Patent GB-1277774-A (GB)
Title: Follow-the-leader stationkeeper system
IPC: B64D45/00
Filed: 1969-08-14
Abstract: 1277774 Radio navigation SIERRA RESEARCH CORP 14 Aug 1969 [15 Aug 1968] 40730/69 Heading H4D In a follow-the-leader aircraft station-keeping system for producing on each of a plurality of follower aircraft a meter display of (1) the components x = R cos # and y = R sin # of the distance R from a selected other nth aircraft (e.g. the leader aircraft) resolved along and perpendicular to the flight direction of the own aircraft, (2) the altitude difference #A between the altitudes Ao and An of the own and other aircraft, and (3) an intended future manoeuvre of the other aircraft, the distance R is determined by one-way ranging, the relative bearing # of the other aircraft is determined by a rotating directional receiving aerial and altitude and manoeuvre signals An and K are transmitted from the other aircraft. As described each aircraft carries a clock 1 and associated slot counter 2 for establishing a repeating cycle of time slots synchronized to a common standard time by a known form of synchronizer 3 (e.g. as in Specification 1,101,340) and the slot counter 2 produces output reference pulses 31, 33, 36, Fig. 3C, on respective lines 2a, 2b, 2c at predetermined times during each slot. An output pulse 31 is also produced on counter output line 2d during an allotted own slot in which the aircraft transmits from an omnidireetional aerial 9-(1) a coded range pulse signal 32, Fig. 3B, initiated in a coder 6 by the pulse 31, (2) a coded altitude pulse signal 34 digitally delayed relative to the reference pulse 33 in accordance with the aircrafts own altitude Ao stored in a register 18, and (3) a coded pulse signal 37 digitally delayed relative to the reference pulse 36 in accordance with a signal K indicating a selected one of a plurality of possible future manoeuvres, e.g. up-down, left-right, as given by a pusn-button controlled coder 12. Alternatively (i) the three signals 32, 34, 37 may be transmitted in corresponding time slots during three successive cycles and (ii) pulse width modulation may be employed. In order to display data x, y, #A relative to another aircraft which transmits in the nth time slot, i.e. the nth aircraft, a slot selector 4 is adjusted to produce an nth time slot gate signal which enables a gate 4b to apply (1) the range reference pulse 31 to a time-to-voltage converter 24 and (2) the altitude and manoeuvre reference pulses 33 and 36 to a range compensation unit 2e; the reference pulses 31, 33, 36 produced during the nth time slot are denoted 31<SP>1</SP>, 33<SP>1</SP>, 36<SP>1</SP> in Fig. 3D. The signals 32, 34, 37 transmitted by the other aircraft are received by a rotating directional aerial 21 and decoded at 23 to give corresponding decoded signals 32<SP>1</SP>, 34<SP>1</SP>, 37<SP>1</SP>, Fig. 3D, on decoder output lines 23a, 23b, 23c, respectively, the decoded range pulse 32<SP>1</SP> being applied to the converter 24 to give during the nth time slot an analogue range voltage R of amplitude proportional to the time interval 41 between the pulses 31<SP>1</SP> and 321 which is applied to-(1) a resolver 26 ganged to the rotating aerial 21 to give voltages x = R cos # and y=R sin 0, and (2) the range compensation circuit 2e to delay the pulses 33<SP>1</SP> and 36<SP>1</SP> applied thereto by the time interval 41 to give corresponding delayed output pulses 33<SP>11</SP> and 36<SP>11</SP>, Fig. 3D. The pulse 3311 turns on a bi-stable 20a thereby enabling a gate 20 to apply clock pulses to an input/output counter 14 and the bi-stable 20a is turned off by the subsequent decoded altitude pulse 34<SP>1</SP>; the resultant binary count in counter 14 represents the altitude An of the nth aircraft and is applied through gates 14c and 27a to a storage register 27 whose output is applied together with the binary own altitude Ao from register 18 to a subtractor 19 to give a binary output #A which is converted to a corresponding analogue voltage in a D/A converter 28. The analogue voltages x, y and #A are applied to corresponding zerocentre meters 47, 48, 46 in a display unit Fig. 2 (not shown); when displaying data relative to the leader aircraft the meters 46, 47, 48 are biased to display deviations from predetermined values of x, y and #A. During the aircrafts own time slot, the altitude reference pulse 33, Fig. 3C, enables a gate 13 to set the complement of the binary own altitude Ao into the input/output counter 14 and also turn on the bi-stable 20a to enable the counter input clock pulse gate 20 so that the counter 14 produces an overflow pulse which is delayed relative to the reference pulse 33 in accordance with the own altitude Ao, said overflow pulse being applied to (i) reset the counter 14 and (ii) a telemetry encoder 15 to give the coded altitude signal 34. The coded manoeuvre signal is produced in a corresponding manner by the reference pulse 36 and the binary manoeuvre signal K from the coder 12.