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Aviation History
1944
1944 - 1657.PDF
AUGUST IOTH, I944 FLIGHT 159 with the engine, i.e., overhaul life of engine. In future it will be essential to obtain the overhaul life of the whole -power unit, and this will make all the difference. For instance, suppose that the overhaul life of the engine has been laid as 500 hours, but that the power-unit flight tests reveal a defect; that failure occurs on an item outside the engine main assembly at approximately 150 hours, and that this particular component can be repaired or replaced without removing the engine. If such a failure will affect the functioning of the power unit sufficiently to cause the aircraft to force land, then it must be treated as equal to an engine failure, in which case the engine overhaul life is no morg^fehan 150 hours. This clearly indicates that the all-important factor for reliability is the overhaul life of the power unit and not of the engine in itself. I am quite certain that in future, before an airline com pany decides to purchase an aircraft complete with engine, they will want to know the overhaul life of the power unit and how it was obtained. If any useful purpose is to be served, the flight tests in question will have to be carried out over the actual route on which the aircraft will eventually operate, and, what is more important, the tests must be carried out by the airline pilots, and the engine- running care and maintenance carried out by and under 'ithe supervision of their engineers and mechanics. In other words, no outside assistance or advice other than that which could be normally obtained can be permitted. Problems of Peace We are now rapidly approaching the return of civil aviation. Therefore it is of the utmost importance to take stock of the position in this country. British civil aviation has a stiff uphill job in front of it, and, apart from having the right type of reliable aircraft, it must also have the right type of power unit, with a reliability equal to that of competitors. In order to ensure this, everything will depend on the overhaul life figure of the power unit and not just? of the engine itself. Many people are asking if it is possible to convert for civil air transport the aircraft engines now being used in military aircraft. Without going into all thp details, the answer is yes. This has already been confirmed in the case of the York, and the same applies to other types of engines. However, it is difficult to see where suitable engines of sufficient power can be obtained from any of the present military types for the large types of aircraft, even of the present size and all-up weight of the York. [ I am now suggesting that in spite of the fact that the ' York is already flying with a military engine of the liquid- cooled V type, it is not the most suitable type or power of engine for this size of civil long-range aircraft. As I have already mentioned, the air-cooled radial engine, which is obviously more suitable and in greater favour, has nq^ yet been considered for this civil version. Further, when con sidering the still larger types of 100 tons recently mentioned, the power units for this size are certainly not in sight. So far as the British air-cooled radial engine is concerned, there is no alternative, it is either the air-cooled sleeve- valve type or nothing; all the eggs are in one basket, and this may yet prove to be a great drawback in the future. The U.S.A., on the other hand, are in a very different and better position, having, as I have previously mentioned, adhered to her pre-war policy of sticking to one type, which over many years of development has proved itself to be very reliable and the most favoured type of engine for civil aircraft. There is still Mo reason to doubt that the U.S.A. are keeping pace with the latest requirements for increase of power for immediate post-war civil require ments. If, as has recently been published, this type of engine has reached the 3,000 h.p. mark for a single unit, then the Americans certainly lead the world. On the other hand, if the reason for not choosing the air-cooled radial fel the British civil post-war version of aircraft is due to sorhething being not entirely satisfactory, then it is reason able to assume that there is only one road open, and that •s to use the U.S.A. engines for our immediate post-war Virtually a double-crankshaft version of the Allison 1710 vee engine, the Allison 3420 is a four-bank 24-cylinder liquid- cooled engine. civil requirements. That is, of course, only so far as the large long-range aircraft type is concerned. To sum up*T my forecast of the aircraft engine post-war position is as follows: Military types can and will be modi fied and converted. Liquid-cooled V-type engines will be used immediately after the war as a stop-gap, but will be discarded later in favour of other types, especially for outputs above 1,200 h.p. U.S.A. will lead the world with the air-cooled radial poppet-valve type. The overhaul life of the power unit for any civil type will not be less than 750 hours. The most useful size of aircraft will be similar to the York, having approximately a total weight ol 60,000 lb. ^/ The progress of the larger types will depend entirely 011 the development and introduction of the power unit of between 1,500 h.p. and 3,000 h.p., with an overhaul life of not less than 750 hours. The maximum number of power units for an aircraft will be six. The 100-tons total weight aircraft fitted with reciprocating air-cooled radial engines of British type is a long way off. It is to be very much regretted that the Armstrong- Siddeley air-cooled radial poppet-valve type of engine was allowed to-die out. Here was an engine which showed great promise, as has been amply confirmed in the Cheetah, a smaller engine of approximately 250 h.p. This was the most reliable engine ever produced of its type in this country, having an overhaul life in the Anson aircraft of 1,200 hours I am of the opinion that the U.S.A. have «8a more suitable and reliable engine than this country in the air-cooled radial poppet-valve class. When I recently referred to U.S.A. leading the world, I was referring to this particular type of engine. Before the war it had a higher overhaul life figure as compared with British engines of similar type and output. Government Control It is difficult to find the reasons for this, especially/when taking into consideration one important fact, that the work manship and finish of British engines is second to none in the world, and certainly much superior to that of U.S.A. There is also more handwork in the British engines, but this may be a drawback. I should say it is largely due to the difference in general policy. For instance, this country for many years past has given financial support to all the main aircraft engine firms for design and development; this has allowed a certain amount of Government control, which usually destroys initiative and promotes so-called spoon-feeding. Thee U.S.A. have designed aircraft engines and developed the<h without Government control and with complete success. This does not in itself account for what we are looking for, but it does introduce a factor which to many passes unnoticed: when a major defect arises in design, a firm under Government control must take the line of least resistance and cost, with the result that where it would be better to scrap the whole design of the particu lar part or component, a modification may be introduced, sometimes with success but sometimes not, and then a furthejr modification is made. This, I suggest, is the real trouble.
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