452 



POLAR PROBLEMS 



Direction Finding and Steering a Course 

 By Magnetic Compass 



The conventional method of finding direction and steering a course 

 by magnetic compass has many disadvantages when used in flights 

 in the polar regions. ^^ Apart from the fact that at present the polar 

 regions are not adequately charted magnetically, the horizontal com- 

 ponent of the earth's magnetism is very weak and, except for the 

 region on the other side of the true pole to the magnetic pole, the lines 

 of equal magnetic declination come very close together. Conse- 

 quently the process of flying along a great circle by magnetic compass 

 is very complicated. 



But the magnetic compass^^ continues to be used and will con- 

 tinue to be used as a means of determining direction for flights because 

 of its simplicity and because it functions in fog. As a guide in steering 

 a course it is not likely to be much used in the future, although, again, 

 until the radio compass is perfected it will remain the only method 

 available in fog. 



By the Use of Sun Azimuth Tables 



A more satisfactory method of finding direction when flying in the 

 polar regions, in that it indicates true north rather than magnetic 

 north, is by the sun. Assuming that one's position has been deter- 

 mined approximately, then, knowing the 

 Greenwich apparent time and consequently 

 the difference in longitude between the posi- 

 tion and the heavenly body (easily deduced 

 from the chart) and knowing the declina- 

 tion of the heavenly body and the latitude, 

 the navigator has sufiQcient data for solving 

 the astronomical triangle (see Fig. 3). Now 

 as one proceeds towards the pole the azi- 

 muth of the sun (measured S by W in north 

 latitudes, N by W in south latitudes) be- 

 comes more nearly equal to the hour angle. 

 Consequently it is herewith suggested by 

 the writer that the most convenient astro- 

 nomical way to determine azimuth in the 

 polar regions is by applying to the sun's 

 hour angle, from tables previously comput- 



POLE 



ZENITH 



Fig. 3. 



SUN 



13 The instrumental errors that have to be taken into account in finding direction and steering 

 a course by magnetic compass are fully described in Boykow and others, op. cit., pp. 43-47. 



1* J. A. C. Warner: Aircraft Compasses^Description and Classification, Natl. Advisory Committee 

 for Aeronautics Rept. No. 128, Washington, 1925, pp. 22-50. 



The Magnetic Compass in Aircraft . . . Air Ministry (Directorate of Research), Air 

 Publication 802, H. M. Stationery Office, London, 1922. 



