Aviation in the pioneer era

Full details of the Wright Brothers' flight control system was published in l'Aérophile in the January 1906 issue,[6] making clear both the mechanism and its aerodynamic reason. Nevertheless, the crucial importance of lateral control in making controlled turns was not appreciated, and the French experimenters instead aimed to construct inherently stable aircraft.

Illustration of Santos-Dumont's 12 November 1906 flight on the cover of Le Petit Journal

In the late summer and autumn of 1906 Alberto Santos Dumont made the first successful powered heavier-than-air flights in Europe in his 14-bis, culminating in a flight of 220 m (722 ft) on the grounds of the Parisian Chateau de Bagatelle on 12 November, winning an Aéro-Club de France prize for a flight of over 100 m. Initially relying on pronounced dihedral to provide stability, by the November flight, octagonal-planform interplane ailerons somewhat like Esnault-Pelterie's design had been fitted to the aircraft.

Earlier that year Gabriel Voisin had established an aircraft construction company at Boulogne-Billancourt: his first successful aircraft, which lacked any provision for roll control, was the Delagrange No.1 biplane, named after its owner Leon Delagrange. This was first flown by Voisin on 30 March 1907.[7] and in February 1908 a second example flown by Henri Farman won the Archdeacon-de la Meurthe Grand Prix d'Aviation for the first officially observed closed-circuit flight of over a kilometer. Among the most persistent French experimenters was Louis Blériot, who after a brief partnership with Gabriel Voisin, had established Recherches Aéronautiques Louis Blériot and produced a series of monoplane designs. On 16 November 1907 he successfully flew his Blériot VII, a monoplane with tail surfaces moved differentially for roll control and in unison for pitch control. This aircraft, which is recognised as the first successful monoplane, was soon wrecked in a crash, but was quickly followed by his eighth design, the first aircraft ever to essentially have the original form of flight control setup used to this day.[8]

In North America, the Canadian-American Aerial Experiment Association was founded by Alexander Graham Bell, who had made a number of earlier experiments with tetrahedral kites, and John McCurdy and his friend Frederick Walker Baldwin, two recent engineering graduates of the University of Toronto, on 30 September 1907. The AEA produced a number of fundamentally similar biplane designs, greatly influenced by the Wright's work, and these were flown with increasing success during 1908. Baldwin flew their first design, Red Wing on 12 March 1908, flying 97 m (319 ft) before crashing and being damaged beyond repair: its successor, White Wing, equipped with ailerons, made three flights in May, the best of 310 m (1,017 ft), before being destroyed in a crash. On 4 July 1908 their next aircraft, the June Bug piloted by Glenn Curtiss, won the Scientific American trophy for the first officially observed one kilometer flight in North America. After the AEA's disbandment at the end of March 1909, one of its American members went on to start a growing US-based aviation firm.

Henri Farman winning the Grand Prix d'Aviation, 13 January 1908

In 1908 Wilbur Wright finally visited Europe and in August made a series of flight demonstrations which convincingly demonstrated the superiority of their aircraft, particularly its ability to make controlled banked turns, to the European aviation community. The first flight only lasted 1 minute 45 seconds, in which two circles were flown, but the effect was profound, Louis Blériot saying "I consider that for us in France, and everywhere, a new era in mechanical flight has commenced. I am not sufficiently calm after the event to thoroughly express my opinion. My view can be best conveyed in the words, 'It is marvellous!' " [9] Leon Delagrange simply said "We are beaten". Following these demonstrations, Henri Farman fitted his Voisin biplane with ailerons in order to achieve the full controllability demonstrated by Wilbur Wright: following a falling-out with Gabriel Voisin he then started his own aircraft manufacturing business. His first design, the Farman III (the Farman I and II were Voisin designs that he owned) was one of the most successful aircraft designs of the pioneer era, and was widely copied by other manufacturers, including one soon-to-be-prominent British firm.

Vickers R.E.P. Type Monoplane preserved in the Musée de l'Air in France. Note wire-braced steel tube fuselage.

Most pioneer era aircraft were constructed from wood, using metal sockets to joint members and making use of piano wire or stranded steel cable for bracing. Although aircraft of the era are often described a constructed of sticks and canvas their construction was of considerable sophistication. Wooden construction typically involved several different types of timber, with careful use of different woods according to their mechanical properties; ash and spruce were the most commonly used, although hickory, mahogany and poplar were among the other timbers employed. Struts were frequently hollow members formed by spindling out two pieces of wood and then glueing them together, usually using a tongue in groove joint to strengthen the joint. Wing spars were also often composite members, and the wing ribs were complex structures. When flying replicas of the 1910 Bristol Boxkite were made for the 1966 film Those Magnificent Men in their Flying Machines, a modern stress analysis was performed, and concluded that the airframe was close to conforming to modern requirements.[19]

The use of metal for airframe construction was by no means uncommon: Robert Esnault-Pelterie used steel tubing to construct the fuselage of his aircraft as early as 1907, and Louis Breguet was another notable pioneer of metal construction, using steel channel sections for fuselage construction, steel tube for wing spars, pressed aluminium for wing ribs and aluminium sheeting for fuselage covering[20] – this would not be improved upon until the second half of 1915.

The era also saw the first use of monocoque construction, first seen in Eugene Ruchonnet's Aero-Cigare and notably used in the Deperdussin Monocoque of 1912, which won the Gordon Bennett race in both 1912 and 1913. Another structurally advanced and influential (although unsuccessful) concept aircraft designs was the Antoinette Monobloc, which was the first monoplane design concept to have a cantilever wing without any external bracing wires.

Early aircraft were covered in a variety of fabrics including rubberised cotton and varnished silk. The development of aircraft dope in 1911 was a major technical development, and its use was quickly adopted by all manufacturers. This performed a number of functions, proofing the fabric against oil and petrol contamination, and also tightening the fabric.

Typical aircraft of 1911: an illustration from Flight of competitors in the 1911 Daily Mail Circuit of Britain race

At the 1909 Grand Semaine d'Aviation the competing aircraft were of two different basic configurations: tractor configuration monoplanes such as the two types flown by Blériot and the Antoinette; and pusher configuration biplanes with a forward-mounted elevator, represented by the Voisin, licence-built copies of the Wright Brother's aircraft, Glenn Curtiss' No. 2 biplane and the Farman III. All the competing aircraft with the exception of the Voisin biplanes had roll control, using either ailerons or wing-warping[21] The Wright design differed from the others in having no rear-mounted horizontal stabilising surface. Constructors of pusher biplanes almost universally adopted the use of a rear-mounted horizontal stabiliser and designs began to appear in which the front elevator was removed: the Wright Brothers adopted this configuration for their Model B of 1910. The tractor monoplane and the pusher biplane were the dominant configurations for the next couple of years, although designers experimented with various other configurations.

One of the most successful pusher biplanes was the Farman III, developed by Henri Farman following a falling-out with Gabriel Voisin: he retained the basic layout of the Voisin, but incorporated ailerons (as added to his Voisin), modified the undercarriage by adding skids to prevent the aircraft nosing-over on landing and modified the structure, eliminating the nacelle in which the pilot sat and mounting the forward elevator on outrigger booms. This design was copied by many constructors, and was so influential that when Mervyn O'Gorman created a scheme for classifying the products of the Royal Aircraft Factory according to their configuration such aircraft were classified as "F.E" for "Farman Experimental. All tractor aircraft were designated "B.E" for "Blériot Experimental", although all the B.E. designs produced were biplanes, unlike the designs for which Blériot was known.

The tractor biplane, which would become the dominant aircraft configuration until the 1930s, was a later development. The first aircraft of this type was the De Pischoff biplane which was built in 1907 but was not successful. The first aircraft of this type to fly was the Goupy No.2, flown in March 1909: the design was described by flight as "somewhat unusual",[22] and Breguet described his Type III tractor biplane as a "double-surface monoplane". The configuration did not become widespread until 1911,[23] with the production of the Avro 500 and the Royal Aircraft Factory BE.2. The Avro 500 was developed into the Avro 504, which continued in use until the 1930s. Avro also produced the first aircraft with fully enclosed crew accommodation, the Avro Type G of 1912. (The Blériot Aero-Taxi of 1911 had enclosed accommodation for the four passengers but an exposed pilot's position)

Other configurations were experimented with. The tail-first canard configuration used by the Wright brothers and also notably employed by Santos Dumont in the 14-bis was used by Henri Fabre for his Hydravion canard monoplane, the first successful seaplane in 1910. Other canard designs of the period include the Voisin Canard and the ASL Valkyrie monoplanes, and the configuration was thought promising enough to be used for the first aircraft designed by the Royal Aircraft Factory, the S.E.1, but the configuration was generally discarded. Examples of other configurations such as the annular wing and the tandem wing were also constructed, but with little success.

Early aircraft had a variety of control arrangements. The use of a joystick to control roll and pitch had been patented by Robert Esnault-Pelterie in 1907 and a similar arrangement was used by Blériot, but the Antoinette monoplanes were controlled by a pair of wheels, one on either side of the cockpit, one operating the wing-warping (or ailerons, as with the Antoinette IV) and the other the elevator [24] and the Wright Model A had one lever to control wing-warping and rudder and a second to control the elevator.[25] The first design to have the roll and pitch controls connected to a single joystick, with the yaw control operated with one's feet, was Blériot's Type VIII design of 1908–09, pioneering the basis for the modern aircraft flight control system still in use in the 21st century.[26]

Sikorsky Bolshoi Baltisky of 1913

With very few exceptions aircraft of the pioneer era were relatively small designs powered by a single engine and designed to carry at most two or three people. Early multiple-engine designs were produced by the Short Brothers, who constructed a number of variants of their Farman-type Improved S.27 design. However the intention of using a pair of engines in these aircraft was to safeguard against engine failure rather than to permit a larger machine, and even a large aircraft such as the Voisin Aero-Yacht, intended to carry six people and with a wingspan of 22.5 m (73 ft 10 in), was powered by a single engine. The first large multi-engined aircraft was Igor Sikorsky's Bolshoi Baltisky, first flown in May 1913 with two engines and later equipped with four.

The Gnome Omega

Lucien Chauvière, designer of the Integrale propeller for the Blériot XI's cross-Channel flight.

Early aircraft development was heavily reliant on the development of the internal combustion engine, and the problem of staying in the air was largely a matter of having an engine which was not only sufficiently powerful but was also lightweight and reliable. Most early engines were neither powerful nor reliable enough for practical use, and the development of improved engines went hand-in-hand with improvements in the airframes themselves.

The Wright Brothers had been unable to find a satisfactory engine and, with the help of their mechanic, had manufactured their own. They used a single flight engine, a 12 hp water-cooled four-cylinder inline type with five main bearings and fuel injection.

The first internal combustion piston engine design to be widely used for powering aircraft was the Antoinette water-cooled V8 engine, believed to be the very first V-form eight-cylinder internal combustion engine ever placed in production, designed by the Frenchman Léon Levavasseur. The Antoinette 8V incorporated direct fuel injection, evaporative water cooling and other advanced features, weighed 95 kg (209 lb) and produced 37 kW (50 hp). Introduced in 1906, these engines were used by, among others, Santos Dumont, the early Voisin aircraft and Samuel Cody. American aviation engine designers quickly picked up on the V-8 engine concept from 1906 onwards as the era progressed, with both Glenn Curtiss' firm designing a series of liquid-cooled V-8 aviation engines culminating in the Curtiss OX-5 by the early years of World War I—another major American engine manufacturer, Hall-Scott, had their A-2[27] and A-3 overhead valve, liquid-cooled V-8s in production as early as 1908.

The British Green C.4 of 1908 followed the Wright's pattern of a four-cylinder inline water-cooled design but produced 52 hp (38 kW). It powered many successful pioneer aircraft including those of A.V. Roe.

Horizontally opposed designs were also used with some success. Santos-Dumont's Santos-Dumont Demoiselle No. 20 monoplane used first the 18 kW (24-hp output Dutheil et Chalmers liquid-cooled opposed twin engine, later replaced by a 22 kW (30 hp) Darracq-built engine of the same layout. The four-cylinder water-cooled de Havilland Iris achieved 45 hp but was little used, while the successful two-cylinder Nieuport design achieved 28 hp (21 kW) in 1910.

1909 saw radial engine forms rise to significance. The air-cooled Anzani 3-cylinder semi-radial or fan engine of 1909 (also built in a true, 120° cylinder angle radial form) developed only 25 hp (16 kW) but was much lighter than the liquid-cooled Antoinette, and was chosen by Louis Blériot for his cross-Channel flight. A major advance came with the introduction of the Seguin brothers' Gnome Omega seven-cylinder, air-cooled rotary engine, exhibited at the Paris Aero Salon 1n 1908 and first fitted to an aircraft in 1909. This radial-configuration engine was constructed in such a way that the entire crankcase and cylinder assembly rotated around a stationary crankshaft, itself fastened securely through the engine's rear attachment to the airframe, ensuring an adequate flow of cooling air over the cylinders even when the aircraft was not moving. Although this type had been introduced as long ago as 1887 by Lawrence Hargrave and built two years later by Hargrave for compressed-air power—with an experimental five-cylinder internal combustion rotary engine used by French inventor Félix Millet that same year to power an early motorcycle design — improvements made to the Seguin brothers' Gnome series of engine designs created a robust, relatively reliable and lightweight design which revolutionised aviation and would see continuous development over the next ten years. Fuel was introduced into each cylinder direct from the crankcase meaning that only an exhaust valve was required. Producing 37 kW (50 hp) for a dry weight of 75 kg (165 lb), this engine soon became one of the most widely used powerplants; the company went on to produce a number of similar engines producing more power, first by increasing the engine capacity and also by producing two-row variants. The larger and more powerful nine-cylinder. French-made Le Rhone 9C 80 hp rotary was introduced in 1913 and was widely adopted for military use.

Inline and vee types remained popular, with the German company Mercedes producing first a small number of water-cooled inline four-cylinder engines, then a series of water-cooled six-cylinder models. In 1913 they introduced the highly successful range of 75 kW (100 hp) to 120 kW (160 hp), SOHC-valvetrain design engines: the D.I to D.III series.

Another area of advance was the development of specialist manufacturers of propellers. Although the Wright Brothers had developed their own highly efficient propellers and Hiram Maxim had also carried out research on propeller design, much of this work was unknown, and the early pioneers such as Voisin and Santos Dumont had used inefficient propellers with flat aluminium blades mounted on a steel tube. The first truly efficient European propeller design was produced by Lucien Chauvière, who had studied the theory of propeller design while a student at the École des Arts et Métiers in Angers. Chauvière pioneered a sophisticated construction technique using laminations of walnut. A Chauvière propeller was used by Blériot in his flight across the English Channel, and the importance of Chauvière's contribution was recognised by his being awarded a silver medal by the Aero-Club de France.

The achievement of powered flight led to the establishment of centres for aeronautical research in many countries. In 1907 Ludwig Prandtl, who had joined the University of Göttingen university in 1904, founded the Modellversuchsanstalt für Aerodynamik der Motorluftschiff-Studiengesellschaft [society for testing aerodynamic models of powered airships ]. The University of Göttingen would become a world leader in aerodynamic research.[28] In 1909 Henri Deutsch de la Meurthe endowed a department devoted to aeronautics at the University of Paris[29] In France the famous engineer Gustave Eiffel performed a series of experiments to investigate the effects of wind resistance on moving bodies by dropping test apparatus down a wire suspended from the Eiffel Tower: he later built a wind tunnel at the base of the Tower, in which models of many pioneer French aircraft were tested and carried out pioneering work on aerofoil sections.