GB2302318A

GB2302318A - Aircraft landing procedure

Info

Publication number: GB2302318A
Application number: GB9611536A
Authority: GB
Inventors: Uwe Georg Hingst
Original assignee: Bodenseewerk Geratetechnik GmbH
Current assignee: Bodenseewerk Geratetechnik GmbH
Priority date: 1995-06-14
Filing date: 1996-06-03
Publication date: 1997-01-15
Anticipated expiration: 2016-06-03
Also published as: GB2302318B; FR2735445B1; DE19521600A1; FR2735445A1; GB9611536D0

Description

1 Landing Procedure for Unmanned Aircraft 2302318 The invention relates to

a landing procedure for aircraft which comprisea flight guidance system, an image resolving sensor and an image processing system.

Unmanned aircraft are used for the purpose of aerial reconnaissance. Such unmanned reconnaissance aircraft are often equipped with an image resolving sensor and an image processing system, in order to be able to recognize targets also at night or poor visibility.

One problem is the landing of such unmanned aircraft. Usually, no normal airfield is available for this purpose. According to the prior art, landing of such unmanned aircraft is effected by means of a parachute or of impactdampening air cussions.

More complex, vertical take-off, unmanned aircraft are known. Such aircraft require so much weight and space for the drive, that the range or payload of the aircraft are substantially limited.

Other unmanned aircraft are landed by means of radio remote control. This requires highly qualified ground personnel.

The landing requires a sufficiently large landing strip.

Furthermore, landing can take place at daylight only.

It is an object of the invention to provide alanding procedure for aircraft, in particular unmanned aircraft of the type described hereinbefore, which 2 permits landing of the aircraft on an easy to prepare landing field and proceeds automatically and without high requirements on qualification of the ground personnel.

According to the invention, this object is achieved with an aircraft of the type mentioned in the beginning by the following steps:

(a) marking a landing field at well-defined relative positions by marks which can be recognized by the sensor, (b) determining the positions of these marks within the field of view detected by the sensor, (c) determining approach parameters by means of the image processing system from the positions of the marks within the field of view, and (d)'applying the approach parameters thus determined to the flight guidance system for guiding the aircraft to land on the landing field.

Thus, according to the invention, the aircraft lands normally for example on a meadow. The aircraft may land on skids. The landing field is marked. The marking is detected by the image resolving sensor such as an IR-video camera.

By means of the image processing system, the position and attitude of the aircraft (altitude, elevation and azimuth) relative to the landing field and relative to a touch-down point can be determined. The flight guidance system controls the azimuth angle to zero. Then the elevation 3 relative to the touch-down point provides the glide path angle. This elevation angle is then maintained by the control as glide path angle. Thereby, the aircraft is guided to the touch-down point. In many cases, the unmanned aircraft is provided with an image resolving sensor anyhow for aerial reconaissance purposes. This sensor can then be utilized for the landing procedure.

If the landing field is marked by infrared-emitting marks and the sensor of the aircraft responds to infrared radiation, it is possible to land in the darkness. The landing field is not visible for the enemy, unless he has also an infrared-sensitive sensor.

Modifications of the invention are subject matter of further sub-claims.

An embodiment of the invention is described hereinbelow with reference to the accompanying drawings.

Fig. 1 is a schematic-perspective illustration and shows the guiding of the unmanned aircraft towards the landing direction.

Fig. 2 is a plan view of the landing f ield and shows the meaning of the variuos designations.

Fig. 3 shows an unmanned aircraft approaching at an angle with respect to the longitudinal direction of the landing field.

Fig. 4 shows the image, which is detected by the sensor responding to infrared radiation and arranged in the aircraft, if the aircraft has the attitude and position illustrated in Fig. 3, measures to be used 4 in the picture processing being added to the picture.

Fig. 5 shows a side elevation of the landing field and of the aircraft during its approach.

Fig.6 is a block diagram and illustrates schematically the sensor, the image processing system and the flight guidance system.

Fig. 7 shows the image of the landing f ield detected by the sensor at a distance of 900 meters.

Fig.8 shows the image of the landing f ield detected by the sensor at a distance of 200 meters.

Fig. 9 shows the image of the landing f ield detected by the sensor at a distance of 25 meters.

Fig.1 shows a landing field 10 embedded in a landscape-The landing field is elongated-rectangular and marked out by four marks 14, 16, 18 and 20 on a substantially plane area 12, for example a meadow or a f ield. The marks 14, 16, 18 and 20 are heated plates or hemispheres, which emit infrared radiation but no visible light. The two marks 14 and 16 define the approach-side narrow side of the landing field. Numeral 22 designates a longitudinal center line of the landing field 10. A fifth mark 24 in the form of a landing-T or a landing cross is placed on the longitudinal center line halfway between the two approach-side marks 14 and'16.

An unmanned aircraft 26, for example an unmanned aerial reconnaissance aircraft, flies along a trajectory 28. The aircraft 26 is steered up to a point "X" by the navigation means provided for its mission such as satellite navigation (GPS), inertial navigation or directional radio beacon. At the point "X", an image resolving sensor provided in the aircraft detects the landing field 10. By means of an image processing system also provided in the aircraft, the aircraft 26 is guided to the point "Y" approximately in the direction of landing. The touch-down point can be recognized by means of the landing-T 24, which is arranged at the approach-side narrow side of the landing field 10. The landing direction results from the extension of the longitudinal center line passing through the landing-T.

Fig.2 shows a plan view of the landing field 10. The length A - B of the approach-side narrow side of the landing field between the marks 14 and 16 is BL. The length D - C of the narrow side of the landing field remot from the approachside between the marls 18 and 20 is bL. In the present case, BL = bL. The length of the longitudinal sides of the landing field 10 is LL

Fig.3 is a perspective illustration of the landing field 10 and of the unmanned aircraft 26. The aircraft 26 is located on a line of sight 30 as viewed from the landing-T 24, this line of sight forming an angle a with the longitudinal center line 22. The projection of the line of sight 30 on the horizontal plane forma an angle a' with the longitudinal center line 22.

Fig.2 shows the image which is "seen" by the image resolving sensor of the aircraft 26 with this configuration. This image is a perspective one: The two parallel longitudinal sides A - D and B - C of the rectangle and the longitudinal center line 22 intersect, in the perspective, at a vanishing point 32. The image of the approach side narrow side A - B is longer than the image of 6 the narrow side D - C remote from the approach side. The length of the former image is Bi, the length of the latter image is Bi. The distance of the images of the two narrow sides, which appear substantially parallel, measured normal to the direction of these images is designated by hi.

Furthermore, the line of sight from the aircraft to the landing-T 24 has been added in Fig.4 as dotted line.

It can be recognized from the oblique position of the longitudinal center line 22 in the image of Fig.4 that the unmanned aircraft 26 is located lateral from this longitudinal center line 22. A steering signal can be derived herefrom by the image processing system, this steering signal being applied to the flight guidance system, taking the aircraft to a vertical plane containing the longitudinal center line 22, and maintaining the aircraft in this plane.

This yields a situation as illustrated in Fig.5.

The aircraft 26 is located substantially in a vertical plane passing through the longitudinal center line 22 of the landing field 10. Its altitude above ground is H, The horizontal distance of the aircraft 26 ftom the landing-T 24 is Xu. The elevation angle, at which the aircraft is seen from the landing-T, and thus the glide path angle of the glide path 34 which the aircraft 26 has to follow in order to touch down at the landing-T 24 is designated by P. These parameters can be determined from the image (Fig.4) of the known landing field 10 as received by the sensor. It is:

4 H. = gIL',[X,,+LLI B, L, 7 Z1 b, X - 8,-b, 81 0 = arctg [ 6, L, 1 These values are applied to the flight guidance system of the unmanned aircraft 26. The flight guidance system keeps the glide angle 0 constant through the thrust setting and/or spoilers. Influences of head wind or tail wind are automatically taken into account by the thrust setting or the extension of spoilers. Thereby, the aircraft 26 is guided to the landing-T 24. The aircraft 26 touches down with skids. Prior to reaching the landing-T 24, a flaring procedure under the control of altitude and distance information can be initiated, in order to achieve softer touch down of the aircraft on the landing field.

Fig.6 is a block diagram and illustrates the sensor 38, the image processing system 40 and the flight guidance system 42.

The sensor 38 is an image resolving sensor responding to infrared radiation similar to a video camera. The image processing system 40 is designed to recognize and identify the marks in the f ield of view and to determine in the image both the distances of the marks thus recognized and the direction of the longitudinal center line 22. The direction of the longitudinal center line provides a measure of the lateral deviation of the aircraft 26 from the vertical plane passing through the longitudinal center line 22. The flight guidance system, through the rudder, controls the trajectory and the attitude of the aircraft such that, in the image detected by the sensor, the angle a becomes substantially zero, and the longitudinal center line 22 extends in the middle and substantially vertical in 8 the image of Fig.4. Furthermore, the image processing system 40 provides the glide angle P. The flight guidance system then keeps this angle 0 constant through the thrust setting and the spoilers.

Figs.7 to 9 show the images of a landing field having dimensions of 15 meters x 100 meters consecutively detected by the image resolving sensor during the landing at distances of 900 meters, 200 meters and 25 meters, respectively. It can be seen from Fig.9 that during the end phase of the landing approach, the sensor no longer detects the whole landing field 10, but that the front corners are cut off by the frame limits. In the above equation for the elevation angle 0, however, only the quantities bi and hi appear, i.e. the width of the rear narrow side of the landing field, appearing in the image, and the length of the landing field measured along the longitudinal center line 22, als appearing in the image. These quantities can still be gathered even from Fig.9- BL and LL are known parameters inputted prior to the mission. Therefore, the landing procedure described operates also during the end phase of the landing approach, when the sensor no longer "sees" all of the landing field.

This indicates, that only three marks are sufficient for marking the landing field to guide the aircraft 26 along the glide path 34, namely the two rear marks 18 and 20 and the landing-T 24. Instead of the landing- T, an ordinary mark may be used which is identical in design with the marks 14 to 20.

The described landing procedure permits the use of unmanned aircraft also during darkness or poor vision.

9

Claims

1. A landing procedure for aircraft (26) which comprise a flight guidance system (42), an image resolving sensor (38) and an image processing system (40), comprising the steps of (a) marking a landing field (10) at well-defined relative positions by marks (14,16,18,20,24) which can be recognized by the sensor (38), (b) determining the positions of these marks (14,16,18,20,24) within the field of view detected by the sensor (38), (c) determining approach parameters by means of the image processing system (40) from the positions of the marks (14,16,18,20,24) within the field of view, and (d) applying the approach parameters thus determined to the flight guidance system (42) for guiding the aircraft (26) to land on the landing field.

2. ' A landing procedure as claimed in claim 1, characterized in that the landing field (10) is marked by infrared-emitting marks (14,16,18,20,24), and the sensor (38) of the aircraft (26) responds to infrared radiation.

A landing procedure as claimed in claim 1 or 2, characterized in that a rectangle is marked as landing field (10) by four marks (14,16,18,20,24), the dimensions of the rectangle being inputted as parameters into the image processing system (40) of the aircraft (26) prior to starting on the mission.

4. A landing procedure as claimed in claim 3, characterized in that a fifth mark is placed in the middle between the marks (14,16) determining the approach-side narrow side of the rectangle.

5. A landing procedure as claimed in claim 3, characterized in that the fifth mark (24) is designed to form a landing cross or landing-T.

A landing procedure as claimed in claim 4 or 5, characterized in that the distance xu of the aircraft (26) from the touch-down point and the glide path angle 0 are determined in accordance with the relations L L b, X = 8, -b, h Bt,

6 = arcig[ b, Lfl 1 wherein BL is the width of the landing field (10), LL 'is the length of the landing field (10), Bi is the width of the approach-side narrow side of the landing field (10) in the image detected by the sensor (38), 11 is the width of the narrow side of the landing field (10) remote from the direction of approach in the image detected by the sensor, and is the distance of the narrow sides in the image detected by the sensor (38).

7. A landing procedure as claimed in anyone of the claims 1 to 6, characterized in that the aircraft is unmanned.

8. A landing procedure substantially as hereinbefore described with reference to the accompanying drawings.