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Aviation History
1936
1936 - 1037.PDF
432 FLIGHT. APRP. 23, 1936. LIGHT AIRCRAFT EQUIPMENT A Review of some of the More Popular Items of Optional Equipment for Machine and Pilot now on the Market : Instru ment " Whys and Wherefores" Explained for the Benefit of the Newcomer DURING the earliest days of fly ing, the unfortunate—or fortu nate, according to one's point of view—aeroplane pilot had a joy stick and a foot bar to operate, and usually a '' blip switch '' for con trolling his engine, and very little else. He was supposed to judge what his aeroplane was doing by "feel," and his only means of knowing, or rather guessing, how his engine was going was by listening to its note. The early aviators became surprisingly skilled at telling by such crude means whether or not all was well. They had to ; their lives depended upon it. Nowadays it is a different matter. All sorts of instruments have been placed at the disposal of the pilot for keeping him informed exactly of what is hap pening to his aeroplane and engine, and although the choice of instru ments lies partly with the owner, a certain number of instruments are regarded as essential to the safe hand ling of an aircraft. Airspeed Indicators Most important, from a safety point of view, is perhaps the air-speed indi cator. From the very beginning of his school period the budding pilot is taught to watch his A.S.I, so that he may never let the speed drop below a certain mini mum, depending upon the particular type of aeroplane he is flying. Funda mentally, as most readers know, the air speed indicator depends upon the effect of dynamic pressure, which is "col lected," so to speak, in the pitot tube, while another tube, known as the static, has its end shielded so that it is merely open to still air. The tubes lead to a flexible diaphragm, which is in turn linked to the pointer on the dial, and the difference in pressure on the two sides of the diaphragm is read off as speed in m.p.h. Other types are used, but to a smaller extent—such as the very simple strut type produced by the De Havilland firm as an auxiliary check. Next in importance, although not strictly speaking a flying instrument, comes the engine revolution counter. The A.S.I, and the rev. counter con stitute the absolute minimum of instru ments with which anyone could think of taking a machine into the air; and they would suffice merely for flying around Although not abso lutely typical, the instrument layout of Lord SempiU's Puss Moth is in teresting. It in cludes an R.T.E homing receiver, while in the centre panel are the Sperry artificial horizon and direc tional gyro and the homing indicator. an aerodrome. As soon as the pilot aspires to something more ambitious than that, he will begin to feel the need of quite a number of other instruments. For one thing, he will certainly require an altimeter to tell him at any time at what height he is in relation to his point of departure. There are several makes of these three instruments on the market, but those most commonly found are, like many other aircraft instruments, products of Smith's Aircraft Instru ments, of Cricklewood, London, N.VV.2, and of Short and Mason, Ltd., Aneroid Works, London, E.17. The altimeter is virtually a barometer, which depends for its action upon the surrounding air pressure, which compresses a small metal capsule. The difference in pressure is translated into altitude in feet. " Bradshaw " Flying "Flying by Bradshaw" is an ex pression which denotes finding one's wav across country by following a known and identified railway line. For serious cross-country flying some knowledge of air navigation is essential, and the first requirement is a reliable compass. Of these there are quite a number on the market, Owing to the ability of an aeroplane to make very rapid manoeuvres, it is desirable to use a type of compass which is "dead beat," so that the needle does not get into a series of violent swings which would make it difficult to use the compass with any degree of accuracy. A very popular type is the Husun Mark IIIA, marketed bv Smith's. Other makes which have been used extensively are the "Sestrel," obtainable from Short and Mason, and the large and small compasses made by Kelvin, Bottomley and Baird, Ltd., of 18, Cambridge Street, Glasgow. Usually the aeroplane manufacturer standardises one or other of these types, but changes can usually be made if the purchaser so desires. Generally-speaking, the magnetic mffl- pass is very reliable and can be trusted provided its small peculiarities are understood. On northerly courses these are most in evidence, and during recent years instruments have been introduced which supplement the compass by pro viding a more accurate and delicate in dication of small departures from the course originally set by compass. These instruments have as their basis a small gyroscope which tends to remain in the position in which it was originally set in motion. This fact is made use of by linking the gyroscope to the indicator needle or pointer. If the machine swings slightly off its course, the gyroscope tries to remain in its original position, though the framework which carries it moves with the aeroplane. According to whether the instrument is of the " free or '' restrained '' type this movement is indicated on the instrument dial as the actual displacement or by a swing of the pointer, showing the rate of left or ngm turn, as the case may be. Turn-and-Banh Indicators Sensitive course-keeping was the origi nal object of the gyroscopic turn inoica tor, but during recent years its ran tions have been applied more speciKa;;? to what is known as " blind flying . that is to say, flying entirely byjnsu rnents, in weather conditions wnen ^ ground and horizon cannot be see",. such conditions the pilot's turn indira tor will tell him if he is wandering on course, but it will not tell him « "^ sideslipping gently all the *""«• if other instrument becomes^ nfC"*jlabie. this information is to be aval Known as a bank indicator, it sno pot
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