GB2152319A

GB2152319A - Positioning hovering helicopter

Info

Publication number: GB2152319A
Application number: GB08430046A
Authority: GB
Inventors: Donald Roy Charles Price
Original assignee: GEC Avionics Ltd
Current assignee: Allard Way Holdings Ltd
Priority date: 1983-12-21
Filing date: 1984-11-28
Publication date: 1985-07-31
Also published as: FR2557319A1; FR2557319B3; GB8430046D0; DE3446447A1

Abstract

A helicopter is maintained at a fixed position in relation to a selected ground position by deploying a reflector 19 from the helicopter to the selected ground position, and scanning a light beam across the reflector 19 from the vehicle. The helicopter is then controlled in response to light in the beam which is reflected back. Details of the scanning device are given. <IMAGE>

Description

SPECIFICATION Method and apparatus for maintaining the position of a hovering vehicle This invention relates to a method and apparatus for maintaining a hovering vehicle, for example a hovering helicopter, at a fixed position with respect to a desired ground position.

It is frequently necessary for a helicopter to hover over a selected ground position, for example in battlefield operations. In such operations it is desirable for the helicopter to be able to maintain its position over selected ground position with a minimum of effort on the part of the helicopter crew, so that a pre-assessed line of fire of weapons can be maintained, and also so that the helicopter does not drift into obstacles.

A known solution to the above requirement includes the use of a weighted cable the end of which rests on the ground, the cable dangling from the helicopter. Such a method is described in French Patent Specification No. 2,502,772. Use of such a cable, however, can lead to problems in the battlefield due to entanglement of the cable with fixed objects. Furthermore the firing of weapons may deflect the cable.

It is an object of the present invention to provide a method for maintaining a hovering vehicle at a predetermined position in relation to a selected ground position, and apparatus for use therein, whereby these problems are avoided.

According to one aspect of the present invention a method for maintaining a hovering vehicle at a fixed position in relation to a selected ground position comprises: deploying a light reflective object from the vehicle to the selected ground position; directing a light beam onto the object from the vehicle; and controlling the position of the vehicle in response to light in said beam which is reflected back to said vehicle by said object.

In a preferred method in accordance with the invention the light reflected by the object is directed onto a light position sensor within the vehicle, and the position of the vehicle is controlled to maintain the reflected light at a predetermined position on the sensor.

The invention also provides apparatus for use in a method according to the invention comprising: a light reflective object; means adapted to deploy said object from the vehicle to a selected ground position; a light source; a light position sensor; optical means for focusing light from said source into a beam directed onto said object when deployed and to direct light reflected from said object onto the light sensor; and means responsive to the output of said light sensor to provide an output representative of the position of the vehicle with respect to said object.

In a preferred form of the apparatus said optical means includes beam deflector means for controlling the direction of the said beam; and said means responsive to the output of said light sensor comprises: servo means for controlling said beam deflector means so that the reflected light impinges on the sensor array at a predetermined position.

One method in accordance with the invention, together with apparatus for use therein, will now be described, by way of example only, with reference to the accompanying drawings in which: Figure lisa schematic diagram of the apparatus in use; Figure 2 is a part sectional view of part of the apparatus carried in the hovering object; Figure 3 is a part sectional plan view of the part of the apparatus shown in Figure 2; and Figure 4 is a schematic diagram of the part of the apparatus deployed on the ground in due.

Referring firstly to Figure 1,the main part of the apparatus consists of an optical system located in a helicopter, and includes a light source 3, arranged to direct light through a lens system 5, the lens system being effective to produce a beam of light of magnified width from the light produced by the source 3. The magnified beam is arranged to pass through a beam deflector 7 and then through a transparent window 9 located in the floor 11 of the helicopter 1. The optical system within the helicopter also includes a beam splitter 13 positioned in the light path between the source 1 and the lens system and adjacent to the beam splitter a light position detector 15. An output from the detector 15 is connected to a servo 17, the servo 17 being effective to control the beam deflector 7.

Adjacent to the window 9 in the floor 11 of the helicopter there is provided an exit tube (not shown) through which a light reflective object 19 carried in the helicopter may be dropped to a selected ground position.

In use of the apparatus, the light reflective object 19 is first ejected through the tube out of the hovering helicopter. The direction of the beam through the window 9 is at this time set by the beam deflector 7 such that the object 19 passes into the beam path, and light reflected by the object which passes back into the optical system is deflected by the beam splitter and falls onto the detector 15. The detector 15 produces an electrical output signal indicative of the deviation of position of the light impinging from a datum position on the detector at which the light impinges when the object is centraiised within the beam, which signal is applied to the servo 17 together with helicopter altitude data derived from the helicopter altitude gyros (not shown).The servo 17 adjusts the beam deflector such that the object 19 is maintained in a central position within the beam. Thus as the object 19 falls to the ground it is tracked by the light beam, and when the object 19 reaches the ground 21, it remains in a central position in the patch of the ground 23 illuminated by the light beam.

If the helicopter subsequently moves laterally, the output signal from the servo 17 will then be indicative of the lateral displacement of the helicopter 1 with respect to the position of the object 19 on the ground. This signal may be directly fed to a helicopter automatic flight control system indicated as 22 for use in causing the helicopter to resume its former lateral position or alternatively may be used to present a display indicated as 24 to the helicopter pilot which he can use to adjust the position of the helicopter himself.

Helicopter altitude and attitude data is applied to the servo 17 to enable changes in the servo output signal due to changes in the helicopter altitude or attitude rather than lateral movement of the helicopter to be identified, and to remove demands on the servo loop due to helicopter altitude or attitude changes.

Details of a practical embodiment of the optical system carried within the helicopter 1 are shown in Figures 2 and 3. In this embodiment the light source 3 comprises a light emitting diode, or a low power laser, the light emitted by the source being pulse coded for ease of identification of the reflected light.

The lens system 5 comprises three convex, and one concave lens arranged as shown in Figure 2. The beam deflector 7 comprises two wedge prisms 7 and two electric motors 25, 27 each arranged to rotate one of the wedge prisms 7 about a common axis passing perpendicularly through the centre of the bases of the prisms. Sensors 29, 31 are provided to monitor and stabilise the prism servos.

In operation of the optical system, when the prisms 7 are arranged with their inclined faces parallel the beam passes through the prisms without deflection. If the prisms are then rotated relative to one another about the above mentioned common axis the beam is deflected through an angle proportional to the angle of rotation 1 and when the prisms are rotated together about the common axis the beam follows a circular path of radius equal to the angular deflection. Thus the beam may be centred on any selected ground position within a circular area by means of the beam deflector 7.

The reflective object 19 may take various forms. In its simplest form, it will comprise a specular reflector so that at least some of the reflected light, when the object is in the beam path, will re-enter the optical system. A preferred form, however is the device shown in Figure 4. This consists of an object having four telescopic legs 33, 35, 37, 39 which are deployed by springs (not shown) as the object is ejected from the helicopter 1. The legs 33, 35, 37, 39 are so disposed on the object so that the object will always assume a position with the same surface uppermost on landing on the ground, after ejection from the helicopter 1, the legs also ensuring that on landing the object is unlikely to bury itself. On the surface of the object which is uppermost after the object has landed there is provided a pattern of corner reflectors 41. Each corner reflector 41 is effective to reflect light back along the direction from which it arrives at the reflector. A more efficient use of the light beam is then achieved. The pattern of corner reflectors ensures that the object is readily identifiable.

Claims

1. A method for maintaining a- hovering vehicle at a fixed position in relation to a selected ground position comprising: deploying a light reflective object from the vehicle to the selected ground position; directing a light beam onto the object from the vehicle; and controlling the position of the vehicle in response to light in said beam which is reflected back to said vehicle by said object.

2. A method according to Claim 1 wherein the light reflected by the object is directed onto a light position sensor within the vehicle, and the position of the vehicle is controlled to maintain the reflected light at a predetermined position on the sensor.

3. A method according to Claim 2 in which the direction of the light beam with respect to the vehicle is controlled to maintain the reflected light at a predetermined position on the sensor.

4. A method according to Claim 3 in which light in said beam reflected by the object is monitored by the sensor during the deployment of the object.

5. A method for maintaining a hovering vehicle at a fixed position in relation to a selected ground position substantially as hereinbefore described with reference to the accompanying drawings.

6. An apparatus for use in a method for maintaining a hovering vehicle at a fixed position in relation to a selected ground position comprising: a light reflective object; means adapted to deploy said object from the vehicle to the selected ground position; a light source; a light position sensor; optical means for focusing light from said source into a beam directed onto said object when deployed and to direct light reflected from said object onto the light sensor; and means responsive to the output of said light sensor to provide an output representative of the position of the vehicle with respect to said object.

7. An apparatus according to Claim 6 in which said optical means includes beam deflector means for controlling the direction of the said beam; and said means responsive to the output of said light sensor comprises: servo means for controlling said beam deflector means so that the reflected light impinges on the sensor at a predetermined position.

8. An apparatus according to Claim 6 or Claim 7 including means responsive to vehicle altitude data to identify changes in the output of said light sensor due to changes in vehicle altitude.

9. An apparatus according to any one of Claims 6 to 8 including means responsive to vehicle attitude data to identify changes in the output of said light sensor due to changes in vehicle attitude.

10. An apparatus according to any one of Claims 6 to 9 including an automatic flight control system responsive to said output representative of the position of the vehicle with respect to said object to cause the vehicle to maintain said fixed position in relation to said selected ground position.

11. An apparatus according to any one of Claims 6 to 9 including means for displaying a representation of said output representative of the position of the vehicle with respect to said object.

12. An apparatus according to any one of Claims 7 to 11 wherein said beam deflector means includes two wedge prisms arranged for rotation about a common axis passing through the prisms.

13. An apparatus according to any one of Claims 6 to 12 wherein said light source is arranged to provide coded pulses of light.

14. An apparatus for use in a method for maintaining a hovering vehicle at a fixed position in relation to a selected ground position substantially as hereinbefore described with reference to the accompanying drawings.

15. A light reflective object for use in a method according to any one of Claims 1 to 5, or for use in an apparatus according to any one of Claims 6 to 14 including at least four spring loaded telescopic legs deployed on landing and disposed on the object such that the object will tend to assume a position with a light reflective surface uppermost on landing on the ground.

16. A light reflective object according to Claim 15 wherein said light reflective surface includes a pattern of corner reflectors, each corner reflector being effective to reflect light back along the direction from which it is incident on the corner reflector.

17. A light reflective object for use in a method for maintaining a hovering vehicle at a fixed position in relation to a selected ground position substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.