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Aviation History
1951
1951 - 0574.PDF
356 FLIGHT, 23 March, 1951 CORRESPONDENCE The Editor of "Flight" does not hold himself responsible for the views expressed by correspondents in these columns. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. Inherent Stability YI/TTH reference to the article "Infallible Glider" in Flight of * * March 9th, 1951, the following may be of interest. The late Robert Kronfeld, in his book Kronfeld on Gliding and Soaring, quotes Etrich (of Taube fame) as follows: "We, too, were prepared to learn from Nature. We studied the flight of birds and even enlisted as teachers two living vampire bats. Among my father's many books on flying we found a work by Prof. Ahlborn, of Hamburg, on The Stability of Kite-like Planes. In this work the investigator drew attention to the flying seeds of a Javanese palm, Zanonia Macrocarpa, which can cover wide distances. "We regarded this phenomenon as a signpost of Nature. We made paper models, increasing their size as we gained experience. In 1904 a big model of a gliding machine, carrying a load of 56 lb, made quite considerable flights. A year later we designed a large machine with a span of 40ft, which was completed in the following year. Started from a rail trolley and carrying a bag of sand it flew down into the valley in beautiful, calm gliding flight, and landed smoothly without any artificial steering, a thousand feet from its starting point. "How was this possible without any steering gear? The chief peculiarity of the flying seed is that its wings have a pronounced backward and upward curve. The action of the Zanonia's surface is therefore the same as that produced by the combined effect of a wing and a stabilizing plane. The typical feature of my flying machine was that it consisted of nothing but carrying surfaces, which were nevertheless stable." Grangetown, Sunderland. J. T. ROBSON. Navigation Aids T SHOULD like to reply to the latest letter (March 9th) from A Mr. W. Gregson, on the subject of the Decca Flight Log versus V.O.R./D.M.E. I believe he is aware that one of the best- qualified American companies has been engaged for a considerable time on the development of a map presentation for V.O.R./D.M.E. This rather disproves the statement that "it is quite simple . . ." and also shows that it is doubtful if the consensus of opinion, even in the U.S.A., is today in favour of a course-and-distance indicator. As I understand that Mr. Gregson is attending the Montreal I.A.T.A. Convention (Radio Aids Group), he should also be familiar with the following extract from the M.C.A. report on the experimental Flight Log which has been submitted to that Con- vention by B.E.A. :— •". . . it has been shown that, when using the Flight Log, the execution of holding patterns; take-offs and flights to denned outbound points; controlled departures from specified holding points along defined paths to a second defined point j straight-in approaches from arbitrarily defined points; and en-route naviga- tional flights—can be performed with a higher standard of flexi- bility and precision than is possible with any other known pilot- presented navigational aid in civil use." The map presentation of V.O.R./D.M.E. information could not be any more accurate than that permitted by defects in the basic system. Furthermore, presentation of a courss-to-steer and distance-to-go is useful only when the information is given from the point to which you want to go. In Europe and in America, flights are rarely a question of going straight from one place to another. In the busier areas, they have to conform to a flight pattern which, as in the case of London, Paris and New York, can be followed most satisfactorily by a map presentation. Obviously there is no space to go into a detailed analysis of the voluminous A.I.L. report, but my comments on Mr. Gregson's points are : (1) Calibration of error is believed to be impractical as* well as inconvenient, e.g., correction cards for each V.O.R. would not be welcomed by pilots; and altering the nominal alignment of an airway to conceal the inaccuracy in the V.O.R. concerned would raise great difficulties if that V.O.R. went unserviceable and the stand-by beacon, having a different error, had to be brought into operation instead, naturally at the shortest notice. (2) The receiver in question was the best available and very expensive, contrasting with the claimed advantages of being able to use cheap equipment with V.O.R. Furthermore, the results were obtained under the carefully regulated conditions to a scale and scientific survey and such serviceability could not be reasonably expected in day-to-day commercial operations; (3) this statement is strictly true, but begs the question, since the errors that remain long enough to affect the aircraft's track are serious. The statement from a reader of your paper that four-course M.F. ranges should suffice for some years is astounding. It completely overlooks the justified publicity you have given to the splendid performance of the Comet and the Viscount, whose long periods of ascent and descent will require lateral separation to be applied on a scale completely beyond the scope of four-course ranges. The statement belittling the need for accuracy of the en-route navigation aid not only ignores this point also but overlooks the fact that in a congested air space of parts of Europe, particularly the U.K., civil aircraft must keep accurately within air space intended to protect them from non-controlled flying and such other factors as danger areas. As mentioned previously, the Track Guide and the Integrated Track Range are about to be tested and discussions of their detailed performance should obviously await results of these trials. How- ever, it is worth pointing out to Mr. Gregson that the Track Guide will not give a homing bearing like A.D.F. but a track line which is highly preferable from the point of view of navigation and descent from altitude. Decca trials have been carried out in the highest- noise zones of South Africa and Borneo and I can assure Mr. Greg- son that there will be no difficulty in locking the distant slave. THE DECCA NAVIGATOR CO., LTD., London, S.W.9. H. F. Schwarz. Competitive Trials RECENT competitive trials, between the two anti-submarineprototypes built respectively by the Fairey Aviation Company and Blackburn and General Aircraft, raise the interesting problem of how an aircraft may be fairly assessed in such circumstances. What, for instance, constitutes an ideal formula for differentiating between similar aircraft which have been designed to satisfy the same specification? Let us assume that we have any two Naval prototypes which have undergone the protracted programme of contractors' flight trials, assessment by the A. and A.E.E. and/or R.A.E., deck-land- ing tests, operational trials, maintenance conferences, etc. At the conclusion of this .period, which does in fact occupy many months, the aircraft should not only fulfil but excel the requirements of the Admiralty. One machine will, of course, be a little better here and the other will gain a little there, but on the whole the two machines will have progressed very much in parallel. But how is it decided which is the better of the two and, hence, which shall be produced for the Navy ? There are many features which must influence the decision, and for the sake of clarity the suggested eight salient features may be tabulated thus :— (a) Flying Qualities.—General handling, stability, performance, etc.(b) Take-off Performance.—Length of run, directional control, etc. ' (c) Landing Performance.—View, undercarriage shock-absorption,flying controls, etc. (d) Operational Trials.—Assessment on actual service trials.(e) Maintenance.—Engine, airframe, inspection, interchangeability, etc. (f) Crew Comfort.—Grouping and accessibility of instruments andother equipment. (g) Development Possibilities.—Incorporation of bigger and betterweapons and more and more equipment (as usually occurs in Naval Aviation!).(h) Production.—Simplicity of production, costs, availability of labour, and allied factors. Having decided on the main features, the question of assessing their individual values is the next problem—is a machine with 100 per cent flying qualities but only 90 per cent in maintenance features of greater war potential than one which gains 100 per cent for maintenance and 90 per cent for flying qualities ? Or do well-designed crew compartments outweigh good view and responsive controls for deck landing? In order to provide a target at which aeronautical experts can shoot, some suggested marks for the various features of our imaginary Navat prototypes are set out below and they are so arranged that an ideal aircraft would score a total of one hundred:— (a) Flying Qualities, 22. (e) Maintenance, 15.(b) Take-off Performance, 8. (f) Crew Comfort, ir. (c) Landing Performance, 12. (g) Development Possibilities, 9.(d) Operational Trials, 18. (h) Production, 5. Now within these classifications the same problem arises : what values are to be allocated to the various features ? For instance, in the 22 marks for flying qualities, how many does one deduct for longitudinal instability, ailerons that heavy-up in a dive, or a vicious stall ? Alternatively, does access to the power unit count more in the maintenance evaluation than the fact that the hydraulic com- ponents are hidden in some remote corner? Some expert opinion: would be welcome. Leeds. ONLOOKER.
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