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Aviation History
1914
1914 - 0077.PDF
JANUARY 17, 1914. CORRESPONDENCE. An American Stabilizer. [1821] In the January 10th issue of FLIGHT, page 49, mention is made of a new form of stabilizer that is being tried in AnWira •H JSSE ^ lhich'from the K«SX^S ,ts ateral slability." Four years ago in New York I tried out almos an identical device with Mr. Walden on a monoplane but™ teado using one large central plane there were two small flat ones, each tilted up on its inside edge, and mounted about 2 ft. above the extremity of each wing tip, as shown in the accompanying photo- graph. Like Mr Fiske's arrangement, these small planes were supposed to combine the good qualities of a dihedral without any of the disadvantages, but I must admit that the result of experi ments made at the time showed the machine to be more stable without them than when they were in place Whenever a side-gust struck these auxiliary surfaces the machine (/JJGHT] would rock violently, so that they had to be discarded. Theoretically, they might have restored balance in the case of a side-sip, but as in those days one did not indulge in such things intentionally, and I never had the misfortune to do it accidentally, I never determined whether they would work or not. The machine was shown at the first aero-motor show in New York, and was commented upon in the technical press at the time. It would be interesting to know that, if the device used on the Curtiss biplane really does improve its lateral stability, whether a plain vertical fin mounted in the same position would not ba equally effective. G. M. DYOTT. A Warning to Pilots. [1822] After reading Mr. Harris Booth's interesting article on the subject of air speed indicators, I expected to find your last issue full of correspondence on the subject. Is it that pilots take no interest in the instrument which is going to be the means of saving innumerable lives, or is it that they think the liquid gravity con trolled air speed indicator good enough ? I am a little doubtful about writing on this subject, as having myself placed a spring controlled air speed indicator on the market I do not want to appear to be pushing my own inventions ; on the other hand, the matter is so important that I think it is my duty to back up what Mr. Booth has said on the subject. Without going deeply into details as to the most usual types of accidents to aeroplanes, I think it may be safely stated that more occur due to " stalling" than to any other cause, consequently any instrument that can be depended upon to give an exact indication of the speed at which the machine is moving through the air must be of immense value, as provided that the speed is kept within the flying limits of the particular machine, stalling cannot take place. Take an example of a machine capable of flying normally at 65 m.p.h., its most efficient climbing speed maybe in the neigh bourhood of 45 m.p.h., and its most efficient gliding speed will probably also be about 45 m. p.h. Fitted with a spring-controlled air speed indicator of reliable make, it will be quite safe to elevate the head of the machine to such an extent that the speed drops until it shows 45 m.p.h., and the pilot will then know that he is climbing safely at such an angle that he will arrive at a maximum height in the minimum time. (A small allowance is required for loading.) NoWj supposing the motor slowly loses power, the pilot still keeping his speed indicator at 45 m.p.h. To do so he will find he has to move his elevator so as to climb less steeply, and the morelhe engine fails the more he will have to lower the head of the machine uniil in the extreme case the motor stops altogether. The head of the machine, to maintain the 45 m.p.h., will by this time have had to be lowered until the machine is planing at approximately its best gliding angle, and all this has been done simply by the pilot keeping the pointer of his air speed indicator on 45 m.p.h. The above machine'gliding at 45 m.p.h. will probably glide efficiently at something under this speed, so that the machine will always be well in hand by observing the air speed indicator, and keeping it anywhere between 40 and 50 m.p.h. If a gust hits the machine, the indicator records the change in speed immediately, so that an inexperienced pilot with an air speed indicator can get better results all round than a more experienced pilot without such an instrument. All the previous remarks are based on having a spring-controlled instrument', and do not apply at all where a gravity-controlled one is used. Returning to our machine climbing at 45 m.p.h., suppose as before the engine starts to lose power or the pilot elevates the head of the machine so much that the speed falls to such an extent that it begins to pancake. This means an acceleration downwards acting on the column of liquid, thereby causing the liquid to rise in the tube and to show a much higher speed than that which should be shown due to the pressure on the Pitot tube. The pilot gets a false impression of his speed, and if not very experienced he thinks he can put the head of the machine up still more, whereas the opposite movement is what is immediately necessary. In the case of a machine gliding at its proper speed, the pilot through inattention or changes in the atmosphere may drop the speed of the machine somewhat. Acceleration downwards takes place, and the reading on the liquid air speed indicator may actually show a higher speed than before, although the speed of the aeroplane may be much slower and actually in a state of stalling. There is not the slightest doubt that liquid air speed gauges must go, and in fact several other gravity-con trolled instruments as well, and the sooner the better, as every pilot who goes aloft relying on one is relying on not only an instrument which gives wrong readings, but unfortunately gives a false sense of security at the very moment when the air speed indicator should be of the utmost value, namely, in bad winds, in climbing, in gliding and banking, and in landing. I think Mr. Booth deserves great thanks from all interested in aviation for pointing out this important matter, E. HOLLOCOOMBE CLIFT, A.F.Ae.S. Sinclair Road, W. [1823] With regard to Mr. Harris Booth's interesting communi cation on the failure of the Pitot tube liquid gauge to indicate changes of speed relatively to the air caused by gusts, it seems pertinent to remind your readers that a Pitot-tube anemometer,* with a spring control, and balanced for the inertia effects Mr. Booth discusses, was exhibited at the International Congress at the Paris Aeronautical Exhibition just over a year ago. With regard to inertia effects in general, instruments and apparatus for use on aeroplanes are being put forward in large numbers, whose action depends on the action of gravity on pendulum bobs, columns of mercury and so on. Sometimes the models are pretty and ingenious mechanical arrangements, and work nicely on a table. But in all such cases the application of an ounce of theory, in the shape of the elementary rule that the effective weight of the columns of mercury, &c, is compounded of the earth's attraction and the reversed acceleration of the instrument relatively to the earth, can alone predetermine whether the apparatus is sound in principle and should be experi mented with, or unsound and to be dropped. If " practical" engineers prefer to try to find exceptions to Newton s laws of motion by mounting expensive full-site apparatus on aeroplanes, they are not the only people in the world spending money on schemes that are predestined to fail. ARCHIBALD LOW. [• Mr. Low presumably refers to the Toissiant Lepere air-speed recorder, described in FLIGHT for July 5th last, in which the two leads from the Pitot tube are connected to two chambers, each of which contains a concertina bellows, and so arranged that whilst the outsides of the latter are subjected to the Pitot tube pressures, their interiors are open to the atmosphere. A spring is incorporated in this instrument to regulate the movement of the bellows and of the pointer attached thereto.—ED.] 77
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