Patent GB-1185301-A (GB)
Title: Obstacle Indicating or Detecting Apparatus for Aircraft
IPC: G01S13/935
Filed: 1958-10-27
Abstract: 1,185,301. Pulse radar. SPERRY RAND CORP. 27 Oct., 1958, No. 34392/58. Heading H4D. An automatic control system for an aircraft enabling it to fly at a low altitude and causing it to climb to avoid obstacles in its flight path comprises radar equipment providing signals dependent upon the range and elevation of an obstacle lying forward of the aircraft, a computer receiving the said signals and further signals dependent upon the flight condition of the aircraft, the computer providing, in dependence upon the input signals, an output corresponding to the maximum load factor to which the aircraft would be subjected in following a certain path avoiding the obstacle, and means adapted to produce a characteristic signal when the computer output is equal to a predetermined value, the characteristic signal actuating means controlling the displacement of the aircraft elevators whereby the aircraft follows the avoidance path. In the embodiment described the aircraft executes avoidance manoeuvres having a constant load factor and follows a circular path which passes tangentially with clearance the obstacle, a typical flight path P avoiding obstacles A, B, C being shown in Fig. 2. The radar beam 1 is shown scanning in a vertical plane including and lying above the time of flight of the aircraft and when the aircraft arrives at position 2 the value of the continuously computed positive load factor from the computer is such that a pull-up manoeuvre is initiated, the radar beam being immediately switched so that it scans a sector including and lying below the line of flight. The computer now computes negative load factors and when the aircraft arrives at position 3 the load factor attains such a negative value that the pull-up maneouvre is terminated and a push-over manoeuvre is initiated to clear the summit of A. The radar is immediately switched to again scan the sector above the aircraft line of flight whereby at position 4 a further pull-up manoeuvre is initiated to avoid obstacle B, the radar being switched again to scan below the flight path so that a push-over manoeuvre is initiated at 5. When obstacle B has been cleared no further obstacles are detected by the upwardly scanning radar beam and the aircraft commences a horizontal flight path 6, a signal being simultaneously presented to the pilot whereby he may order a push-over manoeuvre so as to fly nearer the ground. If he makes such a decision a pull-up manoeuvre will be automatically initiated at 7 to avoid obstacle C. In a block diagram of the invention, Fig. 3, the base 8 of the radar antenna 29 is stabilized against aircraft roll by a gimbal 9 driven by motor 10 in response to an error signal derived from difference circuit 11, the circuit 11 having one input from a roll gyro 12 and another from a pick-off 13. The other axis of the base 8 is stabilized along the aircraft velocity vector in response to a signal derived from a difference circuit 17 which is fed to a motor 20, the circuit 17 having one input from an angle of attack sensor 15 and another from a pick-off 18 which measures the angle between the base and the longitudinal axis of the aircraft. The antenna 29 is given an oscillatory scanning motion about the axes of a shaft 24 by a motor 28 and the position of the central portion of the scan is determined by the position of the shaft which is rotatable by a reversible motor 26 through gearing 27. The antenna is coupled by a line 34 to a ranging unit 33 (described in detail with reference to Fig. 4, not shown) which produces signals R having amplitudes proportional to the obstacle ranges, the signals being fed to a computer 32 (described in detail with reference to Fig. 6, not shown). Further signals # representing the angle between antenna and the aircraft velocity vector are monitored by a pick-off 30 and supplied to the computer via line 31. A third input V to the computer is derived from airspeed sensor 43, a fourth input Y being derived from a difference circuit 44 producing a signal proportional to the flight path angle (i.e. the angle between the horizontal and the velocity vector). The circuit 44 receives one input from a vertical gyro 45 and another from the angle of attack sensor 15 (the angle of attack being the angle between the velocity vector and the aircraft longitudinal axis). The computer 32 continuously computes values of load factor n where n is given by the equation where V = aircraft velocity, γ = flight path angle, # = elevation angle of obstacle relative to aircraft velocity vector, R = range of obstacle and g = gravitational constant. The signals n are applied to a sequence control 61 (described in detail with reference to Fig. 8, not shown), the control 61 also receiving signals from a load factor selector 62, a rate-of-climb sensor 63, and a pilot control stick 64. The characteristic signal for causing operation of the elevator 86 is produced when the value of n equals a predetermined load factor reference signal produced by the selector 62. The selector 62, Fig. 7, has a manual setting knob 69 controlling a potentiometer 67 to produce on the line 74 a signal corresponding to a desired positive load factor for a pull-up manoeuvre, and a setting knob 70 for similarly producing on the line 75 a signal corresponding to a desired negative load factor for a push-over manoeuvre. The signal from 74 or 75 is also applied to a line 82 depending upon whether contacts 76 or 77 are closed by relays 78, 79. The relays 78, 79 are energized by the sequence control 61 through lines 80, 81 such that the contacts 76 may be closed when the computer 32 is computing positive load factors and the contacts 77 may be closed when negative load factors are being computed. Hold on circuits in the sequence control 61 ensure that the contacts 76 remain closed when the computer subsequently computes negative load factors until the determined negative load factor is reached whereupon the contacts 76 open and contacts 77 close. The signal on line 82 is supplied to a difference circuit 83 which also receives a signal from an accelerometer 84 measuring the acceleration of the aircraft in a direction parallel to the yaw axis whereby an automatic flight control system 85 is caused to move the elevator 86 so that the aircraft executes a constant load factor manoeuvre, the value of this load factor being determined by the setting of knob 69 or 70. A signal appearing on line 80 or 81 also causes rotation of the motor 26 to cause the scanning of antenna 29 to change from above the flight path to below the path or vice versa. The push-over manoeuvre is terminated when the signal from the rate of climb sensor 63 becomes zero and the aircraft assumes level flight. During level flight positive elevation signals # are passed by diode 107 to gate 108 and in the absence of any range signals R the gate produces an output to energize indicator 109 and warn the pilot he may initiate a descending manoeuvre. To descend, the pilot moves control stick 64 having a mechanical link 87 with elevator actuator 85, this action overriding any signal from the circuit 83. The control stick 64 is also connected by linkage 88 to the sequence control 61 whereby the pull-up mode of operation, which is automatically initiated when the aircraft has descended to a given height from the ground, is terminated when the signal from the rate of climb sensor 63 commences to increase in the positive direction, and thus the aircraft assumes a horizontal line of flight nearer the ground.