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Aviation History
1910
1910 - 0088.PDF
I/OGHT] In the " Encyclopaedia Britannica" (article "Screw"), an Admiralty experiment is described, in which a gunboat was fitted with a four-bladed screw, and its performance noted. Then two blades were removed, and it was found that horse-power was saved without loss of thrust. Then why does Bleriot use four, and Davidson as many as the boss will hold ? There is a toy consisting of a metal screw with a hollow conical boss, by means of which it can be perched on the end of a steel rod, and violently rotated by pulling off a string wound round the cone. I have made these with varying numbers of blades. With two blades the lift was good and the string-pull easy, also with three ; with four the pull required was harder and the flight no better, and by increasing the number of blades, as in a fan or the gyropter, a point was reached at which the thing would not lift at all. Yet a two-bladed screw, made heavy by loading the boss, lifted better than one in which the extra weight was put in in the form of more blades. It appears to me that some information as to the efficiency oi small screws might be obtained on these lines, the screw revolving free in air and exempt from mechanical friction, if the string were of definite length and a pull obtained by the fall of a definite weight. But the two-bladed form must have a rim to give it stability if this form of drive is used. With a stud carrier and multiplying gear, suddenly accelerated and then checked in its motion to release the screw, no rim is required, and it is easy to secure a perfectly vertical flight, but it is hard to be sure of the exact peripheral velocity at the moment of release. I hope to be told of something more convenient than either of these. Will you kindly tell me what is meant by the expression " gaining pitch " ? Trusting you will not find this too long. N. Finchley. F. C. HARROP. [The above interesting letter draws attention to a very important consideration in propeller design, the most efficient number of blades. The sole purpose of a screw is to exert thrust by a rearward acceleration of a column of air. If it can accelerate this column equally well with two blades as when using four blades, there is so much less skin friction to be overcome in forcing the blades them selves through the air. So far as practice goes at the present time, it would seem that two-bladed propellers are very well suited for aerial work, but it must be borne in mind that constructional con siderations have considerable weight, and when it comes to making a wooden propeller the two-bladed type is unquestionably the cheapest form. In marine work three-bladed propellers are in common use, mainly, we believe, on the score of good balance. We have not yet seen a three-bladed propeller for aerial work. The question of testing the efficiency of propellers on the lines suggested in the above letter is one worthy of consideration, although the precise arrangement described is scarcely suited to delicate work. We have ourselves thought that it might be possible to gain some interesting information by spinning a propeller on a vertical pole, and allowing the propeller to fall under its own weight while spinning. If successful these conditions would convert the blades of the propeller into two aeroplanes gliding down a spiral path, whence the time taken for the fall might be used as a measure of efficiency in the same way that the gliding angle of modern gliders is employed for similar calculations. With reference to the term " gaining pitch," we should like to know the context in which it occurs.—El).] MODELS. t330] Will any of the models on the market, if suspended by cord, end on, lift their own weight by propeller thrust ? Hall Green. W. VALE. POINTS TO NOTE. MESSRS. G. H. SMITH AND W. H. DOREV, LTD., is the title of a new firm which has been established at 14A, Great Marlborough Street, as wholesale aeroplane and motor accessory merchants and agents. Both the principals of the firm are well known by reason of their long connection with the motor trade. The aeroplane catalogue of the firm is promised shortly^ ® ® ® ' ® PUBLICATIONS RECEIVED. Catalogues. Propellers, Aeroplane Fittings, &fc. Cochrane and Co., 26, Clarges Street, W. All-British Aeroplanes. Howard T. Wright, no, High Street, Marylebone, W. Flying Machines, Models, Propellers, <Srv. The Twining Aero plane Co., 29.B, Grosvenor Road, Hanwell, W. JANUARY 29, 1910. DIARY OF FORTHCOMING EVENTS. British Events. 1910. Feb. 4-5 Mar. 11-19 1910. Feb. 6-13.. April 2-10 April 3-10 April 10-25 May 10-16 May 14-22 May 20-30 June 5-12 June 5-15 June 18-24 June 26-July 10 Manchester Ae. Exhibition. C. Model Flight Exhibition at Olympia. Foreign Heliopolis. Biarritz. Cannes. Nice. Berlin. Lyons. Verona. Vichy. Budapest. St. Petersburg. 10 Rheims. 1910. July n-17 Flight Meeting, place not fixed. Aug. 6-13 Flight Meeting, place not fixed. Events. 1910. July 14-24 Rheims to Brussels, cross country event. July 24-Aug. 10 Belgium. Aug. 25-Sept. 4 Deauville. Sept. 8-18 Bordeaux. Sept. 24-Oct. 3 Milan. Oct. 18-25 America. Gordon-Bennett Balloon Race. Oct. 25-Nov. 2 America. Gordon - Bennett Aeroplane Race. Aeronautical Patents Published. Applied tor In 1000. Publislud January 27^/1, 1910. 123. A. CLEMENT. Dirigible aerostats. 307. J. T. PICKERSGILL. Aeroplanes. 8,849. F. W. LANCHESTEK. Steering of flying machines. 9,525. R. W. ROGERS. Aerial wing machines. BACK NUMBERS OF FLIGHT." SEVERAL back numbers are now very scarce, and have been raised in price as follows :— Price. s. d. No. 2, Jan. 3 ., * » 6, Feb. 9, containing Table of Propellers Engines ... ... 3 Engines at Paris Salon .. 3 6 " How Men Fly" 1 o Aeronautical Bibliography. Wright Bros.' Elevator Patents. 8 ,,20 ,, Flying Ground at Fambridge 1 o Illustrated Glossary. 10, Mar. 6 ,, Human Side of Flying ... 1 o Aero Club Ground at Shellbeach. Military Aeronautics. 12 ,,20 ,, Souvenir Supplement ... 1 6 15, Apr. 10 ,, Engines at Olympia 1 o 16 ,, 17 ,, Prize List 3 6 Models at Olympia. 31, July 31 .„ Bleriot Flyer 2 O (Full page drawing.) Other back numbers, post free, \\d. each (including descriptions and scale drawings of the Voisin, Curtiss, Cody and Farman biplanes, the Santos Dumont, Antoinette, and Grade monoplanes, and of a full-size Wright glider. BINDING COVERS for Vol. I, price 2s. 3d., post free. TITLE PAGE and INDEX for Vol. I, i^d., post free. Ready shortly. Readers' own copies bound, price 4s. per part (in cluding cover, title page, and index, but excluding postage). VOLUME I, bound complete with all the above scarce numbers, price 25s., post free; in two parts, 28*. 6d., complete. Ready shortly. Prices of special binding on application. FLIGHT. 44, ST. MARTIN'S LANE, LONDON, W.C. Telegraphic address: Truditur, London. Telephone : 1828 Gerrard. SUBSCRIPTION RATES. FLIGHT mill be forwarded, post fiee, to any part of the world at the following rates:— UNITED KINGDOM. ABROAD. 3 Months, Post Free . 6 >» »» 2 » * •» s. d.\ . 1 8 -35 ..6 6 3 Months, Post Free ... 6 „ „ 12 „ „ ... s. 2 5 10 Cheques and Post Office Orders should be made payable to the Proprietors of FLIGHT, 44, St. Martin's Lane, W.C., and crossed London and County Bank ; otherwise no responsibility will be accepted.
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