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Aviation History
1938
1938 - 0432.PDF
156 FLIGHT. FEBRUARY IJ, T938. fighter (or more correctly pursuit) category has been announced, so it may be that the outcome of tests with the Bell are being awaited before an order is placed. So, at the moment, the destiny of the two-seater fighter is in the balance. It may survive for years yet as a single- engined type or it may be developed with two engines, in which case it will be in competition with the three-seater, with front and rear guns, and with still larger types, after the style of the Bell. The rear armament, which has always been regarded as such an essential item of the two-seater's stock-in-trade, should be particularly effective in breaking up formations of fast bombers which, like the Blenheim and Dornier Do. 17, have no free gun in the nose, depending on cross fire from the rear turrets or on breaking formation and using the forward fixed gun, if attacked from in front and below. The old argument that the rear gun is useful for covering retreat after an attack still holds good, though the employ- ment of all free guns has been heavily restricted. For Fleet work a two-seater fighter may be employed alternatively as a dive bomber, as, for example, the Blackburn Skua. Furthermore, the rear gunner might come in very useful after a low-flying attack. If, in face of influence from abroad, a crew of two is retained, designers will have some nice problems relating to view, disposition of armament and field of fire. In all probability there will be room, for some years to come, for the single, two- and three-seater fighter, though the practicability of larger crews is decidedly problematical. AMONG the NEW BOOKS Astronomical Navigation : World Travel "Astronomical Navigation Made Easy," by G. W. Ferguson, M.C., A.F.C.; 5s., Sir Isaac Pitman and Sons, Ltd.T HE author, Capt. Ferguson, has had much practical ex- perience of piloting and of instructing young pilots in the air and on the ground, as countless grateful pupils will testify. He has now interested himself in astronomical navigation and approaches the subject by putting himself in the position of a pupil who does not know how to commence the study of the problem, and who finds himself surrounded by a mass of exist- ing text books dealing with an apparent mystery. A number of text books have been examined and have pro- vided the author with the essential material and formula;, which are then clearly set out and expounded—in some cases with ingenious variations from the orthodox—in an '' easy reference' manner. It is, perhaps, unfortunate that the book was compiled just before the Air Ministry Air Almanac was published in October, 1937. The Greenwich Hour Angle method adopted therein of rapidly finding the Hour Angle of celestial bodies (which is the chief difficulty in navigational calculations), has rendered obsolete, so far as air navigation is concerned, the well-known and well-tried, but more lengthy and laborious methods based on the data tabulated in the Abridged Nautical Almanac, which are quoted in the book under review. We feel, therefore, that we must completely disagree with the statement in Appendix II, apparently inserted after the appearance of the Air Almanac, that the latter "does not provide, at sight, certain quantities necessary for astronomical computations." Disagreement may also be expressed with the methods expounded of obtaining longitude by means of ex- meridian sights, particularly in the section on p. 55 headed "I am somewhere in the Atlantic. Where am I ? " In this latter example both latitude and longitude are held to be ob- tainable by means of a single ex-meridian observation of the sun; the determination of position by means of one sight has been the dream of all navigators since celestial observations were first made, but so far has proved very difficult to achieve in practice. The fly in the ointment in this particular example is that reliance is placed on a compass bearing of the sun taken when that body is near the meridian. Practical experience shows that a bearing taken under these conditions is normally unreliable owing to the rapid change in azimuth, and, usually, is mech- anically impossible to obtain with the bearing compasses in common use. In addition, in order to obtain the True Bear- ing, it is necessary to know accurately the Deviation and the Variation—for the latter, good dead reckoning is essential. In the particular case stated, late in October, with an alti- tude of 26 deg. it would no doubt be possible to obtain a fairly satisfactory compass reading—but it would not be possible in the latitude quoted (50 deg. N.) at other seasons of the year, as the altitude increases. The limitations of the method should have been made clear to the tyro, who is otherwise liable to be misled into thinking that it can be generally used. D/R is the basis of navigation, and single celestial observations taken in aircraft serve primarily to check the accuracy of the D/R, either for latitude or for longitude, depending on the true bearing of the body and the track being followed. In the example quoted the navigator must have largely disre- garded this important principle, as the "position" obtained from the single sight is admitted to have a possible error of 1 deg. of latitude and 3 deg. 36' of longitude, primarily owing to a possible Variation error of 4 deg. due to bad D/R. The check of D/R thereby provided is not very reassuring. In conclusion, while the author's industry and exposition of mathematics is admired, it is considered that the value of the Astronomical Navigation portion of the book will be greatly increased for air navigation purposes when the Greenwich Hour Angle system of finding the Hour Angle has been ex- pounded in a future revised edition, and an explanation of quick-working methods included. " A Passport Round the World," by Charles H. 'Holmes, author of " We find Australia " ; 12s. bd., Hutchinson and Co. Ltd.M ANY people have flown from Australia to England by Qantas Empire Airways and Imperial Airways, and have written about the experience. Plenty of people have also travelled on to the United States, written about what they have seen, and completed the circuit of the world by steam- ing across the Pacific to Australia. Mr. Holmes just adds one more to the list of those who have described such interesting travels. Probably there are an infinite number of observations which might be made about the various countries traversed, and, therefore, there is always room for another book. Mr. Holmes describes things very well. One fancies that he sometimes consulted guide books, and he has made some slight mistakes in the history of Moghul India which he lias jotted down ; but his book makes attractive reading, and can be recommended Forthcoming Events February 21-March 4. British Industries Fair. February 25. Hampshire Aeroplane Club. Annual Dinner and Dance, South-Western Hotel, Southampton. February 25. Liverpool and District Aero Club: Annual Ball, Grosvenor Hotel, Chester. March 3. R.Ae.S. Lecture * : " Riveting Methods in Germany," by Dr.-Ing. W. Pleines. March 4. Cambridge University Air Squadron : Annual Dinner, University Arms Hotel, Cambridge, March 10. R.Ae.S. Portsmouth Branch Lecture : " Air Raid Precautions," by Set. Barnes. March 11. Cinque Ports Flying Club: Annual Dinner and Dance, Grand Hotel, Folkestone. March 23. R.Ae.C. : Annual General Meeting, 6.30 p.m., 119, Piccadilly, London, W.I. March 24. R.Ae.S. Portsmouth Branch Lecture: " Refuelling in the Air," bv Sir Alan Cobham. March 25. Portsmouth Aero Club : Annual Ball Pavilion Ballroom Southsea. April 1. Bristol and Wessex Aeroplane Club, Ltd.— Annual Dance, Victoria Rooms, Clifton. April 7. R.Ae.S. Lecture* : " The Manipulation of the Boundary Layer," by Mr. E. G. Richardson. April 21. R.Ae.S. Lecture* : " High-altitude Flying," by Prof. J. E. Younger. April 28. R.Ae.S. Lecture* : " Factors Controlling the Development of Electrical Ignition on Aero Engines by Dr. G. E. Balrsto. May 14-22. Finnish Aero Show, Helsinki. Ail these lectures take piacc at the Institution of Mechanical Engineers, Storey's Gate, St. James's Park, London, S.W.I., beginning at 6.30 p.m.
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