The Rise of the Flying Machine

Percy Pilcher (From 1895 to 1899)

Lilienthal’s most brilliant follower was the British inventor and pioneer aviator Percy Sinclair Pilcher. Born in January 1867, after seven years in the Royal Navy from the age of thirteen, Pilcher undertook an apprenticeship in a Glasgow shipbuilding firm, subsequently being appointed as assistant lecturer at Glasgow University in 1891. After his appointment Pilcher started flying experiments, inspired by newspaper reports of Lilienthal’s successful gliding flights.

Pilcher built his first glider early in 1895. He stated that he purposely finished his own machine before going to see Lilienthal so as to get the greatest advantage from any original ideas he might have. This first glider was named the “Bat” and was a monoplane with a pronounced dihedral, weighing 45 lbs and with a wing area of 150 sq ft.

In its first form the “Bat” was therefore defective in lateral stability and, having no horizontal tail, in longitudinal stability as well. According to the historian of aviation and biographer of Pilcher Philipp Jarrett, the “Bat” was not completely finished in April 1895 when Pilcher travelled to Germany for a visit to Otto Lilienthal.

Lilienthal must have been delighted to meet such an appreciative and intelligent pupil and, on his second visit in June 1896, Pilcher was allowed to fly one of the biplane gliders Lilienthal was then using. Lilienthal taught him a great deal and inculcated in him the necessity for inherent stability, a lesson that Pilcher never forgot. Back in Britain he reduced the dihedral angle of the “Bat” and added a fixed horizontal tailplane.

Pilcher began is first flying test on 12 September 1895 starting from the slopes of a grass hill on the banks of the Clyde near Cardross in Scotland. For his second test, in order to be able to take off from low ground he devised a system whereby a team of horses going at a gallop towed the glider into the air against the wind so that he was able to make gliding flights of up to a minute without the need to continually climb hills as Lilienthal was doing.

He then thought of installing an engine and built a second glider which he called the “Beetle” because, with its broad square wing, it looked like one. The wing of the “Beetle” had no dihedral at all and covered 170 sq ft but it was heavy at 80 lbs when empty. There was no light engine to be had at that time and the “Beetle” was not much of a success as a glider. Pilcher found he was unable to control it in the air, because this had to be done by shifting his body just as Lilienthal manoeuvred his gliders. He thereupon returned to his earlier “Bat” and, after several modifications, carried out various successful flights.

In the spring of 1896 Pilcher built his third glider, the “Gull”. In a bold move, the wing area was enlarged to 300 sq ft and the weight was kept to a low 55 lbs, but Pilcher had gone too far in lowering the wing loading and the “Gull” was nearly unmanageable in any kind of wind.

The “Gull” did not last long either and was replaced by a smaller version of it, named the “Hawk”, which became Pilcher’s most successful machine. The wing area was reduced to 180 sq ft and it weighed 50 lbs. The need for inherent stability was kept firmly in mind and when Lilienthal crashed to his death in August 1896, Pilcher, who had heard about the redesigned movable tail, offered what was probably the correct diagnosis of Lilienthal’s accident, which was probably due to the abandonment of inherent stability in favour of positive control.

The “Hawk” was such a success that Pilcher again began to look around for an engine capable of overcoming the force of gravity, the glider’s source of power. “The object of experimenting with soaring machines” wrote Pilcher at that time, “is to enable one to have practice in starting and alighting and controlling a machine in the air. They cannot possibly float horizontally in the air for any length, of time, but to keep going must necessarily lose in elevation. They are excellent schooling machines and that is all they are meant to be, until power, in the shape of an engine working a screw propeller... is added.”

Pilcher, at that time heard rumours of an engine in the US which gave 1 hp for a weight of 15 lbs, but which never materialized. So, like most of the pioneers of that decade, Pilcher decided that he would have to build an engine himself. He designed a two-cylinder horizontally-opposed engine which he calculated to give 4 hp for a weight of 44 lbs and, after achieving some very good flights, especially one in June 1897 during which he covered 750 ft under perfect balance, he started to build a powered aeroplane.

In 1897 Pilcher had formed a company in partnership with W. G. Wilson, and in November had begun corresponding with Chanute. In January 1898, whilst he was working on his engine, he wrote to Chanute that he intended to make “a machine like one of your multiple sail ones”. Chanute replied that Pilcher was welcome to make a multiple-wing machine, but he ruled the biplane out because Chanute did not wish to incur Herring’s wrath.

Pilcher thereupon designed a project for a quadruplane, but finally decided on a triplane, as favoured by Chanute, including the stabilizing tail at the rear which was fixed according to Lilienthal’s directions. But before he could finish his engine so as to have the triplane ready for tests in flight, Pilcher’s fate overtook him.

In the midst of a drive for raising funds to help defray the cost for the powered machine, Pilcher decided to make a demonstration flight in the “Hawk” in the presence of a select group of visitors, among whom were Major B. F. S. Baden Powell, secretary of the Aeronautical Society and later its president, who had come down from London for that purpose.

On 30 September 1899 the visitors were present and Pilcher was anxious not to disappoint them and, although the weather was unfavourable with gusty winds and light showers, he decided to go ahead. His take-off system at that time consisted in having his plane towed by means of a tackle that multiplied the speed of the two horses that drew it. A first attempt was successful but the line broke. On the second attempt one of the guy wires holding the tail in position broke and the “Hawk” dived down out of control and crashed.

Pilcher died two days later of the injuries he had sustained, the second victim of heavier-than-air machine experiments and the first victim of structural failure during flight. He was also the first of several airmen who suffered accidents which resulted from risk taken in adverse circumstances so as not to disappoint spectators who had come to witness a flight.

Stability versus Control

Most of the aviation pioneers of the nineteenth century were handicapped by their inability to differentiate unequivocally between stability and control. Again it was Sir George Cayley who put the problems in their proper perspective. He argued that the first requisite for a flying machine was lift; the second was stability in the air, and once these qualities were assured then control had to be added.

Pénaud’s model aeroplanes were inherently stable, but he later incorporated methods of control in the specifications of his patent. On the other hand, the bird and its admirable way of flying had given too many people the idea that it would be easy to manage an aeroplane in flight by a multitude of controlling devices, while disregarding stability altogether.

In Lilienthal’s case it is easy to see why he abandoned the inherent stability of his most efficient gliders, those which he used from 1892 to 1894. It was because he wanted to achieve longer flights, which in turn demanded larger wings, and as he also wanted to fly in stronger winds, this required better control and, added to that, he also wanted to incorporate a motor. All these factors made for larger and heavier aeroplanes, but the steering of these by means of movements of the body was becoming increasingly hard with every pound of weight that was added.

The idea of introducing movable auxiliary surfaces for better control was correct, but the relinquishment of inherent stability was not. It would take ten more years before the aircraft designers became conscious of the fact that controls had to be superimposed on an inherently stable construction and that to abandon stability in order to obtain better control was a grave mistake.

Octave Chanute (1890/1894)

Ader, Maxim and Lilienthal were not very interested in each other’s experiments. Maxim called Lilienthal a parachutist and Lilienthal countered by referring to Maxim’s costly trials as “how not to do it”.

But in the United States a man who was keenly interested in all aeronautical pioneers was becoming active and was preparing to devote the last years of his life exclusively to the promotion of human flight. By so doing he came into contact with most of those who were involved in aviation during the eventful last decade of the nineteenth century. This man was Octave Chanute.

His interests soon turned him into an indefatigable letter-writer. One of the first letters he wrote when he returned from his trip to Paris was to Mouillard, along with a copy of the paper Chanute had delivered at the International Aeronautical Conference of 1889.

Mouillard replied on 16 April 1890, thanking Chanute for his pamphlet but commenting on his “deplorable habit of paying little attention to writings pertaining to pure mathematics” and indicated that he was proceeding instinctively and was being moved by his tremendous enthusiasm. He ended his letter with “enthusiastic greetings”, after referring to his “professors” in the following terms: “In case some theoretical problems are confronting you in your experiments I would like to put my professors at your disposal; they are neighbours of mine, two vultures, which are brilliant demonstrators.”

It was clear that Mouillard remained completely devoted to the intricacies and wonders of bird flight and his enthusiasm was soon shared keenly Chanute, who became as convinced of the necessity of imitating the “instinct of the bird” as Mouillard.

Now that Mouillard had found a kindred spirit there was no stopping him, and on 20 November 1890, in another long letter to Chanute, he explained how a bird warped the tip of its wing in order to arrest its movement through the air on that side, thereby inducing a powerful turning movement. Mouillard explained that he had reproduced this movement several times and that the displacement of the body (just as Lilienthal was able to do a few years later) or the diminishing of the wing surface was far less effective than the warping of the wing tips which he called a “brutal means of steering”.

Chanute was greatly impressed by Mouillard’s elucidations and this was to have a far-reaching effect on the aviation movement, although that effect was not unequivocally beneficial.

Meanwhile Chanute worked assiduously to sort out the notes on aviation that he had been making since 1855, and which he now arranged for a series of articles that were published in The Railroad and Engineering Journal, starting with the October 1891 issue. The series continued through twenty-seven issues up to January 1894.

As though his voluminous correspondence and his articles were not enough, Chanute had returned from Paris with the intention of organizing an international air conference like the one held in Paris in 1889.

He was assisted in the organization of this new undertaking by a young professor at Notre Dame University, Albert Zahm, who became secretary to the conference. It was held in Chicago from 1 to 4 August 1893 in connection with the Columbian Exposition. It was the third international aeronautical conference after the one held in London in 1868 and the other in Paris in 1889.

The first paper was posthumous. It was a very cogent study, “On the Problem of Aerial Navigation”, written by C. W. Hastings in 1892, shortly before his death at the age of just thirty-three.

Hastings explained that the first requisite of flight was lift and remarked that scientists were willing to admit that “when sufficient progress shall have been made in mechanical science, true aerial navigation will be possible and will be accomplished.” This gainsays the popularly held theory that most scientists at some time or other had declared human flight to be an impossible dream.

Hastings then continued by explaining that the second requisite for a flying machine was stability. “If an apparatus possessed the necessary supporting surface and a sufficient motor and motive instrument to propel it through the air at sufficient speed, yet aerial navigation would be far from accomplished. The machine might still lack stability.” These ideas were clear and concise and were formulated in 1892 by a scientist of great insight.

Hastings proposed the dihedral angle for transverse (lateral) stability and suggested that a vertical keel should be added, explaining that “Such keel cloths may terminate in a vertical rudder and thus allow of steering the machine.” The vertical fixed tailfin for stability and a vertical rudder for steering were here proposed as a combined tail as exists on nearly all modern aeroplanes.

For longitudinal stability Hastings advocated the fixed horizontal Pénaud tail at the rear, but remarked that “it will be somewhat wasteful of power”, which was correct but inevitable. The different methods proposed to obviate this slight waste of power by designing a fixed tail at the front (the so-called canard form) were never able to provide safety equal to the still universally adopted Pénaud system.

There was no mention of lateral control by means of ailerons or similar devices, so that Hastings followed in the footsteps of Sir George Cayley and Alphonse Pénaud when specifying the priorities required of a machine able to carry a human operator.

Many of the papers presented at the conference were dedicated to the intricacies of soaring flight, including several by Frenchmen. Chanute probably translated these himself.

He had also asked Mouillard to contribute, and Mouillard (who lived in Egypt) duly obliged with a paper entitled “A Programme for Safe Experimenting”. Mouillard’s idea of experimenting safely was to use a tailless glider “so designed as to admit of adjusting the wings to the speed of the wind and of thrusting their tips forwards of backwards of the center of gravity so as to change the angle of incidence at which the machine needs the wind”. He duly referred to d’Esterno and Le Bris and repeated his conviction (which he had already propounded in his book of 1881) that: “Ascension can be effected by skillful utilization of the power of the wind and no other force is required.”

In Mouillard’s opinion, one had only to move the tips of the wing forward sufficiently for the machine to be lifted. He also insisted on “powerful means of steering it horizontally” so as always to be able to meet the wind head on. This steering effect was to be obtained by lowering the tip of a wing, as he had already explained in his letter of 20 November 1890.

Chanute had become so intrigued by Mouillard’s supreme confidence and the means he proposed, that he not only assisted Mouillard financially to build a glider (that was never tested) but he also helped him to apply for a patent in the US. Based on his idea of a wing-warping glider, Mouillard’s patent was filed by Chanute on 24 September 1892 and issued on 18 May 1897. Claim 12 clearly covered a soaring machine “having (the wing’s) rear edge free from the (main) frame of the wing and cords attached to said rear edge for pulling it downward”.

Another renowned contributor was S. P. Langley who, although not committed to the unstable soaring machine, as his future activities would show, had become interested in finding a reason for the problem that still appeared inexplicable to many: why a bird could remain in the air with outstretched and unmoving wings for long periods of time without losing height. The solution Langley had found was condensed in the title of the paper he submitted, “The Internal Force of the Wind”. Although it was an interesting theory it was not the correct one.

A similar theory was offered by Zahm in a paper that sought to explain the problem by the existence of windgusts, whilst the Frenchman Bretonnière ventured the theory that the heat of the sun was the moving force and in this he was much nearer the mark.

Lilienthal contributed with parts of an article about his glides of 1892 and the Austrian Wilhelm Kress was also at hand with a theory of his own. Additionally, one of the oldest theorists of fixed-wing flight, Charles de Louvrié, contributed a paper about “The Theory of Soaring Flight”.

De Louvrié, who had written his first paper about aeroplane-type flight nearly thirty years before, again hit the mark by indicating the ascending wind as the principal cause of the horizontal flightpath of the great soaring birds and he added the keen observation that: “Such a thing as a horizontal wind hardly exists, we need but to watch the whirling of dry leaves in Autumn”. De Louvrié had proposed fixed-wing flight at a time when very few people believed in it and his paper at Chanute’s Congress was his swansong before his death the following year.

Another pioneer who was experimenting with gliders was J. J. Montgomery, who discussed various theories on soaring flight; and from Britain there was an article submitted by B. F. Baden Powell entitled “The Action of a Bird’s Wing”.

The most interesting papers, however, were presented by those who were busy working with kites and who necessarily were confronted by the overriding quest for stability. The most important of these papers was read by Lawrence Hargrave. This Australian researcher had progressed from flapping-wing to fixed-wing aeroplane models, and in 1892 had started a series of experiments on supporting surfaces to find out how lift and stability could be obtained with the least possible expenditure of power.

He experimented with a series of kites until he hit on the famous box kite, which was an inherently stable construction. Hargrave thereupon committed himself enthusiastically to the achievement of inherent stability. In the biplane box kite construction Hargrave turned to Wenham for inspiration, and he explained that he had not found additional support in the use of a second superposed wing but had accepted the results obtained by Langley in 1889 on an experimental biplane construction.

So, it may be said that the biplane evolved from the general theory of superposed planes proposed by Wenham in 1866 and from the experiments made by Langley in 1889. But here also the origins can be traced back to Cayley who, horrified at the extension of the monoplane wing in Henson’s project of 1843, proposed a triplane construction in the following terms: “to compact it into the form of a three decker, each deck being 8 or 10 ft from the other to give free room for the passage of air between them”.

Hargrave declared that the tandem-wing construction he used was more stable when separated by an interval than when conjoined. As he invariably gave everybody his due, in his paper he referred to a patent of 1871 by Danjard and the building of the first tandem-wing aeroplane model by D. S. Brown in 1874.

The box kite was more wasteful of power than the Pénaud construction because of the additional drag caused by a second cell at the rear and by the vertical curtains at the sides. Hargrave also experimented with flat and curved wing sections and he discovered that curved wings pulled twice as much as flat ones.

Another kite experimenter who contributed was William A. Eddy. He had arrived at the conclusion that the motive power of a flying machine should be applied at the forward end and that “a drag should be trailed from the rear”. This again was the stabilizing action of the Pénaud tail, and Eddy added perceptively that the fixed tail should be put at a certain distance from the centre of gravity for optimum stability. Here we notice that the modern aeroplane form was again attained by experimental work on kites.

Professor Zahm contributed with a second paper about “Stability of Aeroplanes and Flying Machines”, and although he did not cover any new ground with regard to stability, he did point out the importance of having the stabilizing fins and tails far removed from the centre of the mass. He also caught a glimpse of aileron action because, in imagining the wings at both sides of an aeroplane fuselage as a series of slats, he indicated that the pilot “could wheel to right or left by giving one set of slats a little different slope from the other”.

There can be little doubt that the basic shape of the modern aeroplane appeared before the end of the nineteenth century. Langley probably interpreted what most pioneers believed during the last decade when, in an article in the magazine Century in September 1891, he wrote: “Progress is rapid now and it is possible, it seems to me even probable, that before the end of the century we shall see this universal road of all embracing air... travelled in every direction.”

In the issue of Scientific American of 15 September 1894 in which the Maxim flying machine and its boiler were described, a sensational notice appeared, stating: “Last Tuesday, July 31st, for the first time in the history of the world, a flying machine actually left the ground fully equipped with engines, boiler, fuel, water and a crew of three persons. Its inventor, Mr. Hiram Maxim, had the proud consciousness of feeling that he had accomplished a feat which scores of able mechanics had stated to be impossible.”

It is not difficult to imagine that this text emanated from the proud inventor himself, especially when it went on to say that “its very success was the cause of its failure for not only did it rise but it tore itself out of the guides placed to limit its flight and for one short moment it was free”.

In the same year (1894), Chanute published Progress in Flying Machines, a book which comprised a series of articles by him that had appeared previously in the Railroad Journal. It was the most complete description of all experiments with heavier-than-air machines that had ever appeared and it immediately became required reading for all those who were interested in aviation, at least in the English-speaking world, as it was never translated into French.

At the time of publication Chanute had studied so many forms of flight that he had become slightly confused, and more so because he was just then under the influence of Mouillard and dutifully described all Mouillard’s theories about continuous soaring without the assistance of any kind of engine. In a discussion about the promotion of longitudinal stability, Chanute mentioned three ways of attaining this: first by placing “additional surfaces at a slight angle to the main surface”, which was Pénaud’s system and is now universally adopted. The second, “by placing several surfaces behind each other” which was a reference to the method adopted by Hargrave and taken up by the French in 1905. The third method was the one “universally employed by the birds”. Chanute did not indicate his preference and so left the aviation experimenters without any clear indication as to the way ahead.