J.Zynk Polish Aircraft 1893-1939 (Putnam)
Stefan Drzewiecki, grandson of a Polish Napoleonic legionary (born in Kunka in Podole on 26 December, 1844), holds a unique place in the history of aeronautics as the first Polish aviation theorist and scientist of international standing. A brilliant and versatile railway and marine engineer with various inventions and pioneering work in the field of submarine development to his credit, he became one of the principal contributors to the early art of aviation science and exercised a profound influence upon the shaping of ideas on heavier-than-air flying machines. Although some historians credit him with the design of an 'aerovelocyped' (or aerovelocipede), which was a muscle-powered helicopter-type device with two airscrews, in 1875, there is no documentary evidence in existence to connect him with such a machine.
His documented aeronautical activities date back to the early 1880s. In 1882 he was elected to the post of vice-president of the Aerial Navigation Branch of the Tsarist Russian Technical Association in Petersburg, and in a lecture on the theme of dynamic flight, delivered to that association on 13 April, 1885, Drzewiecki put forward his theory on the subject. During the same year he began to publish scientific articles, treatises and books, mainly in Russian and French, which expanded and explained his theory of flight and contained very advanced and original thoughts and observations. He declared himself against the lighter-than-air class of designs and decisively in favour of a fixed-wing aeroplane (as opposed to ornithopter and helicopter-type aircraft), advocating such a machine as the most efficient and rational type of flying device. In his book Aeroplany w prirodie (Aeroplanes in Nature), Petersburg, 1887, he set out the idea of an aeroplane provided with an engine and airscrew. During the same year he repeated his views in Paris, causing a major controversy and gaining the friendship of such pioneers as Chanute, Mayer and Mouillard, whose ideas largely coincided with his own.
Drzewiecki's greatest contribution to the development of aviation was his pioneering work in the field of airscrews. His airscrew theory, sometimes known as the Drzewiecki Elemental Blade Theory, which was published in its initial form in Petersburg and Paris in 1892, became the first comprehensive, scientific work on the subject and described, for the first time in world technical literature, practical methods of mathematical calculations for the design of airscrews. His original airscrew theory, later amended and supplemented by him and other scientists and better known as the Froude-Drzewiecki general airscrew theory, was closely studied by such pioneers as Chanute and the Wright brothers, providing one of the foundations of modern aeronautics. Extensive research in this field led Drzewiecki to the publication of his classic major works Des Helices Aeriennes (Paris, 1909) and Theorie Generale de l'Helice (Paris, 1920).
Quantity manufacture of airscrews to Drzewiecki designs was undertaken by Pierre de Ratmanoff Compagnie of Paris, in 1909, these being marketed throughout Europe under the trademark Helice Normale. The Normale airscrews were used by a number of great pioneers, including Bleriot, Illner (Taube), Labouchere, Latham (Antoinette) and Paulhan, and several world records and outstanding nights were accomplished on aircraft equipped with them. After the war, during the years 1926 to 1929, Drzewiecki developed a constant-speed airscrew, which was made in prototype form.
Drzewiecki understood better than most people the need for scientific research in aeronautics and in 1909 launched a public campaign, writing a booklet and various articles calling for the creation of extensive aviation laboratory and research facilities. He advocated that wind-tunnel experiments should form the basis for all the work in this field and outlined proposals and designs for such a tunnel. His appeals met with good response, Count Henri Deutsch de la Meurthe subscribing the equivalent of some $10,000 towards the provision of such research facilities, and helped to speed up the completion of the famous St Cyr Aerodynamic Institute.
In the first years of the 20th century Drzewiecki showed increasing interest in the problem of aircraft stability and flight safety. Inspired by Joessel Law in hydrodynamics, he adapted Law's theories to aerodynamics, and an extensive study of the relationship between the wing incidence and the centre of pressure and gravity led him to ideas for automatically-stable aircraft. In France, in December 1909, and March 1910, he patented his first proposals for such a machine. As a result of further theoretical and practical investigations, he developed completely revised proposals for an automatically-stable aeroplane later in 1910. The Drzewiecki automatic (or natural) stability principle in its ultimate form was based upon the utilization of the difference in air pressure arising from the employment of different aerofoil sections in a design of tandem-wing configuration.
The machine's smaller and more lightly loaded, movable front wing was of a specially developed Eiffel aerofoil section (No. 8), in which the lift increased comparatively slowly between 5 deg and 18 deg, the lift coefficient being 0.058 and normal angle of incidence 8 deg, whilst the larger fixed rear wing was of conventional section (Eiffel No. 13bis or Bleriot XIbis), having a lift coefficient of 0.041 and being set at an angle of 5 deg. Loading of the front wing was in the region of 40 kg/sq m (8.2 lb/sq ft) as against the 22 kg/sq m (4.5 lb/sq ft) of the rear wing. Thus, when the equilibrium was disturbed and the aircraft became tail down, the lift of the rear wing increased more rapidly than that of the front wing and a restoring couple was set up. Conversely, in a dive, the lift of the rear wing decreased more quickly and produced a restoring couple in the opposite sense. In this way longitudinal stability was maintained automatically, and climb and descent could be effected by an increase or decrease in the engine power, without the pilot touching the flight controls. In addition, exceptional safety was claimed for the aircraft, which, with the C.G. in the centre between the two wings, could not nose-over during landing and was as stable on the ground as in the air.
The selection of the most suitable combination of wing sections was made after protracted wind-tunnel experiments in the Eiffel aerodynamic laboratory, which were conducted in 1910 and 1911. A 1:10 scale-model of the machine underwent further wind-tunnel tests with particular reference to its reaction to C.G. movements and changes in the angle of incidence of the wings. The Drzewiecki tandem-wing monoplane was therefore one of the world's first designs to undergo comprehensive wind-tunnel trials. The aircraft, constructed in the Pierre de Ratmanoff factory in Paris, was completed in the autumn of 1912 and shown on the Ratmanoff stand at the 1912 Exposition Aeronautique in Paris. The machine, powered by a 70 hp Labor four-cylinder inline water-cooled engine, which was installed in the fuselage and drove a pusher two-blade Drzewiecki airscrew with a diameter of 2.6 m (8 ft 6 3/4 in) via an extension shaft, was universally acclaimed as the only real novelty and the most interesting design in the show.
After some slight alterations to the landing gear, the aircraft began flight trials at Chartres airfield early in 1913 and proved satisfactory from the outset. In the course of the year the machine made several flights during which it fulfilled the designer's expectations and perfectly maintained automatic stability, fully confirming that Drzewiecki's principle worked in practice exactly as anticipated. However, because of the troublesome powerplant, which was liable to malfunction, pilots did not like flying the machine, and the designer, then already 69, could not fly it himself.
In view of the engine difficulties and the fact that the weight of the airframe considerably exceeded the original estimate, the inventor began research on an improved, lighter development of the basic design in the latter part of 1913. He intended to submit this aeroplane for the design contest for the safest aircraft. The new project differed from its predecessor principally in having a more powerful 80 hp Gnome Monosoupape seven-cylinder rotary engine, which was mounted at the rear of the fuselage, obviating the need for an extension shaft, and its front wing was moved higher up and attached above the fuselage to a steel-tube cabane. A number of minor structural and aerodynamic refinements were also introduced. The machine had an overall span of 9 m (29 ft 6 3/4 in) and its total wing area was 24.9 sq m (268 sq ft), 16.4 sq m (176.5 sq ft) for the rear and 8.5 sq m (91.5 sq ft) for the front wing. Its normal maximum loaded weight (as a two-seater and with fuel for 5 hr) was 625 kg (1,377 lb) and estimated maximum speed was given as 110 km/h (68.3 mph). A scale-model of this development was fully tested in the Eiffel wind-tunnel and construction of the aircraft began in the spring of 1914, but nothing is known about its completion. Presumably the outbreak of World War 1 prevented its being built.
Although working abroad, Drzewiecki showed a keen interest in the development of flying in his native country and publicly emphasized his Polish nationality on several occasions. He became an honorary member of the Lwow 'Awiata', helping this association in various ways, and sent his airscrews as exhibits for the First Aviation Exhibition in Lwow in 1910. Remaining in France after the war, where in spite of his age he was still conducting scientific research (his last work being on the kinetic theory of gases), he made a very substantial donation to L.O.P.P. towards the building of the Warsaw Aerodynamic Institute. He died in Paris in April 1938, leaving in his will all his works, scientific documentation and tremendous library to Poland. Unfortunately, they were entirely destroyed in Warsaw during the war. His outstanding contribution to the world of science was widely recognized, and he was honoured by several nations, including Russia, France, Great Britain and Poland, with decorations, diplomas and tributes, among them a Commendation of the Academy of Science in Paris, a British diploma of Naval architecture, and the third honorary membership of L.O.P.P. to be awarded (after the first two awarded to the Polish heads of state. President Moscicki and Marshal Pilsudski).
Construction: The Drzewiecki aircraft was an experimental two-seat wire-braced tandem-wing monoplane of wooden construction. The rear, fixed wing, having an area of 18 sq m (193.8 sq ft) and a chord of 2.4 m (7 ft 10 1/2 in) at the root, slightly tapering towards the tips, was a two-spar double-surfaced structure covered with fabric. It was attached to the upper portion of the rear fuselage and braced by wires to a cabane incorporating the fin and to the fuselage and rear landing-gear framework. It was normally set at a 5 deg angle of incidence, but this could be adjusted on the ground, the limit of adjustment being 3 deg. The front wing, wire-braced to the cabane in front of the pilot's seat and to the front undercarriage members, had a span of 5.6 m (18 ft 4 3/4 in), a constant chord of 1.5 m (4 ft 11 1/2 in) and an area of 8 sq m (86.1 sq ft), the total area of both wings being 26 sq m (279.9 sq ft). Each half of the front wing, a single-spar double-surfaced structure pivoting round a horizontal tube which ran across the fuselage just above its lower longerons, moved independently, being in no way connected with one another. Each half was operated by a which could be adjusted on the ground in accordance with the loading. Acting differentially, the front wing halves assumed the function of ailerons; operated together, they acted as elevators, permitting the pilot to control longitudinal stability, which was otherwise maintained automatically. The fin was mounted centrally over the rear end of the fuselage and directional control was effected by two pivoting rudders, one on each tip of the rear wing. Each rudder was operated independently by a foot pedal and rotated outwards with its broadside towards the direction of flight, forming an air brake.
The fuselage was a rectangular-section structure covered with fabric, except for the underside below the engine, which was covered with sheet metal. Two open seats in tandem, with the pilot in front, were situated at the front of the fuselage, with the fuel and oil tanks in the centre and the engine further aft. The undercarriage comprised two separate units. The front unit consisted basically of two steel-tube side Vs. a cross-axle and a central skid, the upper ends of the rear arms of the Vs being attached to a horizontal oleo-pneumatic shock-absorber which was mounted under the fuselage. On landing, the wheels receded and the central skid came into contact with the ground. The rear landing unit featured two strong wooden trailing skids and two small-diameter wheels on leaf-spring shock-absorbers. All four wheels were additionally sprung with rubber cords. Overall dimensions included a span of 9 m (29 ft 6 3/4 in) and a length of 8 m (26 ft 3 in). Empty and normal maximum loaded weights (as a two-seater and with fuel for 5 hr) were 500 kg (1,102 lb) and 750 kg (1,653 lb). Cruising and maximum speeds were 95 km/h (59 mph) and 105 km/h (65.2 mph).
L.Opdyke French Aeroplanes Before the Great War (Schiffer)
Deleted by request of (c)Schiffer Publishing
Flight, November 16, 1912.
THE PARIS AERO SALON.
ON the Ratmanoff stand, in addition to "Normale " propellers, is exhibited a peculiar type of double monoplane, constructed to the designs of M. Drzeweicki, under whose licence, by the way, those excellent propellers are constructed. Its central unit of construction is a totally covered-in fuselage of rectangular section, at either end of which are arranged the wings. Those in front are of smaller dimensions than those behind, but meet the air at a greater angle of incidence. They, in addition to sustaining a portion of the weight of the machine, control its altitude in flight. Some little distance behind them sits the pilot, and at his back is the engine, a Labor-Aviation, which drives a propeller at the extreme rear end of the machine through a steel shaft. Steering is effected by vertical rudders pivoted to the tips of the rear wings. Each end of the machine is provided with a landing chassis of its own. In front there are two wheels whose flexibility is controlled by pneumatic springs extending along the base of the body. There is also a nose skid, but it seems to be placed too high to be of much service. The chassis at the rear of the machine is a combination of wheels and skids, the disposition of which can be gathered from one of our sketches. The wheels are sprung by laminated steel springs, such as were used on the new Bleriot racer shown at last year's Salon. The machine has not yet flown.