The altitude record for aeroplanes was raised in 1937 to more than 50,000 feet, at which height continued research is being carried out by the Royal Air Force to explore the possibility of establishing regular military and commercial flights in the upper atmosphere
TAKING OFF ON A RECORD-BREAKING ASCENT. The Bristol monoplane 138a was built in 1934. In September 1933 Squadron-Leader Swain reached a height of 49,944 feet in this plane. The record was broken again in June 1937 by Flight-Lieut. Adam, who reached a height of 53,937 feet.
THE history of research in the stratosphere — a region extending upwards to a height of thirty or fifty miles, and having its “floor” at a height varying between six and ten miles — may be said to have started on May 27, 1931, when Professor Auguste Piccard made the first ascent into the unknown regions.
Before that date, many altitude-seekers had lost their lives at heights of five or six miles because of the lack of oxygen. Piccard solved the problem with his ball-car or sealed gondola, and he prepared the way for many balloon ascents to heights between nine and fourteen miles above the Earth.
The objects of balloon stratosphere ascents are scientific. Such ascents are invaluable for the collection of material relating to the physical properties of the upper atmosphere. In more recent years, however, many high-altitude flights have been made in heavier-than-air machines. The object of aeroplane stratosphere research is to conquer the upper atmosphere for military or commercial purposes and, if possible, to make it a highway for the future passenger traffic of the world. Strictly speaking, aeroplane ascents should be classified under the heading of “substratosphere” research, for in the rarefied regions of the upper stratosphere there is insufficient air for a machine driven by an airscrew to operate.
The altitude record for balloons has been raised from 51,775 feet in 1931 to 72,395 feet in 1935; in June 1937 the record for aeroplanes was raised to 53,937 feet. These figures are a practical reminder of the vast difference between the two lines of research.
For many years the Royal Air Force has been making a systematic study of the problems involved in stratosphere flight. High-altitude research has an extremely important bearing on future aircraft design and construction, and flight at 30,000 feet or more has both a commercial and a military interest.
Above 30,000 feet clouds are rarely encountered and visibility is nearly always perfect. Astronomical aids to navigation can thus be used to their full advantage. Vertical currents are almost entirely absent at such heights, and flight is therefore exceedingly steady. High speeds may be attained with engines and aircraft specially designed for flight at high altitudes, and much valuable information about engine development is obtained from a close study of the problems of such flights.
THE SPECIALLY INSULATED COCKPIT of the Bristol 138A monoplane, designed for flying in the stratosphere. Seated in the cockpit is Flight-Lieut. M J Adam, who took the plane up to a record height of 53,937 feet on June 30, 1937. A sliding roof of transparent material enables the cockpit to be enclosed, and emergency instructions tell how the pilot may be extricated if he is unable to free himself.
In 1936 and again in 1937 it was announced that the world’s altitude record has been broken by a British aeroplane. These announcements were outward and visible signs of the R.A.F.’s activity in the sphere of high-altitude research. They were merely means to an end — which has not yet been reached.
Record breaking of any kind is always associated with a certain amount of publicity that tends to mask the tremendously important work which continues unceasingly. The altitude records are no exception. They may be regarded as valuable stepping stones along or up the road of progress, but in themselves they are less important than the data which are accumulated in the course of high-altitude research.
In September 1936 Squadron Leader F. R. D. Swain, of the Royal Aircraft Establishment at Farnborough, Hants, gained the record for Great Britain by flying to a height of 49,914 feet. The aeroplane and engine used were not specially built for the purpose of record breaking; they had been designed for carrying out high-altitude research and had been ordered by the Air Ministry in 1934, when an order had been placed with the Bristol Aeroplane Company for an aeroplane suitable for flights at levels of 50,000 feet or more.
A LOW-WING CANTILEVER MONOPLANE, the Bristol 138A is built almost entirely of wood, because of the need for the lightest possible structure. The plane weighs 4,391 lb, or 5,310 lb when fully loaded for a high-altitude flight.
This aircraft was to be used as a high-flying laboratory to gain experience in the operation of engines, equipment and instruments in the attenuated atmosphere and low temperatures of the great heights.
The aircraft was a low-wing cantilever monoplane known as the Bristol 138a, and it had many interesting constructional features. Except for the engine mounting and the cowling, it was built entirely of wood, because of the need for the lightest possible structure.
The complete plane weighed 4,391 lb., but when it was fully loaded for the high-altitude flight its weight was 5,310 lb. It had a wing span of 66 feet and a length of 44 feet. A conventional type of fixed undercarriage and a tail skid were used for the sake of lightness; retractable undercarriages are standard practice on modern planes, but involve a considerable amount of extra weight.
Insulated from Cold
The plane was built primarily as a single-seater, but provision was made for its rapid conversion into a two-seater. In two-seater form it would be equipped with radiotelephony and with an electrically controlled camera. The use of a sealed pressure cockpit was considered, but as a sealed pressure suit somewhat resembling a diving suit had been specially developed and successfully tested, it was decided to use an ordinary enclosed cockpit.
This cockpit, aft of the rear wing spar, was exceptionally roomy and comfortable considering the size of the plane, and it was well insulated from cold, provision having been made for warming it by air flowing past the lubricating oil coolers in the wing. These oil coolers were designed to form the leading edge of the centre section of the wing on either side of the body. A pump was used to force the oil through the pair of coolers on its way from the engine back to the oil tank. The airscrew was made of wood and was a four-bladed type of fixed pitch, the pitch having been modified after some experience of high-altitude flying.
The cockpit was equipped with a sliding roof of transparent material, and a handle was arranged by which the pilot could open it to any desired extent. A quick release for use in possible emergencies was also fitted. The windscreen was provided with a wiper, and the pilot was faced with instruments such as an altimeter reading up to 60,000 feet, a turn indicator, fore-and-aft level, oil pressure gauge, oil inlet and outlet thermometers, boost gauge for the supercharger, revolution indicator, air speed indicator and fuel tank contents gauge.
THE ARRANGEMENT OF THE COCKPIT of the Bristol 138A monoplane is shown in this drawing. The pilot wears a special suit, resembling a diving dress. The suit is made of rubberized fabric. Oxygen is injected into one side of the helmet and the flow is controlled by a lever near the pilot’s left hand.
Special precautions were taken to ensure that no controls should go out of action in the intense cold. In some previous flights, controls lubricated by grease had been known to freeze up. In the Bristol 138a all controls were fitted with ball bearings, and these bearings and the controls were dipped in thin oil, drained and then fitted in locked and sealed compartments. No grease caps or nipples were provided.
The engine (illustrated in the chapter “Aircraft Engines”) was a special unit of the Bristol “Pegasus” series, and was known as the P.E. VI. S. It was equipped with a two-stage supercharger which helped it to develop its maximum power at great heights. All the metal parts in the front of the fuselage, including the engine and its mounting, were electrically bonded together and metallically connected to the tail. Thus all metal parts of the plane were bound to be at the same potential and no trouble was expected to arise from the accumulation of electrostatic charges during flights at high altitudes.
At all altitudes above about 43,000 feet the atmospheric pressure is so low that breathing must be artificially assisted in some way. The system of supplying pure oxygen from a cylinder through a simple face mask is effective up to 43,000 feet or thereabouts, but it is unsafe or useless above that height.
One convenient way of solving this problem is the use of a completely sealed suit which can be inflated to a pressure adequate enough to sustain life at any altitude. In a suit of this type, pilots have been taken into a special low-pressure chamber at the Royal Aircraft Establishment. In this chamber they have been subjected to pressures corresponding to those which would be encountered at an altitude of 80,000 feet, and the suit has worked perfectly.
The suit is made of rubberized fabric and the headpiece is fitted with a large curved double window. Oxygen is injected into one side of the helmet, and the pilot’s exhaled breath passes out at the other side. The carbon dioxide and moisture are removed from this “exhaust gas” by a special chemical process, and pure oxygen is recirculated through the system. The suit enables a pilot to remain at altitudes of about 50,000 feet for some two hours.
The altimeter on the instrument board serves only as an indication, for the pilot’s benefit, of the approximate height at which the plane is flying. The maximum height attained is recorded on an instrument known as a barothermograph. This instrument makes a continuous record of atmospheric pressure and temperature on a sheet of smoked metal which is mounted on a rotating drum. The lowest pressure recorded gives an accurate indication of the highest altitude reached, but the barothermograph is sealed and is not visible to the pilot.
THE GASEOUS ENVELOPE OF THE EARTH is divided scientifically into several layers. The troposphere, or breathable atmosphere, is about ten miles deep at the Equator, six miles deep at the Poles. Between troposphere and stratosphere is a variable region called the tropopause. At thirty miles the density of the stratosphere is only one-thousandth that at sea level. Above the stratosphere come the Kennelly-Heaviside layer of ozonized air, the Heaviside layers, or ionospheres, and the Appleton layer, important for their various effects on the reception of wireless messages.
Record attempts are officially observed by a representative of the Royal Aero Club, and sealed barothermographs, which are housed in the wings, are sent to the National Physical Laboratory for examination after an attempt on the record has been made.
When Squadron Leader Swain made his flight in September 1936 the minimum barometric pressure recorded was 92·0 millimetres of mercury; the minimum temperature was -49·8° centigrade. This figure is equivalent to approximately -58° Fahrenheit, or 90 degrees of frost.
The height attained on this flight — 49,944 feet — was considered to be less than that of which the plane and engine were capable, although it regained for Great Britain the altitude record, which had previously stood at 48,698 feet, and had been established by the French pilot G. Detre some six weeks before Squadron Leader Swain’s attempt.
The designed practical ceiling (maximum height attainment) of the Bristol 138a was 54,000 feet, and certain small changes were made to the plane in readiness for another high-altitude flight. Smaller wheels were fitted, to reduce weight and head resistance; the wheel brakes were removed to save still more weight; and slight modifications were made in carburation and in the pitch of the airscrew.
The designers’ estimate was justified with extraordinary accuracy when, on June 30, 1937, Flight-Lieut. M. J. Adam took the Bristol 138a up to a height of 53,937 feet. A few weeks before this an Italian pilot, Lieut.-Col. Mario Pezzi, had attained a height of 51,362 feet, but the Italian claim had not received formal acceptance by the International Aeronautical Federation when Flight-Lieut. Adam raised the figure to 53,937 feet.
A WING SPAN OF 66 FEET is a notable feature of the high-altitude monoplane Bristol 138a. The plane has a length of 44 feet and is engined by a radial nine-cylinder “Pegasus” engine with a capacity of 28·7 litres.
The flight in June 1937 was preceded by six or seven trial ascents, on each of which the plane climbed to approximately 50,000 feet. On the record flight the Bristol 138a was in the air for two and a quarter hours, and Flight-Lieut. Adam encountered a fierce westerly gale in the upper regions, the force of this gale rising to nearly 100 miles an hour.
Unbroken cloudbanks blotted out his view of the Earth for long periods, and hid most of the landmarks by which he might have checked his position. In these circumstances the achievement was outstanding, a fact which was recognized by the Air Ministry, whose official account of the flight contained these words: “High praise is due to the pilot for the sustained flying effort which has enabled the existing record to be broken by a substantial margin”.
Height Record Regained
The account ends as follows: “Since the height record was broken by this aircraft in September 1936, certain essential researches into the conditions of flight at great heights have been carried out, and the aircraft will continue to be employed upon work of this character”.
The flight was comparatively uneventful because of the perfect way in which plane, engine, pressure suit and equipment behaved. Flight-Lieut. Adam’s report makes interesting reading, but resembles the report of an everyday flight rather than the record of an achievement which regained an important record for Great Britain. These facts seem to indicate that stratosphere flying, as a commercial proposition, is not so far off as it is often imagined to be.
The ascent took an hour and thirty-five minutes, and the pilot switched on the second supercharger at a height of 35,000 feet. At 38,000 feet frost began to form on the inside of the cabin, the hood and the windscreen. At 50,000 feet the pilot had not seen the ground for half an hour. After some time the altimeter was registering 55,000 feet, and the rate of climb had decreased to zero. At this point Flight-Lieut. Adam was fairly certain that he had beaten the record by a substantial margin, and began his descent. He closed the throttle, switched off the engine and did not use the engine again. He landed at Farnborough, Hants, two and a quarter hours after he had taken off, reporting that he had experienced no physical difficulty whatever.
The Bristol “Pegasus” engine, from which the special P.E. VI. S. type used was developed, is a radial nine-cylinder engine with a capacity of 28·7 litres. Performance figures of the special version with its two superchargers are not available, but in every way it was designed specially for high-altitude work, and the observations made during the record-breaking flights, and the trials preceding them, were of the utmost value to the designers.
Commercial designers are fully alive to the importance of the splendid research work carried out by the Royal Aircraft Establishment. For commercial purposes, however, sealed pressure suits are impracticable, and designers are at work on sealed cabins in which passengers may safely be transported over long distances at great heights immune from the effects of the weather and flying over the highest mountain ranges in the world.
For military purposes, stratosphere flying is no less important. A successful stratosphere machine would involve a complete change of aerial strategy and tactics. Defensive problems would be revolutionized.
FLIGHT-LIEUT. M. J. ADAM and the pressure suit which he wore on his record-breaking flights into the stratosphere. On the right is Wing-Commander J. W. Woodhouse, D.S.O., M.C.