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Aviation History
1938
1938 - 0668.PDF
FLIGHT. MARCH IO, 1938. CORRESPONDENCE The Editor does not hold himselj responsible:for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. BROADSIDE FIRE REFERRING to Mr. J. D. North's letter in your issue otMarch 4, on the subject <if broadside lire from aircraft, it would SI'L-IU " that the Magnus effect should result in a con- siderable disturbance in the trajectory of a projectile fired from a fast aeroplane at right angles to its flight path. On one side ot "the aeroplane one would expect the trajectory to be raised and on the other side lowered. The exact amount of the deflection is impossible to calcu- late as one of the velocities concerned is considerably above the speed of sound, and I know of no data on Magnus effects at such velocities. But it would be reasonable to expect that sights adjusted for normal conditions would be of little use to the gunner under the special circumstances considered here. London, YV.r. \V. O. MANNING. I HAVE read the correspondence re broadside fire in Flightof March 3 ami feel that your reply is very much to the point, as obviously it :s very difficult to provide answers to Mr. North's list of questions. Mr. North took exception to the effet de Cazaux, forgetting it seems, that this is only one ot the arguments against broad- side fire. One must also take into consideration the angular velocities of high-speed aircraft in action, for it is ridiculous to expect enemy formations to follow parallel, almost pre- arranged, courses at the same speeds. The faster machines will obviously take advantage of their better performance and use the armament which is more accurate—their axial guns. The question of axial velocities has been studied very thoroughly by the French expert, C. Rougeron (who, inci- dentally, is now Directeur des Armements AeYiens at the French Air Ministry), and I would refer to his very conclusive remarks on p. 125 of the April, 1937, issue of the Royal Air Force Quarterly. His deductions were confirmed in practice during the Spanish War. Here is an extract from an article, entitled Les Lecons de la Guerre d'Espagne, by General Armengaud in the Revue des Deux Mondes of August 15,J 937 : "The pursuit machine remains by reason of its great speed, the fire power of its axial armament and the relative precision of its close-range fire the redoubtable opponent of the bomber or observation machine, which is, obviously, more bulky and slower. The lire of bombers outside the axial plane is almost impossible with the present speeds of aircraft and it cannot, in any case, be accurate. A speed equal to that of the pursuit machine, or, in any case, very near it, plenty of manoeuvrability, small size, and especially axial armament— these are the conditions for the protection of bombers against aerialand terrestrial weapons." General Armengaud refers to the '' insufficient protection '' of the big Savoias, Capronis and Junkers, and cites as proof of his argument the success of the smaller and faster Russian Katiouska and the German Dornier—presumably the Do. 17. He is a well-known authority on aerial warfare and I do not think his conclusion could be questioned. Should Mr. North still require specific references in the French press to the effet de Cazaux I would refer him to Les Ailes for March 15, 1934, Page 7> an<3 April 19, 1934, page 6. London. TACTICIAN. RESISTANCE WELDING I WELCOMED the inclusion in Flight (November 11, 1937)of an article on the resistance welding of aluminium alloys. Making an extract for future reference I soon found that I was in difficulties with several of Mr. Fassler's points. They are as follows : (1) "The weight of molten material in a spot -,3gin. diameter in two sheets of 16 gauge duralumin we find to be 3 grams." The weight of a core of duralumin -fgin. diameter and o.i28in. thick is 0.16 grams, approximately, and by the subsequent argument it is this core to which the author refers. The effect of this alteration on the energy required for welding (if we accept the heat losses as 7,000 per cent, of the useful work done) is to decrease the figure of 19,800 calories to 1,050 calories. Doing the arithmetic-of adding 25 per cent, to this figure and avoiding the printed 20 per cent., we arrive at the fact that to perform the weld in one second the power required is 1.3 kilowatts (instead of 100 kilowatts). Latent heat may be neglected, but the 7,000 per cent, has a swamping effect on any calculated values of heat required. (2) The next problem is to find the resistance of the weld. It seems that an error has occurred in using the temperature coefficient, the resistance being .0000x46 ohms and* with the 80 per cent, increase, .0000263 ohms. A more importantcriticism is with regard to the area of 20 sq. cm. (which is very approximately the area of the spot). Does this notimply that contact between the sheets is only at the weld? (3) Under the cross-heading '' Further Investigation '' thereis a third reference to Joule's Law (the first reference is in fact not an application of Joule's Law at all). The sentenceis: — " Joule's Law reads as follows:0.24 x I2 x K x T seconds = gramme calory seconds." Surely the product of PR and time is a quantity of workand must, therefore, be stated in calories? (Again, on the first page of the article a most remarkable unit appears calleda "gramme calory Watt second." The correct unit in the latter case is the joule.) Continuing with Joule's Law, Mr.Fassler proceeds to show, with the aid of a "practical figure for impedance," that the weld may be done in 0.4 seconds inspite of the fact that using the same power he has already accepted that it takes one second. No doubt the figures which Mr. Fassler gives are based onpractical experience, but to deduce them from fundamentals seems to require liberal imagination as well as Joule's Law. Hitchin, Herts. H. K. P. PATTERSON.[The reason for the delay in publishing this letter is that Mr. Fassler was, and still is, recuperating in Switzerland, andit was desired to publish his reply at the same time as the letter. So far we have not succeeded in obtaining that reply. —ED.] NAVIGATION—THE BRIGHT SIDE A GOOD deal has been said and written in criticism of therecently issued modified syllabus of the examination for the Second-class Navigators' Licence. While the syllabus, as a whole, has not, in my opinion,reached a generally satisfactory degree of perfection, I am definitely strcngly in favour of the inclusion of those itemswhich, according to Mr. C. W. Martin (Flight, March 3, p. 207), constitute astronomical navigation but which actuallyare only introductory elements of that branch of navigation. It is, I consider, most regrettable that anyone connectedwith navigational training should present to students and pro- spective students a gloomy picture of difficulty and complica-tion when both are, in reality, non-existent. The determina- tion of the hour angles of the sun, planets and stars is avery simple arithmetical problem, which, if properly presented and carefully explained, is capable of quick and accuratesolution by anybody possessing a brain of average capacity ; it is certainly far from being a task so involved as to bestrictly reserved for treatment by a mathematical or scientific genius, as Mr. Martin seems to indicate. The questions ofthe daily apparent motion of celestial bodies and of the recog- nition of planets and stars are likewise simple elements ofbranch-subjects, while the use of ephemeral tables is easily learned. With regard to meteorology, the general question of frontsis now a routine item in everyday meteorology and I am surprised that Mr. Martin should seek to render it obscure byemploying terms like " frontology " and " frontologists" when referring to such an elementary consideration. Considering the present rate of progress in the design ofaircraft and the continual advancement of aviation generally, it is high time that our navigational knowledge extendedbeyond simple air pilotage and that everybody concerned faced the subject fairly and sanely. It is, I assert, incumbent uponall those engaged in navigational training to present navigation in its entirety as a normal science capable of being masteredby all who are possessed of average calibre. In conclusion, I would like to express the opinion that thereis no need for any prospective candidate to fall into a state of despondency, as, 'provided that he is guided aright and isprepared to devote a little time to study, he will follow a very pleasant path to success. H. W. SIMS-WHITE. Perth. NO HARM ? SURELY it's rather a silly rule that nobody under the ageof 17 years is allowed to hold a flying licence. I mean, if one has the ability to fly and can come through the tests, however strict, with flying colours, there can be no harm 1 granting him his licence. I wonder if any of your read can point out where I am wrong. Deal. I. S. PHIIXOX. (13 yfS-)-
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