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Aviation History
1911
1911 - 0407.PDF
MAY 6, 1911. Weaver in his letter in spite of himself. For he there states that in a flying machine the factor of safety "has to be almost entirely disregarded," and then goes on to say that the fact that flying machines are thus constructed "is borne out, only too sadly, by most of the fatal accidents to aviators." As a matter of fact, the importance of a factor of safety in the construction of flying machines is now being recognised, and the advances that have lately been made in these machines are solely due to truer mechanical construction and the allowance of a more or less reasonable factor of safety. Mr. Weaver now proposes a helicopter type of machine of a total weight of 15 cwt., or 1,680 lbs. To be fitted with a 100-h.p. engine to drive a pair of helical (or lifting) screws 10 ft. in diameter, and also with a 50-h.p. engine to drive two screws 7 ft. in diameter (one as a tractor and the other as a propeller). The machine, in addition, to be provided with supporting planes (after the manner of an aeroplane) to have, as I take it, a total area of 25 ft. by 8 ft. = 200 sq. ft., and be provided with ailerons for steering purposes. If we take out the various weights of the above we shall find that it is impossible to construct the machine within the limits of the total of 15 cwt. The 100-h.p. engine, at the low weight of 4 lbs. per horse-power, will weigh, without the radiator and con nections, 400 lbs., and the 50-h.p. engine, on the same basis, 200 lbs., a total of 600 lbs. for the two engines alone. The radiators with their connections and necessary water, at a modest estimate, will weigh 50 lbs. Then there is the fuel and oil, if enough is carried for only one hour's consumption we shall require, at the rate of J lb. per horse power per hour, 75 lbs. of petrol, which with its container will weigh say 85 lbs., and allowing 5 lbs. for the lubricating oil and its container, makes a total for engines, radiators, fuel, water, oil and tanks of 740 lbs. The two helical screws, 10 ft. diameter, which have to transmit 50 horse power each and support the whole weight of the machine, will weigh, at a moderate estimate, with their shafts and spindles, thrust-blocks and bearings, 200 lbs. each, or 400 lbs. for the two, and the transmission gear from the engine to these screws, with attachments, would weigh at least another 50 lbs., making a total for the helical screws and all attachments and gears of 450 lbs. ; each of the 7 ft. screws, with their shafting, gearing, bearings and attachments, would weigh at least 40 lbs., or a total of 80 lbs. for the two. The planes, at the low estimate of I lb. per square foot, will weigh 200 lbs., making a grand total up to now of 1,470 lbs., which deducted from 1,680 lbs. leaves a balance of 210 lbs. only out of which we have to construct the body of the machine capable of carrying all this and the weight of the driver as well, besides being strong enough to transmit the strains due to the exertion of 150-h.p. within it on a medium outside it ; which, to my mind, is impossible. If Mr. Weaver can do this, both myself and others, I am sure, will be deeply interested to learn how it can be done, and to see the actual machine when it is made. Maidenhead. CHARLES J. REYNOLDS. f^^ Steering by Compass. [1164] The article by R.A. on the above subject in your issue of April 22nd is of much interest in view of the present vogue for cross country flights and the pending long-distance races, and you will perhaps pardon one who has spent the greater portion of his life " steering by compass" adding a few remarks on a subject which, I am glad to see, aviators who are undertaking cross-country flights are taking an increasing interest in ; in fact, some knowledge of the use of this instrument and its limitations is absolutely essential to any of them who aspire to get out of sight of their native aerodrome. A series of articles on this subject by me were published in the Aero in February, in which I dealt with the subject of aerial naviga tion from a purely nautical standpoint, and special stress was naturally laid on the premier navigational instrument—the compass. With regard to this instrument, there is no difficulty whatever in providing a compass of a standard design which will fulfil all the necessary conditions when used in flight, on any type of machine, if the vibra tion is damped in the way advocated in my article, i.e., the bowl placed in a receptacle packed with horsehair or other suitable material. This has been successfully tested on various types of machine—Bleriot, Farman, &c. There are, of course, numerous systems of taking up the vibrations on board ship which have been found effective to a greater or less degree on board vessels of every type, from battleships and ocean liners to turbine torpedo boats and trawlers ; but what is required for airwork is a simple system effective on any make ot machine, and one in which gimballing to keep the bowl horizontal should be unnecessary, when used with a properly designed compass, and compasses which fulfil these conditions are now in use. But, as was pointed out in the articles referred to, though a steady and well-designed compass is a sine qud non, the instrument will be worse than useless unless designers of machines take an interest in the matter and provide a suitable position for it in the centre fore- and-aft axis of the machine, in a good magnetic position ; and also that the moving parts, such as steering pedestals, foot control, &c.f be made of some non-magnetic material. This detail is, I understand, being provided for in certain types, notably the later Howard Wright design. Given a moderately satisfactory position, there is no greater trouble "adjusting" a compass in an aeroplane than there is_ on board a ship, and certainly far less than is the case in most ships, especially compasses placed in between-deck positions. For the benefit of the uninitiated, I may say that the term "adjustment" means the elimination, as far as possible, of errors due to the unavoidable proximity of disturbing factors, such as the engine, stays, &c. The north point of the card is made to point as nearly as possible to the correct magnetic north when the machine is headed in any direction; this can be done by the aid of small magnets suitably placed by one who is accustomed to the work. R. A. does not consider that '' leeway" is the proper term to apply to the deflection from the course due to the wind, and I think that from the ordinary definition of the term accepted by seamen this is not " leeway," and "drift" expresses what is meant far more satisfactorily. The question of providing some method of correcting the course for "drift" is one of peculiar interest to the aviator. For over-sea flights he is in much the same position as the navigator in a current, and must make his allowances and steer a steady course, trusting that his judgment is fairly correct, but for cross-country flights there is undoubtedly a field for experiment in R.A.'s observations, though I would suggest that, instead of introducing glass, talc, or similar materials into the construction of aeroplanes, the object would be achieved by providing a species of "grating" of light metal rods in the bottom of the machine ; these rods should be placed parallel to the fore and aft axis of the machine, between the aviator's legs, and in consequence would be in line with the "lubber line "of the compass. This would also have the advantage of allowing the pilot to get a better view of the ground, a point which certainly requires attention in some types of monoplanes. With regard to R.A.'s last paragraph, it is hoped that a method of rapidly and economically arriving at the direction and speed of the wind at various heights at a given place without the aid of kites will be possible in the near future, should the trials now being carried out prove satisfactory. It is to be hoped that the naval officers taking up aviation will especially study the navigational aspects of flying, for which their sea training should be of special value, and no doubt with their assistance the art of "aerial navigation " will make great strides as soon as they have got the aerial equivalent to " sea-legs." Horsell. C. O. [1165] May I thank your contributor, " R.A. (Retired)," for his remarks on my article, " Steering by Compass" (FLIGHT, Septem ber 24th, 1910). Owing to an unfortunate mis take, the lubber-point was omitted altogether from my diagram, although it was mentioned in the text as being there. This lubber- mark on the compass-case, travel ling round parallel with the line on the glass plate, corresponding to the adjustable arm, such as " R.A. (Retired)" suggests, the plate and compass-case being connected together in the manner described. With regard to the relative resistance of aeroplanes and dirigi bles, my contention only holds good, of course, in the case of gusty or puffy winds. A short gust striking an aeroplane and a dirigi ble at right angles to their course would have the effect of carrying the latter further to leeward than the former. The ratio of inertia of resistance of the aeroplane being greater than that of the dirigible, it would take longer to set the aeroplane drifting at the wind than the dirigible ; although in a steady side-wind they would, as your con tributor states, both drift to lee ward at exactly the same speed. L. GRAHAM DAVIES. Anerley. LUBBER POINT ;; ON COHPA&S C/\s£ 409
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