Patent GB-912214-A (GB)
Title: Improvements in indicating apparatus for use with piloted craft
Inventor: SNOWDEN CHARLES
IPC: G01S1/02
Filed: 1960-03-22
Abstract: 912,214. Cathode-ray tube circuits; radio navigation. SHORT BROS. & HARLAND Ltd. March 7, 1961 [March 22, 1960], No. 10174/60. Class 40 (7). [Also in Group XXXIII] Indicating apparatus on a piloted craft comprises a cathode-ray tube (C.R.T.) and means for producing a display on the C.R.T. screen in the form of closed curves which appear to an observer to define a tunnel along the desired craft path and which move in response to changes in the position and attitude of the craft. The invention is particularly described as an indicator for the pilot of a " vertical take-off and landing " aircraft, the flight path of which is a straight line glide to a predetermined position from which vertical descent to the landing area is made. Gyro-compass 11 generates a D.C. yaw signal, artificial horizon 12 generates a D.C. pitch signal, radio apparatus 13 generates a D.C. range signal (the magnitude of which varies with the range R from the landing area) and I.L.S. indicator 14 is adapted to generate two signals, one of which is a D.C. of magnitude varying with lateral displacement LD from a predetermined glide path and the other being a D.C. of magnitude varying with h, the height relative to the glide path. The rings on the C.R.T. screen are produced by quadrature-phase voltages from phase splitter 17. Divider 18 produces eight output oscillations of magnitudes which decrease from one oscillation to the next in a predetermined manner; these are applied to a circuit 19 which is controlled by a gate generator 20 to apply the eight waves in succession, and cyclically, to terminal 21. Similar treatment is imposed on the quadrature output from the phase splitter. Concentric circles with the common centre at the centre of the C.R.T. screen thereby ensue ; and the amplitude diminution law in dividers 18, 23 is such that the circles define a conical funnel along the glide path, the apex of the funnel coinciding with the end of the glide path above the landing area. The yaw signal controls the D.C. level of the output of circuit 19 and causes the circles to shift bodily to left or right in dependence on the magnitude and sign of yaw angle; in like manner the pitch signal causes the circles to shift bodily upwards or downwards. The range signal produces at divider 26 an output D.C. of magnitude varying with the reciprocal of range, and this output increases the gain of the X and Y amplifiers as range increases and vice versa. Divider 26 produces at terminals 28, 29 a D.C. signal of magnitude varying as LD/R and a D.C. signal of magnitude varying as h/R respectively; divider 30 is arranged to produce eight output D.C. signals whose magnitudes decrease inter se in accordance with a predetermined law and these signals are combined with the eight output oscillations from divider 18 such that the largest oscillation is combined with the largest D.C. &c. The circles then tend to take up positions in which they have a common vertical tangent near the centre of the C.R.T. screen. Similarly, the circles are displaced vertically by differing amounts so as to tend to bring them to a position where they have a common horizontal tangent. The aircraft roll is indicated by a rotatable marker carried on the front of the C.R.T. screen or the circles may be replaced by ellipses. Each time sharing unit comprises an adding circuit and a stepping switch, the stepping switches being controlled by a motor energized from a gate generator, Fig. 2 (not shown), or known electronic switching utilizing diodes or transistors may be employed. Divider 26 incorporates a servo amplifier and a servomotor driving four potentiometers, Fig. 3 (not shown). To indicate to the pilot that the aircraft is departing from a predetermined velocity/R ratio a pulsed note, of high frequency for excessive speed and low frequency for insufficient speed, is emitted, the pulse rate increasing as the speed discrepancy increases; when the aircraft speed is within a predetermined tolerance range both notes are emitted simultaneously. In a modification a " lock-follow " radar is mounted in the nose of the aircraft and locks to a responder at the landing area; deviations from a desired glide path are obtained by comparing the angle of the airborne radar beam with required glide angle, and range is measured directly.