These systems are used in the cockpits of civil and military aircraft
10 to present the pilot with essential information relating to piloting or navigation.
The information is displayed superimposed on the exterior landscape. These
systems are known notably by the English term "See-through HMD", "HMD"
being the acronym of "Head Mounted Display". They may be monocular or
binocular.
15 This type of system always comprises two main sub-assemblies,
the viewing system proper and a posture detection system allowing the
posture of the user's head to be ascertained perfectly with respect to a
known datum. Thus, it is possible to display information in a perfectly
determined zone in space.
20 The viewing system mainly comprises a micro-imager which
generates a synthetic image, relay optics and an optical combiner or mixer
which makes it possible to superimpose the image arising from the relay
optics on the exterior landscape.
Various techniques exist which make it possible to pinpoint an
25 object in space. It is possible to use electromagnetic detection. An emitter is
disposed in the fixed reference frame and a receiver in the moving reference
frame. It is also possible to use optical detection which may be passive or
active. In the latter case, the viewing device carries light-emitting diodes, the
position of whose emission is pinpointed by cameras. All these techniques
30 are known to the person skilled in the art. They are compatible with real-time
operation and adapt easily to the viewing system according to the invention.
One of the advantages of this type of system is that it is possible
to present information, notably symbology information, in a conformal
position, that is to say perfectly superimposed with the position that they
35 would occupy in the exterior landscape. Thus, it is possible to present the
basic piloting information superimposed perfectly on the exterior.
Conventionally, this information is gathered together in a view known by the
terminology "AD!", the acronym standing for "Attitude Director Indicator".
Basically, this view comprises an aeroplane mockup symbolically
representing the craft and symbolics representing the attitude and the speed
5 of the craft in terms of roll and pitch with respect to a terrestrial datum. This
symbolics comprises at least one artificial horizon line and a roll scale. It is
understood that, in order for this symbology to be easily interpretable, it must
lie on the axis of the aircraft. When an ADi configuration is presented on a
"See-through HMD", it also includes a symbol called the "Speed Vector", also
10 referred to as the "Flight Path Vector" and known by the acronym "FPV". This
symbol represents the trajectory of the aeroplane, that is to say the direction
towards which the aircraft is steering instantaneously. It therefore represents
the course or "track" parameter, known by the acronym "TRK" and slope or
"Flight Path Angle" parameter, known by the acronym "FPA". On the other
15 hand, the aeroplane mockup represents the direction of the nose of the
aircraft in terms of heading angle and trim angle. The principles described
hereinbelow are illustrated on the FPV, but they can apply to the aeroplane
mockup if the FPV is not represented in the ADI.
One of the difficulties in presenting piloting information in a head
20 viewing system is that, when the user turns their head, if the "ADI" symbolics
is represented conventionally, it exits the visual field thereof.
To alleviate this difficulty, "parking" algorithms exist which bring
the symbols required for piloting back to the field boundary. However, parking
these symbols has the effect of causing them to lose the coherence of the
25 information that they bear. For example, under a certain aircraft attitude
condition, the speed vector may be parked above the horizon line, whilst in
reality, it is situated below. Moreover, the representation of the symbol may
no longer be suitable for a particular moment of the mission or of the flight
phase.
30
The method according to the invention does not exhibit these
drawbacks. Indeed, the "attitude director indicator" can be represented in a
reference frame tied to the head support and, consequently, it is constantly in
the user's field of vision. More precisely, the subject of the invention is a
method of displaying an "attitude director indicator" in a head viewing system
for aircraft, the said head viewing system comprising:
- a head support bearing a viewing device;
- a detection of posture of the said head support;
5 - sensors for detecting the various parameters defining the
attitude of the said aircraft;
- means for computing and graphically generating the said
attitude in the said viewing device, the set of parameters
displayed in the form of symbols being termed the "attitude
10 director indicator", the said attitude director indicator being
displayed in a determined angular field;
Characterized in that, when the head support is oriented in a
determined direction making, with the horizon line and/or with the "speed
vector" of the aircraft, an angle greater than a first determined value, and/or
15 when at least one of the attitude parameters of the aircraft becomes greater
than a second determined value, the attitude director indicator is displayed in
a terrestrial reference frame or locally in a reference frame tied to the head
support and in the field of the viewing device.
Advantageously, the attitude director indicator comprises a central
20 symbol in the form of an aeroplane mockup representing the speed vector of
the aircraft, this mockup comprises a first central circle surrounded by two
symmetric straight dashes called winglets and surmounted by a third straight
dash perpendicular to the two previous dashes.
Advantageously, when the head support is oriented in a
25 determined direction making, with the horizon line and/or with the "speed
vector", an angle greater than a first determined value, the attitude director
indicator comprises a symbol representative of this situation.
Advantageously, the representative symbol is a second circle
whose angular diameter is a few degrees, the said second circle being
30 centred on the first circle of the aeroplane mockup.
Advantageously, when the head support is oriented in a
determined direction making with the "speed vector", an angle greater than a
first determined value, the three dashes of the mockup have as common
point the centre of the first circle.
Advantageously, when the angle of roll exceeds a second
determined value, a roll scale appears in the form of at least one circular arc,
the number of arcs or the dimension of the arcs or the thickness of the
dashes of the said arcs increasing with the increase in the roll, the said arcs
5 being centred on the first circle.
Advantageously, when the angle of pitch exceeds a second
determined value, a pitch symbol appears in the form of a chevron
comprising, inside these two branches, a travelling scale, the travel rate
being representative of the rate of variation of the pitch.
10
The invention will be better understood and other advantages will
become apparent on reading the following nonlimiting description and by
virtue of the appended figures among which:
Figure 1 represents a general view of a head viewing system
15 implementing the method according to the invention;
Figure 2 represents a first variant of the symbology implemented
in the method according to the invention;
Figure 3 represents a second variant of the symbology
implemented in the method according to the invention;
20 Figure 4 represents a third variant of the symbology implemented
in the method according to the invention;
Figure 5 represents a fourth variant of the symbology implemented
in the method according to the invention;
Figure 6 represents a fifth variant of the symbology implemented
25 in the method according to the invention;
Figure 7 represents a sixth variant of the symbology implemented
in the method according to the invention;
Figure 8 represents a seventh variant of the symbology
implemented in the method according to the invention;
30 Figure 9 represents an eighth variant of the symbology
implemented in the method according to the invention.
The head viewing system according to the invention is
represented schematically in Figure 1. It comprises:
- an equipped head support or headset C comprising an
optoelectronic display assembly V. This viewing assembly can be monocular
or binocular. When the head support or the headset is worn by a user, this
assembly gives a collimated image arising from a display. This image is
5 superimposed on the exterior landscape by an optical combiner or mixer;
- a posture detection system DDP for the head support or for the
headset making it possible to determine the position of the support or of the
headset in the reference frame of the aircraft. There exist various detection
systems which are well known to the person skilled in the art. Mention will be
10 made of magnetic-detection systems in which a receiver measures the
components of a known electromagnetic field and optical-detection systems
comprising an emitter and a receiver which is able to determine the position
and the orientation of this emitter by shape recognition. The position of the
aircraft in a terrestrial reference frame is itself known by means of various
15 sensors such as the inertial platform of the aircraft;
- an electronic assembly or a computer, not represented in Figure
1, ensuring the computation and the generation of a symbology S
superimposed on the exterior landscape by the optoelectronic display
assembly. This symboiogy generally comprises the basic information
20 required for piloting such as the various indications of the speed, of the
altitude and of the trim, the position of the horizon, etc. Conventionally, the
set of parameters defining the attitude of the aircraft is termed the "Attitude
Director Indicator", also known, as was stated, by the acronym "ADI". To
ensure this function, the various sensors of the aircraft provide the computer
25 with the information required. The headset orientation detection system gives
it the position information and orientation information making it possible to
display the symbology either in a conformal manner, that is to say in a
terrestrial reference frame independent of the movements of the aircraft and
of the movements of the headset, or in a non-conformal manner, that is to
30 say in a reference frame tied to the user;
- control means, generally one or more control posts making it
possible to select, to modify or to validate the information and the data
displayed by the viewing device. These control means can also be disposed
on the control stick or be activated by voice control.
Conventionally, the attitude director indicator is displayed in a
conformal position. One of the difficulties in presenting piloting information in
a head viewing system is that, when the user turns their head, if the "ADI"
symbolics is represented conventionally, it exits their visual field. That is to
5 say that, on a head movement, it is possible to lose the display of the FPV or
of the horizon line or of the roll scale which is a key element of the ADI when
banking is engaged. In the method according to the invention, the
representation of the FPV becomes, as a function of the direction of the head
and of the flight parameters, the support to the symbology of the ADI, it being
10 possible for this FPV representation to be tied to a terrestrial reference frame
or to the headset. The attitude director indicator can therefore be displayed
locally in a reference frame tied to the head support and in the field of the
viewing device.
The method according to the invention is therefore advantageous
15 when display in a conformal position is no ionger possible. Hence, this
method is implemented only, when the head support is oriented in a
determined direction making, with the horizon line and/or with the "speed
vector", an angle greater than a first determined value. It is also beneficial to
implement it, when at least one of the attitude parameters of the aircraft
20 becomes greater than a second determined value.
Moreover, it is beneficial that the ADI according to the invention
has a small visual "footprint". That is to say that it comprises a minimum
number of symbols. Consequently, the symbology comprises solely the
symbols that are indispensable to the ADI and/or the symbols that are
25 representative of a critical situation.
In the first typical case, the local ADI appears when the speed
vector or the horizon line become limited, typically when the pilot wishes to
look in a direction which positions the speed vector out-of-field. By "limited"
symbol is meant a symbol not represented in a conformal position. When the
30 pilot averts their gaze to perform a task other than piloting, the new
representation of these flight parameters starts with a small visual footprint
during nominal flight conditions and becomes augmented when the attitudes
of the aircraft deteriorate.
In the second typical case, the local ADI appears when the
35 attitudes of the aircraft become excessive as a function of parametrizable
7
thresholds. So as not to mask the exterior vision of the pilot potentially
accomplishing another task, the visual footprint level is gradual and
increases when the parameters of the aircraft deteriorate greatly.
Figures 2 to 9 illustrate, by way of examples, these various
5 configurations of symbologies S. To give an order of magnitude of the
angular dimensions of the various symbologies seen by the pilot, the circle
10 which appears in Figures 2, 3, 4 and 5 has an apparent angular diameter
of about 5 degrees. All these figures are to the same scale. The symbols
consist essentially of dashes whose angular thickness is of the order of a
10 milliradian or a few miliiradians. All these symbols can be represented in
monochrome or comprise several different colours. Generally, these
symbols are green in colour. The colour red can be reserved for critical
symbols.
All the Figures 2 to 9 are centred on an aeroplane mockup 1. It
15 represents the speed vector of the aircraft. This mockup comprises a first
central circle 2 surrounded by two symmetric straight dashes 3 called
winglets and surmounted by a third straight dash 4 perpendicular to the two
previous dashes.
20 Figures 2 to 5 illustrate the first typical case which corresponds to
the appearance of the AD! when the speed vector or the horizon line
become limited. These four figures are all surrounded by the circle 10 which
appears when the speed vector or the horizon line become limited. This
circle 10 is centred on the FPV 1. In these figures, the horizon line is
25 represented by a dashed line 5.
Figure 2 represents the simplest configuration. It comprises the
FPV 1 and the circle 10 indicating that the horizon line 5 is limited, the
horizon line has exited the display field. The three dashes 3 and 4 of the
FPV which are representative of the wings and of the fin are deployed,
30 indicating that only the horizon line is limited, the speed vector or FPV
having a nominal value. It is therefore still displayed in a terrestrial reference
frame. The absence of roll indication in this figure also signifies that the roll
remains within nominal limits. This limit is, for example, +/-10 degrees.
In Figure 3, the speed vector or FPV has a limited value. It is
35 displayed at the field boundary in the direction in which the head must turn
n
to "retrieve" it. The three dashes 3 and 4 of the FPV which are
representative of the wings and of the fin are then retracted and pass
through the centre of the circle 2. The absence of roll indication in this figure
also signifies that the roll remains within nominal limits.
5 in Figures 4 and 5, the roll has become more significant. Two roll
bars 20 whose inclination is representative of the value of the roll appear at
the periphery of the circie 10. A roll scaie 21 also appears. The angle of
inciination between the horizon bar and the roll bars is representative of the
angle of inclination of the speed vector with respect to the horizontal. This
10 angle is known by the acronym "FPA", standing for "Flight Path Angle".
in Figure 4, the three dashes 3 and 4 of the FPV which are
representative of the wings and of the fin are deployed, indicating that only
the horizon line is limited, the speed vector or FPV having a nominal value.
In Figure 5, the speed vector or FPV has a limited value. The three dashes 3
15 and 4 of the FPV which are representative of the wings and of the fin are
then retracted.
Figures 6 to 9 illustrate the second typical case which
corresponds to the appearance of the ADI when the attitudes of the aircraft
20 become excessive as a function of parametrizable thresholds. For greater
clarity, in these examples, the speed vector and the horizon line are not
limited and do not therefore appear in these figures.
Figures 6 to 8 illustrate the case of a roll becoming increasingly
significant. In Figure 6, the roll is around 10 degrees. As in Figure 5, the bars
25 20 and the roll scale 21 appear. In Figure 7, the roll is greater than 30
degrees. The roll scaie is accompanied by several concentric circular arcs
22, indicating to the pilot an excessive roll. In Figure 8, the roll is greater
than 60 degrees. The concentric circular arcs 22 get stronger. The symbol
composed of several concentric circular arcs makes it possible also to retain
30 the notion of the direction of roll when it approaches the limit values.
Thus, the number of arcs or the dimension of the arcs or the
thickness of the dashes of the said arcs increase with increasing roll, the
said arcs being centred on the mockup.
Figure 9 represents the symbology in the case where the pitch of
35 the aircraft becomes excessive. When the angle of pitch exceeds a
determined value, a pitch symbol appears in the form of a chevron 30
comprising, inside these two branches, a travelling scale 31, the travel rate
being representative of the rate of variation of the pitch. This information
gives the pilot a more precise feel of the dynamics of their aircraft during
5 more abrupt manoeuvres. If the pitch variation is very significant, it is
possible to anticipate the rate of vanation of the pitch so as to remain below
the limit values.
When the local ADI is displayed, the real horizon line is erased
around the local ADI so that the pilot cannot confuse the various types of
10 representation, one being conformal and represented by the standard ADI
and the other non-conformal and represented by the local ADI.

CLAIM
1. Method of displaying an "attitude director indicator" in a head
5 viewing system for aircraft, the said head viewing system comprising:
- a head support (C) bearing a viewing device (V);
- a detection of posture (DDP) of the said head support;
- sensors for detecting the various parameters defining the
attitude of the said aircraft;
10 - means for computing and graphically generating the said
attitude in the said viewing device, the set of parameters
displayed (S) in the form of symbols being termed the "attitude
director indicator", the said attitude director indicator being
displayed in a determined angular field;
15 characterized in that, when the head support is oriented in a
determined direction making, with the horizon line and/or with the "speed
vector", an angle greater than a first determined value, and/or when at least
one of the attitude parameters of the aircraft becomes greater than a second
determined value, the attitude director indicator is displayed in a terrestrial
20 reference frame or locally in a reference frame tied to the head support and
in the field of the viewing device.
2. Method of display according to Claim 1, characterized in that
the visual footprint of the attitude director indicator is gradual and increases
25 when the parameters of the aircraft deteriorate.
3. Method of display according to one of Claims 1 or 2,
characterized in that the attitude director indicator comprises a central
symbol (1) in the form of an aeroplane mockup representing the speed vector
30 of the aircraft, this mockup comprising a first central circle (2) surrounded by
two symmetric straight dashes (3) called winglets and surmounted by a third
straight dash (4) perpendicular to the two previous dashes.
4. Method of display according to one of Claims 1 or 2,
35 characterized in that, when the head support is oriented in a determined
l°
1
direction making, with the horizon line and/or with the "speed vector", an
angle greater than a first determined value, the attitude director indicator
comprises a symbol (10) representative of this situation.
5 5. Method of display according to Claim 4, characterized in that,
the representative symbol is a second circle whose angular diameter is a few
degrees, the said second circle being centred on the first circle of the
aeroplane mockup.
10 6. Method of display according to one of Claims 1 or 2,
characterized in that, when the head support is oriented in a determined
direction making with the "speed vector", an angle greater than a first
determined value, the three dashes of the mockup have as common point the
centre of the first circle.
15
7. Method of display according to one of Claims 1 or 2,
characterized in that, when the angle of roll exceeds a second determined
value, a roll scale (21) appears in the form of at least one circular arc, the
number of arcs or the dimension of the arcs or the thickness of the dashes of
20 the said arcs increasing with the increase in the roll, the said arcs being
centred on the first circle.
8. Method of display according to one of Claims 1 or 2,
characterized in that, when the angle of pitch exceeds a second determined
25 value, a pitch symbol appears in the form of a chevron (30) comprising,
inside these two branches, a travelling scale (31), the travel rate being
representative of the rate of variation of the pitch.