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Aviation History
1911
1911 - 0921.PDF
OCTOBER 21, 1911. pjGHT CORRESPONDENCE. The name and address of the writer (not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. Correspondents communicating with regard to letters which have appeared in FLIGHT, would much facilitote ready reference by quoting the number of each letter. Naturally Stable Machines. 1394] Since the publication of my letter and photos in FLIGHT I have bad a number of letters on the subject of the " diamond-shaped box plane " from others who have experimented with it, notably from Mr. " Redivalls," who tells me he has taken out a patent in connection with it. I congratulate him. My object in writing to you now is to call your attention—and possibly that of your readers—to the fact which my correspondents are practically unanimous in emphasizing, viz., that aviators and builders ot full-sized machines will not even consider the adoption of this member as a means of obtaining automatic lateral stability, on the ground that it has been tried and proved to be unsafe. One can only imagine that it is being identified with the " square- ended " or " side curtain " arrangement used on the early Voisins. But there is all the difference in the world between the action of the square-ended box plane and the point-down box plane, as anyone who tries them will instantly discover. The monoplane with dihedrally up angle, fitted with a goint- down box plane, ot suitable size at its centre, and properly balanced longitudinally, will recover an even keel immediately, however much it may have been canted over, even if it should have been entirely capsized. Moreover, the same effect takes place irrespective of the horizontal speed of the machine. Speed lessens the liability of the machine to cant at all, it is true, but the righting impulse is equally rapid, and equally unfailing, at whatever speed the machine is moving hori zontally ; the slightest movement having a downward tendency seems to put it into instant operation. I hold no brief for " Redivalls " or anyone else. I am an amateur experimenter pure and simple. But here is a feature so absolutely startling in its stabilizing effects that it could not fail to convince anyone who actually tried'it, or saw it tried, and yet I am told that those most actively interested in aviation have obviously never even taken the trouble to consider wherein this " box plane ' differs from the old square-ended " box planes " of the past that are now very rightly voted unsafe—still less to try it for themselves, when they simply could not fail to be convinced. One feels, as one deeply interested in the new science, how very much is probably being kept hidden by conservative tendencies of this sort. Downham Market. (REV.) HAROLD KELK. Twisting Tail for Steering. CI39S] I wish to thank Mr. Cochrane (1372) for his courteous reply to my query contained in a previous issue of this paper. The principle involved in my idea is dissimilar to that which he patented in 190?. By very careful and thorough experiments with a model monoplane I have obtained a very efficient tail by which altitude and direction can be governed. The model was launched The glider which has been built at Aberdeen by Messrs. Anderson and Singer has been making some excellent glides. The photographs were taken after certain altera' tlons had been carried out as a result of experience gained, and with the machine seen in our pictures the most suc cessful glide obtained was about 25 to 30 yards. so that whilst it was " gliding "or " flying " it would pass several windows opened on one side of a hall. By this means it was sub jected to sharp draught at short intervals. It was extremely interesting to note how directly the model felt the draught it veered out of its course by banking, but the tail, by its peculiar movements, adjusted itself and almost immediately brought the model back to the direction in which it was launched. Lowestoft. Roj. F. RICHARDS. Long-Distance Flyers Propelled by Elastic. [1396J I read with much bewildered interest Mr. Mann's letter in these columns regarding the limit of long-distance flyers propelled by elastic. I contend that the results obtained with a 30 in. model provided with 6 stiands of elastic need not be less meritorious than one provided with 12 strands of the same elastic, provided of course that the power was properly used. I may say that I have a 36 in. model fitted with 2-8 in. propellers, each driven by 4 strands of f'j in. strip elastic purchased from Messrs. Warburton and Allen, Leicester. I have had fairly good results with this somewhat low powered model. On more than one occasion it has remained in the air for more than 30 seconds, and covered 300 yards in that time, at an altitude of about 20 or 25 feet. I will be very much interested if Mr. Mann can suggest where there is any waste about this model. Success depends on efficiency, not on high power. Mr. Mann states in his letter that a propeller develops power. This is something new. I was always of the opinion that it transmitted power. Re his wish to see a scale model fly half-a-mile, this is hardly a fair challenge, because the twisted elastic flying-stick is not a practical aeroplane, and should not be compared alongside an engined scale model which is practical and more worthy of credit if it is able to fly at all. I am sorry I am not able to boast of having constructed an engined model myself, but am confident that I will some day be able to materialise something better and more practical than twisted elastic. Glasgow. BUITRE. fx397] I have read Mr. Mann's criticism (1,385) of my letter (1,368), and would like to reply to a few of his questions and statements. Mr. Mann seems to interpret my letter as an attack upon rubber as a motive power for models. I would ask him :—Is stating the limits of rubber making an attack upon it? Mr. Mann says further, that I describe all elastic-driven machines as " flying sticks," but I think that if he will look again at the heading of my letter, he will see that it is long-distance models I am dealing with ; and surely long-distance models, with no chassis, with their planes, which are usually merely a length of wire bent round, with two or three ribs, or a rectangle of wood, may be called " flying sticks," which term he says has hitherto been applied to models intended to win competitions. But is not a long-distance flyer designed to fly a long distance, and are not model designers engaged in an eternal competition to achieve record distances ? The power is, as I said before, the rate of doing work, or the rate of giving out energy, and it is not correct to speak of the power of a skein ot elastic when the amount of energy that can be stored up in it is meant. When Mr. Mann talks about the power of the six and twelve-strand elastic motors it is the torque he means, or the force pressing on his finger when he winds them up. Perhaps by taking the figures of his motors I may be able to make it clearer. I may say that I noticed in an old copy of FLIGHT that 'i lb. of elastic would store upwards of 1,000 ft.-lbs. of energy; thus taking the value at 1,300 ft.-lbs. per lb., we get that the six-strand motor, since 1 ^00 x ^ it will weigh nearly x\ oz., can store - , -ft.-lbs. of energy. Now, if this motor runs down in, say, 30 sees., it will give out 1,300x5 . ft.-lbs. of energy every second, or its power is 16 x 12x30 1,300x5 16 x 12 x 30 ft.-lbs. per sec. Similarly, if the 12-strand motor runs down in 30 sees., its power will be ' . ft.-lbs. per second. ° r 16x6x30 v Thus, if both the motors run out in the same time, the power of the 12-strand one will be just double the power of the 6-strand one. But, now, suppose the 12-strand one to run down in 60 sees. ; then I 300 X C its power will be - ' •>- ~~ ft.-lbs. per sec, which is the same as I 300 X C ,,-' •„„ • or the power of the other. So now the 12-strand motor ID X 12 X xO is only giving the same power as the 6-strand one, and it is quite obvious that the former motor, running down in 2 mins., will only 923
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