly, largely unpublicized, and they ceased flying after mid-October Figure 12.4: Orville Wright made the world’s first powered flight with a heavier- than-air machine on 17 December 1903 near the Kill Devil Hill in North Carolina. PART THREE: TRANSPORT 624 1905 to avoid risking premature disclosure which might invalidate their patent application. After the patent was granted, they spent two years negotiating with various governments and commercial syndicates for the exploitation of their invention, and only resumed flying in 1908. They practised for a week in secret in May to renew their piloting skills, and then started flying in public— first in France in August 1908 and then near Washington, USA, in September. These flights demonstrated their total pre-eminence in the art of flying, and firmly established their claim to priority. EUROPEAN PIONEERS By this time other reasonably practical aeroplanes were in existence, or imminent. The development of reasonably light petrol engines for motorcars and boats, especially in France, provided the power source which the nineteenth-century aviators had lacked. Spurred by news or rumours of the Wrights’ activities, a number of Europeans had been experimenting since 1904. Their machines employed a variety of configurations, but the first one to achieve a realistic flight was the biplane built by the Voisin brothers in France for Henri Farman. In November 1907 he flew this for over a minute, and on 13 January 1908 won a prize of 50,000 francs for an officially observed closed circuit flight of just over 1km in 1 1\2 minutes. Farman’s machine was superficially not dissimilar to the Wrights’ configuration, with biplane wings and forward elevator, but the large tail surfaces were mainly fixed stabilizing surfaces with a limited rudder. The machine was deliberately designed to be as stable as possible, and there was no roll control at all. During the next few months the Voisins built several similar machines for other pilots, and Farman modified his aircraft: in these, vertical fin surfaces (called side-curtains) were added between the wing struts, and the stabilizing tail surfaces somewhat reduced. By September 1908 the modified Voisin-Farman was capable of long flights of up to 45 minutes’ duration, and after fitting ailerons to obtain roll- control (as a substitute for the Wrights’ wing-warping), Farman made the world’s first cross-country flight from Bouy to Reims (27km (18 miles)) in 20 minutes, on 30 October 1908. Subsequent developments effectively brought the Wright and Voisin-Farman configurations closer together, the Wrights moving towards more stable designs and other designers following Farman towards more effective controls. By mid-1909 the so-called box-kite design (which retained this nickname although the side-curtains which had suggested the soubriquet were soon discarded) had become dominant—biplane wings with ailerons on the outer trailing edges, a forward elevator, and a rear stabilizing tail unit incorporating elevator and rudder surfaces, powered by a petrol engine of around 37.3kW (50hp) driving a directly-coupled pusher propeller. The ‘fuselage’ of these AERONAUTICS 625 machines was a boxgirder, usually totally uncovered, and the basic structural materials were wood, fabric and steel wire. Among the wide variety of configurations tried by other would-be aviators, another practical shape emerged: the tractor monoplane. The first successful machines of this type were the Antoinettes designed by Frenchman Léon Levavasseur, but the most famous example of the breed was the machine in which Louis Blériot made the first flight across the English Channel on 25 July 1909 (Figure 12.5). This had a monoplane wing of wood and fabric, wire- braced to a steel frame structure above the fuselage. The fuselage itself was a simple uncovered wooden box structure with internal wire bracing, carrying a vertical rudder and a fixed horizontal tailplane at the rear end. The outer third of the tailplane was hinged to operate as the elevator for control in pitch. On the front of the fuselage was a sturdy well-sprung undercarriage with wire wheels, and the 18.6kW (25hp) three-cylinder Anzani engine driving a two- bladed wooden airscrew. This was Blériot’s famous ‘Type XI’, designed by Raymond Saulnier, which was built in very large numbers for several years, with increasing engine power Figure 12.5: Louis Blériot standing on the seat of his Type XI aircraft, in which he flew the English Channel on 25 July 1909. The 3-cylinder Anzani engine and wooden Chauvière propeller are well shown in this picture, but the top bracing wires are less clear. PART THREE: TRANSPORT 626 and stronger structure. It inspired numerous imitations, but monoplanes in general acquired a poor reputation as a result of various accidents which led to an official (but temporary) ban by the British War Office in September 1912, and somewhat similar lack of faith on the part of some military organizations. Insofar as there was any common basis for these accidents, they seem to have arisen from a lack of knowledge about the distribution of loads on the wing, and a tendency to overstress the structure by excessively tightening the wing bracing. The third standard type of aircraft was the tractor biplane, which eventually supplanted the pusher ‘box-kite’ and numerically dominated the world’s skies up to about 1940. The first of these was the otherwise insignificant Goupy II biplane, built in the Blériot factory in March 1909; more significant was the Breguet I of July 1909, because the manufacturer continued in business for many years and his later machines introduced metal structure for the wings (covered in fabric) and fuselage (covered with aluminium sheet). The classic type of tractor biplane was surprisingly late in emerging, the first important example being A.V.Roe’s Type D, first flown at Brooklands in April 1911, of which half a dozen were built. Roe had previously built a number of triplanes, all with a tractor engine installation—the first two had a fixed triplane tail unit and were controlled in pitch by varying the incidence of the wings. The next triplanes retained the triplane tail unit, but this was now hinged to act as an elevator control and the wings were fixed rigidly to the fuselage. Roe’s final triplane and his Type D biplane, however, had a simple monoplane tail unit with fixed tailplane and hinged flap-type elevator. There was no vertical fin, simply a rudder. In December 1911, the Royal Aircraft Factory at Farnborough produced a tractor biplane designed by Geoffrey de Havilland which they designated B.E.1 (for ‘Blériot Experimental No. 1’ —Blériot being regarded as the pioneer of the tractor form of aeroplane). This had a water-cooled 45kW (60hp) Wolseley V-8 engine, shortly replaced by an air-cooled 60hp Renault of the same configuration. B.E.1 became the progenitor of a long line of aircraft, and the vehicle for many experiments by the Factory’s research staff. MILITARY AND COMMERCIAL APPLICATIONS The most significant development was the search for an aeroplane which was inherently stable, so that the military pilot could concentrate on his observation of the ground and the troops upon it, but was adequately controllable. The solution was found in a practical application of G.H.Bryan’s theoretical work, together with aerodynamic measurements of scale models in a wind tunnel and on a whirling arm. The principal vehicle for these experiments was an aircraft designated R.E.1 (for ‘Reconnaissance Experimental 1’) in which the wings AERONAUTICS 627 were rigged with a dihedral angle of about 3°, and large ailerons replaced the wing warping used on early B.E.s. A successful conclusion to the experiment in March 1914 led to large-scale production of variants of the B.E. by British industry; unfortunately wartime experience from August 1914 onwards demonstrated that the stable aeroplane was unnecessarily stable, and lacked the manoeuvrability needed for aerial combat (Figure 12.6). By the time the First World War broke out in August 1914, the aeroplane could be considered as a technically sound machine, although it lacked any clearly defined operational use in either civil or military roles. Probably rather more than 4000 aeroplanes had been built world-wide, the vast majority being single-engined machines of up to 75kW (100hp) carrying one or two persons at up to 130kph (80mph). World records at the end of 1913 were all held by French aircraft: 1021.2km (634.54 miles) distance in a closed circuit by A. Seguin on a Farman pusher biplane; 6120m (20,079ft) altitude by G.Legagneux on a Nieuport tractor monoplane; and 203.8kph (126.67mph) by M.Prévost on a Deperdussin monoplane with a streamlined monocoque fuselage made of overlapping thin strips of wood. Figure 12.6: The classic biplane configuration was adopted by the Royal Aircraft Establishment to produce a stable aeroplane for military reconnaissance. This is a B.E.2E, first delivered to the Royal Flying Corps in 1916. PART THREE: TRANSPORT 628 Practical machines had been developed in several countries which could take-off and land on water, and a few experimental amphibian machines had appeared. A flying boat built by Benoist was used for a few weeks in 1914 to run the world’s first scheduled service for passengers on a 35km (22 mile) route from Tampa in Florida; and the Curtiss company was testing a large twinengined flying-boat in the USA for a projected transatlantic flight when the war broke out. The largest aeroplanes in the world at this time were the four-engined Bolshoi and Ilya Murametz machines built by Igor Sikorsky in Russia. The latter, which flew in January 1914, was powered by four 75kW (100hp) Mercedes motors, and carried up to 16 passengers in an enclosed cabin. It was essentially of conventional configuration, with biplane wings on which the four engines were mounted driving tractor propellers, and a conventional tail unit at the rear of the fuselage. Technical innovations in aeroplane design during the First World War were surprisingly few, but the scale of aircraft manufacture increased enormously: around 200,000 machines were built in those four years. By the end of the war, engines of 300kW (400hp) were available in quantity, so the average speed and weight of aircraft had increased considerably. Multi-engined machines were built in several countries, and aerial bombardment became an accepted form of warfare, while effective fighter aircraft armed with machine guns were developed as a counter to both bombers and reconnaissance aircraft. The vast majority of aircraft were still mainly built of wood, but metal construction was introduced on a significant scale, especially in Germany. The Fokker company produced welded steel tube fuselage structures on a production scale, but few other manufacturers followed suit because of the problem of adequately inspecting the welds. More significant was the development of the metal cantilever wing by the Junkers company. The founder, Professor Hugo Junkers, had been granted a patent in 1910 for a thick wing which needed no external bracing, but this was not successfully built until December 1915 when the J.1 appeared, with an all-metal structure mainly in steel. Two years later the J.4 biplane appeared, using the high-strength aluminium (dural) alloys which had been developed for airship construction. A cantilever wing made it possible to set the fuselage on top of the wing, and subsequent Junkers all-metal designs were mainly of this low-wing monoplane configuration. The most significant design of this type was the F.13, developed in 1919 as a civil transport aircraft carrying four passengers in an enclosed cabin. The two pilots originally occupied an open cockpit, but later models were fully enclosed. The F.13 can reasonably be regarded as the world’s first airliner, and over 300 were built, continuing to serve in various countries for about 18 years. The same basic structure, with corrugated dural skins covering a skeleton of dural spars, ribs and fuselage frames, was used by the Junkers company for a AERONAUTICS 629 range of transport aircraft up to the three-engined Ju 52/3m, built in very large numbers, including the four-engined 6–38 of which only two were built, whose wing was thick enough to house six of the 34 passengers. THE INTER-WAR YEARS With the end of the war, a large number of aircraft, aircrew and trained mechanics became available, and a small proportion of these assets were employed on civil flying, mainly passenger carrying. These services started with converted wartime bombers (Figure 12.7); although these were soon superseded by aircraft designed for the purpose, for some years there was little change in basic configuration (except for the Junkers machines mentioned above). A typical British airliner design introduced in 1927 was the Armstrong Whitworth Argosy, a biplane with three 300kW (400hp) Jaguar engines, carrying 20 passengers in a rectangular fuselage with steel-tube frame covered in fabric. The wing frames were also of steel construction. Another typical transport aircraft of the period was the Fokker F.VII/3m, built in both the Netherlands and the USA. This had Fokker’s welded steel tube fuselage, fabric covered, coupled to an all-wooden cantilever wing mounted above the fuselage. Figure 12.7: The first passenger services from London to Paris in 1919 were flown by converted bombers like this Handley Page 0/7. Ground facilities for the passengers were limited, but curtains were provided in the cabin. PART THREE: TRANSPORT 630 Three engines of about 224kW (300hp) were fitted, and up to 10 passengers were carried. The almost universal preference for three engines in transport aircraft at this period was an insurance against engine failure—few twin-engined aircraft were capable of maintaining height on the remaining engine if one failed. Typical cruising speeds of these aircraft were about 160kph (100mph), flight times were around three hours, and operating heights below 1000m (3000ft). Flight at night or in clouds was rarely risked. Military aircraft of this period were, in general, no more technically advanced than their civilian contemporaries, but there were advances in the specialized area of high-speed contest flying, exemplified by the international competition for the Schneider Trophy for seaplanes. Remarkable speeds were achieved by streamlined machines with small frontal area and large engine powers —boosted by exotic fuel mixtures. Consecutive Schneider Trophy contests were won in 1925 by the Curtiss R 3 C-2 at 374.3kph (232.6mph), in 1926 by the Italian Macchi M.39 at 396.7kph (246.5mph), in 1927 by the British Supermarine S.5 at 453.3kph (281.7mph), and in 1929 by the Supermarine S.6 at 528.9kph (328.6mph) (Figure 12.8). In 1931 the series ended when the Supermarine S.6B achieved 547.3kph (340.1mph) in an uncontested event. Figure 12.9: The 21-seat Douglas DC-3 of 1936 was the first truly effective civil airliner capable of providing a regular, reliable transport service and generating a profit for its operator from passenger revenue alone. AERONAUTICS 631 These aircraft were in no sense practical vehicles, but they pointed the way to a new generation of military and civil aircraft which appeared in the 1930s. The modern airliner was born in the USA, when the Boeing 247 first flew in February 1933. This was an all-metal aircraft, in which the fuselage and wing skins contributed to the torsional stiffness of the structure: this stressed-skin principle had been foreshadowed in the wooden monocoque fuselages adopted by a few manufacturers, but henceforward became universal in all fast aircraft. The 247 had two engines, each powerful enough to maintain height if one failed; aerodynamic research had demonstrated how these engines could be cowled to reduce drag while maintaining adequate air cooling. The undercarriage was retracted by electrically driven screw-jacks to reduce drag further, and wing flaps were fitted to improve the wing lift at low speeds. Much research was undertaken at this period to improve the lifting efficiency of wings, allowing a progressive reduction in the wing area (and therefore wing weight and drag) needed to support the aircraft’s weight. This improvement in wing loading (i.e., weight divided by wing area) over the previous generation of airliners, coupled with improved streamlining, produced higher cruising speeds—around 250kph (155mph). The Boeing 247 was rapidly followed by Figure 12.10: A Supermarine Spitfire VII of 1942, typical of the high-performance fighter of its time, with all-metal structure and thin cantilever wings. The engine is a 1120kW (1500hp) Rolls-Royce Merlin 61 with two-speed supercharger and the cabin was pressurized to allow operation up to 12,000m (40,000ft) altitude. . led to an official (but temporary) ban by the British War Office in September 1912, and somewhat similar lack of faith on the part of some military organizations. Insofar as there was any common. few other manufacturers followed suit because of the problem of adequately inspecting the welds. More significant was the development of the metal cantilever wing by the Junkers company. The founder,. wing bracing. The third standard type of aircraft was the tractor biplane, which eventually supplanted the pusher ‘box-kite’ and numerically dominated the world’s skies up to about 1940. The first of these