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Aviation History
1914
1914 - 0907.PDF
AUGUST 28, 1914. USUI DIRECTION OF FLIGHT IN A WIND. PROBLEMS relating to the course of flight in a wind are best solved graphically. For example, a machine capable of 70 m.p.h. flies in a wind of 30 m.p.h. A line representing the wind in direction and velocity is drawn from one end of another line representing, to the at right-angles to the direction in which it is facing is similarly found to be 27 m.p.h. If the machine turns into the wind as shown in the right-hand diagram, its course speed is reduced to 50 m.p.h. The lower diagrams show the effect of wind on the apparent _ •• —__———, AEROPLANE TO MP.H. —1—1—1—1—1—1_—1 , i_ /GO SCALE OF VELOCITY —1— 1 COURSE 50 M.PH. 10 20 30 AO 50MPH HORIZONTAL tO"""^-"*.^. ^ r***"--^**^ M,pH 1 U- r- IN CALM IN VJIND. WIND 30 M.PH. " Vligbt" Copyngm Diagrams Illustrating graphic solutions to problems relating to the effect of winds cm the flight of aeroplanes. same scale, the calm air flight speed and direction of the aeroplane. A third line completing the triangle gives the resultant course and speed of the aeroplane relatively to the ground, and when measured is found in thisinstance to be 62 m.p.h. The lateral drift of the machine ® ® LIFT COEFFICIENT AND WING LOADING. IT is becoming the general practice to express the results of model wing tests in absolute coefficients, so that they may be directly com parable in all countries without reference to the system of units employed. The result of the N. P. L. test on the wing section Eiffel No. 13 tit is shown in the diagram, and the lift coefficients are absolute. A lift coefficient of 0*3 implies that the wing will lift:— v2 lbs./sq. ft. gravity, and v = flight speed in gliding angle of the machine as visible to the eye. In calm, the machine glides as shown on the left ; in a head wind of 30 m.p.h. it descends more steeply,'as shown on the right, but its true gliding angle through the air is unchanged. ® ® Diagram illustrating the method of plotting the lift of a wing in terms of absolute coefficients and angle of incidence in degrees. 0.3 t g where p = density of air, ft. /sec. For approximations, the following table, given in the Technical Report, is useful for converting absolute coefficients into lift in pounds per square foot. Speed, m.p.h. 40 So 60 Conversion factor. 8-15 127 18-3 Speed, m.p.h. 7° 80 Conversion factor. 25-0 32-6 Speed. m.p.h. 90 100 Conversion factor. 41 '5 51-0 t z y u For example, a lift coefficient 0-3 indicates that the wing will lift °"3 x i8'3 = 5'S lbs. per sq. ft. at 60 m.p.h. In Eiffel's work, the lift, and also the resistance of the wing are given simultaneously by what is called a "polar curve." The coefficients employed may be converted into absolute coefficients by multiplying by 8. ® ® The Price of "Shell." THE distributors of " Shell" motor spirit announce that by arrangement with the Society of Motor Manu facturers and Traders no more than the following prices will be charged by their members to the public in England and Wales :— RESISTANCE OE 01 > 4 8 is it so "Flight" Copyright. On the right, Eiffel's polar curve method of showing the lift and re sistance of a wing by a single graph. The scale of Eiffel's curves may be converted into absolute coefficients by multiplying by 8. ® ® Shell, is. gd. per gallon ; Shell II, is. "\d. per gallon ; Crown, 1*. 6d. per gallon. Users should advise the Company immediately if the prices charged are in excess of the above. It is imperative that cans should be returned immediately they are empty. 907
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