GB2176073A - Bird avoidance system - Google Patents

Abstract

Apparatus which assists avoidance of harmful birds of a size or configuration to cause damage to an aircraft comprises a radar mounted on the aircraft and arranged to probe an area ahead of the the aircraft. Signals received from said radar probe are analysed to determine whether a harmful bird is present in said area, for instance from the modulation imposed on the returns by the bird's wing beat. In response to the determination of the presence of a harmful bird a warning may be initiated or a control system of the aircraft instructed to take avoiding action. An infrared system may be used additionally to help distinguish between animate and inanimate objects. <IMAGE>

Description

SPECIFICATION Bird avoidance system The present invention relates two a systemforavoiding birds striking aircraft. More particularly, but not exclusively, it relates to an aircraft mounted system.

It is well known that birds, which expression includes such otherflying mammals as bats, can be a great hazard to aircraft. The most usual danger is that birds are ingested into jet aircraftturbo engines where birds which weigh in the region of 500 gms orgreaterwill damagetheturbine blades and cause the engine to cease functioning. The birds can also strike other parts of the aircraft, such as cockpits, where the damage may be equally as serious. In the case of multi-engine aircraft, particularly civil aircraft, loss of an engine in this manner may be expensive and possibly serious, but only occasionally does it prove disastrous. However, in the case of single engine, possibly military, aircraft the loss of the single engine is almost certainly disastrous and possibly fatal.

The majority of birds fly at heights less than 5,000 feet above sea level, which height is less than the cruising heightof most aircraft. Thus the critical times are during takeoff and landing. At these critical times, in the region of airports, great care is taken on the ground to detectthe presence of birds and either to scarethem away orto warn the aircraft of the probability of a bird strike. Nevertheless, accidents still do happen.

The problem is even more acute in the case of military aircraft which regularly undertake low level training flights away from.the vicinity of airfields. In such cases,there is no warning of possible bird strikes otherthan the reaction of the pilot. With an aircrafttravelling at possibly 1,000 knots, the pilot has possibly four seconds in which to avoid a bird 1 mile ahead. At such speeds, it is difficult to spot a bird at this distance, particularly at low level where it may be hidden against the ground. The problem is even more acute at night time and in the case of pilotless jet engined aircraft or missiles.

It is an object of the present invention to provide an apparatus which overcomes the above difficulties and which can be mounted, preferably to an aircraft to assist in avoiding birds. As stated above, birds of less than 500 gms do not in general damage engines on impactandthusthis invention is concerned only with the avoidance of "harmful birds" which expression encompasses hereafter birds of weight in the region of 500 gms or greater orthose so configuredthatthere exists a possibility ofdamagetothe aircraft iftheycollidewith it.

According to the present invention there is provided an apparatus for use in an aircraftto assist avoidance of harmful birds, the apparatus comprising radar means mounted to the aircraft and disposed to probe an area ahead ofthe aircraft, means to analyse signals received from said radar probe to determine therefrom whether a harmful bird is present in said area, and means responsive to the determination of the presence of a harmful bird to initiate a warning.

Preferably the warning may be a command to the control apparatus of the aircraft to take a predetermined avoiding action. In this case, switch means may be provided to allow manual override. This is particularly important at times of takeoff, landing or combat, where safety depends on the skill and reaction ofthe pilot and unexpected movement for automatic avoidance of birds may be counter-productive.

Before automatic avoiding action is initiated, the radar means may probe a second zone or a peripheral part of the zone ahead of the aircraft into which the action would take the aircraft, and the signal received is also analysed. In the event that a bird is present, a second or other predetermined avoiding action may be initiated.

The radar means is preferably adapted to probe a zone: sufficiently far ahead of the aircraftto enable avoiding action to be taken timeously; sufficiently close to the aircraftthat the presence of a harmful bird therein makes collison likely; sufficiently small that birdstherein can be detected substantially individually or at least separated from largerscale phenoma such as rain; and sufficiently largeto detect birds which may enter the center of the zone by the time the aircraft has reached the zone.

The zone ideally extends to a distance in the region of 5000 ft (1550 metres) ahead of the aircraft.

Advantageously the radar means comprises a phased array radar having a plurality of selectively energisable elements each adapted to probe a substantially separate partofthe area ahead of the aircraft.

The apparatus may further comprise infra red detector means mounted to the aircraft and disposed to probe a substantially similar area ahead ofthe aircraft.

The signal analysis means may be computing means, which analyses signals received, firstly to discard extraneous signals, for example those generated by rain and other weather conditions or from the ground itself, and secondly to determinewhetherthe signal represents a harmful bird oronewhich is not harmful.

The second stage of the signal analysis may comprise comparison ofthe received signal with known characteristic signals of various bird species, particularly but not exclusively, by means of characteristic wing-beatfrequency.

The second stage of the signal analysis may also comprise the determination of bird size and flight speed, which aid identification of species.

An embodiment of the present invention will now be more particularly described by way of example and with referenceto the accompanying drawings, in which: Figure 1 shows schematically a front elevation of a phased array radar head for use in the invention; Figure2 is a diagrammatic plan view representation of a zone to be scanned; and Figure 3 is a diagrammatic side elevational view ofthe zone to be scanned during low level flight.

Referring now to Figure 1, the preferred type of radar is a phased-array having at least one hundred and seventy five elements, each being gallium arsenide or a microwave tube. The wavelength ofthe radar is between 2 and 6 cm, preferably eitherX band at3cm orC band at 5.5 cm.

The elements are arranged in five zones each arranged to look at a selected area ahead ofthe aircraft. This is shown diagrammatically in Figure 2to an apprdximate scale of 4cms-- 1000ft. In orderto pick-up a bird,the resolution cell (area of radar beam at a particular range) fora range of the order of 1 mile should be approximtely 61,000 sq. ft. or a circle of diameter280ft. For shorter ranges, where the return echo would be stronger, a larger resolution cell can be used.

Zone 1 elements are arranged centrally of the phased array and are intended to look directly ahead ofthe aircraft (the seven innermost areas of Figure 2). There are preferably 50 such zone 1 elements, each having a resolution cell of c. 41500 sq. ft.

Arranged around the zone 1 elements are 25 zone 2 elements, each having a resolution cell of c. 61580 sq.ft.

and adapted to look atthe areas adjacent the innermost.

Zone 3 has 20 elements each of resolution cell 61550 sq. ft. Zone 4 has 38 elements of resolution cell 69220 sq. ft. and Zone 5 has 42 elements each of resolution cell 282780 sq. ft. The outer zone 5 cells can be largersince there is no need to probe at maximum range outside the direct line offlightofthe aircraft. The steps of Figure 2 are somewhat exagerated for purposes of explanation. In factthe area probed falls within a relatively smooth curve.

Itis not necessaryto pick-up birds in the outerzones so quickly as in the innerzones since there is far less chance ofthe birds entering the aircraft'sflight path, unless of course the aircraft is about to turn into or through an outer zone. The worst case, so far as detection is concerned, would be a bird flying from outsidethe scanned area directly into the path ofthe aircraft.

Birds fly slowly, relatively to the aircraft, and would be detected in one ofthe outer zones in good time forthe aircraftto take avoiding action before the bird reached a zone 1 position. Some of the fastest birds in flight are ducks which can fly at43 knots or72 ft. per sec., and falcons which can fly at mph ore 17 fit per sec. In a dive these speeds can increase respectively to55 knots or92.8 ft. per sec. and 120 mph or 176 ft. per sec. This latter figure can reasonably be assumed to be the fastestspeed with which a bird may close with an aircraft The table below shows the speed in feet (1 ft. = 0.3048m) travelled in a given number of seconds atvarious speeds.

BIRD AIRCRAFT S 80mph 120mph 200knots 400knots 600knots 800knots 1 117 176 337 675 1013 1351 2 234 358 674 1350 2026 2702 3 351 528 1011 2025 3039 4053 4 468 704 1348 2700 4052 5404 5 585 880 1685 3375 5065 6755 6 702 1056 2022 4050 6078 7 814 1232 2359 4725 8 936 1408 2696 5400 9 1053 1584 3033 6075 10 1170 1760 3376 11 1287 1936 3707 12 1404 2112 4044 13 1521 2288 4381 14 1638 2464 4718 15 1755 2640 5055 16 1872 2816 5392 The distance AO in Figure 2 is approximately 2,250 ft and even the fastest moving hawk, at 120 mph would take 13 secsto reach Ofrom A. In 13 seconds an aircraftatXwould have covered the 5000ft.XO distance if travelling at a speed slightly in excess of 200 knots, a verv low speed for low flying jet aircraft and one which allows ampletimefor avoiding action to betaken.

The distance from B tothe line XO is approximately 1500 ft. For the swiftest bird, this would take 8.5 seconds to cover. For the aircraft the distanceto cover would be 3000 ft. and again, in 8.5 seconds, the aircraft speed would need to be slightly less than 200 knots. Thus, it can be seen that the area not covered in the exterior zones is not important to the safety of the aircraft.

The phased array radar system is intended to operate one or possibly more elements at a time for a brief period, after which another one or more elements come into operation, and soon.

The time periods involved may be one or two thousandths of a second. Only selected ones ofthe elements need be activated. At high speeds such as 800 knots, the necessary beam angle for bird detection is 11", and so possibly only zones 1 and 2 elements need be activated. At 600 knots the beam angle increases to 190 when zone 3 elements can be switched in sequentially. The angles for lower speeds are: 400 knots - 28 degrees and 200 knots- 53 degrees, each respectively needing the use of more outerzones.

When the aircraft is about to make a turn, either right or left, or climb or descend, the elements relating to the space crossed by the proposed new flight path can be activated to check whether or not the manouvre is safe, from the point of view of a bird strike. At the same time, those elements relating to the opposite part ofthe beam, which will be outside the safe beam angle when the manoeuvre is completed, can be switched out.

Obviously, there is generally a need for morethan one element two be switched on at the sametime. In order to avoid confusion as to which element has detected a bird, the elements may emit signals of slightly different amplitudes. Alternatively the frequency of the signal emitted by each element may be slightly different.

Once a bird is detected by the radar, it must be analysed to determine whether or not it is harmful. There are a number of experimentally determined factors which can be useful in this respect. The size of the bird may be determinablefrom its radar echoing area, althoughthisto a large extent will vary depending on the attitude of the bird in relation to the aircraft.

Another observed fact in radar echoes of birds is that the received signal is modulated according to a number of factors, of which the most important isthewing-beatfrequency. The factors are collectively known as bird activity modulation. Certain other species of birds intersperse periods of wing-beating with either glide phases or phases where the wings are folded. These are also distinctive for the particular species. In general terms, smaller birds give higherfrequency modulations.

In one embodiment of the invention, a sampletrace of an average bird from each species likely to be encountered may be stored in a memory element of computing means and during the analysis of the signal, similarities between the received signal and the stored traces may be computed, whereby, with other information available, the species can be identified and the risk of damage to the aircraft computed.

Some examples of ascertained data for radar echoing areas and modulation for common bird species are given below.

BIRD SIDE HEAD MODULATION Starling 9sqcm 5sqcm 9.14-10.40 Hz Lapwing 20 sq cm 20 sq cm 4.30 - 7.07 Hz Pidgeon 22.5sqcm 8sqcm 5.63-5.71 Hz Rook 62 sq cm 1 sq cm 3.86- 5.80 Hz Gull (H) 75 sq cm 10 sq cm 3.10 - 4.69 Hz Duck 86 sq cm 10 sq cm 6.95-4.60 Hz Where there are two or more birds in the resolution cell ofthe radar, the modulation will be at an average frequency and the amplitude will vary at beat frequency. It is not however an impossibletaskto resolve such complexwaveforms.Clearly, where the radar probe reveals a flockof birds, it is advisable to take avoiding action since a number of small collisions occurring simultanteously may havethe same effect as a single larger one. During a migration there may beas many as 2500 birds pew square nautical mile.

The use of radar detection does have a number of problems. One such which is particularly applicable to low flying aircraft (for which the detection system is mostsuitable) isthat of ground clutter, i.e. unwanted echoes from the ground and trees and the like. Use of phased array radar minimises this problem. As can be seen from Figure 3, those elements the signals from which would be directed towards the ground, (shown as dashed lines) can be switched out. Which elements are to be switched out can be determined either as a function of altitude, or in conjunction with known terrain avoidance systems.

Other problems with radar detection may be that a number of birds together in one cell will produce a very complex modulated return which may not be easily analysable, and a single bird soaring on a thermal will keep its body and wings stillfora long period oftime and thus twill not give a modulated return.

In a preferred embodiment these problems are overcome by providing additionally to the radar detection system, an infra red detection system. This may also be incorporated into a multi-segment head so that received signals can be allocated to a particular area ahead of the aircraft. Another reason for using a multi-segment head is to allow certain segments to be shut down orfiltered when natural light levels become too high, or other large sources of heat appear in a particular direction. The filtering may be by means of electrically actuated photochromic glass.

It is only envisaged that a proportion of the IR segments will be out of action at a particular time, sincethesun is at a low angle only for a short period ofthe day, and in any event aircraft pilots are reluctantto flydirectly towards it.

The IR detection can identify the approximate size of birds bythe amount of heat received, and can identify movement. Itcannotdeterminethe rangeandthe preferred option isforthe IRtolocatea bird in an approximate position, when the radar elements relating to that position can be kept on. The bird can then be identified and its movement tracked by the radar.

Another advantage of additional IR detection is that it can distinguish immediately between a hailstorm (cold) and aflockof birds (warm)which can appearsimilarin a radarecho.

Itwill be appreciated thatthe time available fortaking avoiding action is extremely limited and forthis reason it is preferred notto involve the pilot butto have the avoiding action chosen and initiated directly by a computer also controlling the detection. For example atan aircraft speed of 800 knots and a range of detection of 5000ft. (the maximum),thetime allowed for avoidance is only 4seconds,which includes a certain amount ofcomputertimefortracking, computing probability of collision, and analysis of bird type.

It is known that startled birds tend often to fold theirwings and drop to avoid danger. The preferred avoiding actions aretherefore: 1. climb; 2. climb/bank/turn; and 3. bank/turn- - in that order. If a preferred option is blocked bythe presence offurther birds, a second option may be selected.Awarning lightorsignal may be given to the pilotto indicate that action is about to betaken.

Forflightin a straight line and a minimum distance of avoidance of 100ft. The angle through which the aircraftmustturn will vary dependant on the distance between bird and aircraft. For example at 5000ft. only a 1.1 degree turn is needed, while at 1000 ft., the angle needs to be 4 degrees.

If the aircraft is in course of manoeuvring when a bird is detected and each manoeuvre is onlyjustwithin the capabilities ofthe aircraft, the chosen avoiding action must not take the aircraft beyond those capabilities.

The computer controlling the system must have a very high speed to process inputs from the two sensing systems,upto 2000 inputs persecond (2 KHz) from each system. In addition tothis,it must be ableto controi switching of radar elements and switching of i.e. segments, provide signal noise/interference rejection, analysethe bird type from inputdata,compute likeiihood of a collision and issue avoidance commands.

One type ofcomputerthat will be applicable is the type in which the inputs are not processed sequentially as is conventional, but which comprise multiple microprocessors able to process the information simultaneously.

It is desirable that the avoiding action can be prevented in circumstances where unexpected course changes may prove more harmful than possible bird strikes. Such occasions areta keoff, landing, and in the case of military aircraft, combat. Forthese occasions a manual override switch may be provided, and the danger of a birdstrike is merely signified to the pilot, leaving him or her to decide on whether or not avoiding action is desirable.

Preferably the computer inputfrom the radar is converted from analog to digital information. This has additional benefits in that the IR input may possibly be given directly in digital form, and that itis easierforthe computer to distinguish ground clutter and the like from bird targets when the information is digital.

Claims (11)

1. An apparatus for use in an aircraftto assist avoidance of harmful birds, the apparatus comprising radar means mounted to the aircraft and disposed to probe an area ahead ofthe aircraft, meansto analysesignals received from said radar probe to determine therefrom whether a harmful bird is present in said area, and means responsive to the determination ofthe presence of a harmful bird to initiate a warning.

2. An apparatus as claimed in claim 1, wherein the warning comprises a command to control apparatus of the aircraftto take a predetermined avoiding action.

3. An apparatus as claimed in either claim 1 or claim 2, wherein the radar means comprises a phased array radar having a plurality of selectively energisable elements each adapted to probe a substantially separate part ofthe area ahead ofthe aircraft.

4. An apparatus as claimed in claim 3, wherein there are at least 175 elements.

5. An apparatus as claimed in either claim 3 or claim 4, wherein the elements are subdivided into a plurality ofzones, the elements of a firstzone being adapted to probe an area directly in frontofthe aircraft and the elements of each other zone being adapted to probe substantially concentric annular areas of increasing radius.

6. An apparatus as claimed in claim 5, wherein the elements of the first innermost zone each have an effective range greaterthan and a resolution cell area less than thatof each ofthe elements of the outerzones.

7. An apparatus as claimed in claim 6, wherein the effective range progressively decreases and the resolution cell area progressively increasesfortheelements of succeeding outerzones.

8. An apparatus as claimed in anyone ofthe preceding claims, further comprising infra detector means mounted to the aircraft and disposed to probe a substantially similar area ahead of the aircraft.

9. An apparatus as claimed in claim 8, wherein the infrared detector means comprises a multi-segmented head having a plurality of detectors each adapted to receive signals from a predetermined part of the area probed.

10. An apparatus as claimed in any one of the preceding claims, wherein the signal analysis means is computing means, to analyse signals received, firstly to discard extraneous signals, for example those generated by rain and other weather conditions or from the ground itself, and secondly to determine whether the signal represents a harmful bird or one which is not harmful.

11. An apparatus for use in an aircraftto assist avoidance of harmful birds substantially as described herein with reference to the accompanying. drawings.