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Aviation History
1931
1931 - 0062.PDF
FLIGHT, JANUARY 16, 1931 flying - boat of normal British type fitted with naturallyaspirated air-cooled engines. From this curve it will be seen that at 22,5001b. the time to take-off is 26 seconds. Thiscalculated time is very close to the actual time taken by this particular boat, in fact the whole of this curve does notdepart from the full size results by three or four per cent. The dotted line in Fig. 13 gives the calculated time to take-off in air of relative density 0-9, from which it will be noted that the time to take-off at normal load of 22,500 lb. isincreased from 26 seconds to 43 seconds, an increase in time to take-off of 65 per cent. Also, from these curves it will be seen that the boat understandard conditions will take-off with a load of approximately 27,500 lb. in 60 seconds, whereas in air of relative density0 • 9, if the take-off time is limited to approximately 60 seconds, the boat will not take-off with a load greater than 24,000 lb.,which is a decrease in load of 3,500 lb. Although the calculations on which these curves are basedhave been made for a particular case, they approximately apply in general ; thus, if a boat takes 50 seconds to get-offunder standard conditions in England, it will fail to get-off in about one day in three in the tropics.Fig. 14 shows the run to take-off in yards plotted against the all-up weight of the machine, these results applying to thesame machine, for which the times to take-off are shown in Fig. 13, from which it will be seen that at 22,500 lb. the run totake-off under standard air conditions is approximately 480 yards, while at air of relative density 0-9 the run to take-offis 680 yards. A relative air density of 0-9 is frequently met with in thetropics. In fact the whole of these calculations are based on air conditions recorded at Alexandria, where conditions arenot so bad as they are at Karachi. At the latter place relative air densities of 0 • 85 have been recorded ; thus thecurves given in Figs. 13 and 14 may be taken as giving results which may be reasonably expected. The conclusion to be 3> <$> drawn from these calculations is that it is essential that allboats that have to operate under tropical conditions should be fitted with engines which are supercharged equivalent to aheight of, at least, 4,000 ft. Successful long-range flying. boats cannot be produced until this condition is fulfilled. The subject of the increase of structure weight of aircraftwith the increase of total all-up weight has received a good deal of attention in the past, and while I do not intend todiscuss this problem in general, I would like to draw your attention to the variation in the weight of floats when com-pared with their displacement. Fig. 15 gives the weights of seventeen floats ranging in displacement from 2,000 to 22,300lb. These floats will in general be designed with 100 per cent, reserve buoyancy, so they will be suitable for aircraft ofweights between 2,000 and 22,300 lb. The whole of the floats are of metal construction, and the chassis supportingpoints are included in the weights. While the whole family is generally similar they have all been model tested and alteredin detail to suit the requirements of the particular machine to which they have been fitted, so I think I may say they aregenerally representative of any floats between their limiting weights. If, now, in Fig. 15, we assume the displacement of a float inpounds, to be equal to the total weight of a seaplane, it will be seen at once that for a seaplane weighing 4,000 lb., thetotal weight of floats will be 400 lb., or 10 per cent., and fora machine weighing 22,000 lb. the weight of floats will be 1,700 ,lb., or 8 per cent, approximately. From the foregoing it will be seen that there is a distinct saving in the weight of floatsas the size of the machine increases, which is rather to be expected as the linear dimensions of similar floats vary asthe %_/ displacement and the areas as (displacement)2". The fact that the relative areas of floats are decreasing withthe weight of the seaplane, is also interesting from the air resistance point of view. (To be concluded.) REVIEWS A USEFUL HANDBOOKMr. C. A. SIMS, the staff photographer of our contemporary The Aeroplane has produced an admirably got up little bookillustrating many well-known types of service and commercial aircraft of the present day. There is a Foreword by C. G.Grey, and the Preface to the Royal Air Force section is in- formatively and authoritatively written by Mrs. C. M. McAlery.Each photograph is accompanied by a page of descriptive text and the illustrations themselves are photogravure repro-ductions from the original photographs. The book itself should form a useful and ready means of getting to know alittle about most of our more common types of aircraft, but like all such catalogues it will date very quickly and reallyneeds to be produced fairly frequently. " DAEDALUS."•'British Aircraft Illustrated;1 by C.A. Sims (A.&- C. Black Ltd.), obtainable from FLIGHT Office. Price 4/- post free. CAN YOU ANSWER THAT ONE ?IN his new book " Air Questions and Answers," Mr. P. M. Henshaw has followed the scheme of those people who supplybooks of questions and answers for those who wish to play that parlour game which takes the form of increasing one'sgeneral knowledge. His book consists of some 1,257 questions with their answers, and finishes with a glossary' of aeronauticalwords. The indexes, both general and detail, are admirably arranged and the reader should have no great difficult y infinding questions referring to any subject he is interested in. All this seems on the face of it admirable enough, but whenone comes to the questions themselves, one cannot help feeling that the answers have been got out too hurriedly andin many cases at the expense of accuracy. There is no doubt that the idea of such a book is extremely good and there is avery great deal in it which is of value both to the man who knows something about aeronautical matters and who wantsthe book for reference and also to the tyro who is searching after general knowledge. There are, however, many answerswhich are frankly so inaccurate as to be ludicrous. To quote one question, No. 20 " How can drag be decreased ? "By streamlining or so shaping the wings that they otter the least resistance possible. Every shape has a differentvalue of resistance, and this factor is called the co-efficient of resistance and is denoted by the symbol K.Naturally, anyone who is conversant with the subject can see what the author is driving at, but anyone who is not,cannot learn much from such a statement. The answer to Question 4 is amplified in the answer to Question 5 andmention is made of a constant which is omitted from the formula in the first place. In the answer to Question 199, thepropeller boss is quoted as a lightly stressed part and there- fore as sometimes being made of elektron ! The answer toQuestion 204 as to what wing loading denotes seems entirely to disregard the weight of the structure itself and merely regard-1'the wings as supporting the load carried by the aircraft. It many places the author uses the word " stress " very loosely,but here no doubt, he has done so with a view to making toe language as simple as possible. Unfortunately, however, Mhas only succeeded in making it misleading. Such inaccuracies one can go on quoting throughout the book, but to do so ismerely destructive criticism and I should like to suggest that a second edition of the book be introduced at a later date, i°rthere is no doubt that properly got out it should fill a ven definite want. " DAEDALUS. "Air Questions and Answers," by P. M. Henshaw ('rale _^ Polden, Limited), obtainable from FLIGHT Office. P.ice *r post free. An Annual Event W. B. DICK & Co., the well-known makers of " Ilo " lubricating oils, held their third annual danfceon Friday night, January 9, at the Quadrant Restaurant, Regent Street. The committee arranged things in an exceptionally able manner, and the directors, their employees, and guests all thoroughly- enjoyed themselves. One of the events of the evening was the exhibition by Mr. Bruce Dick himself, whose superb dancing with Miss Joan Moore put the majority of the younger shame.Memorial to R.101 Designer AT a public meeting held at Walthamstow on J^it was decided that a memorial to Lieutenant-Colonel Richmond, designer of the airship R 101, in which he fis to be raised at Walthamstow, where he lived fo years. men' uuyVincent gristed,
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