THE WINGS ARE AT THE BACK of this German Focke-Wulf Ente aircraft, which is driven by two tractor airscrews. The elevating plane in the front of the aircraft stalls before the main plane. It is thus impossible to tilt the main plane up to an angle at which it would stall and lateral control is ensured always. The Focke-Wulf Ente was produced in 1930.
FROM the earliest days of civilization the achievement of flight has been the inspiration and the goal of countless inventors. Mythology and legend contain frequent reference to various forms of human flight, and the sketches left by Leonardo da Vinci are proof that during the Renaissance the problem of flight was one to attract the daring investigator. The majority of the earlier attempts to produce practical flying machines were concerned with heavier-than-air craft. Most of these early inventions were of the ornithopter, or “flapping-wing” class (see the chapter “Experiments with Ornithopters”), though, in 1640, Cyrano de Bergerac, in a flight of fancy, proposed to soar into the air by means of rocket propulsion (see the chapter “Reaction Propulsion”). He thus anticipated by some hundreds of years the present-day efforts of scientists.
Even the success of the balloon in the latter part of the eighteenth century did not altogether divert inventive genius from heavier-than-air problems. About this time the French aeronaut Jean-Pierre Blanchard, later to become an expert balloonist, produced plans for two strange aircraft. One was a machine propelled by hand-levers and pedals, the other, which he called a vaisseau-volant (“flying ship”), was a species of ornithopter for which he claimed a speed of 75 miles an hour.
Few of these early inventions progressed beyond the stage of theory, but long before the Wright brothers made their historic flights various strange types of heavier-than-air craft had flown. One of the earliest successes was achieved by an Englishman, Horatio F. Phillips. This inventor used an extraordinary multiplane design embodying some fifty wings mounted one above the other. Phillips, whose patents were taken out in 1884, was one of the first investigators to treat the problem of wing sections as a matter for scientific experiment. His researches were carried out in a crude wind tunnel of his own construction.
Phillips’s first machine appeared in 1893, and was 25 feet long 22 feet broad and 11 feet high; it weighed 420 lb. For wings it had some fifty long wooden slats set one above the other in a steel frame, so that the whole machine resembled a large Venetian blind. A steam-engine of about 9 horse-power provided the motive power for a propeller of 6 feet diameter. For trial purposes, the machine was attached to a post by wire guys and allowed to run round a circular wooden track, 100 feet in diameter. Pressure of air under the slats caused the machine to rise some two or three feet above the track when sufficient velocity had been attained. The best flight was achieved on June 19, 1893, when, at a speed of 40 miles an hour, and with a total load of 385 lb., all three supporting wheels of the multiplane were off the ground for a distance of 2,000 feet.
Had there then been available a more powerful engine, permitting the carriage of a human load, Horatio Phillips’s curious multiplane might well have robbed the Wright brothers of the honour of the first controlled flight. As it was, the Wrights caught and passed Phillips, and it was not until 1907, four years after the Wright brothers had made history, that Phillips perfected a multiplane fitted with a 22 horse-power engine, and at last achieved his ambition of controlled human flight.
Special interest attaches to Phillips’s multiplane invention because of its resemblance to the principle of the slotted wing of today. The slotted wing has contributed much to the safety of flight because of the control that it affords at low-flying speeds. Moreover, there are eminent designers today who believe that in the multiplane design may lie the secret of safe and slow flight, and in several countries experiments are in progress with multiple-wing aircraft bearing more than a passing resemblance to the invention of Horatio Phillips.
A BAT-LIKE FORM was given by Ader to his second machine, which was completed in 1897 with funds provided by the French Ministry of War. There is some controversy as to whether the machine, named Avion, ever flew, but its name is perpetuated in the word avion, which is today the generic term in French for all power-driven heavier-than-air craft. The Avion was fitted with two twenty horse-power steam engines.
Another noteworthy aircraft of highly original design which appeared about the time of Phillips’s experiments was the bat-winged Eole monoplane designed by Clement Ader, a distinguished French electrical engineer. Ader’s first experiments were with ornithopters, but he soon abandoned this line of research and produced a remarkable fixed-winged aircraft of bat-like form with a wing spread of about 46 feet and a weight of 1,100 lb. The power-plant was a steam-engine developing some 30 horse-power and driving a four-bladed tractor airscrew. On its first trial flights in 1890 this machine was alleged to have carried its inventor in flight over a distance of 160 feet. The claim was never fully substantiated, nor could the feat be repeated, as the machine was wrecked on landing.
With funds provided by the French Ministry of War — probably the first Government subsidy ever granted to an aeronautical experimenter — Ader then set about building a second machine, which he completed in 1897. This machine, which Ader named Avion, had the arched and bat-like wing of its predecessor, but was driven by two 20 horse-power steam-engines operating four-bladed, feather-like airscrews. The machine ran on three small wheels; control in flight was effected by a wing-warping device and a foot-lever for actuating the tailplane.
Whether the Avion ever flew or not has provided one of the keenest controversies in the whole history of aviation. Two military witnesses at the official trials took directly opposite views. One witness claimed that Ader had made at least two sustained and fully-controlled flights, the other credited him merely with a few short “hops”, due chiefly to the strength of the following wind.
Public opinion was at variance over the authenticity of this alleged flight. Even today historians are divided on the question of whether or not Clement Ader deserves the credit for the first power-driven controlled flight. The one point upon which there is general agreement is that Ader’s machine, whether it flew or not, was certainly capable of flight. Ader died a disappointed and an embittered man, but his memory is perpetuated in the name of his machine, for avion is today the generic term in French for all power-driven heavier-than-air craft.
Vuia’s “Butterfly”
The triumph of the Wright brothers in America in 1903 gave added impulse to the efforts of inventors all over the world. France, in particular, was a centre of great aeronautical activity. Prominent among the group of enthusiastic French aeroplane experimenters of that time was Traian Vuia, destined to become the second Frenchman to leave the ground in a power-driven aeroplane. Vuia’s machine, which he called Papillon (“Butterfly”), was a monoplane with wide transparent wings and a fuselage built entirely of steel bicycle tubing. It had bat-shaped wings reminiscent of Clement Ader’s Avion. The pilot sat in the open framework below the wing, and the framework was supported on four pneumatic-tyred wheels. Vuia first succeeded in making a short “hop” of about ten yards on March 2,1907, but found himself seriously handicapped by his highly-experimental type of engine, which was driven by “liquefied carbonic acid gas”.
A few weeks later he replaced this engine with a 29 horse-power Antoinette engine and, with this new power plant, succeeded in flying a distance of 22 yards, at a height of 5 feet, on July 3, 1907. His performances were, however, altogether eclipsed by those of Bleriot and Farman in covering distances of upwards of half a mile in the next few months, and Vuia and his quaint-looking “Butterfly” soon faded into obscurity.
Most inventors of those days were content with modifications of the already proven design of the Wright brothers’ biplane, but there were still a few adventurous spirits who preferred to continue their own original lines of experiment.
One of these was the Marquis d’Equevilly-Montjustin. In 1908 this inventor produced an aircraft of such revolutionary design that he might have been accused of copying the Great Wheel of the Paris Exhibition of 1900. A multiplane of circular shape, Montjustin’s machine was built up round a framework of steel tubes carrying twelve small planes.
The pilot stood upright in an inner oval cage of steel tubes; the cage was designed to protect him from injury in the event of accident. A two-bladed airscrew was belt-driven from a three-cylinder air-cooled engine of 7-8 horsepower. The whole machine, which weighed about 308 lb., was mounted on an oblong four-wheeled chassis. It measured 16½ feet in span, was 6½ feet
long and had a total supporting surface in the twelve planes of 268½ sq. Ft.
There is no record that the Montjustin multiplane ever succeeded in leaving the ground. Its chief claim to fame appears to lie in the inventor’s assertion that it was “very resilient, very light, very solid, and cheap”.
AN ALMOST CIRCULAR WING SHAPE was used on the Tilghman Richards annular aircraft of 1913, a model of which is shown in this photograph. Inherent stability is one of the advantages of this type of construction. The first two models built were so stable that they did not manoeuvre properly, but this defect was overcome in a third model. The aircraft carried two people.
A somewhat similar method of construction, though on more conventional lines, was adopted for a British multiplane at the end of 1910. This was the Seddon “tandem” biplane, built by Accles and Pollock for Lieut. J. W. Seddon, R.N. It had two sets of main planes, one behind the other; the planes were supported on a number of transverse hoops of steel tubing.
The first seaplane to achieve successful flight was a distinctly unconventional type of aircraft, with little resemblance to any marine aircraft of today. It made its historic flight on March 28, 1910, when the French pioneer, Henri Fabre, rose from the surface of the river at Martigues and flew for a short distance. Two months later, in the same machine, Fabre made a flight of four miles; he started from and alighted on the water.
The Fabre seaplane was a monoplane of the “canard”, or tail-first type, with the main wing right aft and the elevators, consisting of two smaller planes set one above the other, right in front. Connecting the two sets of planes were two narrow booms, one above the other and some five feet apart. Precariously straddling the upper boom, somewhere about its centre, sat the pilot, whose only controls were a long lever attached to the front elevator and pedals from which cables led to water rudders. On the water, the seaplane was supported by three hollow floats, of aerofoil shape, which formed a triangle with the apex forward.
Lattice-Girder Construction
Fabre made several notable flights on his primitive-looking seaplane until it drifted on to some rocks and was so severely damaged by the sea that it was never flown again. It is now in the French Government’s Aeronautical Museum at Chalais-Meudon. The machine is of special interest from a constructional viewpoint because of the lattice-girder method used in building-up all its main spars and booms.
This method of construction, of which Fabre was a pioneer, was adopted towards the end of the same year by another famous French aviator. Louis Paulhan built a novel type of biplane in which all the main spars, as well as the booms running fore and aft, were built up in lattice-girder fashion. A great point was also made of the fact that the whole canvas covering of the airframe could quickly be removed if the machine had to spend a night in the open. The lattice girders gave the Paulhan machine a most curious “open-work” appearance, but it flew well on the power of a 50 horse-power Gnome engine and, after extensive trials, was accepted by the British military authorities. Its principal dimensions were a span of 40 feet and a length of 20 feet. It weighed 880 lb. Loaded.
Another innovation in constructional methods which appeared in France in 1910 was the Moisant sesquiplane. This was one of the earliest aeroplanes, if not the first aeroplane, to have no wood in its construction. The framework of this machine was of steel tubing and the planes were made of sheet aluminium, corrugated to give rigidity.
The main wing measured 18 feet in span and the pilot was seated in an open cockpit below it and resting on the small metal lower wing. The elevator was carried on outrigger booms projecting some distance ahead, and beyond the 50 horse-power Gnome engine in the nose which drove a tractor airscrew. The tail-unit, carrying a rudder and a perforated fin, was of aluminium and there was a tail-wheel in place of the more usual tail-skid.
Though it appears never to have left the ground, the Moisant sesquiplane is of interest both because of its all-metal construction and because of its designer. He was John B. Moisant, an American of Spanish descent, who went to France in 1909 and learnt to fly on a Bleriot monoplane at Etampes, near Paris. He was at one time a well-known Bleriot racing pilot. On September 18, 1910, he flew from Les Baraques, near Calais, to Dover; he was accompanied by his mechanic, Fileux. Moisant thus made the first passenger aeroplane flight across the English Channel.
A TWO-SEAT PTERODACTYL AIRCRAFT of fighter type powered by a water-cooled engine driving a tractor propeller. The first tailless aircraft was produced by J. W. Dunne in Scotland in 1911 and was successfully flown, After this the tailless aircraft was neglected until 1926, when Captain G. T. R. Hill produced his first tailless aeroplane. This first Pterodactyl was a single-seat light aeroplane driven by a pusher airscrew. The aileron controls of a Pterodactyl can be used in unison when it is desired to make the aircraft climb or dive. An American design of tailless aircraft has one semicircular wing in place of two swept-back wings in the form of an arrowhead.
The war of 1914-18, which created an unprecedented demand for heavier-than-air craft, might seem to have offered a golden opportunity to the resourceful aeronautical inventor and to have led to the production of many aircraft of unorthodox design. In the event, this demand caused rapid development on certain definite lines dictated by the urgency of the situation and there was little time or opportunity for experiment to be made on unconventional lines.
True, the authorities of all the belligerent nations were inundated with offers of “revolutionary” designs of warplanes from enthusiastic inventors; but, for the most part, aeronautical activity during the war was concentrated on the steady improvement of existing methods of design and construction which had already proved successful.
After the war attention could once, more be diverted to experiment. One of the first firms to take advantage of the lessons learnt during the war in the development of large bombing types of aircraft was the Italian Caproni Company. This concern set to work late in 1918 to produce the largest and certainly the strangest-looking aircraft which had ever been attempted up to that time.
Unique Triple Triplane
In the winter of 1920-21 there appeared an enormous Caproni flying boat; it was the only example of a triple triplane that has ever been built. Resembling nothing so much as a huge house-boat surmounted by three great sets of triple wings, this flying boat was some 100 feet in length and was driven by eight engines developing a total of 3,000 horse-power. These engines were divided among the two outer sets of triplane wings. Four engines were mounted in the front set of wings, where they drove tractor airscrews; the other four were installed in the third or rearmost set of wings, where they faced aft and drove pusher propellers.
A covered corridor, suspended above the hull on a level with the middle wings, allowed access to any of the engines in flight for repairs or adjustment. The pilot’s cockpit was located in the nose of the hull, which was so spacious that comfortable accommodation could be provided for about a hundred passengers. An illustration of this colossal machine appears in the chapter “Italian Enterprise”.
In post-war aeronautical inventions generally, it is possible to distinguish between two broad lines of development, which, however, tend to intermingle. In one class the inventor has sought no more than to improve, on some point in conventional aeroplane design as it is.
To this class belongs such a device as the Handley Page slot (see the chapter “How An Aeroplane Flies”) which removes certain inherent defects of the fixed wing, and the Townend engine ring, which improves the aerodynamical characteristics of the ordinary radial engine.
On the other hand there are inventors who have foreseen no real future for aviation without a radical change in the aeroplane as we know it today. The “Autogiro” aircraft is the outstanding example of the successful application in practice of an altogether new principle of flight; but for this one success there are a hundred other revolutionary ideas which have failed to fulfil their early promise.
VARIABLE-CAMBER WINGS were fitted to this aircraft, which was the invention of an Italian, Ugo Antoni. The aircraft was demonstrated in 1933. By variation of the camber of the wings their lift was altered. The aircraft thus had a short take-off and landing run, and a steep climb. Flattening of the camber increased the top speed of the aircraft in level flight and an increase of the camber of the wings provided the greater lift required to improve the take-off and landing properties of the aircraft.
Among the more interesting may be included the American “Pendulum Plane”, a high-wing monoplane so designed that the fuselage was supported on struts about six feet below the wing. The engine, driving an ordinary tractor airscrew, was mounted in the centre of the wing, which also carried a conventional tail-unit, a duplicate of one on the end of the fuselage, on an outrigger boom projecting some distance astern of the main wing.
The idea behind this highly unorthodox design was that the fuselage, being free to swing, would act like a pendulum and so keep the machine in a state of constant equilibrium. On trial the inventor’s object was attained only too well, for the “Pendulum Plane” proved so obstinately stable as to be virtually uncontrollable in flight.
Many inventors, in their efforts to revolutionize flying, have turned their attention either to improving upon the propeller or replacing it altogether. In the first category was a German inventor, Karl Schapel. He designed a monoplane fitted at nose and tail with a propeller shaped like the thread of a screw, the “threads” being extended outwards to form the curved blades of a propeller. Efficiency much higher than that of an ordinary airscrew was claimed for this design, and it was also believed that the rear propeller, when reversed, could be used as a “brake” to facilitate landing or to retard speed in a dive.
A more successful attempt to improve upon the efficiency of a propeller was the recent invention by Luigi Stipa, an Italian engineer, of a “tubular” aeroplane, embodying the principle of the venturi tube. The Stipa, which was built by the Caproni Company, was a mid-wing monoplane whose fuselage consisted of a short and dumpy barrel-shaped metal tube, open at either end.
Elevators, fin and rudder were attached on the outside of the rear end of the tube, and the engine, with a tractor airscrew, was mounted inside the front, open end of the tube. The tube had been carefully shaped internally to smooth the airflow from the revolving propeller. As there was no room for the pilot inside the tube, he was accommodated outside in a streamlined nacelle on top of the tube.
Combined Propellers and Wings
A number of successful flights have been made with this curious-looking aircraft. Its revolutionary design is claimed to afford exceptionally high lift; also to lend itself to the ready assembly, side by side, of any number of these tubular units to make one multi-engined aircraft of any desired size and power.
Several inventors, including Dr. Adolf Rohrbach, the German aeronautical engineer, have been attracted by the possibility of substituting “paddlewheels” not only for the airscrew but also in place of an aeroplane’s wings. Such aircraft are generally known as “Cyclogiros”. Though each inventor may modify the details, the broad principle of all that have been designed so far is much the same.
Essentially, the “Cyclogiro” consists of a fuselage in which the fixed wings of a conventional aeroplane have been replaced by two large paddle-wheels, one on either side, and both rotated by a common worm-drive from a centrally-mounted engine. Each “wheel” carries four or more long thin horizontal blades of aerofoil shape and is attached to a common horizontal shaft.
As this engine-driven shaft rotates and the blades, or miniature wings, move through the air they develop lift. Part of this lift acts vertically and sustains the “Cyclogiro”; the rest of the force is applied forward and pulls the aircraft ahead. Thus the paddle-wheels are both propellers and wings.
In the Rohrbach “Cyclogiro” design the blades on the paddle-wheels are mechanically “feathered” like oars as they move through the air. By regulating the extent of this feathering, the “Cyclogiro” could, it is suggested, be made to rise almost vertically and the paddles, acting as powerful controls, would also enable the craft to be turned or rolled.
When the machine is gliding with the engine off, the paddle-wheels are rotated by the relative wind, as are the rotors of an “Autogiro” aircraft, thus permitting a slow and almost vertical descent under full control. It is even claimed that a simple alteration in the angle of the blades, which could be carried out in mid-air, would enable a “Cyclogiro” to be flown backwards.
FEATHERING PADDLE-WHEELS replace the airscrew on this aircraft, which was invented by Ernest Schroder and experimented with at San Francisco, California, in 1930. Numerous designs in which the airscrew is replaced by some other device have been produced. In some, known as “Cyclogiros” the paddle-wheels take the place of the wings as well as the propeller.
No “Cyclogiro”, however, has yet made a sustained flight. Thus the many advantages claimed for it are still largely theoretical. On the other hand, the design has been the subject of considerable research and wind-tunnel experiment. Moreover, as its principle of flight has been shown to accord with modern knowledge of aerodynamics, it may yet rival the “Autogiro” aircraft in the field of successful rotating-wing aircraft.
A type of aeroplane which has received attention from experimenters since the early days of power-driven flight is the tail-first machine, in which the main planes are at the rear and the tailplane in front. Such a machine is known as a canard in France and as an Ente in Germany, both words meaning “duck” in English.
This unorthodox layout has the special advantages that such a machine cannot be “stalled” in the air, nor turned over on the ground when landing. The first feature is due to the fact that the forward wing stalls before the main plane. It is, therefore, impossible to pull the main wing up into the stalling position and, therefore, lateral control is never lost.
The pioneer of tail-first aircraft is the German aeroplane designer, Henrich Focke, who built and flew the first tail-first machine in September 1909. His interest in the type has continued ever since and a modern example of the tail-first aeroplane is his twin-engined commercial monoplane which was produced in 1930. Known as the Focke-Wulf Ente, it is a high-wing cantilever monoplane with a fuselage of a peculiar shoe-like shape and providing cabin accommodation for a pilot and three passengers.
The main plane of the Ente is placed aft on top of the fuselage and just ahead of the fin and rudder. Two 110 horsepower radial engines, driving tractor airscrews, are mounted, one on either side of the fuselage, under the main plane.
Tail-First Aeroplane
Ailerons are fitted to each tip of the main wing, as well as small fins which serve to increase directional stability. Right in the nose is the small forward wing, which is adjustable for incidence and can also be rocked laterally by the pilot to supplement the directional control of the main rudder.
As a type, tail-first aircraft are not notable for high performance. The Focke-Wulf Ente, with a top speed of only eighty-nine miles an hour and a landing speed of fifty-two miles an hour, is no exception to the rule.
Other experimenters have sought to achieve stability in flight by a directly opposite process and have produced aircraft without any tail at all. The first of these tailless craft was invented by J. W. Dunne in Scotland in 1911 and was successfully flown with its controls locked to demonstrate its inherent stability. After that the tailless type was neglected until Captain Geoffrey T. R. Hill produced, first a glider without a tail and then, in 1926, a tailless light aeroplane which he called a “Pterodactyl”.
Like the earlier Dunne machine, the Pterodactyl is a monoplane with swept-back wings in the form of an arrowhead. The wing-tips are movable either oppositely to give aileron control, or in unison to give control equivalent to that of the elevators of an aeroplane. The rudder of a conventional aeroplane is represented on a Pterodactyl by split flaps under the wings which, when opened out, increase the drag of that wing and so turn the machine.
A MOVABLE-WING AIRCRAFT produced in America in 1934. The wings are pivoted where they join the fuselage. This permits their angle of incidence to be varied by a lever in the cockpit. These photographs show the wings in two positions which indicate the range of movement available. In the lower illustration the wings are at a greater angle of incidence than in the upper illustration.
The first Pterodactyl was a single-seater pusher light aeroplane. A much more powerful two-seater fighter type was built later; it was fitted with a water-cooled engine driving a tractor airscrew. For military use, the tailless aeroplane has the great advantage that it presents an unobstructed field of fire for the rear gunner, who is in no danger of damaging his own tail-unit when repulsing attacks made on him from the rear.
Another modern example of the tailless aeroplane is to be found in the United States, where the Arup Manufacturing Company has built a number of experimental full-size machines to the designs of Dr. Cloyd L. Snyder and Raoul J. Hoffman. The Arup design differs from that of the Pterodactyl in that, in place of two swept-back wings, it has an unbroken wing surface in the shape of a semicircle.
The straight edge of the semicircle faces forward and corresponds to the leading edge of the wing, which has, in the centre, a built-in two-seater nacelle, or cabin. An engine, driving a tractor airscrew, is mounted in the nose of this nacelle, and a normal fin and rudder are set above the circular trailing edge of the wing, which also incorporates twin elevators.
In its latest form, and fitted with an 85 horse-power engine, the two-seater Arup has a top speed of 135 miles an hour. Its greatest merit, however, lies in its ease of control, its quick take-off time of six seconds and its low landing speed of 28 miles an hour.
The latest trend in the design of unconventional aircraft now seems to be towards machines embodying wings of variable area. In France, experimental flights have been in progress
for some time past with two different machines of this type.
One of these aircraft is a monoplane, built to the design of a Russian engineer, Ivan Makhonnie; the other is a biplane which has been invented by M. Jacques Gerin.
In the Makhonnie monoplane, the wing consists of three portions, the inner part being hollow and attached to the fuselage. The middle and outer sections on either side are movable and can be telescoped to slide inside the inner portion by an arrangement of levers controlled from the pilot’s cockpit.
Telescoping Wings
With both wings fully extended, the machine has a wing area of 280 square feet. Retracted, the wing area shrinks to 68 square feet. Development of this machine has been in progress, with financial assistance from the French Government, since 1931. Plans are now in hand for a twin-engined monoplane embodying a similar wing principle.
Gerin’s variable-wing machine, which he calls the “Varivol”, achieves the same result as the Makhonnie, but by a different method. In Gerin’s machine the extensible part of each wing can be rolled up inside the fuselage or wound out along the leading and trailing edges of the fixed portion. The flexible portion of each wing is covered with a special rubberized fabric The leading edge of each movable portion is made of spring steel, which can be rolled up when desired but which, when unrolled, becomes perfectly rigid. These variable wings are wound in and out by an electric motor, either together or independently.
The prototype machine, fitted with a 230 horse-power engine, has proved so successful in flight tests that the inventor is now developing a new “Varivol” in which it will be possible to vary the wing surface from 137 square feet to 818 square feet. With engines totalling 1,400 horse-power and a loaded weight of 16,500 lb., Gerin expects to be able to attain a maximum speed of 382 miles an hour with the wings retracted, yet to be able to land at only 50 miles an hour, using his full available wing area. Maximum range is estimated at 1,552 miles and service ceiling at 31,000 feet.
The advantages of an aeroplane whose wings can be extended or retracted at will during flight are many and great. At high altitudes wing area could be increased to supplement lift in the rarefied air, and the flying speed of fast aircraft could be stepped up without causing a corresponding increase in landing speed. Such aircraft would also be able to use their full wing area in taking off with a heavy load. Once in the air, they could reduce the area of their lifting surface and thus improve their performance.
Today such aircraft are included among the unconventional types because their practicability is as yet unproven. But he would be rash who would assert that aeroplane development is yet in sight of finality, or that the unconventionality of today may not become the commonplace of to-morrow.
THE PRINCIPLE OF THE BOX-KITE was used by Santos-Dumont in his aeroplane 14 bis, which he built in 1906; a model of this aircraft is illustrated above. The wings consisted virtually of two three-cell kites set at a pronounced dihedral angle. Control was obtained by means of a single-cell movable box-kite in front of the aircraft, which was propelled by an eight-cylinder engine driving a pusher airscrew.
