Fundamental principles of flight. Glinders. Aeroplane flights. Maxmim's flying engines
The atmosphere is a gaseous envelope encircling the earth, and though invisible, it is a real thing. We become aware of its existence when we move rapidly and experience the resisting effect offered to the passage of our bodies, and also when the air is in motion giving rise to a wind. If the hand is put under an air pump and a vacuum be formed underneath it, by withdrawing air, then we become aware of the atmOSpheric pressure, as the hand is pressed down with a force of 14'7 lbs. per square inch at sea level.
The air is elastic, and has weight, and so the lower layers of air are more compressed than the higher layers, and hence the density varies at different heights above sea level. The density being dependent on the pressure to which the air is subjected, the higher strata must of necessity be very much rareﬁed. At a height of about 100 miles the density of the atmosphere is extremely small.
In order that a body may be able to ﬂoat in the atmosphere it is necessary that it must be lighter than the quantity of air which it displaces. This is the reason a balloon will, and a feather will not, ﬂoat in still air, because the weight of the latter being greater than the quantity of air it displaces, it falls to the ground.
The force of gravitation, acting on bodies, is proportional to their inertia, Le. to their mass. The greater the extent of horizontal surface they present to the atmosphere the more slowly do they fall, hence the importance of having aeroplanes or wings of large area in ﬂying machines in order to give them the required support.
When a body falls it must of necessity compress the air underneath it to some extent, but as air is elastic it is found to move immediately away from the falling body in that direction which most quickly restores equilibrium. When an aeroplane, driven by a propeller, pasSes through the air it meets with resistance from the air currents encountered . There is the air pressing against the planes in a horizontal direction, and also that in a vertical direction ; it is this last that gives the sustaining or lifting effect to the machine. By resolving these two forces into a parallelogram we ﬁnd that the resultant force or diagonal acts on the centre of pressure of the machine, and if the intensities of the two pressures coincide with that line (which passes through the centre line of the machine) the motion of the aeroplane will be directly forwards.
In a ﬂying machine the centre of pressure is the point of suspension, when the machine is balanced for the speed at which it is travelling, this point will then be vertically under and coincide with the centre of gravity. If the angle of incidence diminishes, the centre of pressure shifts in front of the centre of gravity, stability is upset, with the result that the front part of the machine tilts up and the rear downwards, and unless the speed be increased it will fall. If the angle of incidence gets behind the centre of gravity, the opposite effects occur, the front part tilts downwards and the rear upwards.
In reading through “Travels in the Air,” published in 1871, we felt rather surprised to come across the following :“The conclusion of this dissertation, then, may be summed up by stating that men will some day or other ﬂy through the air, not by means of their own physical strength, but by means of some winged apparatus (or helices), set in motion by some powerful physical agency such as steam or electricity.” This prophecy has now come true, thanks, neither to steam nor electricity, but to the petrol engine alone.
Man seems now, after repeated failures, to have solved the problem of ﬂight, and has constructed a heavier than air machine which will really ﬂy, and so what was long considered by scientiﬁc men to be impossible has now become an accomplished fact, viz. that man is able to ﬂy. Many problems yet remain to be solved before the ﬂying machine can be used either for commercial or military purposes, it is only able to ﬂy on a calm day and against a slight wind, certainly not in a gale."‘ As the speciﬁc gravity of the atmosphere is low, and as thousands of pounds of it must be acted on per minute in order to give sustaining eﬂect, it follows that the machine must be made of large size, with a great spread of wings, and must have a high forward velocity constantly maintained in order to sustain the lifting power. The resistance during ﬂight is fully four times that of any other mode of locomotion, and from twenty to thirty times greater than that on the railway, so the power required to drive a ﬂier at any given speed is far greater than for any other mode of locomotion, and the velocity of ﬂight should be, at least, not less than from 30 to 40 miles per hour. The ﬂying machine cannot hover over a given spot, it requires to be started up to speed by some initial force ; for instance, the Voisin. (a) The kite - his apparatus we pass over, and a description of it must be sought for elsewhere.
(b) The Helimpler is a kind of ﬂying machine, having two sets of propellers ; one is ﬁxed onahorizontal shaft, and is used for forward motion only, the other is ﬁxed on a vertical shaft, and is used for vertical or ascending propulsion . Theoretically, a machine of this kind ought to be able to ascend vertically, from a state of rest on the ground to a given height by means of the rotation of the vertical propeller, and then ﬂy forwards by means of the horizontal propeller, the one propeller being thrown out of gear when the other is in action ; or both could be kept rotating together, and so cause the machine to ascend in a slanting direction instead of vertically upwards; an example of this kind of machine is seen in the Ouviere helicoptere.
(c) Gliding machines, or Gliders, have no engine and propeller; the motive power is gravity. The course of ﬂight is always inclined towards the earth. A Glider must be constructed to have very little resistance, so that it may glide easily through the air a good distance before touching the ground. Many experiments have been performed (some of them terminating fatally) with these machines down hillsides against the wind by such men as Lilienthal, in Germany (he used wings of light framework covered with cloth), Chanute, Wright brothers in America, and Pilcher in England.
Lilienthal discovered that with suitably curved surfaces the lift was greater and the tendency to drift backwards less, than when plane surfaces were used. He discovered much about the supporting power of plane and curved surfaces, wind pressures, etc. He attempted to solve the problem of how to so alter the centre of gravity of his glider, as to make it coincide with the ever-shifting centre of wind pressure. He was killed in 1896 by a fall from a height of 50 feet. Percy Pilcher, an assistant at Glasgow University, carried out many experiments, near Glasgow, on the same lines, but was killed in 1899, at Rugby, owing to the framework of his wings giving way. His glider has lately been repaired by Messrs.
In Fig. 12 is shown a Wright-Clarke glider, which was lately constructed by Mr. Clarke, who has kindly allowed me to use the illustration.
Chanute, by his gliding experiments, showed that the double-decked aeroplane was more stable and more easily controlled than the single decker, as large supporting surfaces can be got without a large spread, which means increased leverage for the wind to act upon. He also pivoted
the planes, so that their angles could be altered by the pilot.
The Wright brothers, of Dayton, Ohio, began gliding experiments in 1900. They used two superposed curved surfaces ,' they could also present one end of the wings to the wind at a greater angle than the other. A horizontal rudder controlled the vertical movements. The stability of this apparatus was so good, that the pilot could assume the horizontal position on the lower deck in order to reduce air resistance.
(d) The Aeroplane, or ﬂying machine, is propelled through the air by means of one, or it maybe two, screw propellers, and some of them have a slight ﬂapping action of the wings or planes in addition. There are two types, known as the Monoplane, having one set of wings or planes only (example, Bleriot’s ﬂyer), and the Biplane, having two sets of wings or planes (example, Wright’s ﬂyer). The principle of both is the same. The machine depends entirely upon its rapid motion for the pressure on the under surface of the planes which is required to keep it aﬂoat in the air. The biplane is said to be more stable and easier to start than the monoplane.
In 1893 the Wright brothers in America ﬁrst used a petrol engine to drive their ﬂyer. They made short ﬂights in 1904 and 1905, and astonished the world by their performances ,- but many people would not credit the reports of their wonderful ﬂights, as their experiments were carried out in private, and nobody knew whether the reports of these early performances were true or false. The ﬁrst man in France to ﬂy with a machine heavier than air was said to be M. Ader. He ﬂew for a distance of 32 5 yards, with an apparatus furnished with bat-like wings, driven by a steam engine, in the year 1897. Santos Dumont not only experimented with airships, but also with aeroplanes. He constructed a double-decked ﬂying machine, with a box-shaped rudder, which moved horizontally. It was propelled by a 50 horse-power petrol engine, and he ﬂew for 230 yards in Paris. (He is said to have been the ﬁrst in France to use a petrol engine as a motive power for a ﬂying machine.)
A year or two after this M. Farman ﬂew for 1300 yards, following this up later by a circular ﬂight of 1600 yards at Issy-les-Moulineaux. He won the Armen grand prize by ﬂying for 20 minutes 20 seconds. In some of his ﬂights he reached a speed of 36 miles per hour.
Wilbur Wright, by his performances in France in 1908, set all doubt at rest, and has turned the most sceptical person into a believer in the ﬂying machine. On his ﬁrst ascent Wright travelled three times round the Hunaudieres racecourse, near Le Mans, France, covering a distance of 1% mile in 2 minutes. In later attempts he was able to do the distance in 1 minute 33 seconds. The machine ﬂew like a bird, varying its height and direction with ease, and was looked upon as the greatest marvel of the age by all who saw it. He also covered a distance of 5 miles, manoeuvring round the racecourse and over the pine plantations.
Wilbur Wright ﬂew for 1 hour 9 minutes 45 seconds at Le Mans in October, 1908. His brother, Orville, in America, also ﬂew for 1 hour 5 minutes 52 seconds. In September, 1908, Wilbur Wright beat all previous records by a ﬂight of 1}, hour, and won the ,6 200 prize given by the Aero Club, and the “ Michelin ” Cup, valued at £800. In this ﬂight he reached a speed of 39 miles per hour. On October 12, 1908, Wilbur Wright ﬂew for 1 hour 9 minutes and 45 seconds, with a passenger on board his machine. This was M. Pairleive, a member of the Institut de France, Vice-President of the Commission.
On December 18, 1908, Wright ﬂew about 95 miles in 1 hour 53 minutes 59 seconds, beating this, on the 31st of that month, by ﬂying for 2 hours 20 minutes 23 seconds, covering nearly 80 miles.
The French aviator, M. Paulhan,* now (November, 1909) holds the world’s records: (I) for duration of ﬂight; (2) for the speed attained; (3) for the greatest height reached. At Brooklands he was 2 hours 49 minutes 20 seconds in the air, and ﬂew 96 miles, and also, at Mourmelon-leGrand , he rose to a height of 1150 feet.
Very little has been done in England with ﬂying machines compared with what has been done in France and America. Henson, an Englishman, in 1843, designed a ﬂying machine (monoplane type) and, along with Stringfellow , constructed a model which was driven by two propellers, power being obtained from a steam engine. The actual machine was never made.
In 1888, Sir H. Maxim (the inventor of the rapidﬁring army gun) experimented with machines heavier than air. He made a double-decked aeroplane, composed of steel frames 40 feet long, and covered with canvas which formed the hull. Above this was a large main plane, and ﬁve long narrow planes projected from each side. Those attached to the sides were 27 feet long, thus making the total width 104 feet, there was a fore and aft rudder.
Two wooden screws, covered with canvas, each 17 feet 10 inches diameter, were driven by a compound steam engine, working up to 300 horse-power. There was a light tubular boiler for rapid steam generation, heated by 7000 naphtha jets. The weight, with three men on board, totalled 8000 lbs. It ran on four ﬂanged wheels on rails, and was driven by two screws, revolving rapidly in the air, which gave it initial velocity for ascension. Four other wheels were outrigged, and placed so as to come in contact with a line of planking, ﬁxed above the railway, so that when the machine rose from the ground these wheels came in contact with the line of planking and controlled it, so that it did not rise free into the air. When the engines were run with 320 lbs. pressure per square inch, the speed got so great that the machine rose clear of the running rails and all the top wheels engaged on the upper track ; but this was too much for the retaining planking, and it gave way, at the same time bending the wheel axles. Sir Hiram was quite satisﬁed with his experiments, and the lifting effects of the planes were shown to be 2'5 lbs. per-square foot. We are indebted for the above notes to “ Artiﬁcial and Natural Flight,” by Maxim.
One or two trials have been made in England with ﬂying machines, as well as with a British Army aeroplane. The Aeronautical Society and Aero Club of Great Britain have secured suitable grounds in Essex where experiments are being carried on. Mr. Cody has made some good ﬂights in his ﬂyerInear Aldershot, and has carried a passenger along with himself on his machine.
M. Bleriot, at Issy, on June 12, 1909, was the ﬁrst man to carry two passengers besides himself on his monoplane. Farman performed a similar feat on his biplane shortly afterwards.