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Aviation History
1946
1946 - 0485.PDF
MARCH 7TH, 1946 FLIGHT 251 CORRESPONDENCE The Editor does not hold himself responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. THE D.H. GOBLIN II Net Thrust Calculations IN a descriptive article on the D.IT. Goblin II in Flight, Feb.21st, on page 187, there was a very interesting diagram giving component axial loads on the various engine units understatic conditions. Below the diagram the net thrust at the engine mountings is stated to be 3,000 lb. Out of interest, and not in any Doubting-Thomas spirit, Itotalled .these loads and made them equal only 2,500 lb. Per- haps my arithmetic is not all it should be ...VIVIAN CRISP. [The reader's arithmetic is probably quite sound, but didhe notice that his thrust of 2,500 lb. was also "in reverse." The explanation is that among the total figures is one of-5,500 lb load, transmitted by the centre casing. This figure is.only indicative of the load carried in this portion of theengine framework. It is labelled '' no gas load on this com- ponent," and should not be included in the sum of componentaxial loads. Adding again we get:—(a) +300 +6,800 +800 +600=+8,500 1b.; (b) —3,100-2,400=—5,500 lb.; subtract-ing: 8,500—5,500=+3,000 lb.—ED.] AIR MAIL RATES Why are They So Very High?C AN someone explain why it costs 5/- to send a 2-ounce airmaH letter from London to New York, as compared with 3|d. for the same letter by sea mail:1 The a!bove air mail rate works out at about 27/3 per tonmile, which is a ridiculously high figure even for a most iiiefficiently run airline operating the most uneconomical air-craft. It is, in fact, of the order of ten times the figure which should apply for operation of a good modern aircraft, such asthe Tudor or Constellation. The current passenger fare works out at roughly twice thefirst class sea passage, and Pan American seem to believe that even these airline fares are higher than need be. Mails needless in the way of amenities during the trip than passengers, and can hardly require higher handling charges either. If we assume the average airline passenger, with his freebaggage, to weigfi 200 lb, and take his fare at the present rate of £94, then this corresponds to a charge of only 1/2 per2 ounce, or 6/5 per ton mile. "ALL FIRST CLASS MAIL BY AIR." ON BEING C.G. CONSCIOUS Loading Errors Can Cause Air Accidents STUDYING the number of air crashes recently the ordinaryperson must be bewildered by the lack of conclusive . evidence as to their cause. Mystery surrounds quite a number.Psychological factors are vaguely mentioned and many hypo^ theses are put forward—overworked pilots, disgruntled groundcrews, outworn equipment, hasty servicing. Though some of, these may be contributory none of them quite solves theproblem. There is always something vague about this sort nf explanation. The point is, are there other factors more important andliifficult to assess? The answer is yes; there is one factor most difficult of assessment, and it is hard -to believe that itis entirely free from blame, namely, incorrect load distribution around the centre of gravity, or even plain overloading. The difficulty ol assessing this factor in finding the causeof a crash lies in the fact that when an aircraft crashes the load is always displaced. If, the pilot does not survive, noone has the faintest idea that loading may have been the cause. If, the pilot does survive he usually refers to trim andthe trim tabs. When it is a matter of repatriating men quickly there maybe some excuse for overloading a very large fuselage. Many an aircraft must have been flown overloaded, during the war,hut there is little conclusive evidence to prove that this factor is responsible for many crashes. It is such a difficult fact toestablish. It may be that when the war ended and men were clamouring to be evacuated, an easy-going attitude wasadopted towards the loading of aircraft which may be respon- sible for some of the crashes recently reported; especially thosethat have .struck high ground or have crashed at take-off. It will be noticed that large numbers of Dakotas have been involved in recent crashes. This is undoubtedly due to thehigher proportion of this type used as Service transports than any other type, but the temptation to overload a tuselage as.spacious as a Dakota must be very strong, and the wing loading of a Dakota is not low by any means. Often merespaciousness is mistaken for unlimited capacity, the density of the freight carried being ignored. A big, spacious fuselagewith only two engines is always a danger. If all freightable volume were of the same density thenloading an aircraft would simply be filling up the cargo space, the designer would see to that, but to stress the obvious, onepackage may be five times heavier than another ol the same volume. As wing loading and cargo spaces have increased,loading and e.g. data has become increasingly important until now its importance cannot be over-estimated. Perhaps load-ing charts could be devised and placed conveniently inside the fuselages as in the Horsa glider.. Probably the abstract terms " moment," "moment arm,""positive and negative moment" used by weight estimators may be responsible for loading and e.g. data not gettingthe consideration it warrants among ground crews, to whom a moment may mean nothing more than a short but unspecifiedperiod of time. In any case it is a very misleading term. Simpler terms could with advantage be devised. Why not callthe e.g. datum the balance point and always clearly mark it inside and outside the fuselage and let it, wherevei possible,approximate to the centre of the cargo space. Everyone who has to deal with civilian air freightage shouldbe e.g. conscious. Its importance to air safety cannot be over-estimated. No designer can make a fuselage foolproof.He may do a lot to stabilize the centre of gravity, but he cannot be held responsible for carelessness in loading. Hisresponsibility is the preparation of, carefully compiled loading and e.g. data, and if a pilot or person responsible for loadingfails to translate this data into practical terms of safety, lives will be jeopardized. The story of the crash caused by two fat ladies walkingaft to the toilet at the same time may be mere fiction, but • it contains a word of warning. JOHN HOWARD. R.A.F. SLANG The Pukka Gen at Last ? DURING the war I have read so many explanations of the. origin of the eloquent term "gen"—all different and all wrong—that I feel it is about time I informed an unin-terested public of the true derivation of the word which is now an indispensable noun in the weird terminology of theR.A.F. Your recent correspondent " Ex-Halton Boy " (Flight, Feb.21st) has guessed the nearest so far, but it is still wrong. However, he is more or less correct when referring to the timeof its birth. I, personally, would put it a little later, circa 1929-30. Certainly the word was born at Halton in my time.Well, here it is ! Halton, like other camps everywhere, was always buzzingwith rumours, but if an " erk " could conscientiously say, "It's genuine," then one knew that the buzz was true. Thenone day, of course, someone said, perhaps accidentally, per- haps purposely, "It's GEN"; and there you are! For a long period gen, to every Halton boy, stood for theabsolute, tried and trusted truth. But, alas, the word left Halton with its devotees as they passed out to men's service,where its stainless character was soon corrupted. No longer could the gen be relied upon. It was suspect, and thus theterms "pukka gen" and " dufl gen" arose, signifying posi- tive and negative gen respectively. These additions were nodoubt appended by men returned from India, and appeared about 1932. After the inspiration that produce^ 'sad anti-climax, and I myself coul'" guardly terms. Perchance this 1«from the ex-Haltonite from who' slang first fell. May I take this opportunityand a bit sentimental) of wi- enemies the best of luck.
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