GB2258112A - Rendezvous apparatus - Google Patents

Abstract

Apparatus for enabling a rendezvous between two aircrafts to refuel one comprises an optical transceiver on each aircraft of which the transmitter is initially scanned in azimuth and the receiver detects and identifies the direction of the transmitter on the other aircraft, each transceiver also acting as a transponder. Once contact has been established the aircraft are both flown along the line joining them (in the same direction) and the transmitter on each aircraft is pointed along the line. Use of a transponder allows the range between the aircraft to be found, and their relative speed to be controlled thereby. <IMAGE>

Description

Rendezvous Apparatus This invention concerns apparatus for effecting a rendezvous between, for example, two aircraft particularly for the in-flight refuelling of one aircraft by the other.

It will be appreciated that, for in-flight refuelling of an aircraft by a tanker aircraft, the aircraft must rendezvous. In the case of military aircraft, where there may be a requirement for radio and/or radar silence, the rendezvous is generally pre-arranged. Using a satellite navigation system such as "NAVSTAR" or even by dead-reckoning, the two aircraft usually both succeed in reaching the rendezvous location. The first aircraft to arrive usually circles the actual or calculated rendezvous location, the diameter of the circle being up to five miles.

In conditions of good visibility this may suffice but in poor visibility or at night, the rendezvous will not be made if covert conditions of radio and radar silence are maintained. It is normally essential that the rendezvous is made and, accordingly, radio and/or radar silence then has to be broken. Refuelling in flight is a hazardous manoeuvre on its own without it being brought to the attention of an enemy.

Similarly, a rendezvous may be effected between ships at sea, an aircraft and a ship or between, for example, a survey party on the ground, perhaps in difficult terrain and a supplying or rescue aircraft such as a helicopter.

It is an object of the present invention to provide a method of and apparatus for effecting a rendezvous wherein it is unnecessary to break radio and/or radar silence or when radio or radar is not available to the parties to the rendezvous.

According to the present invention, there is provided a rendezvous enabling apparatus, mountable on a first vehicle, the apparatus comprising an optical transceiver having a transmitter arranged for azimuth scanning, optical detector means for receiving an optical signal from a second source and for identifying the azimuth bearing thereof, control means for relaying the identified bearing to a controller to enable the first vehicle to turn into alignment with the identified bearing, and means for aligning the transmitter with the identified bearing.

The invention also provides a method of effecting a rendezvous between a first and a second aircraft, the method comprising the steps of transmitting by each aircraft an optical signal scanned in azimuth, detecting optical signals transmitted by the other aircraft and identifying the azimuth bearing thereof, turning the first aircraft tail-on into alignment with the identified bearing and turning the second aircraft nose-on into alignment with the identified bearing, aligning the transmitters with the identified bearing, and adjusting aircraft speeds to effect the rendezvous.

The invention will be described further, by way of example with reference to the accompanying drawings, in which: - Figure 1 is a representation of two aircraft, in flight, having effected a rendezvous for refuelling; Figure 2 is a diagrammatic side view of an optical transceiver forming part of a rendezvous enabling apparatus of the present invention; Figure 3 is a schematic diagram illustrating the method of enabling a rendezvous in accordance with the present invention; Figure 4 is illustrative of a preferred arrangement of optical receivers of rendezvous enabling apparatus of the present invention; Figure 5 is a view, similar to Figure 1, of a preferred modification of the enabling apparatus and method of the present invention;; Figure 6 is illustrative of the use of the apparatus of the present invention for enabling alignment of the aircraft for fuel transfer; Figure 7 is an exploded perspective view of a dual function opto-receiver forming part of the rendezvous enabling apparatus of the present invention; and Figure 8 is a diagram of an enhanced detector means of an opto-receiver of the apparatus of the present invention.

Referring now to the drawings, there is shown in Figure 1, a representation of two aircraft which have made a rendezvous for the purpose of refuelling. A first aircraft 10, a tanker, streams out a refuelling hose 11 on the end of which is a coupling 12. A second aircraft 16 has a probe 15 arranged to mate with the coupling 12 to enable the tanker 10 to pass fuel to the aircraft 15. One method of and apparatus for effecting the coupling is described in our co-pending UK patent application No. 8924246.5 (Publication No. ).

The rendezvous illustrated is the culmination of a standard procedure which is necessarily covert in the situation of refuelling military aircraft in flight. The rendezvous is pre-arranged, both flight crews are instructed in: 1) Time of rendezvous; 2) Geographical location of rendezvous; 3) Height of rendezvous (a tanker aircraft may be assigned a height some 500 feet greater than that assigned to an aircraft to be refuelled); 4) Arrival course and speed of tanker aircraft; 5) Probable arrival course and speed of aircraft to be refuelled; 6) Maintenance of radar and/or radio silence.

There will, of course, be a leeway in the time of rendezvous. This may be several minutes. In any case, each aircraft on arrival, if the other aircraft is not immediately visible, is instructed to circle the rendezvous location.

In conditions, of radio and/or radar silence, the geographical rendezvous location may be achieved by satellite navigation or by dead-reckoning in which case a tolerance, albeit small and reducing as technology advances, exists.

Height, as an absolute altitude, has a small tolerance and there is little or no error in the course and speed of the tanker aircraft.

Under the best conditions, the resulting "rendezvous" may still mean a separation relative to the exact rendezvous location of, for example, five miles between the two aircraft. In conditions of good visibility, visual contact can be achieved and the final rendezvous effected.

Under conditions of poor visibility e.g. at night, it has heretofore been necessary to break radio and/or radar silence to effect the necessary rendezvous.

In accordance with the present invention, the aircraft 10 and 16 are each equipped with a rendezvous enabling apparatus shown diagrammatically at 19 and 20 respectively in Figure 1.

Referring now to Figures 2 and 3, each apparatus 19 or 20, which are preferably identical, comprises a transceiver having a rotating transmitter 22 comprising a convex mirror 24 and a concave mirror 26 mounted on a hollow shaft 28 for corotation, by a motor 30, about an axis. A light source 32, preferably a laser, directs light down the hollow shaft 28 to strike the mirror 24 and be reflected onto the mirror 26. The optics are such that a beam of light is formed having typically an azimuth spread of less than, for example, 10 and an elevation spread of, for example, 100, i.e. sufficient to cope with the assigned and a possible further height differential between the two aircraft. The light source 32 preferably produces infra-red radiation but a visible e.g. red light source may be used. Control means 34 may be provided for varying the output power of the source 32 enabling operation in a "whisper/shout" mode i.e.

operation is firstly at low power and only if fruitless is power increased in stages until detection occurs. Further, masking over a predetermined arc or arcs of the source may be effected in some applications where the angular range of the target is known, and transmissions outside this angular range are undesirable.

Each apparatus 19, 20 also comprises a receiver 36.

The receiver 36 comprises a ring of photodetectors 38 each having an associated collector means 40 serving to detect light from a remote source such as the transmitter 22 on the other aircraft and identify the direction from which the light was received. The collector means are shown as lenses in Figures 2 and 3 but, as shown in Figure 7, they are preferably constituted by horns, which may have a rectangular cross-section, and act as non-imaging light concentrators.

The photodetectors 38 are not evenly spaced around the ring. As shown in Figure 4, more photodetectors 38 are provided about the aircraft axis, forward-looking in an aircraft to be refuelled and rearward-looking in a tanker aircraft. Such an arrangement provides more accurate alignment of the aircraft due to the smaller field of view of the on-axis photodetector. If lenses are used as the collectors 40, each photodetector 38 may comprise a plurality of individual detectors whereby to provide a height differential indication, if this is required.

When light, which may be modulated to provide an identification code, from a remote source is detected by the apparatus 19 or 20 (the apparatus 20 or 19 on the other aircraft should detect very shortly thereafter), the motor 30 continues to rotate the transmitter 26 until it is aligned with the identified direction whereupon the motor 30 is controlled to lock the transmitter to this direction.

Standard procedure (as for normal visual sighting or radar location) is then followed. The tanker aircraft 10 turns tail-on to the joining vector 42 (see Figure 3) and the aircraft 16 to be refuelled turns nose-on to the joining vector 42. For both cases, the motors 30 are controlled to rotate the transmitters 22 to compensate for the aircraft turns so that both transmitters 22 direct light along the joining vector 42. The situation is then that the aircraft 10 and 16, the transmitters 22 and the narrow field photodetectors 38 of the opto-receivers are aligned along the joining vector 42.

The control means 34 has an output relayed to a respective display 44 in the cockpit of each aircraft 10, 16 so that the pilots of the aircraft can effect the turns mentioned above and can maintain the course along the vector.

In order to ensure that the course of both aircraft coincide with that of the joining vector, it may be necessary to modulate the direction of transmission of the "fixed" beam by means of a small amplitude conical scan.

The scanning beam should have a changing code whose instantaneous value be determined by the relative position of the beam in the scan. The scanning pattern is shown in Figure 8 as cross sections of the beam at some particular range, where the optically modulated code is indicated at sequential positions in one scan, and examples of possible off axis positions of a receiving detector are shown at D1, D2 and D3. From prior knowledge of the spatial distribution of the codes during scan, the indication of the code being instantaneously received will give the receiving pilot the information required to apply a course correction such that the aircraft aligns more accurately with the joining vector.

Although a conical scan and 4 simple code numbers have been chosen to illustrate the principle, in fact the scan pattern can be of many forms (e.g. rectilinear or spiral) and any number of coded positions can be used.

The optical links between the apparatus 19 and 20 enable communication to be established between the aircraft 10 and 16.

Thus, the control means 34 includes modulation/demodulation means for modulating the transmitted light from the respective transmitters with voice communications and/or with aircraft flight details such as height, course etc to lock the aircraft onto the same course, the joining vector.

Further, an optical transponder, for range finding, is preferably provided by the control means 34 on at least one aircraft. To this end, the control means includes pulse generating and timing means and the control means on the other aircraft comprises repeater means for receiving and re-transmitting the pulses. The timing means of the generated pulses from the at least one aircraft can then determine the distance between the two aircraft and automatically adjust, or provide information to enable the pilots to adjust, the speeds of the aircraft 10 and 16 so that they approach for a final rendezvous as shown in Figure 1.

The apparatus of the present invention enables covert rendezvous of two aircraft in conditions of poor visibility.

Referring now to Figures 5, 6 and 7, the rendezvous enabling apparatus of the present invention may additionally provide or may form part of a laser warning receiver (LWR) system. The enabling apparatus 20 has a receiver 36 which may take the form shown in Figure 7 (appropriately modified as far as azimuthal resolution is concerned as shown in Figure 4). The receiver 36 there shown comprises a housing 50 having a plurality of windows 52 providing 3600 azimuthal field of view. Each window 52 provides light collecting means which is preferably in the form of a rectangular cross-sectioned horn concentrator 54 but which may be constituted by horns of other cross-section or lenses, as required.

Each horn 54 terminates, at its reduced cross-section end, in alignment with a respective aperture 56 in a mounting plate 58 whereto a circuit board 60 (or circuit boards) may be secured. The circuit board or boards 60 carry photosensitive devices each arranged to receive light, collected by a respective one of the horns 54, through a respective one of the apertures 56. A base plate 62 enables the receiver 36 to be secured to an aircraft 10 or 16. As shown in Figure 5. Each aircraft 10 or 16 has two such receivers 36, one for sensing light received from an upper hemisphere (relative to the aircraft) and one for receiving light from a lower hemisphere. If the photosensitive devices 38 detect illumination of the aircraft by a laser, for example, an appropriate warning is given to the pilot and/or appropriate counter-action is taken.

Preferably, with the arrangement of photosensitive elements shown in Figure 4, such a laser warning receiver may readily be adapted to provide a rendezvous enabling apparatus in accordance with the present invention.

Additionally, a transmitting apparatus 22 as above described is provided.

Referring now to Figures 5 and 6, the rendezvous enabling apparatus of the present invention not only may provide an LWR but also may be used for facilitating coupling between the aircraft to permit refuelling. Thus, the transmitter 22, in addition to its other functions, may form part of a control loop enabling automatic in-flight refuelling.

The control loop may operate as follows: The tanker aircraft 10 is arranged to use its lower hemisphere LWR 20 and the refuelling aircraft 16 uses its upper hemisphere LWR 20. At the assigned refuelling height differential, and with the narrow azimuthal photodetectors 38 of the receivers 20 activated, the 10 azimuthal spread of the transmitting beam assures communication providing both aircraft are flying along the joining vector 42. Thus, the aircraft or one of the aircraft alters elevation from the height differential shown in Figure 5 to that shown in Figure 1.

The probe 15 of a refuelling aircraft 16 has a transmitter repeater on the end of the probe. This may be provided by a fibre optic connector routed to the probe and having its other end arranged to receive light from the transmitter 22 of the refuelling aircraft. The end of the probe 15 then provides a modulated light source as a target for the drogue 2. The probe source may supercede the transmitter 22 as the aircraft approach.

As shown in Figure 6, the drogue 2 streamed out by the tanker aircraft 10 at the end of the refuelling hose 11 incorporates two detector arrays 64, 66 laterally disposed at each side of the coupling. Each detector array 64 or 66 is composed of a plurality of detectors sufficient in number to provide a required spatial resolution of an approaching receptor aircraft. Displacement of the drogue 12 from the trajectory of the probe 15 on the aircraft 16 is readily determinable by the ratio of the displacements, off-centre, of the source images on the detector arrays 64, 66. The flight of the drogue 12 can then be automatically controlled to assure engagement between the drogue 12 and the probe 15 of the aircraft 16.

The invention is not confined to the precise details of the foregoing example and variations may be made thereto.

For instance, a similar apparatus could be used for effecting a covert rendezvous between two surface vessels or vehicles or between a vehicle (airplane, surface vessel or land vehicle) and a stationary party such as a survey party.

The enabling apparatus of the survey party could then be mounted on a tripod. The apparatus 19, 20 have been illustrated diagrammatically merely to illustrate the manner in which a rendezvous is enabled. It will be appreciated that equivalent mechanism to those shown may be employed.

The transmitters 22 may be arranged to scan only, for example, 1800 in azimuth. The source 32 may be an LED but preferably does not operate in the visible spectrum where covert rendezvous is to be effected.

The receiver 36 (having a single photodetector 38) may also be rotatable but preferably at a lesser rate (e.g. a tenth) than the rate at which the transmitter 22 scans.

Such a receiver would be simpler than the segmented receiver described above but would not be employable as a laser warning receiver.

Further, details have not been given of the signal processing necessary to achieve the direction identification, motor 30 control, modulation and demodulation of signals, power output control of the transmitters and the display and voice communication means.

All these integers are well known per se in the prior art and may be effected by any suitable means.

Claims (21)

1. A rendezvous enabling apparatus, mountable on a first vehicle, the apparatus comprising an optical transceiver having a transmitter arranged for azimuth scanning, optical detector means for receiving an optical signal from a second source and for identifying the azimuth bearing thereof, control means for relaying the identified bearing to a controller to enable the first vehicle to turn into alignment with the identified bearing, and means for aligning the transmitter with the identified bearing.

2. An apparatus as claimed in claim 1 wherein the transmitter is arranged to scan through 3600.

3. An apparatus as claimed in claim 1 or 2 wherein the optical detectors are arranged in an annulus.

4. An apparatus as claimed in claim 1 wherein the optical detector means comprises a single optical detector scanned in azimuth.

5. An apparatus as claimed in claim 4 wherein the optical detector means is scanned at a slower rate than the transmitter is scanned.

6. An apparatus as claimed in any preceding claim wherein the transmitter comprises a narrow beam optical source.

7. An apparatus as claimed in any preceding claim wherein the output power of the transmitter is variable.

8. An apparatus as claimed in any preceding claim similarly mountable on the second aircraft, the transmitter of the transceiver of the first aircraft serving as a detectable source for the second aircraft and vice versa.

9. An apparatus as claimed in any preceding claim further including means for modulating optical signals transmitted by the transmitter and means for demodulating modulated optical signals from a detected source.

10. An apparatus as claimed in any preceding claim wherein the transmitter comprises a laser.

11. An apparatus as claimed in any preceding claim wherein the transmitter transmits at an infra-red wavelength or wavelengths.

12. An apparatus as claimed in any preceding claim further including display means for displaying the identified bearing.

13. An apparatus as claimed in any preceding claim wherein the transmitter is arranged to transmit in pulses and further including pulse timing means for determining the range of a detected source.

14. An apparatus as claimed in claim 9 or any claim appendant thereto wherein the modulating means serves to modulate the optical transmission with audio frequency signals.

15. A rendezvous enabling apparatus substantially as hereinbefore described with reference to the accompanying drawings.

16. A method of effecting a rendezvous between a first and a second aircraft, the method comprising the steps of transmitting by each aircraft an optical signal scanned in azimuth, detecting optical signals transmitted by the other aircraft and identifying the azimuth bearing thereof, turning the first aircraft tail-on into alignment with the identified bearing and turning the second aircraft nose-on into alignment with the identified bearing, aligning the transmitters with the identified bearing, and adjusting aircraft speeds to effect the rendezvous.

17. A method as claimed in claim 16 further including transmitting the optical signals from one of the aircraft in pulses, detecting and retransmitting the pulses by the other aircraft, detecting and timing the retransmitted pulses at the one aircraft to determine range and relative speed of the aircraft.

18. A method as claimed in claim 16 or 17 further including the steps of modulating information onto the optical signals transmitted by each aircraft and demodulating the information from optical signals detected by each aircraft.

19. A method as claimed in any of claims 16 to 18 further including the step of transmitting the optical signals as a narrow beam.

20. A method as claimed in any of claims 16 to- 18 further including the step of transmitting the optical signals at an infra-red wavelength.

21. A method of effecting a rendezvous as claimed in claim 16 and substantially as hereinbefore described.