The Rise of the Flying Machine. Hugo Byttebier
to a modern aeroplane as it had a monoplane wing in front and a small fixed tail at the rear. It weighed only 16 grams (0.56 oz) and with a wing that had a surface of 490 square centimetres (0.53 sq ft) the wing loading amounted to merely 0.0714 lbs/sq ft.
It was driven by a single propeller at the rear and, in order to counteract the torque of the revolving propeller, one side of the wing was made longer than the other.
After applying the necessary energy to his rubber strands by giving the propeller 240 turns, the little aeroplane flew for 11 to 13 seconds, covering between 40 and 60 metres (130 to 200 ft.). Because of the low wing loading it flew very slowly at 3.6 m/s (about 13 kph or 8 mph) and yet showed a remarkable steadiness in flight.
Pénaud had discovered the secret of inherent longitudinal stability. He described his discoveries and the calculations related to them in a remarkable article published in L’Aéronaute of January 1872 under the simple title “Aéroplane Automoteur” and with the revealing subtitle “Stabilité Automatique”.
As he stated in the article, “Luckily, after a few investigations, I imagined a very simple device, which achieved the desired goal.” This simple device was a small fixed horizontal tail, inclined downwards with reference to the main lifting wing and at a certain distance to the rear. Just as Cayley had indicated the way to obtain lateral stability by giving a small dihedral to the wings so that they looked like a flattened V when seen from the front, Pénaud now proposed to use the same means in a longitudinal direction because the angle formed by the wing and the stabilizing tail also formed a very flat V.
Because this tail surface was restraining, it produced a certain amount of drag and hence power was wasted by this kind of construction, but it is the toll that has to be paid in return for safety in the air.
The propeller of the “Planophore” was at first situated at the rear, but in 1875 he also flew a planophore with a tractor propeller at the front. The little model plane was so stable that it flew without a vertical fin, but it could only fly in a windless atmosphere, preferably indoors, where most of Pénaud’s exhibitions were held.
His article ended as follows: “Whatever the results, my planophore proves the possibility of the aeroplane system, the possibility of a stable equilibrium surrounded by air and promises a considerable speed for great machines.”
In 1871 it may be said that all the elements of the modern aeroplane form were in existence, excepting again, the engine. Inspired by Pénaud’s research, a new branch of the existing aeronautical society was formed as the Société Française de Navigation Aérienne. Hureau de Villeneuve was appointed its president and Pénaud was the archivist and librarian. He thus had access to all the publications of the society and he studied every one of them.
In the January 1873 issue of L’Aéronaute, he published a theory of the aeroplane entitled “Laws of Gliding through the Air” in which he made reference to Newton, to Navier’s error, to Wenham and to Cayley, whose articles, published in France in 1853, he had also read.
Cayley’s writings aroused his interest and he began to search through British technical literature of the early nineteenth century, eventually coming across Cayley’s triple paper “On Aerial Navigation” in Nicholson’s Journal in 1809 and 1810, referred to previously.
Pénaud thus encountered a mind equal to his own and was astounded by the clarity of Cayley’s essay: “These writings,” wrote Pénaud, “which have lain dormant and forgotten on the dusty shelves of old libraries, are among the most important which exist relating to aerial navigation.”
“Nobody has understood the impact of this mind, nobody has encouraged or helped him, or was stimulated by these life-giving ideas. The tree died before it bore fruit and Cayley’s very existence was unknown in France. It is our duty to raise his name from oblivion.” And he duly did so, as Cayley’s triple paper was translated into French and published in L’Aéronaute during 1877.
The Study of Bird Flight
Meanwhile, Professor Etienne Jules Marey had made profound studies of the flight of birds. After it had been discovered that by putting a kite in motion it could fly like a bird, Marey’s observations showed that a bird is also like a kite, meaning that it follows the same aerodynamic laws as the fixed-wing flying machine.
Marey showed that a bird’s wing consists of two sections; a central part that provides lift like an aeroplane’s wing, whilst the bird’s wingtips provide thrust, working like propellers. The bird flies because it acquires horizontal speed and not because it flaps its wings up and down. “Translation gives three times as much lift as down beating”, said Marey and he gave the definitive proof by tying a bird with a long string to the ground. As soon as the wire became taut and the bird’s horizontal progress was arrested, the poor animal, for all its frantic flapping, fell to the ground.
The bird’s wingtip was at that time called “aileron” by the French, a word that was to acquire, quite by accident, a completely different meaning in 1908.
Marey was not the first to have discovered the true movement of the bird’s wing because Cayley had already become aware of the bird’s mode of flying in 1808 and several others after him, notably Wenham (as Pénaud was quick to point out). Marey himself became involved in a heated controversy with S. B. Pettigrew, Professor of Anatomy at the University of St Andrews, who had described a similar theory of bird flight a year earlier.
But Marey’s publications received wide publicity, and even inspired the Wright brothers’ 25 years later. Another effect was that several of Pénaud’s fellow members of the Société, among them the president Hureau de Villeneuve, were dedicated to the building of flapping-wing models which were patterned, or so they thought, after birds.
Pénaud thereupon built a flapping-wing model himself, with the tips providing thrust and the central part providing lift, as with a real bird. It was tested in 1872 and an improved model was built in 1874 and, as Charles Dollfus wrote, “a better result with a flapping-wing machine has never been obtained”.
Pénaud’s Master Patent
In spite of the optimal results of his flapping-wing model, Pénaud remained convinced that “Only the aeroplanes give hope for building full-size machines”. But Pénaud remained for the time being alone in his outlook. The Franco-Prussian War of 1870-1871, and the contact which the beleaguered city of Paris had with the outside world by means of balloons, had turned the attention of the aeronautically minded towards the emergence of the dirigible balloon, which was thought to be around the corner.
In 1875, Pénaud published a complete theory of soaring flight that, according to his perception, was only possible because rising currents of air counteracted the downward glide of the bird under the attraction of gravity. He had already remarked on this in an article published in 1871 dealing with the possibility of human flight without power. Soaring was, like the flight of the kite, flying by the power of the sun.
At a Société meeting on 3 December 1875 Pénaud declared: “We know the true theory of flight, the demonstration of it has been done. We have now only to replace the elastics by heat engines of sufficient power and capable of continuous action.”
Pénaud worked hard during the year to arrive at the specifications for a great man-carrying aeroplane. Several sketches of modern-looking aircraft have survived though the definitive choice, for which a patent was applied and granted, was a kind of flying wing, a step away from the planophore concept. He was probably anxious to cover as great a wing area as possible and fought shy of the construction problems related to wings of high aspect ratio.
Pénaud’s patent (No. 111,574) of 16 February 1876, applied for in his name and that of Paul Gauchot (a mechanically minded enthusiast with whom he had become friendly) is generally regarded as describing a typical aeroplane but when the patent