Patent GB-1524262-A (GB)
Title: Areamavigation systems for aircraft
IPC: B64C13/18
Filed: 1976-05-27
Abstract: 1524262 Radio navigation SPERRY RAND CORP 27 May 1976 [29 May 1975] 22023/76 Heading H4D In an RNAV system an aircraft 14, Fig. 1, requires to approach a way point 10 along an inbound course 12<SP>1</SP> (Fig. 4) and subsequently away from the way point along an outbound course 13<SP>1</SP>. The transition between inbound course and the outbound course being via circular transition path 30, 15 tangential to the inbound course at A' and to the outbound course at B'. When the aircraft passes through the vertical bisector plane passing through the way point 10 and the turn centre of the transition path, its height is required to be HW. If the aircraft were to carry on towards the way point 10 and not pass on to the transition path at A it would be vertically over the way point at the required altitude HW if it maintained a vertical flight path angle α. A plane 18, Fig. 3, can thus be inclined at an angle α to horizontal and containing the flight path point A' vertically above A at altitude HI, the way point altitude 17 and the point 20 vertically above the turn centre. Due to the turning of the aircraft along the transition path 15, if it maintains the vertical flight path angle α its altitude when it crosses the bisector plane at point 22 will be less than HW. It is therefore an object of the invention to automatically control aircraft such that it flies a spiral path not keeping to the angle α whereby it does reach the required way point altitude HW at point 22. A Vortac beacon 11 (Fig. 2) provides bearing # and range R signals for the aircraft from which a processor 42, Fig. 5, produces the North NAV and East EAV co-ordinates of the aircraft relative to the beacon. A pilot manual data input 44 stores the co-ordinates of the beacons and way points and enables a computer 43 to produce signals representing the bearing # and range r of the way point with reference to the beacon from which a processor 45 is able to produce the North NWV and East EWV co-ordinates of the way point relative to the beacon. Algebraic summing circuits 46 and 47 receiving the two respective North coordinates and East co-ordinates produce North and East co-ordinates NAW, EAW of the aircraft relative to the way point. If #1 and #2 are the inward bound course bearings and outward bound course bearings respectively the turn made by the aircraft during the transition path is equal to #2 -#1 = #. These bearings are again produced by the computer. Also produced by the computer is the radius TR of the transition circle. A function generator 50 receiving the #1, #2 and TR signals produces a signal representing the distance d from the point A to the way point 10. A function generator 51 receives the d signal, the TR signal and the #<SP>1</SP> signal and produces two signals representing the North and East co-ordinates NTCW, ETCW of the position of the turn centre relative to the way point. These two latter coordinates are algebraically summed at 52 and 53 with the respective North and East co-ordinates NAW, EAW to produce North and East coordinates NTCA, ETCA of the position of the turn centre relative to the aircraft. These two latter coordinates are fed together with #1 to a function generator 54 which produces a signal representing the angle of turn # of the aircraft. A function generator 55 receives the #, #1 and #2 signals and produces a signal y representing the ratio between # and # that is the fraction of aircraft turn to the point 22. The altitude HI of the point A' over the point A for the aircraft to reach the way point altitude 17 with the altitude HW is calculated by a function generator 56 using the α, HW and # signals. The distance D gone by the aircraft from point A to 22 is calculated by function generator 59. The altitude of the aircraft HD at a point along the transition path is calculated by subtracting the altitude H1 from the way point altitude HW multiplied by the ratio γ and adding this product to the altitude HI. The altitude HD is continuously compared with the actual aircraft altitude HA from an altimeter 61 and any difference HE serves as an error signal for use with various indication instruments and for the automatic flight control system. The function generators, etc., shown in the arrangement of Fig. 5 may all be incorporated in a specially programmed digital computer (Fig. 6, not shown).