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Aviation History
1931
1931 - 0342.PDF
FLIGHT, APRIL 10, 1931 TRANSPCET SPECIALISING AT LAST! The Air Ministry has recently drawn up Specifications for Air Mail Machines, the Conditions to be fulfilled being briefly : Range, 1,000 Miles at Cruising Speed of 150 m.p.h., and Weight of Air Mail Load, 1,000 lb. S long ago as September, 1928, FLIGHT beganto plead for specialised classification of com- mercial aircraft, pointing out that a machineused indiscriminately for carrying passengers, goods and mails could not possibly be the most.efficient for all purposes. In our Editorial Comment, on September 6, 1928, we said, under the heading : " TheParting of the Ways " : " The time has come when we must design for specific purposes. An aircraft originallydesigned for passenger carrying ... is not, even with its chairs removed, likely to be the most economical freightcarrier which it is possible to produce. . . . On the other hand, a machine originally designed for carrying freightwould not be expected to have the comfort, even if converted, of one designed for passenger work. ... A mail machine,for example, could probably be quite a small single-engined affair requiring no great internal accommodation in thematter of size, mails being fairly heavy for their bulk. Con- sequently, one would not design a mail-carrier with a verylarge fuselage. . . . The point we wish to make is that it is wrong policy to attempt to design any one type of machinewhich may, after a fashion, but only after a fashion, serve for a variety of purposes. The time has come, and indeedis long overdue, when we should try to do better than that, and design specifically for one particular kind of work andthat only." Since that time FLIGHT has continually advocated the policyof specialised design, and not long ago we published in THE AIRCRAFT ENGINEER (Monthly Technical Supplement to FLIGHT) a series of articles by Mr. Frank Radcliffe, of " Glos-ter's " Technical Staff, entitled " Technical Aspects of the Air Mail." Mr. Radcliffe came to the conclusion that a verymaterial increase in performance can be obtained by careful design, but did not overlook the difficulties. Like manyothers, Mr. Radcliffe turned his attention to the single- engined machine, believing that type to lend itself best toreally efficient aerodynamic design. On the other hand. Major Green, chief engineer of the Armstrong-Whitworthand Armstrong-Siddeley concerns, is on record as having stated that the multi-engine aircraft could be as efficient asthe single-engined. As the Armstrong-Whitworth firm is known to have under construction a large four-engined mono-plane passenger machine, one may assume that Major Green spoke from definite knowledge, probably based upon wind-tunnel results of model tests. It is probably significant that. in specifications for air mail 'planes recently drafted by theAir Ministry, designers are left a free hand in the choice of the number of power units. The very fact that the single-enginedtype is, apparently, not barred seems to indicate a change in policy, or at any rate a willingness to consider the claimsof the single-engined type. The specification which has been drawn up will, one pre-sumes, be circulated to aircraft constructors, and tenders asked for. We have not the space here to publish the specifi-cation in full, but we believe that in the following neces- sarily brief summary the main points have been brought out. The Specification. Following are the more important points in the specificationfor an air mail 'plane : The machine to be a landplane, the main requirements being reliability, speed,^and ease ofmaintenance. The machine must have tankage for a range of 1,000 miles at a still-air cruising speed of 150 m.p.h., andthe landing speed must not exceed 60 m.p.h. The mail load, apart from weight of fuel and crew, to be 1,000 lb.As a safety measure the main fuel tank must be capable of jettisoning its contents. Gravity feed is to be used. The machine must have a good degree of positive stabilityaround all axes, and tail trimming gear to ensure ability to fly horizontally without the aid of the pilot at any speedwithin the speed range. The aircraft must be adequately controllable at all speeds, and the aileron control to beadequate and able to stop incipient spin when the machine is stalled. Approved slots are to be fitted. The aileronsmust be so designed that they produce a minimum of yaw when operated. In addition to controllability, the manoeuvra-bility must be good, and the machine must not be tiring to fly. The aircraft is to be of all-metal construction, with theexception of the covering, which may be fabric. Where steel is used in the construction it should, as far as practicable,be of the stainless variety. Anodic and cadmium treatments to be used in their appropiiate places. The crew of the machine is to consist of 2, and the equip-ment is to include wireless, signals, equipment for night and day flying over the sea, and, of course, all the usual instru-ments, etc. Dual control to be provided, with chief pilot on left-hand side. The view from the cockpit must be good, andentrance to be provided elsewhere than through the mail compartment. In the mail compartment a trap door mustbe provided in the floor for dropping and picking up mails, but it is not quite clear whether this stipulation refers toordinary loading and unloading on the ground, or whether there is some idea of the possibility of dropping mail bags inflight. On the assumption that 12i lb. of mails occupy 1 cu. ft., the mail compartment will have to have a capacityof 80 cu. ft. It appears that designers are left a free hand in the choiceof the number of engine units, but the specification stipulates that in a multi-engined aircraft the machine must be capableof flying with one engine stopped at 5,000 ft. There is evidence that the use of air-cooled engines will not be insistedupon, as the specification calls for a reserve of water if required. This is taken to refer to spare water for water-cooled engines working in tropical climates, where the evaporation may be expected to be considerable. The undercarriage is to be fitted with wheel brakes, and atail wheel is called for. The track of the undercarriage is to be wide enough to make the machine stable when taxying in across-wind of 20 m.p.h. It will be seen that the aircraft designer will have some very-pretty problems to solve. A machine which carries fuel for 1,000 miles and a pay load of 1,000 lb. at a cruising speed of150 m.p.h., will tax the ingenuity of designers, and even if no machine is actually produced which complies with all therequirements, the very attempt to design such a machine should teach valuable lessons. It cannot be said that wehave hitherto made any serious attempt to produce a really efficient commercial aircraft. The new air mail plane speci-fication aims high, and should result in some extremely interesting machines being produced. SUMMER SERVICES IN GERMANY A CONSIDERABLY increased programme in theEuropean airways net was announced recentlyby the Deutsche Luft Hansa, some of which was due to start on March 1 and April 1 last. TheLuft Hansa is extending its field of activities by reopening six routes, which means that the daily mileage will beincreased from 8,000 miles to approximately 12,000 miles. With the introduction of further traffic improvements onApril 1, Luft Hansa aeroplanes serve 24 German and 20 foreign air ports—instead of 18 and 11, respectively—along26 flying routes. As can be seen from the increase in the number of foreignairports, the alteration in the flying programme means primarily a vast improvement in the facilities for aeriaicommunication between Germany and other countries. On the one hand, the increase in the mileage covered dailymakes it possible to extend into the neighbouring countries the lines that were previously confined to Germany, and, o- 318
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