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Aviation History
1934
1934 - 1222.PDF
1224 FLIGHT. NOVEMBER 15, 1934. SPEED OF COMMERCIAL AEROPLANES Important Considerations Raised by the Fact that Speeds of 200 m.p.h. at an Altitude > of 13,000 ft. are now Possible : Points from a Lecture by M. Louis Breguet FCTORS governing the speed of commercial aeroplanes"formed the subject of a paper read recently by M. LouisBreguet before the Royal Aeronautical Society—the581st lecture given before the R.Ae.S. since its founda- tion on January 12, 1866. M. Breguet is President of the Societe Francaise de Navigation Aerienne. The problem, said M. Breguet, of increasing the speed of commercial aeroplanes over a determined distance was subject to certain restrictions; for example, an upper limit was placed on the landing speed, while the ratio of paying load to the flying weight of the aeroplane when fully loaded should not fall below, say, 25 per cent, for distances of 300 miles, and about 10 per cent, foi distances of 1,200 miles, when covered at high speeds. Three principal means were designated as possible of use to increase the speed of a given type of aeroplane of minimum drag : (1) An increase in the engine power ; (2) an increase in the wing loading by reduction of the surface of the wings; (3) an increase in the altitude of flight. These factors, if. applied safely to the exclusion of the others, involve certain consequences, namely, an increase in power leads to a reduc- tion in pay load ; an increase in wing loading is limited by the minimum speed allowable for landing, and also in certain cases by the question of take-off, while an increase in altitude necessitates the provision of supercharging devices for the engine, an increase in structure weight, and a general reduc- tion in the thermal efficiency of the engine, that is to say, an increase in specific consumption whereby the range is reduced. From this it is seen that it is advisable to use these three means together. The problem would, therefore, seem to resolve itself into dealing with the braking of the aeroplane, both in the air and on the ground, and to the development of the power of engines at a high altitude. M. Breguet opined that we were to-day witnessing a new birth in the study of the processes of lift of flying machines, and that in a few years commercial aviation would be free for good from the restrictions which safety in landing still imposes on the loading of the wings. Apart from reference to upper and lower surface flaps, slots, wheel brakes, reversible airscrews, and air brakes, he also said he was convinced that in future airscrews which propel the aeroplane would be utilised for giving assistance at the moment of landing, and also for lifting and braking. Even now he thought that wing loading of from 20 to 3olb. per sq. ft. could be contemplated for fast commercial aeroplanes equipped with suitable braking devices. He scouted entirely the view so often expressed that the greater the altitude the greater the speed, and, after discussing the drawbacks and advantages of superchargers, he concluded that the optimum altitude which could not profitably be exceeded for the fast aeroplanes under consideration was 26,000ft. ; but this statement was qualified by his feeling that, taking into account the advan- tages of avoiding the complication of special clothes, breathing apparatus, and so on, flight above 16,400ft. offered no advantages. In justification of these conclusions, M. Breguet had com- piled some very interesting curves substantiated by mathe- matical formulae, these being based, as were all subsequent calculations, on a specific consumption of o.61b. per b.h.p./hr., with the proviso, of course, that a reduction in consumption of approximately 0.441b. per b.h.p./hr. (a figure already within the bounds of possibility) would result in greater useful loads at higher speeds, or over greater distances. M. Breguet also calculated the costs of high speed commer- cial transport, and in this connection stated as one of the advantages of the aeroplane that the expense per mile relative to the power in question does not increase with speed at anything like the same extent at which it does in other means of transport, and that this was an advantage which could not be too strongly emphasised, and which distinguished the aero- plane from all other means of transport. Summing up, the lecturer's arguments lead to the conclusion that speeds of approximately 200 m.p.h. at an altitude of about 13,000ft. were now within the bounds of possibilitv, and would show very great progress if used on routes like the Indian, African, and South American. He considered that it was possible to attain these speeds without detriment on commercial aircraft enterprises, and that the increased revenue which could be expected would make such operation advan- tageous from the financial point of view. CORRESPONDENCE The Editor does not hold himself responsible for opinions expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters intended for insertion in these columns [2976]—Having Flight for November 1 and 8 before me, 1 wish to comment on some of the views and articles concerning the England-Australia Race. First, there is the view expressed both by Mr. G. E. Woods Humphrey and Sir Eric Geddes that the policy of mixing passengers and mails benefits both. Sir Eric argues that the more frequent service necessitated benefits both kinds of user of the service. But if dividing the traffic would halve the frequency of the service, why not halve the size of the machines used ? The service would then be just as frequent, and the mails could be flown by night, if the ground organisa- tion permitted, without inconveniencing passengers. The design of the aircraft could be more specialised. The smaller types could be designed for greater speed, and would make a more mobile fleet. If a small number were kept in reserve, the service could be more nicely regulated to the loads. The question of ground organisation leads us to the views expressed by Mr. Handley Page. He advocates development of ground organisation for night flying. Here, again, unless the passengers are to be subjected to the doubtful pleasure of flying day and night, even in the quiet and comfort of one of Mr. Handley Page's cabins^ separation is indicated. Mr. Handley Page also speaks of the necessity for low land- ing speed, and a steep gliding angle. This implies either that clean, high-speed aircraft with split flaps, etc., should be used, or slow machines comparatively inefficient aerodynamically. If spoilers are not fitted to the former class, the benefits of good speed range are offset by a flat gliding angle. Yet Imperial Airways seem to have abandoned the principle of the necessity of a low landing speed, for they are adopting for their European and other routes the D.H.86, in which com- paratively high speed is accompanied by a flat glide and a landing speed in excess of that of any American commercial aircraft of which I know. [We imagine that this point might be contended.—ED.] Another point was to be noted in Flight of November 1, in the article headed "The Empire Air Routes." In the section dealing with the "Comet's" capabilities as a mailplane, 'he writer works on the assumption that it would carry as mail a weight representing about two-thirds of the full load of petrol carried in the race. But it must be remembered that during the race, though taking off with full load, the " Comets " never landed except with tanks nearly empty. With the commercial loading envisaged in the article, the " Comets " would be landing with two-thirds full load. Though my views may be somewhat narrow on the subject, I am of the opinion that 65 m.p.h. is the maximum landing speed with which the " Comet " should be operated on the Empire routes, and I cannot think that the '' Comet '' would land at less than that speed with the payload suggested. A reduction of its wing loading would give better take-off, while being more fully flapped would reduce the landing speed. As for the necessity for speed approaching that of the "Comet," I would quote Mr. Handley Page: "The speed of the service should be in relation to other competing means of transport." Quite. And if one of the competing means of transport is> K.L.M., flying Douglas D.C.2S ? Stonehaven. .,„ CHARLES BURNS.
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