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Aviation History
1910
1910 - 0369.PDF
CENTRE OF PRESSURE ON ARCHED SURFACES.* By MATTHEW THESE experiments to determine the centre of pressure on some arched surfaces when exposed at various angles \ TEST PICNE- Sketch illustrating the apparatus used by Mr. Sellers in his experiments, parabola and also has a camber of one-twelfth B. SELLERS. adjustable springs, and these springs are set in the first instance to correspond with the zero position of the quadrant. Any movement of the aerofoil upon its pivots takes place against the action of these springs, and is ultimately limited by a suitable stop. A pointer fixed to the framework indicates when the aerofoil departs from its neutral position of equilibrium. In making a test the aerofoil is pivoted on any desired pin, and the quadrant is set to any desired angle. The springs are adjusted so as to bring the aerofoil into its neutral position as indicated by the pointer. The air current is then turned on, and the quadrant is adjusted until the pointer shows no deviation of the aerofoil from its neutral position. The reading on the quadrant corresponding to the neutral position of the pointer indicates the angle of inclination at which the aerofoil under test has a centre of pressure corresponding to the position of the pin upon which it is pivoted. The aerofoils shown in Fig. 2 are 6 in. by 12 ins. Two have the curvature of a circular arc and a versine of \ in. and £ in. respectively. That aerofoil which is marked (1/3) is curved for the front third and flat for the rest of its width. The camber is cne-twelfth of the chord. The aerofoil marked P is the half vertex of a •to a current of air, were made in November, 1906, but have not heretofore been made public. At first a device similar to that employed by Prof. Lang- ley was tried, but it was im possible to get correct reading owing to oscillation of the surfaces tested, and the proximity of even a slender rod used in an attempt to steady them vitiated the re sults. I therefore made the device shown in the sketch, which may be briefly de - scribed as follows :— Attached to the surface to be tested, which I' shall call an aerofoil, is a rib extend ing centrally fore and aft. On this rib pins are suitably located for pivoting the aero foil. A support carries bear ings, which may be sprung over the desired pin, and this support can be tipped in a vertical plane to any desired degree. A graduated quadrant indicates the amount of the inclination thus obtained. The aerofoil is held in a position of equilibrium by * Paper read before the American Association for the Advance ment of Science. C l»« 1 2 .00 3 1 • . ia° q" 6^ 5*" • • »" 4 "' * ." — ^^^^^^^^^_ C l;a* 1" 0 2- 1 ' 0 e a 0 IS IO 6 17 a© is 0 5 3" 1 o 4 1 0 2 V 1 0 0 0 —" —J ffi^ l" 1 n*r 2" 3" 1 ' 1 0 4" 0 0 0 I in 12 P.I'O. I" ' 2" 3" 1 • I OOOOO «*' * fi si 2r— ** 32 M> O 4 1 0 0 Sketches illustrating the planes with which Mr. Sellers experimented. The black lines represent the sections of the planes. Each plane is shown with the longitudinal rib upon which it was pivoted. the chord. In this figure the pins used are shown by dots, and below each pin is shown the degree of inclina tion required to bring the centre of pressure to that point. The distance in inches from the front of the aerofoil is laid off on a scale. C 2 367
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