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Aviation History
1948
1948 - 1857.PDF
SSISiS NOVEMBER 4TH, OVERIDING S.A.S. NEEDLE SETTING I.A.S. CAPSULE I.A.S. POINTER- ANEROID CAPSULE Mn SETTING from this schematic arrangement the operative movements of the instrument may be followed. Incidentally, the bi-metal link is of brass and invar, and its purpose is to compensate for the effects of temperature on the capsule characteristics. the maximum safe air speed indicator is installed in the aircraft,the limiting safe speed is set into the instrument through a hole in the back of the case, which is then sealed. In making thissetting, the value in terms of Mach Number is shown through a window in the instrument face, and a gear train from the settingbar appropriately sets the pivotal geometry of the linkage between the safe air speed pointer and the aneroid capsule.This linkage is nominally of parallel-action type, the contact "between capsule and linkage being made through a curvedcantilever arm on the capsule side and a follower-roller on the linkage. Once the setting has been made, there is only slightmovement between the roller and the arm. As the aneroid capsule expands and contracts, the arm is lifted and lowered,so respectively decreasing and increasing the safe air speed indication according to change in altitude. The operation ofthis can be followed through the schematic diagram It will also be seen in this drawing that an over-riding settingis provided at the front of the instrument for the safe air speed pointer. This is of considerable importance. It may well bethat, although an aircraft can safely fly at a Mach Number of, for example, 0.85 at 30,000ft, its safe limit at sea level may be 551 no more than 0.75 for, aside from flow distortion near sonicspeeds, a further criterion of safety for the aircraft is really a matter of withstanding the applied forces. These are, how-ever, basically affected by density and pressure, and it is in this disparity that the change in safe air speed in termf ofMach Number is evident. Altitude and Indication The hypothetical values we have quoted can be used to illus-trate this. At 30,000ft, our Mach Number of 0.85 is equivalent to 580 m.p.h., whereas, at sea level, a Mach Number of 0.75 isequivalent to 574 m.p.h. At sea level in I.C.A.N. conditions of still air, and disregarding position error, etc., the I.A.S. will bethe same as the T.A.S. However, at 30,000ft, a correction must be applied dividing the true air speed by 1-634 to give indicatedair speed, which in this example is 355 m.p.h. Therefore, although the aircraft is moving through the (assumed still) air at a truespeed of 580 m.p.h., the pilot will only see a speed of 355 m.p.h. indicated by his A.S.I. Conversely, if an aircraft climbs fromsea level to an appreciable altitude at a constant true air speed, the indicated air speed will progressively diminish. • The over-riding setting for the safe air speed pointer is im-portant in that the pointer has to indicate against an I.A.S. scale so that, in common with the I.A.S. pointer, it will, fora constant setting, move back as altitude is increased. Thus, following through our example, although the basic setting of theinstrument is made at Mn 0.85, the S.A.S. pointer will never- theless be set by the over-ride to a limit of 0.75. This will allowthe aircraft to be flown at a T.A.S. of 574 m.p.h. at sea level and a T.A.S. of 580 m.p.h. at 30,000ft, by virtue of the fact thatthe I.A.S. pointer at the latter conditions will be indicating 355 m.p.h. and the S.A.S. pointer is affected by the same laws. The tolerances of indicative accuracy called for in the-specifi-cation are extremely severe. The S.A.S. pointer must indicate to an accuracy of ± 3 knots throughout the total performancerange of the instrument, whilst the I.A.S: pointer must indicate to an accuracy of + 2 knots up to 175 knots ; ^ 3 knots up to430 knots ; and ± 5 knots up to 650 knots. These tolerances apply equally in the metric and m.p.h. equivalent calibrations.The indicator is being produced both in civil and military versions, the respective weights being 18 oz. and 20 oz. A usefuldesign feature is that, unlike most instruments using a front fixing in the case, the movement of this unit can be extractedwithout first removing the pointers and dial. HILLER 360 CERTIFIEDW ITH the granting of a full C.A.A. certificate, the Hil360 utility helicopter is now going into limited product tion at the Palo Alto works in California. The machine wasdescribed in Flight of January 8th, 1948, and is remarkable for the stability given it by its servo-control system (two aero-foil surfaces carried at right angles to the rotor blades). It is interesting to learn that quantity manufacure is not beingundertaken by United Helicopters, who produce trainers and demonstration machines only, but that all major parts andassemblies are being manufactured by sub-contractors in different parts of the United States. CITY AND GUILDSA N advisory committee on aeronautical engineering practice, under the chairmanship of Sir A. H. Roy Fedden, M.B.E., D.Sc, has recently re-drafted the City and Guilds of London Institute scheme of courses and examinations for the practical aircraft apprentice. It is intended that the new syllabuses shall come into operation in technical colleges and schools in September, 1949. In drafting the new scheme, the committee has borne inmind that the College of Aeronautics, Cranfield, and the Royal Aeronautical Society provide for the higher grades of scientificand engineering technicians in the aircraft industry. Never- theless, the young mechanic must acheive his practical pro-ficiency on the floor of the shop, and today the practical mechanic has, in addition, to possess a thoroughly soundtechnical knowledge if he is to be really proficient. The inten- tion of the committee is that the new courses should providethe criterion of the standard required of the modern aero- nautical mechanic.On the grounds that a sound basic engineering training is an essential preliminary to a study of the more advancedfield of aeronautical engineering, the course of instruction and related examinations in subject 63, Machine Shop Engineer-ing, Intermediate Grade, of the existing City and Guilds syllabus (D) has been adopted as the intermediate stage of thescheme in aeronautical engineering practice. This intermediate course should occupy preferably three, but in any case, notless than two, years of part-time instruction. Candidates taking the Intermediate Grade of Machine Shop Engineering as thefirst stage of their studies for a qualification in Aeronautical n 10 Engineering Practice should enter for the Intermediate Examin-ation in Machine Shop Engineering in the normal way. In the final grade, separate courses of instruction arearranged in Section 72 A, Airframes, and 72 B, Power Plants. Each course should occupy at least two years of part-timestudy, and comprises Workshop Technology (airlrames or power plants); Science, Calculations and Drawing (airframes or powerplants); and Scheme of Practical Work (airframes or power plants). In order to be accepted for the examination, a candidatemust, at the time of entry, be certified by the Principal of the college (which term includes a works school approved by theInstitute) as having satisfactorily completed a final course in workshop technology, and science, calculations and drawing (orin science, calculations and drawing when no course in work- shop technology is available) and satisfactorily to have carriedout at least two of the sections of the scheme of practical work. In instances where a workshop practice course has notbeen taken at the college, the works manager may certify, through the Principal of the college, that two sections of thescheme of practical work have satisfactorily been carried out at the works where the candidate is employed. FAIREY AVIATION REPORTI N the course of his speech at the annual general meeting ofthe Fairey Aviation Co., Ltd., Sir Richard Fairey, M.B.E., F.R.Ae.S., chairman and managing director of the company,emphasized the importance of research and development in such a progressive industry and said that to fall behind intechnical progress would seriously damage the company's future prospects. Sir Richard continued by saying that when onereflected that%uch successful aircraft as the Fox, Swordfish, Primer and the Fairey helicopter had all been private ventures,conceived within the organization and financed with its own resources, it was a little bewildering to learn that it had beenstated in the House of Commons from official sources that there was no such thing as private enterprise in the British aircraftindustry. The firm had new and novel types in the prototype stage and on the drawing board, and their latest contributionto Naval Aviation would shortly take the air. Following suc- cessful pioneering efforts the company was being encouragedby the M.o.S. to extend its activities in the guided weapon field.
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