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Aviation History
1954
1954 - 0660.PDF
290 FLIGHT THE HELICOPTER INSTRUCTOR]. . . said that he had merely experienced "some vibration." I then looked at the tail cone and found that the "vibration" had been sufficient to bend it! Buyers of British helicopters come from all parts of the world, and the problem of training a pupil who speaks no English can be solved in one of two ways: the instructor can speak set phrases of the foreign language which he has previously sorted out by sign language and a dictionary; or die pupil can learn set phrases in English which the instructor will adhere to in the air. I have used the first method with Italian pupils and the second with Japanese. Only once has other than a minor misunderstanding taken place. On that occasion the pupil switched off both mag netos instead of switching from servo to manual control. We were at 800ft at the time and die airfield was right below, so there was no difficulty in selection of a forced-landing site. As I said at the beginning, the training of helicopter pilots is usually reserved for those with fixed-wing experience. The time which these pilots take to solo averages five hours. Post-solo dual is generally a minimum of four hours, but naturally this side of training must be kept elastic to cope with different capabilities. For the pupil who has never flown fixed-wing aircraft, the time to solo would average about fifteen hours, and basic instruction would have to cover much more thoroughly such items as the control of air-speed with the stick. During the whole of his train ing and for some time afterwards the ab initio pilot would be at a disadvantage compared with the man with fixed-wing experi ence. The main advantages of having this experience before con verting to helicopters may be listed as follows: — (1) The pupil has air sense, a term which covers a lot of things like being acquainted with the medium in which the vehicle is operating, knowledge of air vehicles and a general appre ciation of the physical sensations to be experienced during vari ous flight manoeuvres. (2) He has a good judgment of height, an eye for the weather and appreciation of air movement relative to ground movement. WITH the introduction of lightweight generating equip ment, the use of electrical surface heaters is now well-established for the protection of aircraft from icing. A new development in this field is the surface-heater element devised by D. Napier and Son, Ltd., the basic arrangement of which is illustrated in the diagrams below. The requirements for an electric heater mat, as determined by the company, were: — (1) A high thermal efficiency, i.e., die heat losses to the structure should be at a minimum, and heat transfer to the external surfaces at a maximum; (2) the resistance of the conductor element should be capable of adjustment in the design stage, in order to give any required power loading at any specified voltage over a wide variation of areas; (3) die physical, electrical and mechanical properties of the heater should be unaffected by temperatures from —60 deg C to +70 deg C, and the neater should be non-inflammable; (4) the external surface finish should be aerodynamically smooth and should have a high resistance to abrasion and rain erosion; (5) the mat should be thin; (6) it should be capable of application to any shape of surface, including those of compound curvature; (7) good adhesion to metallic surfaces, and to light alloys in particular, is essential; (8) the insulation material should have low water-absorption properties and be impervious to fuels, oils and hydraulic fluids; (9) it should be possible to carry out local repairs on the heater; (10) its weight per unit area should be a minimum. These requirements indicated to Napiers that it would be advantageous to fabricate the heater by a spraying process, both for insulation and for the electrical element, directly on to the surface to be protected. Progress along these lines led to the heater mat construction shown below, the base insulation of which consists of a layer of a thermo-setting resin applied by a flame spray-gun. Also applied by a flame spray-gun, the electrical conductor consists of a metallic coating to the resistance and pattern called for by the particular heat distribution required. This coating is provided with suitable terminals for connection with the electrical system. The outer insulation, of similar material to the base layer, is sprayed on and finally finished as a highly polished surface. The Napier heater mat may be applied to the surface of suitable shapes by mechanical means, which normally take the form of traversing gear linked by a suitable mechanism to the workpiece turntable in such a way that the rate at which the spray-gun passes across the workpiece can be controlled. In general, surfaces Diagrammatic section through the heater mat as applied to a surface. (3) The stick and rudder pedals operate in a similar manner in both types of aircraft, hence movement of these controls is instinctive, although their reactions tend to vary. The sole argument which can be raised in favour of the selec tion of a man of no previous flying experience for training on helicopters is that he does not have to "unlearn" anything. But this argument is inadequate, because it takes but a few hours for an experienced fixed-wing pilot to overcome his aeroplane in stincts, and previous piloting experience then becomes an enor mous asset. A brief list of the main differences which a fixed- wing pilot will find when flying a helicopter can be given as follows: — (1) There is a time-lag following movement of the stick. (2) Engine handling is more critical. (3) The aircraft does not stall and lose control when fuselage air-speed is reduced below a pre-determined figure. (4) The throttle is not closed when descending; rather is it used to maintain constant r.p.m. (5) Fuselage attitude does not have such a direct bearing on the flight path. (6) Power changes, especially at slow air-speeds, necessitate a considerable alteration of the rudder position in order to retain a directional heading. (7) In the event of engine failure, the pilot must take imme diate action to prevent the rotor slowing down dangerously. Finally, how does one become a helicopter instructor? There are various requirements for the issue of instructors' certificates, depending on past experience, but let us take the case of a pilot who has just completed 300 hours' flying as pilot-in-charge on fixed-wing aircraft (without doing any instructional flying), and who has just taken up helicopter work. He must first of all carry out 100 hours' flying as pilot-in-charge on helicopters. He then takes a test from a member of the panel of examiners and, if found satisfactory, is rated as an assistant instructor. For up grading he must complete a further 100 hours of instructional flying on helicopters and pass a further test. He is then rated as a full instructor. of single uniform curvature, of aerofoil section, and of spinner section, can be treated by mechanical mediods, while for more complex shapes a combination of hand and mechanical methods is normally used. The method makes possible a very light heater mat. The total thickness is from 0.040in to 0.050in, depending on the conductor thickness, and the corresponding specific weight is 0.26 to 0.32 Assembly of a terminal block, showing how contact is made with the metallic coating. lb/sq ft. A comprehensive series of tests has been carried out on the equipment, including those for vibration, electrical insulation, inflammability, endurance, fatigue, and general serviceability. The maximum operating temperature for the mat is at present stated to be 100 deg C, and overheat protection (in die form of a thermal cut-out utilizing a resistance sensing-element) has been devised. The electro-thermal method of ice protection, and in particular the Napier surface heater method, can be used both for con tinuous anti-icing and for cyclic de-icing, a typical cyclic ratio of "heat on" to "heat off" time being 1:10 for, say, mainplane, tailplane, and fin leading edges. An advantage of the Napier con struction is the ease with which electrical repairs can be carried out, if necessary, by hand spraying. At present, examples of the Napier heater-mat installations in production include the fin leading edge of the Bristol Britannia, the engine and oil-cooler intake for the Short Seamew, the com bustion-heater air intake on the Elizabethan, and the engine air intake on the Fairey Gannet. The compound curvature involved in these parts make the electro-thermal method of protection, compared with either hot gas methods or mechanical methods, the most suitable installation. DE-ICING: A NEW ELECTRICAL APPROACH
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