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ANCILLARIES Rationalizing Aircraft It is possible to indicate on the end of a cable what it is, where it comes from, where it goes to and Secondary Controls and Systems doubtless a whole host of other things, but such over-identification defeats its object and, when the aircraft comes to have overlapping and inter A Plea for More Thought in Early Design Stages dependent modifications embodied, can lead to a state of near-chaos. All that the electrician wants to be told about the end of a cable is where it By W. S. Hollyhock, A.F.R.Ae.S. goes. If the destination is a terminal block, the terminals should have simple numeral identifica tion and then all the cable requires is one simple T is an accepted principle that primary controls being removed or fitted. This may seem like a number to align with that on its particular glimpse of the obvious but it is surprising how should have full consideration during the terminal on the block. This is the irreducible I often such elementary details are overlooked. initial design of an aircraft but there is a minimum and it gives the neatest and most general tendency to ignore secondary controls and Another source of difficulty and irritation, to easily understandable coding, with the minimum systems, such as electrics and hydraulics, until all say nothing of time consumption, is lack of of sleeving on the cable and labels on the other requirements have been satisfied, basic spanner space at connexions. The act of using a terminals. shapes and sizes determined and structural spanner should always be visualized when The general layout of hydraulic piping is a members laid out. connexions are placed and access doors, etc., matter that calls for thought and care if the most should be considered very carefully both as to The result is that 'systems' designers have accessible arrangement is to be achieved. Appear size and also their situation in relation to the an almost impossible task in making their jobs ance, although of lesser importance, should joint to be serviced. A door immediately above or foolproof, fireproof, crashproof, and easy of always be considered, if only for its psychological below a joint is not necessarily so convenient as of access for inspection and maintenance. Inevit effect. It is natural that an installation which one placed slightly to one side, when spanner ably, with the rest of the aircraft completed, one looks right and tidy will receive more careful operation is the criterion. or more of these requirements suffers and at best handling than one which does not and careful the arrangements are far from perfect. At the The much maligned and frequently ill used handling increases serviceability. worst they are downright inefficient, usually in mechanical remote control is another item which the matter of access and not infrequently in does not receive the consideration it deserves. It is To sum up, it is clear that: respect of fire hazard. expected to transfer a movement from one loca (1) early consideration should be given to all tion to another, which is frequently farther With the continual increase in the use of secondary controls and systems; away than the makers ever dreamed of recommen hydraulics and electrics, particularly the latter, it ding, through a run as tortuous as it is long. Then (2) all these should be thoroughly reliable and is rapidly becoming essential that serious thought it is complained that the control is stiff. Of should be given to these so called secondary as simple as possible. course it is stiff; it could not conceivably be items at the commencement of design. (3) they should always be installed with a view otherwise. If a little thought were given to the Furthermore,with the present almost universal to maintenance and servicing. matter at the right time, however, much of the practice of using powered controls for the direction changing could be avoided. Where a primary services, neither electrics nor hydraulics considerable change of direction is essential, bell can be regarded as truly secondary and, therefore, cranks are not unworthy of consideration—if the they deserve fully as much thought as any other CONFERENCE ON FATIGUE designer's approach has a flexibility at all control. comparable with that of the control which he is The irony of the situation is that it requires The Council of the Institution of Mechanical trying to install. such a comparatively small concession in the Engineers is arranging an International Conference on Fatigue of Metals to be held from Monday Sep matter of space at the right time to achieve the In the effort to achieve rationalization, it is not tember 10 to Friday, September 14, 1956, inclusive. desired result. The important consideration is wise to adhere too slavishly to a set procedure. A Sessions for the delivery of papers will be held daily that a suitable channel shall be provided between certain amount of unconventionality will some from 10.00 a.m. to 12.30 p.m. and from 2.30 p.m. to the source of power and the location of the times give a far better result. To take electrical 5.30 p.m. It is hoped to obtain up to sixty papers equipment to be operated. cable looms as an example, working to the rules covering the whole field, and these will be divided into Working on the principle that 'what leaks will dictate that all cables be nicely loomed and, groups, the papers in the various groups being pre in many cases, completely irremovable without should be at the bottom' and, therefore, what sented for discussion in abstract form by reporters. complete dismantling of the aircraft. This is not sparks should be as far away from it as possible, The presentation of the papers will be preceded by likely to meet with much enthusiasm when the an address reviewing the field of knowledge of fatigue. it becomes evident that a clear space or duct The address will be presented by Dr H. J. Gough, aircraft goes into service, however. If, on the should be provided at the bottom of the fuselage C.B., M.B.E., F.R.S., a Past-President and Honorary other hand, a cable which is likely to require from front to rear for hydraulic pipes and a Member of the Institution. frequent replacement for any reason, or is in a similar space at the top for electric cables. Provisional arrangements for the sessions are as Experience will indicate the intermediate places circuit inevitably subject to modification, is follows: at which branches need to be taken off and the laid outside the loom, it may not earn the designer the undying gratitude of the service Monday morning: location of these can be determined at the outset Opening of the Conference by the President, welcome to visitors mechanic, but at least he will have the satis —if sufficiently forceful instructions are given to and outline of arrangements; followed by General Lecture by faction of knowing that he has saved somebody Dr H. J. Gough, C.B., M.B.E., F.R.S, those concerned. Objections will always be raised somewhere a considerable amount of time, money but everybody knows that sooner or later some Monday afternoon, Tuesday morning: and irritation. This is, of course, a question of Stress Effects, thing must be done about these things and, there knowing just when to turn a blind eye to the fore, it is only plain common sense to do it while Tuesday afternoon: the layout is still sufficiently flexible to allow a neat recognized procedure. Effect of Temperature and Environment. and reasonable run. Servicing in general is an important matter in Wednesday morning: Metallurgical Aspects. So far as electrics are concerned, the aim should the maintenance of aircraft and this is nowhere be to provide straight ducts capable of taking all more noticeable than in hydraulics and electrics, Wednesday afternoon: Hasic Studies (i) Mechanism of Fatigue, particularly the latter. To attain the maximum the cables envisaged plus a contingency percen (ii) Statistical Theories. possible serviceability in electrics, it is necessary tage to cover the modifications which will (iii) Crack Propagation. to ensure that only fully tested items of equipment inevitably arise sooner or later—usually sooner. Thursday, Friday morning: are used and to reduce the number of troublesome Easy access should be arranged at all branches Engineering and Industrial Significance of Fatigue. Railways. and ducts between branches should be as straight items, such as relays, to the absolute minimum. Automobiles. as possible, with smooth inner walls, so that It is easy enough t o find an excuse to add another Airframes. Engines: stationary, mobile, aircraft, marine. cables can be drawn through at any time with piece of equipment, but far cleverer to find a way Pressure vessels. out difficulty or risk of damage. Also, adequate of doing without it satisfactorily. Structural engineering: land, ships. Welded Construction: welding, joints. withdrawal space should be provided at junctions, The same argument applies, of course, to Service Experience and Failures in General. for dealing with replacement cables. hydraulic circuits. Reliability is the keynote of Friday afternoon: serviceability, with simplicity running a very good Hydraulic ducts or passages should be dealt Closing Session with reviews by chairman or reporters and second. It is easy to overload the installation with with in a similar manner, not forgetting that when possibly a résumé or problems in the field which remain to be safeguards, and not so easy to dispense with them solved. a pipe is drawn through, it will have a connexion later. on its end. It is useless to allow just sufficient Copies of the papers will be available in advance Coding of cables is another matter on which space for a bare pipe. Furthermore, adjacent of the meeting, and the Proceedings of the Confer there can be much loose thinking. The golden pipes will also have connexions and these must be ence, containing the papers and discussion, will be passed by the connexions on the end of the pipe rule here is also—as in most things—simplicity. published by the Institution in due course. July 1955 223
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jul 1, 1955
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