PILOTING ASSISTANCE SYSTEM FOR AN AERONEF , NOTABLY FOR
AIDING LANDING, DECK-LANDING AND NAVIGATION
5 The present invention relates to a piloting assistance system for an
aeronef, notably for aiding landing, deck-landing and navigation. The
invention addresses the field of aeronautics, and can be applied notably to
aeronef such as helicopters or drones.
10 Common missions for aeronef such as helicopters can be facilitated
by the implementation of various piloting assistance functions.
Firstly, navigation aid functions make it possible to measure and
determine the route of the aeronef to destinations or waypoints.
An aeronef such as a helicopter can likewise have functions on board
15 that can ensure servo-controlled stationary flight, allowing flight to be
maintained above a fixed point, for example for missions such as winching,
preparation for a phase of landing on a fixed area or a mobile platform,
rescue, etc.
It may likewise be invaluable for an aeronef such as a helicopter to be
20 equipped with landing aid functions , notably allowing estimation of the
distance between the helicopter and the ground, the inclines of the landing
area so as to prevent the helicopter from being unsteady upon touchdown,
since the centre of gravity of a helicopter is situated at a relatively high
position in the aeronef. Ideally , a landing aid function must allow the pilot to
25 assess the slopes of the landing surface and , by way of example , to visually
display them on a screen , since direct visualization of the landing surface
may be adversely affected by a screen of dust upon descent, this
phenomenon commonly being called "brownout". Ideally, a landing aid
function must be designed so as likewise to facilitate landing on ground or
30 objects having bumps , or configurations which compromise the stability of the'
helicopter on the ground . It may likewise be desirable for a landing aid
function to facilitate landing on moving platforms , for example ships or
moving vehicles . The reason is that helicopters sometimes need to land on
very precise areas , which are sometimes mobile and /or lack visibility.
35
2
As far as navigation aid functions are concerned, helicopters typically
use systems denoted by the abbreviation AHRS, standing for "Attitude and
Heading Reference Systems", which provide information relating to the
attitude and heading of the aeronef, from measurements coming from
5 gyroscopes or inertial units of various class B, with the information being
displayed, for example, by means of an integrated device of the type denoted
on the basis of the abbreviation IESI, standing for "Integrated Electronic
Standby Instrument". The AHRS may be associated with anemobarometric
sensors, with a satellite positioning device of GNSS type, on the basis of the
1o abbreviation standing for "Global Navigation Satellite System", and radio
altimeters, which typically operate in band C or use a laser beam.
As far as functions that can ensure servo-controlled stationary flight
are concerned, the fixed position of a helicopter cannot be servo-controlled
on a basis of the data from acceleration sensors or from gyrometers; the
15 reason is that a helicopter can drift at constant speed, for example, hence
with a constant orientation and zero acceleration, that is to say that cannot be
detected by this type of sensor. The information provided by a GNSS
receiver does not allow stationary flight to be ensured with sufficient quality
either, since the refreshing of the data and the integrity of the,data are not
20 compatible with this critical function in terms of safety of persons. Known
devices of navigation radar type, commonly denoted by the abbreviation
RDN, allow stationary flight to be ensured, from data coming from speed
sensors in three axes on the basis of ground speed. Furthermore, the
processing of the signal from RDN systems is based on the use of a phase
25 loop, allowing selection and filtering of the useful line of the signal before said
line is measured in terms of frequency and processed. This principle requires
the phase loop to be prepositioned in terms of frequency in order to select
the correct line. This phase loop management calls for complex calculation
means and has a certain number of risks, notably when the aeronef is
30 overflying areas of calm sea, implying that the energy received by the
secondary lobes of the antennas is higher than that received by the main
lobe.
As far as landing aid functions are concerned, there is no known
system which allows such a function for helicopters.
3
Thus, the aforementioned functions may be desirable within the
framework of piloting assistance for aeronef, notably helicopters, and, for
some of them, are implemented in known separate devices, or are
nonexistent.
5
It is an aim of the present invention to overcome this drawback by
proposing a piloting assistance system for aeronef which incorporates all of
the aforementioned functions.
10 To this end, the subject matter of the present invention is a piloting
assistance system for an aeronef, characterized in that it comprises
measuring means which are capable of taking distance measurements from
the aeronef to the ground, and speed measurements from the aeronef to the
ground, on at least three transmission and reception channels corresponding
15 to at least three respective axes, at least the three transmission channels
being independent.
In one embodiment of the invention, the measuring means may
comprise a radar system, comprising at least one transmission antenna
configured so as to produce at least three beams on said at least three
20 channels, at least one reception antenna configured to collect the signals
received as an echo, and radar management means configured to extract
speed and distance measurements from the aeronef to the ground from the
received signals, each distance being determined by measurement of the
frequency shift due to the delay between the signal received as an echo and
25 a transmitted signal, and each speed being determined by measurement of
the frequency shift between the transmitted signal and the signal received as
an echo.
In one embodiment of the invention, the radar system may be
configured such that the waveform of the transmitted signals comprises a first
30 frequency ramp increasing or decreasing with a constant slope over a
determined frequency band and spreading over a period corresponding to
half an illumination time, followed by a second frequency ramp respectively
decreasing or increasing with a constant slope over said determined
frequency band and spreading over a period corresponding to half the
35 illumination time, with the distance and speed on a channel being determined
4
in a single illumination, respectively from the sum of the differences between
the transmitted and received signals over a first period of time during which
the waveforms of the transmitted signals and of the received signals
simultaneously have the shape of an increasing ramp, and from the
5 difference between the differences between the transmitted and received
signals over a second period of time during which the waveforms of the
transmitted signals and of the received signals simultaneously have the
shape of a decreasing ramp.
In one embodiment of the invention, the transmission and reception
1o periods can be implemented simultaneously on the three channels, each
channel being associated with a different frequency of the transmission
signal.
In one embodiment of the invention, the transmission and reception
periods can be coordinated for the measurements taken in the three
15 channels, such that when the transmissions and receptions are implemented
in a given channel there is no transmission or reception implemented on the
other two channels.
In one embodiment of the invention, when there is no transmission or
reception implemented on a given channel test means can perform an
20 integrity test for said given channel.
In one embodiment of the invention, each reception channel
comprises a reception channel and a secondary reception channel, a
reception channel being linked to two secondary reception channels so as to
form a redundancy.
25 In one embodiment of the invention, a piloting assistance system may
furthermore comprise a function for determining a slope of the ground relative
to the aeronef from distance measurements from the aeronef to the ground.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise warning means, which are capable of being activated
30 when said slope of the ground relative to the aeronef exceeds a determined
threshold value.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise a man/machine interface, which is configured to show
a graphical representation of the ground relative to the aeronef that has been
35 established from said distance and speed measurements.
5
In one embodiment of the invention, a piloting assistance system may
furthermore comprise a function for estimating the distance between the
aeronef and the ground that is capable of determining an average height of
the aeronef from said distance measurements in the three axes.
5 In one embodiment of the invention, a piloting assistance system may
furthermore comprise means for crossing said distance and speed
measurements with the data from an inertial unit, with the piloting assistance
system forming an autonomous navigation system.
In one embodiment of the invention, a piloting assistance system may
1o furthermore comprise a digital ground model, and additional means for
crossing said relative distance and speed measurements from the aeronef to
the ground with the data from the digital ground model.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise a function for estimating the inclines of an approach or
15 landing area for the aeronef from said distance measurements in the three
axes.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise a function allowing servo-controlled stationary. flight of
the aeronef, by means of which function the fixed position of the aeronef,is
20 servo-controlled by the data from the speed and distance measurements in
the three axes.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise reception means in at least two beams, and means for
implementing centring by means of direction-finding or deviation sensing
25 measurement for a signal received from a positioning beacon arranged on
the ground or on a carrier transmitting a signal at a determined frequency, in
order to allow approach guidance.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise reception means in at least three beams, and means
30 for implementing centring by means of direction-finding or deviation sensing
measurement for a signal received from a positioning beacon arranged on
the ground or on a carrier transmitting a signal at a determined frequency, in
order to allow precision landing or deck-landing above the beacon, or in
proximity to the beacon.
6
In one embodiment of the invention, a piloting assistance system may
furthermore comprise reception means in at least two beams, and means for
implementing centring by means of direction-finding and/or deviation sensing
measurement for two or more signals received from positioning beacons
5 arranged on the ground or on a carrier transmitting signals at determined
frequencies, in order to allow precision landing or deck-landing relative to the
beacons.
In one embodiment of the invention, a piloting assistance system may
furthermore comprise means for determining a touchdown instant from
1o variations in the touchdown plane, which are determined from said distance
and speed measurements in the three axes.
An advantage of the present invention in the various embodiments
described is that it affords a single dedicated system for providing all of the
15 functions, the latter advantageously being able to be redundant with existing
functions.
Another advantage of the present invention is provided by the
independent and configurable nature of the transmission reception channels,
by having a response to the dual problem which aims to provide an
20 assistance system with both good resilience and good precision, so as
notably to allow deck-landing or landing assistance functions to be provided,
including on moving areas or steep areas, for example.
Another advantage of the present invention in the various
embodiments described is that it affords an autonomous system, which does
25 not require the installation of ground bases, and that is notably independent
of satellite navigation systems.'
Another advantage of the present invention is provided by the
independent and configurable nature of the transmission and reception
channels, allowing a response to the dual problem which aims to provide an
3o assistance system with both good resilience and good precision, so as
notably to allow deck-landing or landing assistance functions to be provided,
including on moving areas or steep areas, for example.
Another advantage of the present invention in the various
embodiments described is that it affords a system that is capable of operating
35 whatever the atmospheric conditions, and notably in brownout conditions.
7
Other features and advantages of the invention will emerge on reading
the description, which is provided by way of example, and which makes
reference to the appended drawings, in which:
5
- Figure 1 shows a perspective view providing an overview
illustration of an aeronef equipped with a piloting assistance
system according to an embodiment of the invention;
- Figure 2 shows a diagram providing an overview illustration of
10 a piloting assistance system according to an embodiment of
the invention;
- Figure 3 shows a diagram providing an overview illustration of
transmission and reception channels in a piloting assistance
system according to an embodiment of the invention;
15 - Figure 4 shows a curve illustrating the waveform of a signal
transmitted by a piloting assistance system according to an
embodiment of the invention;
- Figure 5 shows curves illustrating the waveforms of a signal
transmitted and a signal received by a piloting assistance
20 system according to an embodiment of the invention;
- Figure 6 shows a diagram providing an overview illustration of
a signal processing unit contained in a reception channel of a
piloting assistance system according to an embodiment of the
invention;
25 - Figure 7 shows a diagram providing an overview illustration of
a multichannel reception unit in a piloting assistance system
according to an embodiment of the invention;
Figure 8 shows a diagram providing an overview illustration of
an information processing unit contained in a piloting
30 assistance system according to an embodiment of the
invention;
Figure 9 shows a timing diagram illustrating a first example of
operation sequencing in a piloting assistance system
according to the present invention;
8
Figure 10 shows a timing diagram illustrating a second
example of operation sequencing in a piloting assistance
system according to the present invention.
5 The present invention proposes equipping an aeronef with a piloting
assistance system which allows the association of speed and distance
measurements from the aeronef to the ground, according to three distant
axes. The measurements can be taken by a radar comprising processing
means which allow simultaneous extraction of the distance and speed data,
1o for each illumination.
Figure 1 shows a perspective view providing an overview illustration of
an aeronef equipped with a piloting assistance system according to an
embodiment of the invention.
15 In the example shown in Figure 1, the aeronef is a helicopter 1, the
structure of which forms a main longitudinal axis XA and which has a piloting
assistance system according to the present invention on board. The piloting
assistance system comprises measuring means which are capable of taking
distance measurements from the aeronef to the ground,and speed
20 measurements from the aeronef to the ground on at least three channels
corresponding to at least three respective axes Da, Db and Dc. According to
the present invention, the three channels used for transmission and reception
are independent. Notably the independence of the channels used for
transmission allows greater flexibility, and allows longer illumination times to
25 be implemented for better measurement precision. The measurement means
may be formed by a radar' comprising a transmission antenna and a
reception antenna, for example, these two antennas advantageously being
able to form only a single antenna structure. The transmission channels may
be configured to form three transmission beams FA, FB and FC along the
30 axes Da, Db and Dc, respectively, said transmission beams illuminating the
ground in three illumination areas or "spots" A, B and C. By way of example,
the orientations of the axes Da, Db, Dc may be axially symmetrically with
respect to a main vertical axis ZA of the helicopter 1, which is perpendicular
to the main longitudinal axis XA.
35
9
Figure 2 shows a diagram providing an overview illustration of a
piloting assistance according to an embodiment of the invention.
A piloting assistance system comprises a radar system 20, for
example a radar of Doppler radar type , comprising a radar management
5 module 201 that allows the processing , sequencing , the interfaces and the
operational configurations of the radar system 20 to be implemented. The
use of a radar system, operating in frequency bands such as band X, for
example , makes it possible to ensure correct operation of the piloting
assistance system , whatever the atmospheric conditions , and in brownout
1o situations.
The radar management module 201 interchanges data with a
transmission module 203 , which is itself linked to at least one transmission
antenna 2030 . The transmission module 203 notably comprises waveform
generation modules called "GFOs". The GFOs generate the transmission
15 waves and the local waves are used for frequency transpositions, as
described in detail below . By way of example , the CFOs are formed by
programmable digital frequency generators . The transmission module 203
likewise comprises microwave units, notably implementing filtering and
amplification /attenuation functions.
20 The radar management module 201 likewise interchanges data with a
reception module 205, which is itself linked to at least one reception antenna
2050 . The reception module 205 comprises microwave units, notably
implementing filtering and amplification /attenuation functions , and digital
signal processing units. The processing may be implemented on the basis of
25 fast Fourier transforms or "FFTs": in that way, it is possible to avoid the risks
of frequency prepositioning error that are inherent in systems using a phase
loop, as described previously.
The radar management module 201 likewise interchanges data with
an interface module 207 , allowing the radar system 20 to be interfaced with a
30 man/machine interface or "MMI " 209, for example , and/or with an automatic
pilot system in the aeronef, not shown in the figure.
The main aim of the radar system 20 is to determine the speed of the
aeronef along its three displacement axes Ox , Oy, Oz, and the altitude of the
aeronef relative to the ground , at the same time. It allows determination of
35 the speeds along these three displacement axes , and of the distances of the
10
aeronef relative to the points of intersection of the aforementioned
transmission axes Da, Db, Dc, by measuring a frequency shift or "frequency
offset" and the delay in the echo signal relative to the signal transmitted to
the ground.
5 The transmission module 203 and the reception module 205 are
multichannel modules, the number of channels corresponding to the number
of beams from the radar, for example three. Each transmission or reception
channel is independent and can be associated with the corresponding
number of transmission or reception antennas. All of the antennas may
10 likewise be colocalized. A method allowing the same antenna to be used for
simultaneous transmission and reception is also possible.
Figure 3 shows a diagram providing an overview illustration of
transmission and reception channels in a piloting assistance system
15 according to an embodiment of the invention.
A transmission channel 33 comprise a transmission antenna module
3030, which may be formed by an antenna that is dedicated to this channel
or else which may be contained in a transmission antenna that is common to
a plurality of channels, and a transmission module 303, which is contained in
20 the transmission module 203 described previously with reference to Figure 2.
In a similar way, a reception channel 35 comprises a reception
antenna module 3050, which may be formed by an antenna that is dedicated
to this channel or else which may be contained in a transmission antenna
that is common to a plurality of channels, and a reception module 305, which
25 is contained in the reception module 205 described previously with reference
to figure 2.
A transmission channel 33 may comprise a GFO 3031 which allows
modification, for example on the basis of the mission of the pilot of the
aeronef, of the modulation of the transmitted waves, for example features of
30 the frequency ramps, the waveforms being described below with reference to
Figures 4 and 5. Each transmission channel 33 is independent and can be
configured on the basis of the mission.
A transmission channel 33 furthermore comprises a reference
oscillator 3033 which generates a reference frequency that is used for
35 frequency transposition, which is described below. The reference oscillator
3033 is linked to a frequency generation module 3037 and to a reference
frequency transposition module 3039. The GFO 3031 is linked to a
microwave transposition module 3035. The microwave transposition module
3035 generates the microwave signal from the frequency generated by the
5 frequency generation module 3037. The reference frequency transposition
module 3039 generates an OLR (local reference oscillator) wave which
allows the signal received as an echo to be transposed, as described below.
An attenuator 3032 may be arranged between the microwave transposition
module 3035 and the transmission antenna module 3030, allowing a
1o microwave transmission signal to be restored by adjusting the level of the
microwave signal generated by the microwave transposition module 3035.
A reception channel 35 comprises an automatic gain control or "CAG"
module 3051 which receives the microwave signal sensed by the reception
antenna module 3050, as an echo of a transmitted signal. The CAG module
15 3051 is linked to a microwave receiver 3053. The microwave receiver 3053 is
linked to an intermediate frequency transposition module 3055, the reference
frequency of which is that of the aforementioned OLR wave, which is
generated by the reference frequency transposition module 3039. The
transposition around an intermediate frequency allows the Signal to be
20 digitized. The use of one and the same reference oscillator for generating the
carrier of the. transmitted wave and the reception transposition frequency
makes it possible to ensure consistency between transmission and reception.
The frequency syntheses can be ensured by frequency multiplication.
The carrier frequency of the transmitted signal, denoted Fp, the local
25 oscillator reception frequency OLR and the intermediate frequency Fi satisfy
the following relationship: OLR`= Fp - Fi M.
The intermediate frequency transposition module 3055 is linked to an
analogue/digital converter or "ADC", 3057. The operation of the ADC 3057 is
3o described in detail below with reference to Figure 6. The digital signal coming
from the ADC 3057 is processed by a signal processing module 3059 which
restores the frequency offset owing to the delay in the echo and to the
Doppler effect. More details regarding the structure and the operation of the
signal processing module 3059 are described below with reference to Figure
35 6.
12
The use of digital processing to determine the frequency offset allows
modification of the transmission parameters without such modification
requiring changes to the hardware architecture of the reception channels.
Thus, a radar system according to the present invention can be adapted to
5 operational constraints.
The reception channels 35 are designed so as to be linear with low
noise.
Figure 4 shows a curve illustrating the waveform of a signal
1o transmitted by a piloting assistance system according to an embodiment of
the invention.
According to one particular feature of the present invention, it is
proposed that the speeds of the aeronef carrying the system and the
distances relative to the ground be obtained in a single illumination. To this
15 end, it is proposed that the transmitted signal be frequency-modulated by a
determined modulation allowing simultaneous extraction of the speed and
distance. In a nonlimiting example of the present invention, it is possible for
this modulation to be linear on the basis of two different slopes, or what is
known as "sawtooth" modulation, for example. Other waveforms can be
20 envisaged, for example nonlinear modulation of chirp type. The frequency of
the signal transmitted as a function of time is illustrated by Figure 4. The
waveform illustrated by Figure 4 is shown by way of nonlimiting example of
the present invention.
The transmitted signal can be modulated consecutively by a ramp of
25 increasing frequency followed by a ramp of decreasing frequency, or vice
versa. In the example illustrated by Figure 4, the increasing and decreasing
frequency ramps have the same absolute-value slope, and sweep the same
frequency band. Each ramp thus spreads over a duration equal to half the
illumination time, denoted Te. This modulation not only allows the speeds
3o and distances of the aeronef relative to the ground to be obtained but also
allows distance measurements to be. taken with a high level of precision.
The distance resolution, denoted Re, is defined by the following
relationship:
Re = C (2),
2.Bw
13
where c denotes the velocity of the wave and Bw denotes the
transmitted frequency band.
By way of example, in order to obtain a distance resolution of 4
centimetres, it is possible to choose a frequency ramp of 750 MHz.
5 Interpolation following FFT processing between the frequency cells may
allow the primary resolution of a ratio 6 to be improved. The interpolation
leads to an error of less than 10% on the calculated frequencies, allowing a
distance resolution of less than 4 cm to be obtained. Advantageously, the
generation of the ramps may be dynamically matched to the measured speed
10 and distance. Use of a higher passband for the precision measurement is
possible, for example.
The wave form chosen makes it possible to measure the speeds and
distances simultaneously, by means of a single frequency offset
measurement obtained from a single illumination. The extraction of
15 measurements from the signal received as an echo is clarified below with
reference to Figure 5.
Figure 5 shows curves illustrating the waveforms of a signal
transmitted and a signal received by a piloting assistance system according
20 to an embodiment of the invention.
A first curve 51 corresponds to the waveform of the transmitted
signal Se transmitted during an illumination time Te, already shown in Figure
4 described above. A second curve 52 corresponds to the waveform of the
received signal Sr. Typically, the second curve 52 has the same aspect as
25 the first curve 51, but the second curve 52 has a time shift, and a frequency
shift relative to the first curve 51. The starting point for the second curve 52
has a time shift by a period t corresponding to the delay between the
transmission and the reception, and a frequency shift by the Doppler;
frequency FD. During a first period =of time Trml, the two curves 51 and 52
3o are simultaneously increasing. During a second period of time Trm2, the two
curves 51 and 52 are simultaneously decreasing. If the starting point for the
first curve 51 is arbitrarily placed at the origin of the timelfrequency reference,
the frequency at the crest of the first curve 51 is equal to the passband of the
transmitted signal Bw. The crest of the second curve 52 has a frequency
35 equal to Bw + F0 as an ordinate.
14
A first frequency offset AF1 corresponds to the difference between the
two curves 51 and 52 during the first period of time Trml, and a second
frequency offset AF2 corresponds to the difference between the two curves
52 and 51 during the second period of time Trm2.
5 The frequency offsets can be expressed on the basis of the following
relationships, where k denotes the slope of the frequency ramps:
AF1 =Se-Sr=k.,r-F0 (3);
AF2=Sr-Se =k.ti+FD (4).
10
The sum of the two frequency offsets can thus provide the value of the
delay ti, and the difference between the two frequency offsets can provide the
value of the Doppler frequency F0.
Thus, on the basis of three transmit beams, it is possible to
15 simultaneously determine the speeds and distances along the three axes, the
speeds being determined by the following relationship (A denoting the
wavelength of the carrier of the transmitted signal):
V0 = F0.A/2 (5),
and the distances being determined by the following relationship:
20 D = ti.c (6).
The frequency offsets are determined by the signal processing module
3059 introduced previously with reference to Figure 3.
25 Figure 6 shows a diagram providing an overview illustration of a signal
processing unit contained in a reception channel of a piloting assistance
system according to an embodiment of the invention.
The input of a signal processing module 3059 receives the signal from
the ADC 3057. The input of the signal processing module 3059 can be
30 connected to a phase amplitude detection or "DAP" module 63 which digitally
transposes the signal on two quadrature channels I and Q. The DAP module
63 can be connected to a replica module 65 which substracts the replica of
the transmitted signal from the received signal in terms of frequency and
reduces the useful frequency band, and, in parallel with a phase sign module
35 66, restores a piece of information representing the phase sign of the signal
15
received as an echo. The replica module 65 is connected to a decimation
module 67 which reduces the number of samples required for the FFT
processing. The decimation module 67 is connected to an FFT module 69
which implements the FFT processing.
5 The ADC 3057 digitizes the microwave signal in the sampling period
Tech. The analogue signal is transposed on the intermediate frequency Fi for
which the value is higher or equal to the frequency band of the analogue
signal Bw. This frequency may typically be in the order of gigahertz. The
sampling frequency Fech and the frequency band Bw may be chosen so as
1o to satisfy the following relationships:
Fech > 2.Fi + Bw (7),
Bw = 2. Fi (8).
In this way, it is possible to avoid aliasing during sampling.
15 The DAP module 63 digitally transposes the signal on two quadrature
channels I and Q in order to recover the sign of the Doppler signal. The
digitization of the signal allows better single lateral band rejection, or better
quadrature, in relation to an analogue DAP.
The replica module 65 allows the replica of the transmitted signal to be
20 subtracted from the received signal in terms of frequency. This operation
allows determination of the frequency offset caused by the delay in the
received signal and by the frequency shift therein on account of the Doppler
effect. The result of this processing is contained in a band which is reduced
in relation to the input signals.
25 The decimation module 67 allows the number of samples required for
the FFT processing to be `reduced. The sampling frequency prior to
decimation is given by relationship (7) above.
The decimation ratio can be expressed on the basis of the following
relationship:
30 6 = Bw/2.Bw' (9),
where Bw' is the frequency band reduced by the replica module 65.
The reduced sampling range, denoted Tech', determines the spectral
processing band of the FFT module 69.
16
Figure 7 shows a diagram providing an overview illustration of a multichannel
reception unit in a piloting assistance system based on an embodiment of the
invention.
Figure 3, described previously, shows single transmission and
5 reception channels. The diagram shown by Figure 7 illustrates an example of
the arrangement of three channels in the signal reception unit, according to
one advantageous embodiment.
A multichannel reception unit 70 may comprise three independent
reception channels 71, 72, 73 connected to three reception antennas A, B
1o and C, respectively, these antennas being to be able to be separate
antennas or else being able to be colocalized. According to the
advantageous exemplary embodiment shown by the figure, the reception
channels 71, 72, 73 may be connected to three independent secondary
reception channels 71', 72', 73', respectively, such that the three reception
15 channels are independent and interchangeable. The first reception channel
71 may furthermore be microwave-coupled to the second secondary
reception channel 72', for example, the second reception channel 72 may
furthermore be microwave-coupled to the third secondary reception channel
73', and the third reception channel 73 may furthermore be coupled to the
20 first reception channel 71, for example. By virtue of this architecture, when a
channel is faulty, the coupled secondary channel can take over by virtue of
the microwave coupling of these channels. Moreover, this architecture has
the advantage of avoiding the use of switches, the reliability of which may be
incompatible with the operating safety constraints.
25 In order to prevent the spectra of two signals travelling by two different
channels from being superposed, the carrier wave used in each of the
channels upon transmission can be chosen so as to prevent the received
spectra from being superposed.
This architecture has the advantage of improving resilience, that is to
30 say its capability to self-repair or else to operate in a degraded mode, of a
radar system according to the present invention in relation to known radar
architectures.
17
Downstream of the secondary reception channels 71', 72', 73', each
reception channel may in itself be similar to the structure of a single reception
channel 35, described previously with reference to Figure 3.
The intermediate frequency transposition modules of the three
5 reception channels have respective reference frequencies OLR1, OLR2 and
OLR3. Advantageously, the ADCs in the three channels may be grouped
within the same physical module, controlled by control messages H COD.
Similarly, the signal processing modules in the three channels may be
grouped within the same physical module restoring the three frequency
10 offsets for the three channels.
Each signal processing module may be associated with a memory,
reseptively RAM.1, RAM.2 and RAM.3 for the three channels. The memories
RAM.1, RAM.2 and RAM.3 advantageously allow the data from the signal
processing to be recorded. By way of example, they are configured so as to
15 be able to record the data over a period corresponding to the maximum
duration of the missions, typically approximately two hours of flight. The
recorded data thus allow a posteriori analysis of the hours of flight,
implementation of flight situation simulations, or else of ground simulations of
different flight scenarios, for example.
20
Once the frequency offset measurements have been taken, and the
phase sign of the signal has been determined, the data can be utilized for
speed and distance calculations. This can be accomplished by an information
processing module, for example contained in the radar management module
25 201 described previously with reference to Figure 2.
Figure 8 shows a diagram providing an overview illustration of an
information processing unit contained in a piloting assistance system
according to an exemplary embodiment of the invention.
30 The frequency offsets restored by the signal processing modules of
the three channels, described above,' can form the input data for three units
for identifying the useful line 801, 802, 803 for the three respective channels,
these units likewise being able to be called "calm sea processing units".
Each unit for identifying the useful line 801, 802, 803 is connected to a
35 frequency cell interpolation unit 811, 812, 813, respectively, for each channel.
18
Each frequency cell interpolation unit 811 , 812, 813 is connected to a
calculation unit 821, 822 , 823 for the Doppler frequency FD and for the delay
time ti between transmission and reception , for each channel respectively.
The three calculation units 821, 822 , 823 are connected to a speed
5 calculation unit 830 and a distance calculation unit 840 . The speed
calculation unit 830 and the distance calculation unit 840 are connected to a
systematic error correction unit 850 , comprising a speed correction unit 851,
a distance correction unit 853 , and a memory 855 containing intrinsic
information associated with the physical configuration of the radar system,
1o notably with the antennas , with the base of the radar , etc. The corrected
speeds and distances restored by the information processing unit can be
communicated to the cockpit of the aeronef via an appropriate data bus.
The calculations can be performed as follows:
15 - Identification of the useful line by the units for identifying the
useful line 801 , 802, 803 of each frequency offset for each
channel , from an independent frequency threshold for the
amplitude of the signal;
- Interpolation by the frequency cell interpolation units 811, 812,
20 813;
- Discrimination of the Doppler frequency and of the delay in
the echo signal by the calculation units 821 , 822, 823;
- Calculation of the speeds and distances from the previous
results by the speed calculation unit 830 and the distance
25 calculation unit 840;
- Addition of the intrinsic corrective terms by the systematic
error correction unit 850.
The speeds and distances can be updated upon the refreshment of
30 one of the offset measurements from one of the reception channels.
The frequency cell interpolation units 811 , 812, 813 allow the precision
of flight parameters such as speed and altitude to be increased.
These calculations show the specificity of allowing simultaneous
processing of the information from the three channels . This allows the pilot of
35 the aeronef to know the speeds and the distances in relation to the ground in
19
the three axes. In this way, it is possible for a system according to the
present invention to incorporate functions which facilitate the flight missions,
such as stationary-flight or landing assistance, notably allowing the risks of
accident to be reduced. Examples of such functions are described below.
5
Advantageously, the transmission and reception sequences on the
various channels can be optimized.
In a first implementation example, it is possible to implement switched
transmissions and receptions on three channels.
10 In a second implementation example, it is possible to implement
switched transmissions and receptions on three channels, and to implement
permanent integrity or "self-test" test phases.
In a third implementation example, it is possible to implement
simultaneous transmissions and receptions on three channels.
15 The first second implementation examples mentioned above are
described below with reference to Figures 9 and 10, respectively.
With reference to Figure 9, the radar sequencing can be broken down
into a cycle having three steps:
20 - a first step of transmission of the signal;
a"second step of reception of the signal;
a third step of digital processing of the signal.
The cycle may be of "pipeline" type coordinated on three channels, as
shown by the timing diagram in Figure 9.
25 In normal operation , the radar transmits and receives the signals on
three alternate channels, numbered from 1 to 3, which are connected to
antennas A, B and C, respectively.
The signal processing on each of the channels may be shifted by a'
delay equivalent to the illumination time of each of the antennas.
30 The information processing may be carried out for each frequency
offset measurement coming from each of the three channels. The information
processing may,thus start as soon as the frequency offset measurement
taken on the first channel is available, and the phases of processing
information from the three channels can thus succeed one another without
35 interruption over one cycle.
20
Figure 10 shows a timing diagram illustrating the second embodiment
mentioned above, in which switched transmissions and receptions on three
channels are implemented, in the manner of the first implementation example
5 described with reference to Figure 9, and in which permanent self-test
phases are furthermore implemented.
When one channel is operating in transmission/reception mode, the
other two channels are inactive. This slot of inactivity can advantageously be
used to perform the flight self-tests, in accordance with the timing diagram
1o shown.
This embodiment including self-tests allows better resilience to be
conferred on the radar system.
According to the third embodiment mentioned above, it is possible to
15 implement transmissions and receptions on three channels.
In this embodiment, the three transmission channels can transmit a
wave simultaneously. The waves may thus be transposed in band X with a
carrier that is specific to each of the channels. The shift between the carriers
is chosen to be higher than the frequency band transmitted by each of the
20 channels in order to prevent aliasing at reception. Three reception channels
make it possible to process all of the information contained in the three echo
signals.
Another advantage of a system according to the present invention is
25 that it is progressive. By way of example, it is possible to perform updates for
the information processing system, more particularly for the systematic error
correction unit 850 described previously with reference to Figure 8, for
example, by loading a new piece of software into the memory 855.
30 Some examples of functions which can be implemented in a piloting
assistance system according to the invention are presented below.
In a first example, a piloting assistance system according to the
present invention may comprise a function which allows servo-controlled
35 stationary flight of the aeronef, that is to say that the fixed position of the
21
aeronef is servo-controlled by the data from the speed or distance
measurements in the three axes. The system can be configured such that all
existing functionalities of navigation radars are implemented, while providing
the additional advantage that the speed resolution can be improved, by virtue
5 of modulation of the illumination times which is made possible in a system
according to the present invention, said illumination times being able to be
increased in order to increase the speed resolution as and whenever
necessary, for example.
10 In a second example, a piloting assistance system according to the
present invention may comprise a function for assessing the distance
between the aeronef and the ground, making use of the measurements of
distances permitted by the three beams in order to determine an average
height of the aeronef.
15 A piloting assistance system according to the present invention may
likewise comprise a function for assessing the slope of the ground in relation
to the aeronef from the measurements of distances permitted by the three
beams.
20 In a third example, a piloting assistance system according to the
present invention may comprise a function for assessing the inclines of the
landing area in order to prevent the aeronef from being unsteady upon
touchdown. The position of the ground may be defined by measurements of
attitude for the aeronef from dedicated sensors in combination with
25 measurements of the distances at three points from the three beams.
The precision may typically be chosen to be less than 4 cm in order to
obtain the minimum required incline precision.
In this way, a piloting assistance system according to the present
invention can allow landings or deck-landings in the best conditions, and
3o notably landings or deck landings parallel to the landing area.
In a fourth example, a piloting assistance system according to the
present invention may comprise a function for visually displaying the landing
surface, via suitable visual display means or a man/machine interface
35 suitably configured to this end, for example via the MMI 209 described
22
previously with reference to Figure 2 or via a display device arranged in the
cockpit of the aeronef. By way of example, when the aeronef is descending,
the X, Y position in relation to the ground can be maintained by a speed
servo-control, by virtue of the measurements of speeds in the three axes as
5 permitted by the radar system. Advantageously, this information may be
rendered redundant by information from a satellite positioning system. The
distances of the aeronef in relation to the ground which come from the three
beams from the radar system make it possible to control the height and
attitude of the aeronef in relation to the ground, and the visual display means
1o can allow the pilot to visually display the situation.
In a fifth example, a piloting assistance system according to the
present invention may comprise a function which makes it possible to prevent
the aeronef from landing on bumps or on objects which compromise the
15 stability of the aeronef on the ground. Recordings of the measurements of
heights from the beams when the aeronef is descending can allow a
topography of the ground to be constructed, the term "ground" being intended
to be understood in the widest sense of the word, and being able to defined
by the surface of objects such as vehicles, or highly inclined surfaces such as
20 cliffs or mountain sides. The topography obtained in this manner can be
compared with the landing points or support points of the aeronef, and
warnings can be generated in the event of incompatibility.
In a sixth example, a piloting assistance system according to the
25 present invention may comprise a function allowing facilitation of landings on
moving platforms. The trim of`the aeronef can be adapted to inclines of the
landing platform by virtue of a trim measurement from dedicated sensors.
The distances in relation to the ground which come from the three beams of
the radar system may thus allowcontrol of the height and attitude of the
30 aeronef in relation to the ground. The situation can thus be presented to the
pilot by means of a suitably configured man/machine interface, for example
the MMI 209 described previously with reference to Figure 2.
Advantageously, the determination means can allow evaluation of a
touchdown instant on the basis of the variations in the touchdown plane,
35 which are determined from said measurements of distances and speeds in
23
the three axes. By way of example, French patent application published
under the reference FR 2944128 describes a method for assisting
deck-landing, according to which a command can be sent to the aeronef in
order to start a descent to a deck-landing point, when the height of the
5 landing platform is at the maximum of a typical curve representing the height
of the platform as a function of time when the aeronef is in a position for
preparation for the deck-landing phase, at a first instant. The aeronef must
thus move sufficiently rapidly to contact the deck-landing point at a second
instant, preferably when the platform is at its lowest point, its heave speed
10 being roughly zero at this second instant. When the aeronef touches down
during the downward phase of the heave of the platform, the impact is
dampened; when the aeronef touches down at the aforementioned second
instant, it can be likened to the case of a landing. Preferably, the refresh rate
for the information transmitted to the aeronef is of the order of at least ten
15 times the frequency of the movements undergone by the mobile platform, in
order to correctly anticipate the right deck-landing moment and to be able to
frequently readjust the trajectory of the aeronef until the deck-landing.
The system according to the invention described in the
20 aforementioned patent application FR 2944128 makes it possible notably to
determine, from the platform, the position of the aeronef and the incline of the
platform and to transmit guidance commands to the aeronef in order to allow
it to touch down safely.
25 Furthermore, it should be noted that a system according to the present
invention makes it possible to determine the position and the incline of the
deck-landing platform from the aeronef. Advantageously, the aeronef may be
independent in these measurements. This allows a reduction in the costs of
equipping the platform and of transmission between the platform and the
30 aeronef. This reduction may be considered when an aeronef is able to land
on several platforms. The reliability of the system is likewise increased.
In a seventh example, a piloting assistance system according to the
present invention may comprise a function allowing stationary flight or
35 landing on a designated area on the ground by an operator. By way of
24
example, an operator can designate the point of approach and landing by
means of one or more radio beacons, which are positioned. The piloting
assistance system may thus be configured to guide the aeronef in relation to
the radio beacon by means of direction-finding or angular-deviation
5 measurement between two or three beams formed at reception by the radar
system.
One or more radio beacons can likewise be released by the pilot at
one or more points in all atmospheric conditions, including in brownout
10 situations.
On the basis of the measurements taken by the radar system and one
or more beacon(s), suitable means can allow extrapolation of the movements
of the platform on which the aeronef needs to touch down to be implemented.
15 It is thus rendered possible to determine the optimum point of touchdown for
the aeronef, and to allow the display of information corresponding thereto to
the pilot, or else to control an automatic pilot device as a result.
By way of example, the system may comprise reception means in at
least two beams, and means for implementing centring by means of
20 direction-finding or deviation sensing measurement for a signal received from
a positioning beacon arranged on the ground or on a carrier transmitting a
signal at a determined frequency, in order to allow approach guidance. In
such an embodiment, phases of listening to the signal transmitted by the
beacon may come in between successive transmission phases according to
25 the at least three beams sequentially or simultaneously on the three beams.
Then again, the system may comprise reception means in at least
three beams, and means for implementing centring by means of directionfinding
or deviation sensing measurement for a signal received from a
positioning beacon arranged on the ground or on a carrier transmitting a
30 signal at a determined frequency, in order to allow precision landing or
deck-landing above the beacon, or in proximity to the beacon.
As another advantage, the system may comprise reception means in
at least two beams, and means for implementing centring by means of
direction-finding or deviation sensing measurement for two or more signals
35 received from positioning beacons arranged on the ground or on a carrier
25
transmitting signals at determined frequencies, in order to allow precision
landing or deck-landing relative to the beacons.
Advantageously, a system according to one of the embodiments of the
invention makes it possible to do away with satellite positioning devices if it
5 comprises appropriate means for crossing the measurements of speeds and
distances with the data from an inertial unit, even of relatively low precision,
for example with the data from a system of AHRS type as mentioned above.
Advantageously, a system according to one of the embodiments of
the invention may comprise crossing means which allow a navigation control
1o centre to be reset on the basis of the measurements of the speeds and
distances.
Advantageously, a system according to one of the embodiments of the
invention may furthermore comprise additional crossing means allowing with
a digital ground model, usually denoted by the abbreviation "NMT. By way of
15 example, such crossing allows consolidation of the measured data, or else
an increase in the precision of the navigation, or even detection of objects or
vehicles which are present on an area, for example.
It should be noted that in the embodiments described by way of
example above, the measuring means used are radar-type means; however,
20 other means may be used, such as radio altimeters, optical measuring
means or sound measuring means, for example.
26
CLAIMS
1- Piloting assistance system for an aeronef (1), comprising
measuring means (20) which are capable of taking distance
5 measurements from the aeronef (1) to the ground, and speed
measurements from the aeronef (1) to the ground, on at least three
transmission (33) and reception (35) channels corresponding to at least
three respective axes (Da, Db, Dc), at least the three transmission
channels (33) being independent.
10
2- Piloting assistance system according to Claim 1, characterized
in that the measuring means comprise a radar system (20), comprising
at least one transmission antenna (2030) configured so as to produce at
least three beams on said at least three channels, at least one reception
15 antenna (2050) configured to collect the signals received as an echo,
and radar management means (201) configured to extract speed and
distance measurements from the aircraft (1) to the ground from the
received signals, each distance being determined by a measurement of
the delay between the signal received as an echo and a transmitted
20 signal, and each speed being determined by a measurement of the
frequency shift between the transmitted signal and the signal received
as an echo.
3- Piloting assistance system according to Claim 2, characterized
25 in that the radar system (20) is configured in such a way that the
waveform of the transmitted signals comprises a first frequency ramp
increasing or decreasing with a constant slope over a determined
frequency band and spreading over a period corresponding to half an
illumination time (Te), followed by a second frequency ramp respectively
30 decreasing or increasing with" a constant slope over said determined
frequency band and spreading over a period corresponding to half the
illumination time (Te), with the distance and speed on a channel being
determined with a single illumination, respectively from the sum of the
differences (®F1, 4F2)"between the transmitted (Se) and received (Sr)
35 signals over a first period of time (Trml) during which the waveforms of
the transmitted signals and of the received signals simultaneously have
27
the shape of an increasing ramp , and from the difference between the
differences (®F1, AF2) between the transmitted (Se) and received (Sr)
signals over a second period of time (Trm2) during which the waveforms
of the transmitted signals and of the received signals simultaneously
5 have the shape of a decreasing ramp.
4- Piloting assistance system according to any one of the
preceding claims, characterized in that the transmission and reception
periods are implemented simultaneously on the three channels, each
10 channel being associated with a different frequency of the transmission
signal.
5- Piloting assistance system according to Claim 4, characterized
in that when there is no transmission or reception implemented on a
15 given channel, test means perform an integrity test of said given
channel.
6- Piloting assistance system according to any one of Claims 2 to
5, characterized in that each reception channel comprises a reception
20 channel (71, 72, 73) and a secondary reception channel (71', 72', 73'), a
reception channel (71, 72, 73) being linked to two secondary reception
channels (71', 72', 73') so as to form a redundancy.
7- Piloting assistance system according to any one of Claims 3 to
25 6, characterized in that it furthermore comprises a function for
determining a slope of the ground relative to the aeronef (1) from
distance measurements from the aeronef (1) to the ground.
8- Piloting assistance system according to Claim 7, characterized
30 in that it furthermore comprises warning means , which are capable of
being activated when a slope of the ground relative to the aircraft
exceeds a determined threshold value.
35 9- Piloting assistance system according to any one of the
preceding claims, characterized in that it furthermore comprises a
man/machine interface (209), which is configured to show a graphical
28
representation of the ground relative to the aeronef ( 1) that has been
established from said distance and speed measurements.
10- Piloting assistance system according to any one of the
5 preceding claims , characterized in that it furthermore comprises a
function for estimating the distance between the aeronef ( 1) and the
ground that is capable of determining an average altitude of the aeronef
( 1) from said distance measurements in the three axes.
10 11- Piloting assistance system according to any one of the
preceding claims , furthermore comprising means for crossing said
distance and speed measurements with the data from an inertial unit,
with the piloting assistance system being an autonomous navigation
system.
15
12- Piloting assistance system according to any one of the
preceding claims , characterized in that it furthermore comprises a digital
ground model , and additional means for crossing said relative distance
and speed measurements from the aeronef ( 1) to the ground with the
20 data from the digital ground model.
13- Piloting assistance system according to any one of the,
preceding claims, characterized in that it furthermore comprises a
function for estimating the inclines of an approach or landing area for
25 the aircraft from said distance measurements in the three axes.
14- Piloting assistance system according to any one of the
preceding claims , characterized in that it furthermore comprises a
function allowing servo -controlled stationary flight of the aeronef (1), by
30 means of which function the f ixed %position of the aircraft ( 1) is servocontrolled
by the data from the speed and distance measurements in
the three axes.
15- Piloting assistance system according to any one of the
35 preceding claims , ' characterized in that it furthermore comprises
reception means in at least two beams , and means for implementing
29
centring by means of direction-finding or deviation sensing
measurement of a signal received from a positioning beacon arranged
on the ground or on a carrier transmitting a signal at a determined
frequency, in order to allow approach guidance.
5
16- Piloting assistance system according to any one of the
preceding claims, characterized in that it furthermore comprises
reception means in at least three beams, and means for calculating
centring by means of direction-finding or deviation sensing
10 measurement of a signal received from a positioning beacon arranged
on the ground or on a carrier transmitting a signal at a determined
frequency, in order to allow precision landing or deck-landing above the
beacon, or close to the beacon.
15 17- Piloting assistance system according to any one of the
preceding claims, characterized in that it furthermore comprises
reception means in at least two beams, and means for calculating
centring by means of direction-finding and/or deviation sensing
measurement of two or more signals received from positioning beacons
20 arranged on the ground or. on a carrier transmittinc, signals at
determined frequencies, in order to allow precision landing or
deck-landing relative to the beacons.
18- Piloting assistance system according to any one of the
25 preceding claims, furthermore comprising means for determining a
touchdown instant from variations in the touchdown plane, which are
determined from said distance and speed measurements in the three
axes.