GB127877A - Improvements in Optical Sighting Devices for Air-craft and the like. - Google Patents

Abstract

127,877. Taylor, A., and Gray, P. W. June 11, 1917. S p e c d indicators operating by sighting terrestrial objects.-The speed of aircraft is calculated from observation, through a. telescope on the machine, of the time taken by objects on the earth to pass between adjustable cross-wires in the field of view; the angle of drift is also measured. The cross-wires are separated to a distance corresponding to the height of the machine as read on the altimeter. The distinctive feature of the apparatus comprises the use of a telescope system of which the eyepiece 12, 14 is capable of axial and rotary adjustments only, while the object-glass 45 hangs freely on gimbals 42, 44 mounted in the focal plane of its lenses. The object-glass may be restrained in movement by a gyroscope. The apparatus consists of a main frame 3 secured to a standard 1 and having rubber cushions 5, 7 interposed between it and the standard on its upper and lower sides respectively. A rotary head 20, which supports the eyepiece, has peripheral camsurfaces on its lower outer edge which separate spring pins 25, 26 to displace cross-wires 31, 32 equally from the centre of the field of view. The eyepiece is focused by rotating the milled head 15 and thus moving the lenses axially through the agency of the pin and slot 17. An eye-guard 11 is carried by an overhanging arm 10. The machine is provided with various scales which are used as follows. The angle scale 37 is rotated by the knob 38 until the desired angle of bearing comes cpposite the fixed index 40. The annulus 33, connected to the cross-wire frames, is then rotated until the cross-wires are at right-angles to the line of flight as viewed through the telescope. Incidentally, the reading on the scale 37 opposite the pointer 36 gives the angle of drift of the machine. To determine the speed of the machine, the operation is continued by reading the altimeter and bringing the corresponding height-division on the scale 21 iinto line with the index 35. This operation is performed by rotating the milled head 20, which operates both the scale and the cross-wires. The time taken by an object on the earth to pass between the cross-wires is read by means of a stop-watch mounted in the holder 39.