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Aviation History
1915
1915 - 0503.PDF
JULY 9, 1915. l^JGHTJ Two Tractor Monoplanes. By H. TOMLINSON. *' I ENCLOSE herewith drawings of two ' tractor' monoplanes which I hope will be of use to you :— " Power, 12 strand, ?\ strip ; do. Screw, ' Star ' 9 in. carved ; do. Weigh, 6 ozs. ; sj ozs. Distance off ground, 200 yards ; 150 L, a pointer ; SS\ a spiral spring; R O T N, a system of parallel levers working on pivots, R, O, T, N ; B, a vertical axis on which the whole rotates ; and C D, the plate or disc of known area ; the apparatus is supposed to be graduated so as to read pressure in pounds; it could of course 1* so arranged to read (say) up to 30 lbs. in oz. Jike a Salter's spring balance. In a spiial spring the extension is proportional to the pulling force provided the extension be not too large. Such an apparatus is therefore of a very simple constructional character ami easy to use ; unfortunately, however, anemometers of this kind have not a very wide range—and as recorders of wind velocities are practically useless in a wind of less than 8 to 10 miles an hour. As the indications of the rotary, vane, windmill or screw type the indications of the pressure plate depend more or less upon the character of the vane used to keep it normal to the wind, which, " for the best result, should be light, of moderate length, and with the plates composing it rather widely separated in order to avoid as much as possible eddies caused by the pressure plate itself." [S. P. FERGUSON.] t8 G*u £<? wheels To vnn *nJo Mr. H. Tomlinson's tractor mono, model No. 61. yards. Number of turns, 500 ; 500. Speed, approximate, 10 m.p.h. ; 12 m.p.h. Average height, 40 feet; 30 feet. Gliding angle, I in 6 ; 1 in 8. Duration, 38 sees. ; 30 sees." Pressure-Type Anemometers. Reply to Query. Pressure Anemometer (after Maxim). (Formula : P = -003 A.V2). The diagram shows a form of (spring) Pressure Anemometer invented by Sir Hiram Maxim. A, is a weather vane and recorder ; The Design of Mcdel Propellers. Mr. F. J. Cann, the secretary of the Windsor Aero Club, writes the following interesting notes on propellers :— "I do not think any of our members conform to the usual practice of making the pitch one and a half times the diameter (for single-screw models). Indeed, most of us use propellers of almost as coarse a pitch as one used on canard twin-screws, and yet neither of our single-screw models suffer from torque. A suitable disposition of the rudder has much to do with this question. Many beginners undoubtedly fit too small propellers both as regards diameter and pitch, and consequently have trouble with adjustment to the centre of pressure ; I myself have seen some models dive vertically after the thrust has ceased, resulting from propellers which ' scream.' " In the design of a propeller it is undoubtedly convenient to view it as an aerofoil secured about a central axis, the ' lift' of it corre sponding to the thrust, and using the air as a nut or fulcrum with which to screw itself forward. '' Carved propellers are used entirely by members. The bent- wood may gain a point where weight is concerned, but with regard to efficiency our results show them to be inferior to carved ones j apart from which it is impossible to design a bentwocd to the same extent as one cut from the solid. "The writer's formula for calculating the pitch of a propeller may be found useful. It is P=ird\ax\ A, where P s pitch, ir = 3f, d = diameter, A — tip angle, tan A — a constant. Thus, assuming a propeller to be of 10 in. diameter, and 30" tip angle, we have P = 3 x 10 x tan 30 P- 3-l4l6 x 10 x -5774 = 18-14 approx. The Farnham Aviation Club. Mr. G. P. Gifford, the secretary of the above, writes from " Conewood," Farnham Common, Bucks, that residents and visitors in this district, which embraces Slough, Windsor, Gerard's Cross, and Beaconsfield, may be interested to know that the club has been formed for the study of aeronautics. It is proposed to confine work to building models with a view to the subsequent building of full- sized machines, and the possibility of such improvements in design as are particularly desirable in the present state of war. Those interested can obtain further particulars as to the conditions of membership from the secretary as above. S03
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