WO1991004589A1

WO1991004589A1 - Detection of airborne craft

Info

Publication number: WO1991004589A1
Application number: PCT/GB1990/001461
Authority: WO
Inventors: Jeffrey Charles Broadhurst; Geoffrey Richard Taylor
Original assignee: Dowty Woodville Polymer Limited
Priority date: 1989-09-23
Filing date: 1990-09-21
Publication date: 1991-04-04
Also published as: GB8921540D0; AU6409290A; GB2238175A

Abstract

Airborne craft and appliances of the kind having wings, envelopes, canopies, sails or the like composed of a flexible material which is inflated or shaped by air or gas pressure when in use, is made radar detectable by arranging that the flexible material of the wing (8) or like structure is radar reflective at least in part, and/or providing an additional panel or panels (1, 4) of flexible radar reflective material so that they are tensioned in use and form a suitable radar reflective structure either alone or with the wing. These panels may be tensioned between opposed portions of the wing or enclosed within an envelope that forms the wing.

Description

DETECTION OF AIRBORNE CRAFT This invention relates to airborne craft and appliances of the kind having wings, envelopes, canopies, sails or the like composed of a flexible material which is inflated or shaped by air or gas pressure when in use.

In recent times, there has been a rapid increase in airborne sporting and leisure activities such as parachuting, ballooning, hang-gliding and microlite flying, so much so that the presence of these craft in the air is becoming a hazard to the safety of low flying aircraft such as light aircraft and military aircraft on low flying exercises. This is especially the case because of the small size of these craft and the fact that they are generally invisible as far as radar detector systems are concerned.

An object of the present invention is to make airborne craft and appliances of the aforesaid kind more readily detectable.

This is achieved according to the invention by arranging that the flexible material of the wing or like structure is radar reflective at least in part, and/or providing an additional panel or panels of flexible radar reflective material so that they are tensioned in use and form a suitable radar reflective structure either alone or with the wing.

In one embodiment, it may be sufficient simply to make the wing or like structure radar reflective. However, the shape of the wing may not give it a suitable radar reflective characteristic; for example, reflections may be only of low intensity or may be directionally sensitive so that it can only be detected when viewed in a particular orientation. Preferably, therefore, the craft has attached to it flexible radar reflective panels which are tensioned in use to form a suitable radar reflector, the wing or part of it possibly also being radar reflective to form part of the reflector with the panels. For example, the panels may define an array of corner reflectors such as are well known for their optimum radar reflective characteristics. These panels may be tensioned between opposed portions of the wing or enclosed within an envelope that forms the wing. The invention is illustrated in the accompanying drawings in which:

Figure 1 is a sketch of a hang-glider adapted according to a first embodiment of the invention,

Figure 2 is an underview of the hang-glider of Figure 1,

Figure 3 is a longitudinal section through a hang- glider wing according to a second embodiment of the invention,

Figure 4 is a longitudinal section through a hang- glider wing according to a third embodiment of the invention,

Figure 5 is a longitudinal section through a hang- glider wing according to a fourth embodiment of the invention, and

Figure 6 is a lateral section through the hang- glider wing of Figures 3 and 4.

Figure 1 shows a hang-glider having flexible radar reflective panels 1 tensioned between the king¬ post 2 and the central longitudinal frame member 3 so as to extend longitudinally of the glider and serve as a reflector for radar beams incident from the sides of the craft. Further flexible radar reflective panels 4 are tensioned between the lateral frame member 5 and the bracing wires 6 that support the pilot's grab rail 7 beneath the glider. These panels 4 extend laterally of the glider so as to reflect radar beams incident from the front or rear of the glider. The wing 8 of the glider may also be made of a radar reflective material in which case it forms angled corners with the panels to give improved radar reflective characteristics in the manner of a dihedral reflector.

In the second embodiment illustrated in Figures 3 and 6, the hang-glider is such as to have a frame member 9 along the leading edge of the wing 8 which takes the form of an inflatable tube. This type of inflatable tubular frame construction has been adopted in some designs of hang-glider and gives the opportunity of including a radar reflective construction within these inflatable ε

tubes. As shown in Figure 3, the reflector consists of four longitudinally extending flexible radar reflective panels 10 to 13 connected together along their inner edges at 14 and connected to the tube 9 at their outer edges so that they form a cross with right angles between the panels when the tube 9 is inflated and the panels tensioned. Additional flexible radar reflective panels 15 are provided laterally at intervals along the length of the tube 9 (see Figure 6) and are connected to the wall of the tube and the longitudinal panels 11 to 13 so as to form trihedral reflectors with the other panels where they all meet at right angles in a corner. Thus a plurality of trihedral radar reflectors are formed along the length of the tube 9 at the leading edge of the wing 8, and a plurality of dihedral radar reflectors are formed between these trihedral reflectors in the angles between the longitudinal panels 11 to 13.

In the third embodiment of Figure 4, the whole wing 8 of the hang-glider is formed as a double- walled inflatable structure and a radar reflector is provided within it in the form of a plurality of interconnected flexible radar reflecting panels 16 that are connected to the walls of the wing at their outer edges so as to be tensioned thereby and form a plurality of trihedral and dihedral reflectors in a similar manner to that shown in Figures 3 and 6.

In the fourth embodiment of Figure 5, the whole wing 8 is similarly formed as an inflatable double-walled structure as in Figure 4, however, instead of providing a plurality-of interconnected panels 16 throughout the wing, one or more radar reflectors 17 are located locally within the wing and are such as to have a radar reflecting characteristic over an azimuth of 360°. Each reflector comprises a plurality of interconnected flexible radar reflecting panels connected to the walls of the wing so as to be tensioned thereby. Figure 5 illustrates a reflector comprising a series of trihedral reflectors arranged around a central upright axis in the manner described in our corresponding U.K. Patent Application No. 8903534.

It will be appreciated that the inflatable tube 9 and wing 8 in the embodiments of Figures 3 to 6 are composed of non-radar reflecting materials so as not to screen or effect the reflecting characteristics of the panels within them.

In yet other embodiments of the invention in which the frame of the hang-glider is composed of rigid tubular members, provided these are composed of non-radar reflecting material, they can house within them a radar reflecting structure which may be rigid and could be similar in form to that illustrated in Figures 3 and 6.

It will be appreciated that the illustrated alternative arrangements for providing radar reflectors in hang-gliders, can be readily adapted for use within the envelopes of balloons or within the canopies of para-gliders.

Claims

1. An airborne craft having support means composed of a flexible material which is shaped by gas pressure when in use characterised in that it incorporates radar reflective flexible material which is tensioned in use and forms a radar reflective structure.

2. An airborne craft as claimed in claim 1 in which said radar reflective flexible material comprises at least part of said support means.

3. An airborne craft as claimed in claim 1 or 2 which said radar reflective flexible material comprises a panel separate from said flexible material of the support means.

4. An airborne craft as claimed in any one of the preceding claims in which the radar reflective flexible material comprises two planar portions substantially perpendicular to each other so as to form a dihedral reflector therebetween.

5. An airborne craft as claimed in claim 4 in which the radar reflective flexible material comprises three planar portions substantially mutually perpendicular to one another so as to form a trihedral reflector therebetween.

6. An airborne craft as claimed in claim 3 in which the support means comprises a wing secured to a frame which supports said panel.

7. An airborne craft as claimed in claim 6 in which the frame comprises a central longitudinally extending member which supports said panel so as to extend longitudinally along its length.

8. An airborne craft as claimed in either of claims 6 or 7 in which the frame comprises a laterally extending member across the width of the wing which supports said panel so as to extend laterally along its length.

9. An airborne craft as claimed in claim 8 in which a grab rail is suspended from said laterally extending member for a pilot of the craft to hold, and said panel is supported between said laterally extending member and the grab rail.

10. An airborne craft as claimed in claim 6 in which the frame is inflatable and substantially non-radar reflective, and said panel is supported within and tensioned by it.

11. An airborne craft as claimed in claim 10 in which two panels of radar reflective flexible material are provided within the inflatable frame substantially perpendicular to one another so as to form a dihedral reflector therebetween.

12. An airborne craft as claimed in claim 11 in which three panels of radar reflective flexible material are provided within the inflatable frame substantially mutually perpendicular to one another so as to form a trihedral reflector therebetween.

13. An airborne craft as claimed in claim 11 or 12 in which said two panels extend longitudinally the length of an elongate portion of the frame.

14. An airborne craft as claimed in claim 13 in which lateral panels are provided at spaced intervals along the length of said two panels and are substantially perpendicular to said two panels so as to form trihedral reflectors therewith.

15. An airborne craft as claimed in claim 1 in which the support means comprised a double-walled inflatable wing composed of substantially non- radar reflective material, and said radar reflective material is supported within and tensioned by it.

16. An airborne craft as claimed in claim 15 in which said radar reflective material comprises two panels of radar reflective flexible material provided within the inflatable frame substantially perpendicular to one another so as to form a dihedral reflector therebetween.

17. An airborne craft as claimed in claim 16 in which said radar reflective material comprises three panels of radar reflective flexible material provided within the inflatable frame substantially \l

mutually perpendicular to one another so as to form a trihedral reflector therebetween.

18. An airborne craft as claimed in claim 17 in which one panel extends substantially parallel to the walls of said double-walled wing.

19. An airborne craft substantially as herein described with reference to Figures 1, 2 or 3, 6 or 4 or 5 of the accompanying drawings.