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Aviation History
1910
1910 - 0133.PDF
FEBRUARY 19, 1910. [/U GHT 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 asking questions relating to articles which they have read in FLIGHT, would much facilitate our work of reference by giving the number of the letter. NOTE.—Owing- to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter mill appear Practically in sequence and at the earliest possible moment. PROPELLER PITCH. [354] I am greatly obliged by your reply in issue of January 29th. The term <c gaining pitch," for the meaning of which I inquired, occurs in the "Encyclopaedia Britannica," Vol, 21, p. 825, as follows :— " The causes of loss of work incidental to propellers of different kinds may be summed up as follows : Suddenness of change from velocity of feed to velocity of discharge. Propellers which suffer from this cause are the radial paddle-wheel and the common uniform pitch screw ; while those which in varying degree avoid it are the gaining pitch screw, the feathering paddle-wheel, Ruthven's form of centrifugal pump, and the oar." North Finchley. F. C. HARROP. [The term " gaining pitch " in the above context applies to the cambered blades employed in most modern propellers. Tangents drawn to the face of the blade at uniform intervals between the leading edge and the trailing edge represent a series of elemental portions ctf the blade progressively increasing in angle—i.e, gaining in pitch. By this means the air is received with less shock, and the cause of lost work mentioned above is more or less eliminated. —ED.] MISS LILIAN E. BLAND'S BIPLANE "MAYFLY." [355] 1 enclose two photos of my biplane, the " Mayfly." I made her entirely myself, with the exception of the metal clips, and, of course, the sockets, strainers, &c, were bought from English firms. I think she is the first biplane made in Ireland. I had her out again to-day, wind of 18 m.p.h. My only difficulty is at present to prevent her flying when I do not want her to. To-day I had three men to assist me, two of them knew nothing about it, and she ran the rope through their hands and soared up 20 ft. before anyone was prepared. Fortunately the third man and myself had hold of a long rope, which saved the situation ; in fact, we got the machine soaring beautifully for some time until a down ward gust caught the elevators, which I had fastened, when she dived down and broke both skids, but did no other damage. It is. quite a new sensation being charged by an aeroplane. We then had quite a lively time sailing her down hill to the shed; a 4-ft. bank was cleared in fine style, and indeed the only drawback was the pace, for she wants to go about 30 m.p.h. I have now altered the steering arrangement so that the elevators can be controlled from the ground, which I naturally ought to have done from the first. I am also fitting two side panels, as I cannot very well work the balancing wings from the ground. I have not yet had a chance of ascertaining the gliding angle exactly, but she soars with vertical ropes, and I imagine her angle is about 7 degrees. As I told you, she rises straight off the ground when faced to the wind. If we bring her gliding down in a steady wind she lands as softly as a feather. A. few hours work has made the skids stronger than they were before ; they both broke where the wood was cross-grained, but I have the greatest difficulty here to get good wood. The skids are American elm, which is very springy, and I must say they were severely tried. LILIAN E. BLAND. [Other aviators in embryo will not fail to have read with pleasure Miss Bland's breezy letter of her preliminary experiments, nor to wish her success in all future trials, particularly when she becomes the pilot of her machine. [Soaring tests were carried out by the Brothers Wright with one of their gliders ; the gliding angle is given by the slope of the hill if the glider soars on absolutely vertical ropes and the wind is blowing truly over the surface of the ground.—ED.] SPRING MOTORS. [356] With reference to inquiry No. 316 in your valuable Journal. I have been experimenting with clockwork motors for the past twelve months and have made the motor with interchangeable springs, 10-in. sharp-set propeller; motor complete, less spring, 6 oz. With8oz.spring,\min.,305revs. I Withl2oz.spring,Jmin.,336revs. » 8 » I .. 5i8 » I » 12 „ § „ 580 „ Will furnish photo and particulars if required. Coventry. W. J. JOHNSON. PROPELLERS. [357] The excellent articles that have appeared in your Journal recently on aerial propellers afford one a good opportunity of knowing how the different air machines are drawn through space. The majority of propellers (so called) are practically fans, and have no part of a cemetrical screw on their working surface. The reason why they draw the machine along is—the propeller revolving at such a high speed the blades buckle, and so get a certain per centage of grip and drag on the air. I think with a carefully- designed propeller we can do away with power, and have a smaller power engine, making a considerable economy in weight of engine, and also a saving in petrol consumption. The design of an aerial propeller should be fairly easy, as you are not handicapped with the • go astern' movement as in ship work. The great thing one must try and get is a good centripetal force, then your propeller is doing good work practically to the outer diameter of the boss ; that is obtained by having a deviating pitch and a lay back centre line. Another thing one must carefully study is the shape and design of the leading edge. Miss Lilian E. Bland's biplane," Mayfly," the owner up in the left-hand photograph. On the right S. Girvany, Ballymore, who has made the metal fittinps and helped throughout its construction, is in the pilot's seat. The biplane has a span of 27 ft. 7 ins., area 260 sq. ft., weight with skids 200 lbs., aspect ratio 5'5, angle on skids 6 degs. 129
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