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Aviation History
1923
1923 - 0545.PDF
SEPTEMBER 13, 1923 PAPERS AT THE INTERNATIONAL AIR CONGRESS • -•'.•• . ^ The Technical Development of the Aeroplane BY J. D. NORTH [THEpaper read by Mr. J. D. North, Chief Engineer of Boulton aud Paul, Ltd., of Norwich, was of more than ordinary interest, and had space permitted we should have liked to publish the paper in full. As this is not possible, we have had to confine ourselves to the following extracts, which will, we hope, be found of sufficient interest to show that the entire paper should be thoroughly investigated. This applies particularly to the very excellent appendices to the paper, notably that in which Mr. North has extended Major Hill's method for determining the value of the figure of merit of parts of an aeroplane to include certain factors which were neglected in R. and M. No. 217.] Mechanical flight in the brief twenty years of its existence has passed through four phases, each of an approximately equal period, and which are denned sufficiently clearly to be marked by the observer. There are indications that we are now entering on a fifth phase in the art and practice of avia- tion, the trend of which forms a legitimate field for specula- tion. The first, which may well be called the pioneer age, was a necessary part of that great scheme of mechanical evolution of which the invention of the thermodynamical prime mover is the most significant feature. "Within this period, enduring ridicule of their aspirations and contempt of their achievement, a small band of enthusiasts in America and Europe were concentrating their energies on an endeavour to remain in the air for a sufficiently long period to learn the nature of the problems associated with the flight of the aero- plane. The Wright brothers, leading easily in the race, were the first to discover how to control the attitude of an aero- plane in flight. Once the power of sustained flight had been achieved the practical engineering difficulties were met rapidly, and in 1908 Bleriot's flight across the Channel, though by no means the most noteworthy achievement of the pioneer phase, forced its attention on the world at large and on the inhabitants of the Island in particular. Then came the period of demonstration. People every- where wished to see and to experience the novelty of human flight, and as spectators, passengers, and donors of prizes the community commenced to contribute its quota to the supply of financial lubricant, for lack of which the wheels of progress had revolved but slowly and laboriously. The vaguely defined possibilities of these new machines as weapons of war could no longer pass unnoticed, and State organisations for the development of the science and art of aviation were pro- vided or enlarged. To these organisations, whatever else may be said of them, must be given a large share of the credit for the development of the technique of the aeroplane at a time when the juvenile aircraft industry could barely afford to consolidate its position by demonstrating to the general public that the conquest of the air had been achieved. The various military competitions, like others of more recent date, if they attained no other object, at least served to demonstrate how difficult it is for the most representative judicial com- mittee to pronounce a judgment which will be endorsed by that inexorable court of appeal, the march of events. During the period of demonstration the development of the aeroplane was rather along the line of effectiveness than efficiency. When the 50 h.p. Gnome engine was fitted in the 25 Anzani-B16riot a radical departure was made from the " tangent " class of aeroplane, which was so called because the available power curve was very nearly tangential to the curve of power required for flight. Immediately the power of acccle; ^tion, the speed range, and consequently the manoeuvr- , ability were increased, the climax being reached at the end of this period in the exhibition of looping and other forms of trick flying rendered possible by these means. The war phase which followed ultimately resulted in a struggle for improvement of performance and manoeuvrability. After the Armistice was signed and the war contracts had ; been liquidated the huge industry and technical organisation-: which had grown up during the War passed through a phase of attrition, particularly' painful as following so closely on the period of expansion from 1915 to 1918. Under the economic conditions then obtaining no genuine commercial develop- ment of the aeroplane could take place, and in consequence most of the work of aviation since that period has taken place under national direction, and to some, though by no means so full an extent, at the national expense. Under the pressing necessity for public economy, the funds which have been available for maintaining the aircraft industry and for developing the technique of aviation during this period, have been less than the merits of the case indicated. Those who have undergone this process of attrition may not improperly be said to have had a " thin time," and it is only natural that they should look eagerly for any signs of more generous treatment. They observe that there is apparently an in- creased public interest in aviation which they hope will be reflected in a more adequate public support, without which aviation can be but a shadow of its real self, and it is proper that they should consider in what direction their activities may best be directed to reap the fullest advantage of the improved circumstances. Let us take stock of our technical assets. We have, as has already been pointed out, a large amount of incompleted work which requires sifting and developing to its proper conclusion. We cannot expect to develop the aeroplane on the heroic lines, the achievement-at-any-price methods, which were proper to the war period. Probably we shall be compelled to concern ourselves mostly with small matters out of the multitude of which great things may come. Firstly, there is the development of the aeroplane from the economic stand- point, the improvement of the ratio of the useful load to the gross weight, and the improvement of fineness whereby for given horse-power this gross weight may be given a better performance. These may be attacked either by systematic improvement of detail or more speculatively by radical changes in design. The scope for advance on existing lines may be summarised as follows :— 1. Reduction of Structure Weight.—(a) A more accurate knowledge of external forces in flight. b) More reliable methods of stress computation. (c) Improvements in structural arrangement. (d) Specifically stronger materials.—-Here we have already made a very notable progress in the substitution for timber of steels and alloys of aluminium, and generally in the use of better quality steels. Further substantial advances in this direction are to be expected. (e) Reduction in overall dimensions. 2. Reduction in Weight of the Engine and the Fuel Consumption for a Given Power.—There do not appear to be great prospects of immediate improvement in engine weight or consumption. The most effective results may be expected from the use of suitable supercharging devices for increasing performance and altitude. Such devices are vitally necessary for military aeroplanes, and have been used successfully in the experimental stages. So far as fuel consumption is concerned, where very long journeys are involved there is quite a possibility of refueling in flight. It has repeatedly been shown that aeroplanes can establish contact with one another in the air, and should it become necessary in the future, large civil aeroplanes might be refuelled by tankers from stations at suitable short intervals of 200 to 300 miles. 3. Reduction in Dead Weight.—That is to say, the weight of the crew and their necessary instruments, etc., in relation to the useful load. At the present time this figure is very high on commercial aeroplanes. 4. Aerodynamic Improvement.—In considering the per- formance for a given power load it is necessary to decide what class of performance is required—rapid transport or power of quick manoeuvre. Military aeroplanes may broadly be classified as :— (1) Aircraft for offensive action against aircraft. (2) Reconnaissance machines capable of self-defence. (3) Bombing machines capable of self-defence. (4) Bombing and Transport machines practically incapable of self-defence. The first class will depend for its power of offence on manoeuvrability, speed and climb, which enable it to bring its armament effectively into a&tion. The necessity for these qualities diminishes gradually from class to class till with the fourth class the conditions are much the same as those required for civil aeroplanes. In the machines which are intended for transport purposes the surface loading is prac- tically controlled by the necessity of rising from and landing on certain types of grounds under reasonably safe conditions. There may, however, in the future be this important distinction between military and civil aircraft, at any rate when the latter are used in civilised countries : . that whereas military aero- planes may be required to land and rise from unprepared ground, it may be that in future air lines will run over a series of .flying grounds so arranged as to make possible with safety 545
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