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Aviation History
1938
1938 - 1153.PDF
APRIL 28, 1938. FLIGHT. 399 The technique of landing must be given more considera- tion, and if the stimulated lift derived from multiple air- screws positioned along the span is to be used it is pos- sible that considerable advantages can be obtained in this direction. One has been studying the question of the relative merits of the land machine and the flying boat. My opinion on this point at the moment is that for medium-sized air- craft the land machine is the better, while for very big airliners the flying boat probably has the advantage. For transatlantic work I understand difficulties are likely to be experienced with the flying boat due to the freezing in winter Of sheltered waters on the east coast of the United States; this may, therefore, require the larger transatlantic liners to be land machines. In order to develop big aircraft with the minimum of financial risk I feel that a new technique of flying the machine for the first time must be developed along the lines on which the firm of Glenn Martin are working. Reduced-scale flying '' models '' must be made in order to try out all the aerodynamic characteristics of the project at an early stage. Although we have all experienced a fair amount of trouble with retractable undercarriages in the past, and are even likely to experience similar difficulties in the future, I still feel that such devices are worth-while for large land machines. However, there are indications that it is now possible to build very low-drag undercarriages. We have read a great deal just recently regarding new types of undercarriage. We have the tricycle type with the centre wheel in front and the B.L.G. undercarriage. Both these innovations are exceedingly interesting, and I feel quite certain that they have come to stay. The virtues of being able to land with no incidence and the ability to apply very strong brakes are attractive features of both these two ideas. Dihedral Tails . - Empennages have been getting considerably cleaner of late, and this improvement has not been accompanied with any loss of efficiency. I still think that there is room for improvement, and consider that two tailplane surfaces substantially at 300 to 400 to the horizontal, with no ver- tical fin or rudder, may be a good scheme in the near future. The elevators can then be differentially connected to the rudder bar so that the two control surfaces have both a directional and longitudinal effect. I feel that control and stability, in spite of the vast amount of research which has been carried out, still re- quire further consideration. I would like the Air Ministry and the various operating companies to get together and establish specified degrees of these qualities. At the- moment, if the designer asks the purchaser what kind of control and stability he wants for his particular type of work, there is usually no answer. The use of the auto- matic pilot is now having some influence on this question. With regard to the question of airliner speed, I think It quite likely that the position will be consolidated for some years at cruising speeds between 200 and 250 m.p.h. The question of long range is being studied very much just now, and, I think, is of the utmost importance- There seems to be four ways of achieving improvement in this direction : (a) The Mayo Composite arrangement: I am afraid I do not feel very enthusiastic about this idea. I find it difficult to imagine its being used extensively in the future. (b) Catapults: These again do not seem very practic- able—at any rate, using anything like high accelerations. The machine must have a reasonable climbing speed imme- diately it leaves the catapult, and this alone would make it nearly capable of taking off under its own power. (c) Assisted take-off: It has been suggested that rails might be used on an inclined plane. This seems rather cumbersome. I do think, however, that concrete runways having a definite inclination to accelerate take-off and de- celerate landing may be employed. In this connection my ideal aerodrome would be one in which the terminal buildings was in the centre and on a hill, and with a tunnel giving access. Machines would then, without any taxying, take off down the hill into the wind on one side Mr. A. Hessell Tiltman of the aerodrome and land uphill into the wind on the other. (d) Flight refuel ling: This has still to be proved on a commercial basis, but I think it is likely to be one of the methods which will be used in the future. I have given a good deal of con- sideration recentl - to the question of high wing versus low wing for civil machines. For the flying boat I think the answer is defin- itely high wing. For the land machine the pros and cons are very evenly divided. I had thought that the high- wing monoplane represented the better arrangement, since it gives considerably better view to passengers and is aero- dynamically more efficient. I have lately, however, been working round to -the idea that, taking everything into consideration, the low-wing monoplane is just a little better. The undercarriage problem is very considerably easier, and, in the emergency of having to land on water, the buoyancy is more favourably disposed. A great deal has been written of the possibility of high- altitude flying. This is very often called stratosphere fly- ing, but I do not think we shall be using that stratum for some considerable time. There seems, however, to be quite a lot of advantage to be derived from operating between 20,000 and 30,000ft. if the difficulties can be over- come. Pressure cabins lead us into a vast number of serious problems. With regard to the vexed questions of wood versus metal construction, I think that although there is a great deal to be said for designing certain specifications of military air- craft in wood in order that wastages may be quickly made up in time of war, there is more to be said in favour of all-metal construction for all civil types except perhaps the very smallest. I think most operators will agree that for machines above 12,000 lb. all-up weight the advan- tages of stressed-skin construction are very marked. I believe that improved materials and technique will allow us to improve our structure weights with this construction. New Materials For machines that are to be made of wood, the new materials available show great promise. I have recently made calculations involving the replacement of the usual spruce by compressed-wood flanges on a machine with an all-up weight of 7,500 lb., and I find that the saving in weight, including joints, is of the order of 170 1b. This is a considerable advance. Plastics may also provide new opportunities in the near future, particularly in secondary parts of the structure. The research work carried out on soundproofing has been a very valuable contribution to civil aviation. I think, however, that as machines get larger and engine units become more powerful we shall have to watch very carefully the tendency for tip speeds to increase. This would prejudice the very reasonable quietness of cabins which we are obtaining at the present time. Regarding engine development, I do not feel very quali- fied to talk. I think, however, that the diesel has very great promise, particularly for long-range work. Regarding the size of future airliners, I can visualise very big machines indeed. I feel that if the public can be educated to fly, particularly for long distances, so that the loads are available, machines of 200, 300, and 400 tons all-up weight are quite likely to be built in the next twenty or thirty years. Although in building such machines we shall be faced with a number of new and difficult problems, it will, I think, be possible to do so with higher aero- dynamic cleanliness, reflected in cheaper operation.
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