GB327777A - Pendular sighting device for aerial navigation - Google Patents

Abstract

327,777. France, State of, Minister of Air, (Assignee of Marie, F.). Oct. 19, 1928, [Convention date]. Plane-trigonometry calculators.-A sighting- device for use on aircraft for determining the angle of drift and the velocity and direction of the wind comprises a horizontal graduated circle a having its zero on the longitudinal axis of the craft and an arc of a vertical circle b which can slide round the circle a, the circles a, b, being universally suspended by members m from a support s secured to the aircraft. The arc b carries slidable sights c<1>, c<2>, and a vertical rod v<1> passing through the centre of the circle a and journaled at its lower end in the arc b has at its upper end a sight v. In using the device the arc b is turned until it is parallel to the apparent direction of movement of objects on the ground, and the drift angle is then read off on the circle a. If the altitude is known the ground speed can be determined by noting the time at which an object on the ground is in line with the rod v<1> and the time at which it reaches the sighting line vc<1> or vc<2>. Then if the air speed is known the wind speed and direction are obtained 'by constructing a vector triangle of which two sides represent air speed and ground speed and the angle between them is the angle of drift: the third side then represents wind speed. A calculating-device which may be used to find the wind speed &c. comprises a chart, Fig. 5, and a superposed transparent circle, Fig. 6. The chart has a number of arcs e<1> - - e<5> struck from a point Q and representing air and ground speeds and a number of lines n<1> - - n<5> radiating from the point Q and representing drift angles. The circle is marked with radiating lines l<1>, l<2> &c., and with circles f<1>, f<2> representing different values of wind velocity. If for example with an air speed of 33 metres per second and the rudder central the ground speed is 23 metres per second and the drift angle 10‹ the point R of intersection of the 23 metre and 10‹ lines is noted on the chart and the transparent circle is placed over the chart with its zero graduation in line with the point Q. The point on the circle which lies above the point R is then joined to the centre P of the circle and the line so obtained is the wind vector.