Patent GB-1524261-A (GB)
Title: Area navigation systems for aircraft
IPC: G05D1/02
Filed: 1976-05-27
Abstract: 1524261 Aircraft navigation system SPERRY RAND CORP 27 May 1976 [29 May 1975] 22022/76 Heading H4D This is an RNAV system for aircraft utilizing signals from, e.g. a Vortac beacon 11, Fig. 1, and including on the aircraft, apparatus for guiding it from an inbound course 12 to an outbound course 13 along a circular path 15 tangential to both courses, the apparatus thus comprising a function generator for determining the maximum possible banking angle #m, Fig. 3 as a function of the total turn required ## and the aircraft velocity V, function generators for determining parameters of the circular path including its turn radius TR and deviation means fed with the actual tracking angle and position of the aircraft for producing control signals for constraining the aircraft to fly the circular path. To avoid a sudden banking movement when leaving the inbound course or reentering the outbound course the banking angle is gradually assumed or removed at points A', B' at predetermined distances d' before the transition points. As the aircraft flies along the inbound course 12 the following data is fed from a pilot manual data input 26 into a computer 25 and made available thereby: the bearing # and range r of the way point 10 with respect to the beacon 11, the inbound course angle #1, the outbound course angle #2 and whether the turn is to be clockwise or counter-clockwise. A function generator 32' determines the total turn ## required by the aircraft from the difference between the two course angles. Also available from a function generator 24 is the ground speed V which when fed to a function generator 32 together with the turn angle ## produces the maximum banking angle #m according to the family of curves shown in Fig. 4. #m is then combined with the velocity V in function generator 33 to compute the turn radius TR of the circular path 15 tangential to the inbound and outbound courses. TR is then combined with the turn angle ## in function generator 34 to give the distance d from the way point to the transition point A which distance d is added to a predetermined distance d<SP>1</SP>, to give a total distance which is continuously compared with the distance of the aircraft from the way point. To determine the distance to the way point a function generator 22 produces the North and East co-ordinates NAV, EAV of the aircraft with respect to the beacon and combines these with the corresponding North and East components of the position of the way point with respect to the beacon from a function generator 27 fed with # and r. This gives the North and East components of the position of the aircraft with respect to the way point NAW and EAW whereby the distance between the aircraft and the way point is the square root of the sum of the squares. When d+d<SP>1</SP>=said distance, the aircraft starts to bank whereby at the transition point A it has achieved the full backing angle #m. A function generator 35 fed with the turn radius TR the distance d and the course angle #1 determines the North and East co-ordinates of the distance between the turn centre and the way point NTCW and ETCW. These are combined with the coordinates NAW and EAW at 36 and 37 to produce the North and East co-ordinates of the distance between the turning centre and the aircraft NTCA and ETCA which co-ordinates produce from function generator 40 the angle of turn of the aircraft #1 along the path 15. A function generator 41 fed with the sense of turn signal, a 90 degree signal and the track angle of the aircraft from a function generator 23 produces a track angle error signal TKE. A function general 44 fed with said distance co-ordinates and with the turn radius provide a cross-track error signal XTK. The error signals TKE and XTK are fed to a horizontal situation indicator for the pilot and also to two multipliers 43 and 46. The K 1 XTK of multiplier 46 is combined with the banking angle signal #m at 47, the output of which is combined at 50 with the output K 2 TKE of multiplier 43 to produce a control signal #C for feeding to the automatic control system as a roll control signal. If the aircraft is correctly on the path 15 the roll signal which is used to correct the banking of the aircraft will be 0. The control signal #C is also fed to a flight corrector and to an attitude director indicator for the pilot. The various functions produced by the function generators of Fig. 3 may be incorporated in a specifically programmed digital computer (Fig. 5, not shown).