The pioneers - before the 1914 war
It was appropriate that the first aeroplane should fly in the New World; what is surprising was the lack of enthusiasm which the event occasioned. In Europe there was rather greater interest, particularly in France, always a country eager to accept new ideas. Strangely, though, the first European powered flight was a curiously polyglot affair, being made in France by a Brazilian, Santos Dumont, on October 23rd, 1906. But it was another two years before the aeroplane really arrived, with Farman, Voisin, Bleriot and the rest, in France, and yet another year before Britain came on the scene in the person of A. V. Roe.
Most of these early aeroplanes closely resembled that of the Wright brothers. The biplane layout was chosen because the framework of the wings and their interplane struts formed a girder box giving most strength for minimum weight. The thin, strong steel piano wire joining the ends of the struts diagonally served to keep the structure from losing shape. The top and bottom of the "box" had curved wooden ribs added which, when covered with light fabric, formed a cambered lifting surface. The engine and the pilot were placed, naked and unashamed, on the middle of the lower wing. The arrangement so far had no means of balance. In order to achieve balance in the air there had to be two sets of lifting surfaces, a main one and an auxiliary. The Wrights, and most of the early inventors, took the easiest path and built a bamboo and wire structure out ahead on which they mounted a small plane. Then, to give control, they made this plane movable and added movable vertical surfaces on a similar girder structure aft to act as rudders.
So far, aerodynamic knowledge was more or less limited to an appreciation that a flat plate held at an angle against the wind tried to rise, and that a slightly curved surface gave even more lift. There was not much interest in, or understanding of, streamlines and air resistance. It would, in any case, have been rather optimistic to worry much about shape until flight had been achieved—and, of course, until these pioneers had taught themselves to fly. That is why most of the early pilots were content to sit in the open air and no attempt was made to cover them or their engines. Even two-seaters were like this at first.
However, in 1909, when Europe really started to get into the air, light wooden-framed nacelles covered by fabric were added to protect the legs and part of the bodies of the occupants . Most of these first fuselages were of negligible value from the point of view of. streamline, but they did give passengers some sense, false perhaps, of security.
A pioneer of this period who had original ideas with farreaching effect was Louis Bleriot—first man to fly the Channel, although this was a more emotional success and of less value than many of his other achievements. Bleriot's aeroplanes had two peculiarities: they were monoplanes and they pulled their tails along behind them on an extension of the nacelle containing the engine and pilot. The adoption of this layout showed that the inventor had a tidy and economic mind for, instead of assembling a sprawling collection of parts, he studied how each
could be combined with its neighbour to best advantage. The engine was at the front, with pilot and petrol tank behind and a continuation of the light girder on which these were mounted carried tail plane and rudder. But even Bleriot did not think it worth while to waste weight by covering more than the front half of his fuselage with fabric. He was probably right, for his 25 h.p. engines would not in any case be able to get more than forty or fifty miles an hour out of these aeroplanes because of the drag of their large wing.
The Bleriot monoplane's wing was much like those of contemporary biplanes, but it could not be braced up like a box and, instead, it was supported by a multitude of wires running to posts sticking out above and below the fuselage. These myriad wires on early aeroplanes were a feature that does not show fully in photographs for the strands were usually less than one sixteenth of an inch thick. Some idea of their number can, however, be gathered from the joke of one pilot who said he always took a canary into his biplane with him and if it escaped he knew a wire was missing!
But to return to Bleriot; others took up his idea of the tractor fuselage aeroplane, that is to say one that is drawn along by its airscrew, as being the most practical layout. Many designers, however, clung to the belief that the airscrew should push the aeroplane like a ship's propeller. These men made their machines very much like those of the Wright brothers, only they dropped the chain drive to two propellers and usually mounted one engine and propeller together behind the pilot.
With the limited structural knowledge of the period it was probably simpler to calculate the strength of the tail booms and to make them lighter than a fuselage. Even so, by the outbreak of the First World War the tractor aeroplane was already establishing the ascendancy which it has held, almost unchallenged, to this day.
In these early days most aeroplanes were conceived and built by enthusiasts very different from the highly trained scientists of today. Not a few of these pioneers were almost completely ignorant of basic engineering principles and many progressed, crash by crash, just as they learned their flying. However, by 1912 it had become obvious that aeroplanes were indeed something more than a new circus stunt and a certain amount of financial assistance was forthcoming for the experimenters . A new industry had been born. Once the aeroplane had progressed from being the plaything of "cranks" and "wild inventors" it really started to take shape. Commercial possibilities were seen, the days of encouragement by large money prizes offered by Press barons for nights round Britain were passing and, instead, the business of making money from the "gates" of flying shows was being supplemented by carrying passengers for money and the making and selling of aeroplanes.
In 1911 there was an experimental-cum-propaganda air mail service between Hendon and Windsor; in 1912 the Army held trials for the choice of a military aeroplane; and the Royal Navy followed suit. So much for the customers, they were there, but they did not have much idea of what they wanted. First concrete improvement was the evolution of the fuselage, which now began to take some recognizable shape, particularly in the case of the tractor aeroplane. Since it had to house the engine in the front, the nose was the bulkiest part. At that period there were three types of engine most in use. The in-line, liquid-cooled of four or six cylinders evolved from the automobile engine was at first very popular, since it was reasonably reliable and was fairly compact. It was, however , heavy and fell out of favour, except in Germany, when people started considering payload—that is, when the aeroplane was expected to do more than get its pilot and itself into the air.
The inadequacy of the motor engine led to the invention of special aero-engines. One of these was the air-cooled fan or radial engine. In this, instead of having the cylinders in a block surrounded by a water jacket for cooling, they were separate and covered with fins to shed the heat into the passing air. Most of these early air-cooled motors had three cylinders arranged like the feathers of a fan, or else set at 120 degrees to each other—hence the names "fan" and "radial". Obviously, such an arrangement took up a great deal of space when considered as frontal area. These early air-cooled engines were a very important step and the 25 h.p. Anzani of those days was the ancestor of the 2,500 h.p. Bristol Centaurus in the Airspeed Ambassador of today.
However, the greatest and most far-reaching invention of the period was the rotary engine, patented in France by the Gnome and le Rhone companies. This looked rather like a modern radial, save for being very much simpler, and had its cylinders (usually seven or nine) arranged radially round a short central crankshaft. The revolutionary feature of the design was that the airscrew was bolted to the crankcase and the whole engine revolved round the stationary crankshaft
which was, in turn, attached to the aeroplane. The reason for making this arrangement was that the slow speeds of those days did not cause enough air to flow round stationary cylinders for satisfactory cooling. The rotary engine worked well and was very light, so that it was eagerly adopted by French and British aeroplane constructors. True, it had certain disadvantages: the flywheel effect of the rotating engine caused the aeroplane to react in the opposite direction; because the carburettor could not be whirled round, petrol had to be sprayed into the crankcase from which it was centrifuged to the cylinders; and, to keep the petrol from diluting the lubricant, castor oil had to be used—and castor oil is as corrosive as its smell is acrid! Because of the method of supplying fuel a graduated throttle control was impossible and there was only one setting, full bore, intermediate powers were obtained by "blipping", that is, switching on and off. But to return to the aeroplane and the effect the engine
had on its shape. The whirling rotary was at first enclosed in a cowling that looked rather like a coal scuttle, but later a simple circular shape, slightly less streamlined, but much easier to make, became the most common. In both cases, it was the diameter of the engine, rather over four feet, that set the pattern for the fuselage behind it. This bulkiness led to the characteristically plump nose, with few excrescences, that distinguished the majority of French and British aeroplanes from German ones for almost a decade. Even when, about the middle of the First World War, good British and French watercooled engines came along the habit of making the front of the aeroplane plump had become so ingrained that the designers in these countries mostly continued on similar lines. Behind the engine came the pilot, and any other passengers. Usually, these sat in open cockpits, the pilot behind and his passengers in front under his fatherly eye. One pioneer of the period, A. V. Roe, did have the idea of putting his victims in a closed cabin, but his cabin biplane was not a success.
After the crew had been accommodated the fuselage had no further use save to support the tail, so it was tapered off to reduce its weight. Usually the tapering ended in a vertical post to which the rudder was hinged; but sometimes a horizontal post was used, in which case the elevator was hinged to it. At first designers did not realize that the shape behind the fattest part of the fuselage was as important as that in front and so the early bodies were crude.
The structure of the fuselage was basically simple and four long wooden poles, usually of ash, called the longerons, formed the four edges of the fuselage "box". Vertical and crosswise struts, also wood, held the edges of the box into the correct outline, the whole being cross-braced in each plane by wires.
This structure made a strong, light girder not unlike that of a bridge. The fuselage was finally given an appearance of solidity by covering it with linen or cotton fabric stretched taut by special cellulose varnish called dope. Now, with these four longerons controlling the shape it is obvious that the form of the fuselage was restricted to flat panels curved in one plane. This was not good enough for the French, who with their typical logic soon realized that a square fuselage behind a circular engine was far from ideal. They therefore decided to add fairings to the main structure before covering it. These fairings consisted of light wooden formers supporting thin wooden strips. The framework of such fairings was very light because all the main loads were carried by the longerons and their supporting structure. Somewhat characteristically, British designers showed less interest in such refinements than did the French.
From the faired fuselage followed the logical idea of making the basic structure itself the required streamlined shape. This was not so easy though; first of all it required some ingenuity to make such rounded forms and, secondly, it was more difficult to calculate the distribution of the loads in such a structure. Both these difficulties meant that the result would be heavy and lightness must always be the ruling factor in aircraft design. There was, however, a method of construction used for small racing boats, called diagonal planking, and this led to the evolution of the monocoque fuselage.
Like so many of the early aeroplane inventions, the monocoque structure came from France and the word means "single shell". In its pure form it should be like a lobster's claw, a strong skin capable of great strength and without any internal support. Such a structure is almost impossible in practice, even today with all the latest developments in plastic moulding, but something approaching it was achieved by overlaying two layers of thin wooden strips. When laid on diagonally these strips could follow the double curvature of a rounded fuselage and the method was to put two layers in opposite directions, finally covering the whole with fabric. Some of these early monocoque fuselages were very beautiful, both for their form and their workmanship; but the method was too expensive for general adoption.
So far I have dealt with only the fuselages of tractor aeroplanes , the ancestors of most modern types. It would be wrong, however, to neglect the "pusher" which, even though it eventually proved a dead-end development, was still very much in evidence.
The short fuselage of the pusher was called its nacelle—yet another of the many French words in the aeronautical vocabulary that show how much we owe to the pioneers of that nationality. Apart from housing passengers and engine, the pusher's nacelle had no structural function. The engine in its rear limited the amount of aerodynamic refinement. Also, the fact that the engine had the nacelle in front of it introduced difficulties of cooling which exist even today with the rare pusher engine installations. It is obvious that if you can put your engine, or its radiators, right in front where they get all the wind that is going (including the added blast from the airscrew ) you will get more efficient cooling. This fact meant that either you exposed more engine or had a larger radiator with the pusher than the tractor—that meant more weight, more drag and less performance.
The fuselage or nacelle, however, is but one part of the aeroplane; perhaps one should say a minor part in comparison with the wings. I have already explained how the strength of the wings was obtained from a box or cell layout in a biplane, replaced by pillars, or kingposts and wires on a monoplane. The box shape of the biplane wing was ideal for taking the booms that supported the auxiliary surfaces of pushers, so this type was always a biplane. There were two kinds of pusher, however; those like the original Wright biplane with the "tail plane" in front and the rudder behind, and those with both controls at the rear. The former, known as the canard, because it looked like the long neck of a duck, could be made a very safe aeroplane; but it was cumbersome and the two sets of booms were unnecessarily heavy. Because of this the canard died an early death, but not before the Farman brothers had given it undying fame.
The brothers Henri and Maurice Farman were pioneer pilots who early came to make their own aeroplanes. They both built pushers; but Henri did not believe in the canard, while Maurice did—actually he played safe by having elevators at front and rear. These early Farman biplanes were very safe, and very slow, and upon them were trained most of the service pilots of the First World War. It is on record that a French general was shown a number of these unlovely aeroplanes one day with the remark, "Voild, les vaches mechaniques!" The name stuck and for ever after they were known as the Longhorn and the Shorthorn.
To return to the wings. Before the first War most wings— that is the plain lifting surfaces—were much alike. They were usually straight and without taper. Their aerofoil section was crude: being thin and highly cambered rather like a flattened crescent moon. This shape was gradually modified as the more scientific experimenters got to work methodically in wind tunnels at such research establishments as the Royal Aircraft Factory (now the R.A.E.), Farnborough. In fact, the R.A.F. 15 thin all-purpose wing section became one of the most generally used on British aeroplanes from about 1913 till the end of the First World War.
The wing itself was usually made with a primary structure of two spars, to support the weight when in the air, and crossbracing struts, called compression members, between the spars, which prevented their being bent backward by air pressure. This ladder-like framework was also cross-braced by wires to prevent it from being deformed. The aerofoil shape of the wing was given by the secondary structure, which consisted of curved ribs, usually made from a flimsy wooden lattice for lightness, covered with light cotton or linen stretched taut by dope. The leading edge of the wing was held rigid by a wooden strip to prevent the wind pressure from collapsing the fabric and for the same reason there were usually short intermediate ribs between the leading-edge strip and the front spar. In the earliest aeroplanes, the trailing edge was usually formed by the
joining of the fabric on the top and bottom surfaces, and when it was tightened by the dope a characteristic serrated effect was produced. In France and Germany this type of trailing edge persisted for a long time because the thin wire which was later used to tie the ends of the ribs together would bow considerably under the pull of the doped fabric. In this country it became general practice to use a wooden slat along the trailing edge and this resulted in a much straighter line.
So much for the early wing itself and for the structure that persisted, with little change, on the majority of aeroplanes for some twenty years. I have already said something about the external bracing but now it is time to describe it in some detail. The biplane formed an excellent basic structure. The spars of the top and bottom planes were joined by wooden struts (at first round but soon to be of streamlined section to reduce air resistance) and the ends of each strut were braced diagonally to their neighbours by wires. These wires were adjustable for length so that the whole set-up could be rigged to its correct shape. The fore-and-aft wires were called the incidence bracing, because they held the wings at the correct angle to the aeroplane 's path. The lateral bracing performed two distinct functions: on the ground it supported the weight of the wings and in the air it held the weight of the fuselage suspended from the wings. For these reasons the wires running upward and outward were called flying (or lift) wires and those going outward and downward were called landing (or anti-lift) wires. Usually, the wires were duplicated, particularly the flying ones, so that if one or two broke the others would carry the normal flying loads.
It was common practice on early aeroplanes to make the upper wing of larger span than the lower. This extra length was called the overhang and it was supported in flight, or rather
its share of the total weight was hung from it, by wires running from the foot of the interplane struts to points in the spars. The weight of the overhang when on the ground was taken by wires attached to kingposts protruding from the top plane above the outer pair of interplane struts.
Most of the earliest biplanes had one wing vertically above the other, because it was easier to make them that way, but with this arrangement the flow of air over the one and under the other caused interference and reduced efficiency. That is why these pioneer biplanes had a large, and to our eyes queerlooking , gap between the planes. Soon, however, as structural knowledge increased the aerodynamic advantages of staggering the wings was realized and, in the majority of cases, adopted. Stagger, if rather poor etymologically, was an expressive way of saying that one wing was mounted ahead of the other. By so doing, interference was reduced, the gap could be made smaller, the whole aeroplane became more compact, and both drag and weight were saved.
The pre-1914 monoplane was a simple affair and was so unlike that of today as to be almost unrecognizable. True there was, about 1912 I think, an Antoinette with a cantilever wing —that is, one without external bracing—but it was an exception and was not very successful. Strut-braced monoplanes and low-wing monoplanes were also conspicuously absent. In the days of the pioneer the monoplane was strictly a wing like that already described and it was plentifully braced by wires. In the case of Louis Bteriot's designs the wing was attached to the fuselage as what we would now call a mid-wing monoplane, but the most popular layout was the parasol monoplane. With the parasol monoplane the fuselage was suspended below the wing and in flight it acted like a pendulum, making the aeroplane very stable laterally—and stability was a very desirable, and often elusive, virtue in those days. Bracing and suspension were achieved by the usual multitude of wires and the inevitable kingposts.
This book is not intended as an introduction to the theory of flight and I have assumed that the reader will have a general knowledge of the elements of that subject—such as stability and control, the way lift is obtained from a wing and so on— but what I shall try to do is emphasize some of the problems, some almost forgotten today, met by the pioneers and the way they were faced and overcome. After balancing his aeroplane with wing and tail, the inventor could direct it up and down with a hinged flap, the elevator. Directional control too, with the analogy of the ship, was easily achieved by fitting a rudder. Lateral control, however, was a problem. Before actual flight had been achieved the pioneers showed little concern for lateral control, concentrating their efforts in that respect upon stability. Even the Wrights originally banked their gliders by shifting the weight of their bodies from side to side, but they soon realized that this was inadequate. Furthermore, a little flying soon proved the need to bank aeroplanes in a turn so that air pressure under the wing prevented them from skidding outward.
The Wrights solved this problem by rigging wires to the flexible trailing edges of their wing tips and "warping" them, up one side and down the other. This wing warping was an
effective control and remained in use on some aeroplanes until 1916 or thereabouts, but it had distinct limitations. For one thing it meant designing a flexible trailing edge, which in turn meant limiting its strength, and it was not suitable for the faster aeroplanes. The solution eventually reached was the aileron, or rather the ailerons, hinged flaps, like rudders, that performed the job of lateral control without twisting or straining the wing structure.
Although the Wrights did not invent the aileron, they did invent the "joystick", or control column that operates them— and they patented it. This was a very good thing for them, since during the 1914-18 War the British Government, in order to ensure that no legal wrangling would interrupt armament supplies, paid one million pounds for the use of the invention. Needless to say, the Germans used the invention, but paid nothing.
Before continuing to the effects of the first War on the shape of the aeroplane, I am going to sum up with a few facts that show how remarkable had been the progress in the decade following the flight at Kitty Hawk—particularly when one considers that almost all advances took place in the second half of that period. The illustrations give some idea of the strides made, but some words of explanation are also needed. In addition to such highlights of advanced thought as the Antoinette cantilever monoplane and the Avro cabin biplane there were other outstanding examples, such as the Briguet "Tout-acier", an all-metal biplane; the Sikorsky "Giant" multi-engined biplanes, precursors of the modern air liner; the Glen Curtiss flying-boat, which set the pattern of that class for a quarter of a century; the Sopwith "Bat-Boat" amphibian; and the Bristol "Coanda", with its tricycle undercarriage. The S.E.4 biplane, streamlined almost to modern standards and fitted with landing flaps might well have been the Gladiator of 1934. These are some of the outstanding examples, and by mentioning them and omitting others I am sure to have annoyed quite a few of those enthusiasts who made practical flight possible and who are alive today.
As regards actual performance, the figures for the principal world's records as they existed at the outbreak of War in 1914 , are illuminating. Curiously enough, these records were all held by fairly conventional aeroplanes with a good combination of the characteristics of their day. A German Albatros biplane held the duration record at 24 hours 10 minutes in 1914. The Albatros biplane had also covered 1,200 miles in a closed circuit to achieve the distance record. The straight line distance record had been held by France since 1913 at 487 miles with a Bleriot monoplane. Germany had the height record with a D.F.W. biplane at 25,750 ft.; while France held the speed record with 127 m.p.h. set up in 1913 by a Deperdussin monoplane. The German records, made in sturdy biplanes, were to prove significantly practical in the early phases of aerial warfare. Some remarkable passenger-carrying records of that period also pointed to the practicability of the aeroplane as a vehicle. A Grahame-White biplane had stayed in the air for close on one hour with nine passengers on board and Sikorsky had lifted fifteen passengers to a height of almost one thousand feet in one of his own biplanes.