Power plants for flying machines
Some very early history
[So many of us have to do with flying these days that some early history will not come amiss, and Cecil Clutton, in the article that follows, certainly writes as a true historian. – Ed.]
“And flying machines are possible, so that a man may sit in the middle, turning some device by which artificial wings may beat the air.” – Roger Bacon, 1214-1292.)
Roger Bacon may perhaps be described as the universal genius of the Middle Ages, and aeroplanes were not the only things which he foresaw a matter of seven centuries ahead of their time.
There had, of course, been lunatics throughout the ages who, pinning themselves to, and their faith in, some grotesque device, had hurled themselves to gruesome deaths from a variety of high places. But it fell to the universal genius of the Renaissance, Leonardo da Vinci (1452-1519), to make the first scientific study of flight by watching the action of birds on the wing. He sketched out a fairly sensible scheme for a man-driven flying machine (it was, however, never made, as far as can be ascertained), designed a practicable parachute and discovered the lifting power of a horizontal airscrew. Tiny models of the latter, driven round by a spring, actually rose in the air, and were thus the first heavier-than-air machines to achieve some measure of flight.
But it needed 300 years before another flight was effected, when, in 1783, the Montgolfier brothers began making successful flights in hot-air balloons; but the history of ballooning and gliding is not pertinent to this article, which is concerned with the engines which were later applied to them.
Continuing for the moment with lighter-than-air machines, in 1852 Henri Giffard constructed a cigar-shaped airship, 40 ft. x 144 ft., containing 88,000 cu ft. of gas, and attached to it a steam engine weighing 350 lb. complete with boiler, developing 3 h.p. and driving an 11-ft. airscrew at 110 r.p.,m. It achieved 6 m.p.h. in still air, but was not generally a great success. Some experimenters continued in the same way and others tried electricity as a motive power, but in 1872 Herr Paul Haenlein made the lirst airship fitted with an internal combustion engine. It was a four-cylinder engine using coal gas, which it drew from the envelope, developing 6 h.p. Only captive flights were made with this machine.
The first machine with a genuine petrol motor was made in 1879 by Baumgarten and Wolfert. The motor was a Daimler, probably of 3 1/2 h.p. Dr. Wolfert was killed in later experiments, when an airship with an 8-h.p. motor took fire and crashed.
Turning now to the more interesting subject of heavier-than-air machines, the first genuine flights were made by a model of Stringfellow’s in 1848. This craft was a monoplane of amazingly modern design, and it can still be seen (in times of peace) in the Science Museum. The span is 10 ft. and the tiny steam engine weighed only, 8 lb., having a cylinder measuring 18 mm. x 50 mm. A later engine, weighing 13 lb., delivered 1 h.p. The construction of these engines was a great feat and his grasp of aeroplane design as a whole was some 50 or 60 years ahead of his time. Subsequent experimenters owed much to his pioneer work. A somewhat similar machine, made by Professor Langley in 1896, was a conspicuous success, flying three-quarters of a mile and attaining a speed of 30 m.p.h.
The first man to leave the ground on a heavier-than-air machine was the famous Hiram Maxim, who, in 1894, constructed a monster machine weighing upwards of 3 tons. He powered it with two steam engines delivering a total of 362 h.p. These engines were miracles of lightness, weighing only 2 lb. per h.p. – a figure not surpassed for many years – and even when complete with boiler and water the power-weight ratio was only 5 1/2 lb. per h.p. This machine was only allowed to fly as a captive, but so great was the lift developed that it broke its bonds and took a short, but undoubtedly free, flight before the horrified constructor turned off the steam and it crashed to earth.
It is interesting that further experiments were carried out with steam engines during the thirties and they have, of course, the merit that their efficiency is not diminished by the rarefied atmosphere at great heights.
In 1898 Professor Langley started constructing a full-sized aeroplane which was to be driven by a petrol engine. These experiments went on till 1903, but (whether owing to faulty design or faulty launching gear has never been really decided) the machine never flew and is, therefore, mainly of interest owing to its remarkable engine, which was made by the Professor’s assistant, C.M. Manly. After certain preliminary experiments he produced a positive marvel of efficiency, lightness and advanced design, in the shape of a five-cylinder water-cooled radial, developing 52.4 h.p. at 950 r.p.m., equal to 2.4 lb. per h.p., or 3.6 lb. per h.p. with ignition, tank, radiator and water. The water jackets were brazed round each cylinder (the first experimental engine was cooled by wet cloths tied round the cylinders!). Ignition was by coil and sparking plugs. There was one master connecting rod and big-end, the other four rods being attached to it by collars. The inlet valves were automatic and the exhaust valves were push-rod operated, being actuated by a cam ring turning against the engine. It is indeed sad that such a magnificent effort was not crowned with the success it deserved, for the motor which first carried the Wright brothers into the air was a greatly inferior business.
We now come to the first successful flight by a man-carrying, heavier-than-air machine which, as everyone knows, was achieved by the Wright brothers. The exact date upon which their efforts were crowned with success was December 17th, 1903. They, too, built their own engine, which was a four-cylinder of 4-litre capacity (112 x 100). 1 t ran at 1,300 r.p.m., and while it was never tested on the brake, it was reputed to deliver 12-15 h.p. This would be equivalent to the almost unbelievably low m.e.p. of 20 Ib./sq. in., and it is difficult to believe, even in 1903, that such an engine would not have developed between 18 and 24 h.p. at 1,300 r.p.m. The weight was 240 lb., which, although giving a poor power-weight ratio, was (and would be to-day) very good for what was, in fact, a fairly ordinary motor-car engine of 4-litre capacity. It lay on its side (the aviator, by contrast, lay on his stomach) and had aluminium water jackets round each cylinder barrel – the heads were not cooled at all. The connecting rods were of tubular steel and the pistons of cast-iron. Ignition was by low-tension magneto and the cooling water was circulated by a gear type pump. The valves were horizontally opposed, the inlets being, of course, automatic. In later experiments the Wrights employed vertical four and six-cylinder in line units.
The first successful European aeroplane and engine was the 1906 Antoinette. The engine was a 90˚ V8, developed 50 h.p. and weighed only 5 lb. per h.p. It was technically interesting as being steam cooled and solid fuel was injected into the cylinders by a variable-stroke fuel pump. This system, again, has been the subject of much modern experiment, as it is not affected by the angle of the machine, nor by altitude.
Other pioneers in the field of early aero engines were Anzani, who solved the problem of using head-down cylinders which did not invariably oil up the plugs, and also made the first two-row radials. It was using an Anzani three-cylinder engine that Blériot made the first Cross Channel flight in 1909.
In 1908 appeared an engine which was to sweep all before it for several years to come – the famous Gnome rotary, designed by the brothers Seguin. Even they, however, were not innovators, for in 1895 the firm of Millet had produced a racing motor-tricycle in which the engine was a five-cylinder fixed to, and rotating with, the back axle! This alarming machine was not crowned with success, and the people who were willing to drive it must have been exceedingly few.
The Gnome had the very favourable power-weight ratio of 3 1/2. lb. per h.p., and by 1913 it had grown as many as 14 cylinders in two rows, developing 180 h.p. The hollow crankshaft acted as an induction pipe and pure castor oil was fed in with the mixture, having the merit, for lubricational purposes, that it did not combine with the mixture. The oil consumption was terrific, though the engine needed all it could get. The inlet valves were situated in the pistons, being suction operated, and the exhaust valves were push-rod operated in the heads, which also housed the plugs. Current was led to a terminal and the loose end of each plug lead wiped it as it went past – a delightfully ingenious yet simple solution of an apparently insoluble problem! The engines were, of course, air cooled and revolved at some 1,100 r.p.m. There can seldom have been an engine of such eccentric design which achieved so overwhelming a success as did the Gnome, largely on account of its reliability.
Design in 1909 was adequately dealt with by J. Lowrey in an interesting article in the January, 1942, issue of Motor Sport, and progress thereafter followed fairly normal lines. This article, therefore, is mainly restricted to sketching in outline the development of the aero engine during the 60 years from Stringfellow’s successful model in 1848 to the epoch-making Gnome of 1908.
By comparison modern power-weight ratios represent a marvellous advance: 1 lb. per h.p. is not uncommon, and the record stands at about .75 lb. per h.p. But by comparison with modern low-output aero engines the early units do not show up so disadvantageously, for the ratio of engines now supplied for light aircraft, developing anything from 10 to 60 hp., is seldom better than 2 or 3 lb. per h.p. Again, modern small-car practice works out at 8-10 lb. per h.p., although, of large engines, the V12 Lagonda achieves the very creditable ratio of about 2 lb. per h.p. in Le Mans tune. It would be most interesting to know the ratio on the 1937 Auto-Union and Mercédès-Benz, which must have been lighter than 1 lb. per h.p. by quite a noticeable margin.