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Aviation History
1909
1909 - 0835.PDF
DECEMBER 25, I909. CORRESPONDENCE. *„* The name and address of the writer not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. NOTICE.—Correspondents asking questions relating to articles which they have read in FLIGHT, would much facilitateour work of reference by kindly indicating the volume and page in their letters. PROPELLER DESIGN. To the Editor of FLIGHT. SIR,—In answer to the question re designing a model propeller (by Messrs. " Gravity " and " Pressure ") I should esteem it a favour if you would insert the enclosed in your next issue. I have experi- mented with model aeroplanes for some time past, and the enclosed rough sketch is of a propeller which I have used on one of my models with success. The motive power I use is two strands of £ in. square elastic, 18 ins. in length. This I find gives 200 revolutions at an average speed of about 30 revs, per sec., and an average thrust of 75 oz. The propeller is of 6 ins. diameter and 10 ins. pitch. A To design the propeller, draw a centre line, A—B, set off half the pitch, C—D, and draw lines through these points at right angles. With a radius equal to half the diameter of the propeller, describe a semi-circle, as in the sketch, and complete the parallelogram as shown. Now divide the semi-circle into a number of equal parts, say 12, and divide the sides of the parallelogram into the same number of parts. Draw lines from side to side of the parallelogram, and project the lines downwards from the points in the semi-circle. A line drawn through the lines of intersection is the path of the tip of the blade of the propeller through half a revolution. Also, E—F is the angle which it is necessary to give the tip of the blade in order that it shall travel the pitch distance, viz., 10 ins. The blades of this propeller I made of thin aluminium, and fixed them to a piece of ash 3J ins. long and J in. square. For the spindle I use copper wire, but I think brass would be better. Yours truly, Tufnell Park. NELSON ROWLAND. AUTOMATIC STABILITY. To the Editor of FLIGHT. SIR,—I have read with interest the letter by Mr. V. E. Johnson in your Journal some time ago on this subject, and thoroughly agree with him in this respect. The question to my mind is—do we want automatic stability (so called) that is given us by a mechanism which must necessarily be more or less complicated, and liable to get out of perfect arrangement, or do we want the stability which is inherent in the design of Mr. Latham's " Antoinette," which allows him to take both hands off his steering-gear and light a cigarette ? The critics of his type might say, what would happen if a sudden gust of wind were to strike him at that moment ? Well, he would probably have to grab his wheel pretty quick, but would that be a very great hardship ? In steering a yacht one cannot afford to let go the helm for long, and what would happen to a motor cyclist if he let go his V. handle-bar and struck a big stone when travelling at 50 miles an hour ? The Wright machine certainly does not give this inhered stability, and therefore, though I admire it immensely, and Mr. Wright's handling of it, I do not think that it is a type thai will survive. Personally, I am building a monoplane, and in the near future will aim at cutting down the wing spread, getting as much " automatic stability " as possible by means of a long " floating tail (as differing from the Voisin weight-bearing tail), and giving the machine immense speed. Yours truly, Southampton. GEALE DICKSON. CONSTRUCTIVE DETAIL. To the Editor of FLIGHT. SIR,—In reply to " F. M.," December 4th, page 786, he says that he does not see how the wire D is got through the spar. It is got under the strut at E by boring a hole at an angle of 450 at K. The wire must not be bent too sharp at E, or it will not puH through easily. Nail a small strip of brass at each end of the strut, as at F. By referring to FLIGHT, NO. 13, he will see how the wire is tightened. Struts can be either straight or curved, and can be made of deal or spruce, with a block B placed between the two sides and firmly glued and nailed as C with a pin from the block B into the spar. Struts made in this way are very strong and light, and, of course, can be made any width or length. When the planes are permanently built up the wire must be soldered to the brass strip, and the joints will not work, as a previous correspondent suggested. Yours truly, WALTER YEATMAN. P.S.—I have invented a simple and effective wire tightener since I wrote you last. They could be turned put at 30". a dozen, and sell at is. a dozen. Could you tell me of a firm who would IK: likely to take it up? CONSTRUCTION OF MODEL PLANES. To the Editor of FLIGHT. SIR,—Your correspondents, "Gravity" and " Pressure," ask in the issue of FLIGHT of the 4th inst., "Which is the best way to construct t h e -PL»M of PLUNL- ^ planes" of a model ? I send you herewith draw- ings of a method by which it is possible to easily construct plant's with double sur- face, very light, and of great strength. Ordinary whitewood does very well for t lie spars. Care should be taken to the camber A, B C fepar D E Whalebeme to see that their section is shaped according required. The whalebone strips produce this when screwed on above and below if the holes in them are drilled accurately. The 837
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