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Aviation History
1939
1939 - 1922.PDF
FLIGHT, June 22, IQ3Q. g However, Hughes have now developed and refined an instrument panel compass of this type, graduating the card Into 50 units and supplying it with a course indicator to take the place of the grid wires on the horizontal faced type. It must be admitted that the performance is excel lent for turning error, aperiodicity and steadiness of read ing. It will be in the position that the pilot asks for in the instrument panel, and although it will only be readable to 2$° instead of 1°, as are the large horizontal faced com passes, it wili not be disturbed much more in the instru ment panel by changing magnetic fields nearby than is the other type in front of the control stick. The alternative for an instrument panel compass is some completely new departure in design, such as the Kollsman Direction Indicator. This instrument has powerful mag nets, heavier than usual, enclosed in a float on a pivot. The float is in liquid which takes most of the weight. In a separate compartment above the float chamber there is a slave magnet which must follow the powerful master magnets below; the slave is attached to a vertical shaft and the movement of this is transmitted by means of a pinion drive to a horizontal shaft with an indicator hand attached. The indicator operates in front of a vertical dial in the instrument panel. Somewhat naturally, this instru ment has its own particular characteristics, but it also has the special advantage that it indicates the direction with out the necessity of first adjusting grid wires to the indi cating hand, while, at the same time, it has a grid arrow which can be rotated to show the pilot the course he is trying to keep. Well Established Any magnetic compass in the instrument panel must suffer from disturbance by changing magnetic fields near it as much as, if not more than, a compass in front of the pilot's seat, and both must be much inferior in perform ance in this respect to a compass mounted high above dis turbing forces. Although the magnetic compass is suffering more and more from this changing deviation trouble, and although in its present form it is always more or less out of action in a short steep turn (due to turning error when the vertical component of the earth's magnetic force acts on the com pass magnets in an aDparently horizontal direction, or to acceleration of the aircraft causing the needle to overswing) it will be found a tough customer to supplant. To begin with, it is simple and almost foolproof; a needle on a pivot has very few parts which can go wrong, and a pilot can feel certain of its giving him the north with more or less accuracy throughout every flight for years. The bowl, the needle, the pivot, the lighting, etc., have a number of refinements which demand highly skilled workmanship on the part of the maker, but, generally speaking, it is an inexpensive instrument. If it is properly adjusted for deviation it reads to an accuracy hard to beat. Finally, it is light. What signs are there of any new form of instrument which will take its place or compete with it? Throughout a turn the directional gyro shows the true amount of that turn, and the importance of this cannot be overstressed, not only for blind flying but also for rapid manoeuvring in clear air. Unfortunately, a gyroscope precesses, wanders in azimuth, and must be corrected every few minutes by reference to a magnetic compass. For fifteen years manu facturers have been trying to produce a gyroscope which can be automatically controlled by a magnetic compass. Their first problem was to find a way for the magnetic needle to act on the gyroscope. The difficulty is that the magnetic needle plays tricks during turns and is continually hunting, even if only slightly, owing to accelerations of the aeroplane. At what moment is the gyroscope to be cor rected by the magnetic needle? The human eye can esti mate when the needle is in the middle of a swing, but an automatic device must take its correction from the needle at fixed intervals of time, irrespective of whether the needle is out of truth at that moment. There is the cathode-ray compass and magnetic dip indicator, on which research work is being carried out by Hughes. The lines of equal dip in the Atlantic happen to lie nearly along the flight route, and if an instrument could be per fected to read accurately the amount of dip, aircraft could find their way across by following the line of equal dip. The ideal instrument may be a master compass able to operate three dials at a distance, one for each pilot and one for the navigator. The master instrument can then be placed in the best situation in the plane where the magnetic needle, if it has one, will be less affected by electrical or other disturbance. If absolutely reliable and not too heavy, it will be the answer to the pilot's prayer. WORLDS MOST POWERFUL AIR-COOLED ENGINE t ^~ w.-ia-ht Duolex Cvclone, an eighteen-cylinder two-row radial which A 2,000 h.p. radial : The first photographs released o «M^ P y ^ ^.^^ aero.engine in the world A is stated by the makers to deliver 2,000 h.p ^1S ™U WrSd^Sr Two Duplex Cyclones are fitted in the new Consolidated specially finished version is being di^^tfS in Flight 'recently.
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