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Aviation History
1922
1922 - 0027.PDF
JANUARY 12, 1922 SPECIALISED AIRCRAFT THIS was the title of a Paper read by Wing-Commander W. D. Beatty, C.B.E., A.F.C., before the Royal Aeronautical Society on January 5, 1922. It proved to be a very interesting paper indeed, although scarcely in the way one would have expected from its title. The first part of the paper was mainly historical, and gave a review of the development of military machines from the time of the Military Trials on Salisbury Plain in 1912 up to the end of the War. The lecturer gave in table form particulars of the devlopment of specialised types, under the headings of Training Machines. Fighters, Reconnaissance and Day-Bombing Machines. Night Bombers Ship Aeroplanes, Torpedo Aeroplanes,, Seaplanes, and Flying Boats. On the subject of commercial aircraft, the lecturer mentioned that the first organised services were operated with machines of war type, variously modified to meet civil requirements, and that the need of special designs soon made itself felt. In his opinion, Commander Beatty said, we were now at a stage, as regards commercial design, about equivalent to that of military design at that period of the War when slow two-seaters armed with a rifle or a stripped Lewis gun carried on the general air work of the Army. The real commercial aeroplane has not yet, he said, been developed. Progress has, however, been made in the right direction, as shown by a table of early types of commercial aeroplanes showing the develop ment in useful load and performance, from the Avro with 60 h.p. Green engine (the machine on which the late Lieut. Parke did his famous " dive " at Salisbury Plain) through the Vickers-Vimy Commercial, Handley Page W. 8, and D.H, 18, to modern times. In order to arrive at the user's view of his machines, the lecturer studied them from the point of view of the profit and loss account of the operating firm. In order to reduce expenditure the following qualities are required : Low first cost, economical maintenance, and economical running. By careful design, the lecturer said, manufacture can be simplified and expensive fittings eliminated. Moving parts and friction between them should be reduced to a minimum. Parts which require attention should be easily accessible, and engines must be readily removable. In regard to the latter Commander Beatty said he would very much like to see comparative tests carried out on engines removable complete by themselves and removable complete with their mounting. The latter method, he stated, is probably the quicker in operation, but will have to bear the charges due to the additional capital outlay on spare mountings. The engine should be capable of running for 300 to 500 hours without overhaul. At present he thought we were getting close to a standard period of 100 hours between overhauls. Turning to the receipts side of the account Commander Beatty pointed out that one must have a large load-carrying capacity, but that this is of no avail if the traffic sufficient to fill it cannot be attracted. He then proceeded to deal with the requirements from the point of view of tho passengers, and as this part of the paper was extremely interesting we publish it practically verbatim—with only a paragraph deleted here and there where it has been possible to do so without detracting greatly from the value of the paper :— " Passengers' Needs.—Far more attention is necessary to the comfort of passengers, and this embraces a wide variety of detail. I cannot but think that considerable advance might be made in forthcoming commercial types were designers to travel to and from Paris in each of the various types of aircraft actually in use on the cross-Channel services. This is the slack time of the year for passenger traffic ; why should not the transport companies grant a certain number of free return tickets to bo>ia fide designers, thus affording them opportunities to ascertain in their own vile bodies the various existing causes of discomfort and learn what to avoid ? Passengers are the most important source of revenue for air transport firms at the present time, and each that considers that he has had a really comfortable journey is a walking advertisement for the air line, while each dissatisfied passenger will result in a lowering of possible receipts. " Silence.—First and foremost amongst the important items affecting comfort I would place silence. A " desirable attribute "in 1912, it has never yet been attained in normal practice, and the air line passenger still suffers acute discomfort from the noise to which he is subjected. "It is true that the noise in a machine comes from a •ariety of sources, but it is urgent that some at least should be eliminated. Promising exhaust silencers have appeared experimentally; it is for designers to incorporate them in their designs. Never should an open exhaust point in the direction of the cabin. Get rid of the barking roar of the exhaust, and it becomes possible to identify and so to eliminate the other noises. Probably modifications in the design of propellers may be desirable, and with a silent exhaust it becomes an easier matter to compare the noise effect of two different propellers. Fabric covered fusel ges must also, I think, be relegated to the past ; a stiff wooden covering does not transmit to the interior of the cabin the blows from the slipstream in the same way that fabric does. Vibration and resonance are closely allied to noise in effect on passengers, and should be eliminated. It may be necessary on these grounds to ensure that the two engines of a twin- engined machine never synchronise. I believe Colonel Bristow is trying experiments on these lines. Engine designers will need to utilise motor-car experience, and get rid of that variety of noises from gears and other moving parts which at present are so obvious in an aero-engine when its exhaust does happen to be silenced." Ventilation and Heating.—" The next important detail which designers should carefully study is that of ventilation, to which very little attention has hitherto been given. Adequate ventilation of the cabins of commercial aircraft is a problem that presents considerable difficulty. The cubic space available is very limited, so that the air inside the cabin tends to become vitiated rapidly, while the speed of the machine is such that the velocity of in-coming air is often so high that the passenger feels a draught. In rough weather, therefore, the unfortunate passenger tends to suffer from depression, headache, cold and illness." " For many years the efficiency of ventilation has been determined by the quantity of carbon dioxide present in the atmosphere. The supply of air generally recognised as necessary to remove all sensible impurities amounts to 3,000 cubic ft. per hour per person. In a present-day cabin of 300 cubic ft.—seating ten passengers—the air must be changed 100 times an hour if the standard allowance is to be provided. In practice, such a rate of change is unobtainable, except in unbearably draughty conditions. It is clear then that the measurement of the C02 content is likely to continue to be unsatisfactory." " Professor Leonard Hill, however, has pointed out that the 3,000 cubic ft. figure can be much reduced if the cooling, drying and radiant energy conditions are satisfactory. To afford a means of determining these conditions he invented the ' Kata ' thermometer. Experiments have shown that the information given by this instrument is an accurate guide to the adequacy of the ventilation so tested,, and if its readings average between six and eight the conditions may be considered satisfactory. Now the cooling and drying effects of air depend largely upon its rate of movement, and it may be taken that if the temperature of the air is 55° to 60°, its velocity at the inlet to the cabin should not exceed 4^ ft. per second, if the inlet is 18 ins. or more from the passenger, or 3 ft. per second if it is less than 18 ins. from the passenger." " With inadequate warming arrangements, a change of air more frequently then three to five times an hour is likely to be uncomfortable in the normal cabin, and under such con ditions it may be found necessary to keep the velocity of in-coming air down to i£ to 2 ft. per second. The velocity of out-going air may be as much as 10 ft. per sec. at the orifice, particularly if that is at least 18 ins. from the passenger. Designers should, I think, aim at providing for some twenty changes per hour, taking care to avoid draughts and make satisfactory heating arrangements. If it is found that the air is being changed too rapidly for comfort, it is a very simple matter to close up some of the openings. It is far more difficult for the user of the aircraft so to alter it as to increase the regular supply of air if the original arrangements have proved inadequate." " Now, how is the air to be changed ? Experiments in America on sleeping cars showed that, provided the foul air was expelled, an ample supply of fresh air found its way through cracks and crevices in a swiftly moving vehicle. Personally, I think it better to arrange for the removal of the foul air than to trust to luck to its finding its way out. It should be practicable to design suitable aspirators to draw the air from the cabin of an aeroplane—slightly above the floor level, for, though hot air rises, vitiated air tends to de scend. It is probable that air entering through cracks and crevices will do so at such a velocity as to be a source of discomfort to passengers, particularly as its temperature is likely to be low. Air inlets should, therefore, be arranged 27
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