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Aviation History
1937
1937 - 0360.PDF
i3« FLIGHT. FEBRUARY II, 1937. Correspondence The Editor does not hold himself responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily lor publication, must in all cases accompany letters intended for publication in these columns. REDUCING RADIO CONGESTION I HAVE read with interest in the February 4 issue of Flight (p. 130) the criticisms and proposals of one who, under the non-de-plume of "Critic," questions the ability of the present class of air wireless operators. In some respects " Critic " appears to have inadequate know ledge of the points on which he expresses opinion. Apropos of his desire to see. the standard of air operating raised to that of marine operating, necessitating greater morse speed tests and extensive D/F. experience, does he realise that one of the premier British air lines has, for some time past, recruited ex-marine operators with sea service ranging from three to fifteen years and possessing 1st Class P.M.G. Certifi cates, which qualification covers complete theoretical and prac tical knowledge of D/F., and high-speed morse working of not less than twenty-five words per minute ? While fully agreeing with '' Critic '' in his suggestion that more extensive use of D/F. apparatus on machines would enable a large proportion of the present congestion of the aether to be eliminated, I feel sure he is greatly mistaken in attributing the lack of apparatus to the inability of operators to handle it. With regard to the suggested inauguration of a public radio- telegram service from aircraft, this is a matter requiring more careful consideration than that which '' Critic '' appears to give it. Theoretically, it would seem simple, but when one realises the amount of responsibility of an operator on busy routes, especially in conditions of bad visibility, when his chief task is one of maintaining constant watch for machines in the same vicinity to avoid risk of collision, the idea in practice is subject to much complication. It would be a dangerous possibility for the operator of an air liner to miss important information relat ing to navigation (such as the changing of height of other machines on the same route, etc.) through being engaged with radio-telegram traffic on another waveband, thus prejudicing the safety of air navigation, which, after all, is the primary purpose of aircraft wireless. It would appear, therefore, that the only really practical method of introducing such a service on busy routes without detracting from the efficiency of wireless as an aid to navigation would be to carry more than one oper ator, so that the most important wave watch would not be broken at any time. "Critic's" description of the present standard of payment of air operators is very apt, and any increase on the present duties of operators should certainly be met with an increase of salary. AEROP. Croydon. . CROYDON, GATWICK AND GRAVESEND IN your issue of January 7 there appeared a letter from Mr. Donald G. Southwell, entitled " Croydon, Gatwick and Gravesend," in which Mr. Southwell remarked that " it would \te interesting to keep an official set of figures of Gravesend visibility for a month together with those of Croydon and have them compared." It may be of general interest that, prior to this Company acquiring control of Gravesend Airport, official figures were kept at Croydon and Gravesend over a period of four months —from November, 1933. to February, 1934—and these re-, cords, if I remember rightly, were taken three times daily over this period. Owing to the large amount of figures which these records contained, we compiled a chart from them showing the average visibility over this period, and we enclose a copy which you may find interesting enough to publish. 1 also note that Mr. Southwell considers that Airports, Ltd., are too conservative in their use of electricity for beacons, etc In this respect I would point out that if any pilot wishes any of the lights to be switched on he has only to ask, but most people do not seem to appreciate that to switch on ob struction lights, beacons, etc., every night for a number of hours is a comparatively expensive item in the accounts of an airport, and, where an airport is not owned by a Govern ment or municipal authority, it cannot afford to disregard an expense that can be avoided—especially as it serves no useful purpose except to act as a guidance for pilots on a regular January 1934 February 1934 Croydon and Gravesend visibility compared—the chart referred to by Mr. A. M. Desoutter. service who do not wish to use the airport but may neverthe less be glad to see its lights The difficulty is that the companies operating these airline services will not make any contribution towards the cost of the lighting which their pilots find so useful on days of bad visibility. AIRPORTS, LTD. • Gatwick Airport. A. M. Desoutter, Managing Director. THOSE TAPERED WINGS TN mooting the topical subject of tapered-wing stalling in -•- your columns, I tear I have trespassed on hallowed soil : the sacred ground of the "rationalist," who views all design and research problems as a neatly arranged pattern of scientific deduction and crystal-clear solution. In turning the other cheek for Dr. Lachmann's attention, perhaps I should remind him that all the most inspired designs are created on the back of an envelope pulled from the designer's pocket in a moment of inspiration ; or maybe a fit ot desperation after looking at the other fellow's bad dreams ! However, at the risk of tiresome reiteration—since he accuses me of unanswering his demand for '' rational reasons'' —I must refer him to the third and fourth paragraphs of mv original letter of December 10, also the fourth and fifth para graphs of my letter of December 31. If he will take the trouble to re-read them, dispassionately, he will see that I suggested beginning with the elliptical plan form simply because it is the basic shape postulated in the vortex theory, hence its value as an aerodynamic standard or yardstick. Perhaps Dr. Lach- mann will suggest a more '' rational'' standard for a family of related aerofoil tests. From the contents of his third paragraph, one is now told that he is not against my suggestion for elliptical wing re search, although earlier this was rudely chastised as a "fetish." One also gets the impression that Dr. Lachmani- now wishes to disclaim the advocacy of highly tapered trape zoidal wings, which is a curious volte-face in view of his publi- statements and the physical evidence provided by the product.-' of his own firm. Yet for some irrational reason I am singlea out for his displeasure because I had the temerity to question these excessive taper ratios of 4 and 5 to 1. Apparently, Dr. Lachmann objects to my vivisection of hi- "careful analysis" of profile drags as derived from Gottingei: low-scale tests. (Parenthetically, I am astonished to learn that I have insulted Gottingen's high altars because I queried the use of 1925 aerofoil data by a designer in 1936 ; my criti cism was obviously directed to the latter). But the carefid analysis 15 now seen to consist, as I suspected, of an induced drag term containing an induction correction factor (Glauert'> '' delta '' term) for plan form and span loading—which is the nigger in the woodpile, since the correction factor itself r- under dispute, as I have already shown. Compare, for ex ample, Dr. Lachmann's own assumptions for induced drag derived from Glauert, with those given by Higgins in N.A.C.A Technical Report No. 312, wherein the results have been properly corrected for lift curve slope. Bete in " Aerodynainr Theory" (Vol. IV) gives yet another set of correction factor-
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