Patent GB-1002552-A (GB)
Title: Aircraft navigation aid apparatus
Inventor: GOLD THEODORE
IPC: G01C23/00
Filed: 1961-09-29
Abstract: 1,002,552. Aircraft instruments. SPERRY RAND CORPORATION. Sept. 29, 1961, No. 35232/61. Heading B7W. Aircraft navigation aid apparatus for use in the. manual control of the aircraft to intersect and follow a prescribed glide-path leading to a target point, comprises means for producing, a control signal that is at least approximately, a measure of the algebraic sum of the rate of approach of the craft to the glide path and the angle that a reference line in the craft makes with the glide path, means for defining a line of sight for an operator, and means for controlling said line of sight defining means so as to move the line of sight in proportion to said control signal, whereby when the aircraft is manually controlled so as to maintain the line of sight directed at the target point, the aircraft will approach the prescribed glide path approximately asymptotically. In Fig. 1 the aircraft reference line represents the longitudinal axis of the aircraft and the horizon line is a line, at the altitude of the aircraft, parallel to earth, the angle # between them being the pitch angle of the aircraft. The reference glide path is the desired flight path at an angle γ<SP>o</SP> to the earth and the actual instantaneous flight path makes an angle γ with the earth, the sum of γ and # corresponding to the aircraft angle of attack α. The line of sight between the eye of the pilot and the target makes a target angle # with the horizon line and a deviation angle # with the reference glide path. The sight line is controlled to make with the aircraft reference line an angle # so that if the pilot flies the aircraft to direct the sight line to the target the aircraft will be caused to approach the reference glide path asymptotically. The deviation angle # is a measure of the displacement of the aircraft from the reference glide path and for the approach to be asymptotic the rate of change of the displacement of the aircraft from the path should be proportional to the deviation angle # . In the apparatus a vertical gyro 10 gives a signal representing the pitch attitude # of the aircraft with respect to the horizon. A signal representing the reference glide path Y o  is provided by a glide path selector 12, which may be a potentiometer manually adjustable by a knob 14, and a signal representing the difference between the instantaneous direction of the actual flight path and the direction of the desired flight path i.e. rate of approach to the reference glide path is provided by an approach rate signal generator 16. The three signals are applied to a summing device 18 to provide a control signal which is applied to a servo system 20 to adjust the angle of a mirror 28 about an axis 30. A light source 22 projects, through a mask 24 and a collimating lens 26, an image representing an aircraft on to the mirror 28 which reflects it on to a combining glass 32 mounted on or forming the pilot's windscreen, which is so tilted that the image appears to the pilot at infinity and superimposed on the runway during a landing, thereby providing the line of sight in Fig. 1. When the aircraft is flown so that the image is maintained aligned with the end of the runway an asymptotic approach will be made. In a further embodiment (Fig. 7, not shown) two such systems may be provided, one being responsive only to the signals from the gyro and the glide path selector, whereby the pilot may additionally be given an indication of the actual displacement from the reference glide path by the relationship of two images. In either embodiment the mirror 28 may be adjustable about a yaw axis so that errors caused by cross-winds can be compensated for by manual adjustment. Apparatus is described (Fig. 6, not shown) for compensating in selector 12 for head or tail wind effects. The apparatus is stated to be suitable for assisting a pilot to guide an aircraft on a predetermined flight path relative to the horizon. Specifications 690,985 and 815,137 are referred to.