Note: Descriptions are shown in the official language in which they were submitted.
,
,
METHOD AND SYSTEM FOR DETERMINING A RECIRCULATION EFFECT
FROM AN OBSTACLE ON A MAIN ROTOR INDUCED VELOCITY OF A
SIMULATED ROTORCRAFT
TECHNICAL FIELD
The present invention relates to the field of rotorcraft simulators, and more
particularly to
the determination the recirculation effects from nearby obstruction(s) on the
main rotor
induced velocity of a simulated helicopter.
BACKGROUND
The safe and efficient flight operation of modern helicopters has many
demanding aspects
for the crew and requires an extensive amount of training. This training on
the actual
aircraft can be costly and time consuming and involves a certain degree of
risks. Flight
simulators have been developed to alleviate some of these constraints and
their level of
fidelity has consistently improved over the years. In a typical training
scenario, pilots who
fly simulators can observe obstacles in the scene through a visual system. The
latter is built
based on databases that contain the topography of the terrain and physical
structures such as
buildings, walls, trees, bridges, etc. One challenge of creating a complete
simulation is the
interaction of the simulated aircraft with its simulated environment
represented through the
visual system and the weather selected by the instructor (winds, turbulence,
etc.). It is
possible to have the weather interact with the visual system and the typical
method used is
to generate a series of computational fluid dynamics (CFD) solutions that pre-
calculate the
flow and turbulence fields around the various structures contained in the
visual database.
Although they may generate precise solutions, CFD methods are costly and
usually do not
take into account the effects of the helicopter itself on the flow fields. For
instance and as
illustrated in Figure 1, the helicopter main rotor downwash that consists of a
downward
airflow that can interact with the ground and surrounding obstructions as
illustrated in
Figure 1. As illustrated in Figure 1, the main rotor 10 of a helicopter 12
generates a
downward airflow 14 which can be reflected by the ground 16 and a vertical
structure 18 so
as to be re-ingested by the main rotor 10. This interaction causes a
recirculation of the main
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rotor downwash that can increase the amount of downwash 20 on the side of the
vertical
structure in comparison to the downwash 22 on the opposite side of the rotor.
The main
rotor recirculation leads the following adverse effects: a reduction of the
overall helicopter
performances and un-commanded changes in the helicopter pitch and bank angles,
which
result in the helicopter being momentarily attracted by the vertical structure
until the pilot
takes corrective actions.
The recirculation effects caused by the helicopter interactions with nearby
structures cannot
be captured in static CFD solutions because of the dynamic nature of the
phenomenon, and
of the infinite amount of possible helicopter positions, heading, height above
ground, main
rotor thrust, etc. However, simulating such recirculation effects may be
important to
provide a realistic training.
Therefore, there is a need for an improved method and system for determining
an airflow
velocity at a main rotor of a simulated helicopter in a simulation.
SUMMARY
According to a first broad aspect, there is provided a computer-implemented
method for
determining an effect of a simulated obstacle on a main rotor induced velocity
of a
simulated rotorcraft in a simulation, comprising: receiving an aircraft
airspeed of the
simulated rotorcraft and a height above ground for the simulated rotorcraft;
generating a
line of sight vector having a source position located on the simulated
rotorcraft, a direction
and a given length; determining a distance between the simulated obstacle and
the
simulated rotorcraft using the line of sight vector, the distance being at
most equal to the
given length of the line of sight vector; determining a recirculation induced
airflow velocity
using the distance between the simulated obstacle and the simulated
rotorcraft, the aircraft
airspeed and the height above ground, the recirculation induced airflow
velocity being
caused by a downwash recirculation flow generated by the simulated obstacle;
and
outputting the recirculation induced airflow velocity.
In one embodiment, the direction of the line of sight vector corresponds to an
azimuth
angle.
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. ,
In one embodiment, the line of sight vector is parallel to an Earth horizontal
plane.
In one embodiment, the source position is located along the rotation axis of
the main rotor
of the simulated rotorcraft.
In one embodiment, the source position is located on a hub of the main rotor
of the
simulated rotorcraft.
In one embodiment, the method further comprises varying the azimuth angle of
the line of
sight vector.
In one embodiment, the method further comprises varying a position of the
source position
along a rotation axis of the main rotor of the simulated rotorcraft.
In one embodiment, said generating the line of sight vector comprises
generating a plurality
of line of sight vectors each having a respective source position located on
the simulated
rotorcraft, a respective azimuth angle and a respective length.
In one embodiment, said determining the distance between the simulated
obstacle and the
simulated rotorcraft comprising determining a respective distance between each
respective
source position and the simulated obstacle.
In one embodiment, the respective length is identical for each one of the
plurality of line of
sight vectors.
In one embodiment, the respective source position is located along a rotation
axis of the
main rotor of the simulated rotorcraft.
In one embodiment, the respective source position is located along a rotation
axis of the
main rotor of the simulated rotorcraft.
In one embodiment, at least two of the plurality of line of sight vectors have
a same source
position and a different azimuth angle.
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.,
In one embodiment, at least two of the plurality of line of sight vectors have
a different
source position and a same azimuth angle.
In one embodiment, said determining the distance between the simulated
obstacle and the
simulated rotorcraft comprises: accessing a visual database containing a
topography of a
simulated terrain and simulated physical structures; identifying the simulated
obstacle as
being the closest object from the source position along a direction defined by
the azimuth
angle, the closest object being one of a part of the simulated terrain and one
of the
simulated physical structures and a distance between the closest object and
the source
positon being at most equal to the given length of the line of sight vector;
and determining a
distance between the source position and the closest object, thereby obtaining
the distance
between the simulated obstacle and the simulated rotorcraft.
According to a second broad aspect, there is provided a system for determining
an effect of
a simulated obstacle on a main rotor induced velocity of a simulated
rotorcraft in a
simulation, comprising: a communication unit for at least one of receiving and
transmitting
data, a memory and a processing unit configured for executing the steps of the
above
method.
According to a further broad aspect, there is provided a system for
determining an effect of
a simulated obstacle on a main rotor induced velocity of a simulated
rotorcraft in a
simulation, comprising: a vector module configured for generating a line of
sight vector
having a source position located on the simulated rotorcraft, an azimuth angle
and a given
length; a calculation module configured for: receiving a distance between the
simulated
obstacle and the simulated rotorcraft, an aircraft airspeed of the simulated
rotorcraft and a
height above ground for the simulated rotorcraft; determining a recirculation
induced
airflow velocity using the distance between the simulated obstacle and the
simulated
rotorcraft, the aircraft airspeed, the height above ground and the distance
between the
simulated obstacle and the simulated rotorcraft, the recirculation induced
airflow velocity
being caused by a downwash recirculation flow generated by the simulated
obstacle and the
distance being at most equal to the given length of the line of sight vector;
and outputting
the recirculation induced airflow velocity.
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.`
In one embodiment, the direction of the line of sight vector corresponds to an
azimuth
angle.
In one embodiment, the system further comprising a distance module configured
for
determining the distance between the simulated obstacle and the simulated
rotorcraft using
the line of sight vector.
In one embodiment, the line of sight vector is parallel to an Earth horizontal
plane.
In one embodiment, the source position is located along the rotation axis of
the main rotor
of the simulated rotorcraft.
In one embodiment, the vector module is further configured for varying the
azimuth angle
of the line of sight vector.
In one embodiment, the vector module is further configured for varying a
position of the
source position along a rotation axis of the main rotor of the simulated
rotorcraft.
In one embodiment, the vector module is configured for generating a plurality
of line of
sight vectors each having a respective source position located on the
simulated rotorcraft, a
respective azimuth angle and a respective length.
In one embodiment, the distance between the simulated obstacle and the
simulated
rotorcraft comprising a respective distance between each respective source
position and the
simulated obstacle.
In one embodiment, the respective length is identical for each one of the
plurality of line of
sight vectors.
In one embodiment, the respective source position is located along a rotation
axis of the
main rotor of the simulated rotorcraft.
In one embodiment, the respective source position is located along a rotation
axis of the
main rotor of the simulated rotorcraft.
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In one embodiment, at least two of the plurality of line of sight vectors have
a same source
position and a different azimuth angle.
In one embodiment, at least two of the plurality of line of sight vectors have
a different
source position and a same azimuth angle.
In one embodiment, the distance module is configured for: accessing a visual
database
containing a topography of a simulated terrain and simulated physical
structures;
identifying the simulated obstacle as being the closest object from the source
position along
a direction defined by the azimuth angle, the closest object being one of a
part of the
simulated terrain and one of the simulated physical structures and a distance
between the
closest object and the source positon being at most equal to the given length
of the line of
sight vector; and determining a distance between the source position and the
closest object,
thereby obtaining the distance between the simulated obstacle and the
simulated rotorcraft.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will become apparent
from the
following detailed description, taken in combination with the appended
drawings, in which:
Figure 1 illustrates a recirculation of the downwash caused by a main rotor of
a helicopter
near an obstruction or obstacle, in accordance with the prior art;
Figure 2 is a flow chart of a method for determining an airflow velocity at a
main rotor of a
simulated helicopter, in accordance with an embodiment;
Figure 3 illustrates the distribution of line of sight vectors within a same
azimuth plane
when a simulated helicopter is adjacent to an obstacle, in accordance with an
embodiment;
Figure 4 illustrates the distribution of line of sight vectors within five
parallel planes to the
Earth horizontal plane when the simulated helicopter is adjacent to an
obstacle, in
accordance with an embodiment;
Figure 5 is a block diagram of a system for determining an airflow velocity at
a main rotor
of a simulated helicopter, in accordance with an embodiment;
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.`
Figure 6 is a block diagram of a processing module adapted to execute at least
some of the
steps of the method of Figure 2, in accordance with an embodiment.
It will be noted that throughout the appended drawings, like features are
identified by like
reference numerals.
DETAILED DESCRIPTION
Figure 2 illustrates a computer implemented method 30 for determining an
effect of a
simulated obstacle on a main rotor induced velocity of a simulated helicopter,
i.e.
determining a recirculation induced airflow velocity at a main rotor of a
simulated
helicopter caused by an obstruction or obstacle. The method 30 is performed by
a computer
machine provided with communication means, a processing unit and a memory.
The simulation is configured for training a user to use a helicopter. Images
of an outdoor
are displayed on a display and the displayed images may correspond to what
would be seen
by the user if he would be within a real helicopter.
The simulator used for providing the simulation to the user comprises at least
a display on
which the simulated images are to be displayed, instruments for allowing the
user to control
the simulated helicopter and a simulation engine configured for generating the
simulation
using the commands received from the instruments and displaying the generated
simulation
images on the display. The simulator further comprises a database having
stored thereon at
least topography information about the simulated terrain and simulated
structures such as
buildings, walls, trees, bridges, and moving entities such as landable ships,
and/or the like.
For example, the database may contain information such as the position
information,
dimension information, information about the material from which a structure
is made,
and/or the like.
At step 32, information about the simulated helicopter is received. The
information
comprises the initial airflow velocity at the main rotor of the simulated
helicopter, the
aircraft airspeed of the simulated helicopter and the height above ground for
the simulated
helicopter. In one embodiment, the information about the simulated helicopter
is sent by the
simulation engine and this information may be stored in the database along
with other
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,
information such as the topography information. In one embodiment, the method
30 may
further comprise a step of sending a request for information about the
simulated helicopter
to the simulation engine. In this case, the simulation engine transmits the
information about
the simulated helicopter upon receipt of the request.
At step 34, a line of sight vector is generated. A line of sight vector is
defined by a source
position, a direction and a length. The length of the line of sight vector
defines a maximum
range for the identification of obstacles, i.e. only obstacles of which the
distance from the
source position will be identified and trigger the execution of steps 36 to 40
of the method
30. Any obstacle positioned at a distance greater than the length of the line
of sight vector
will be ignored and will not affect the airflow velocity at the main rotor of
the simulated
helicopter. On the other end, any obstacle positioned at a distance equal to
or shorter than
the length of the line of sight vector will be considered to have an impact on
the airflow
velocity at the main rotor of the simulated helicopter. As a result, steps 36
to 40 of the
method 30 are to be executed.
In one embodiment, the direction may be expressed as an azimuth angle. In this
case, the
azimuth angle represents the angular direction of the line of sight vector
within the azimuth
plane of the simulated helicopter or the angular direction of the projection
of the line of
sight vector in the azimuth plane when the line of sight vector is not
contained in the
azimuth plane of the simulated helicopter. The source position of the line of
sight vector
may be located at different locations as explained in the following.
In one embodiment, the source position of the line of sight vector may be
located on the
simulated helicopter. In another embodiment, the source position may be
adjacent to the
simulated helicopter.
In one embodiment, the source position of the line of sight vector is located
along an axis
which is orthogonal to the azimuth plane of the simulated helicopter. For
example, the
source position of the line of sight vector may be located on the rotation
axis of the main
rotor of the simulated helicopter.
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In one embodiment, the line of sight vector is orthogonal to the rotation axis
of the main
rotor of the simulated helicopter. In this case, the line of sight vector is
either contained in
the azimuth plane of the simulated helicopter or parallel to the azimuth
plane. In one
embodiment, the source position of the line of sight vector is located on the
rotation axis of
the main rotor of the simulated helicopter in addition to being orthogonal to
the rotation
axis. In one embodiment, the source position is located on the hub of the main
rotor of the
simulated helicopter.
In one embodiment, the line of sight vector is parallel to the Earth
horizontal plane.
At step 36, it is determined whether an obstacle is present along the
direction of the line of
sight vector while being within the maximum range defined by the length of the
line of
sight vector. To do so, the distance between the source position and the
closest obstacle
from the source position along the direction of the line of sight vector is
calculated using
the topography information contained in the database. If no obstacle is
present, i.e. if the
distance between the closest obstacle from the source position is greater than
the length of
the line of sight vector, then no recirculation induced airflow velocity is
calculated. On the
other end, if the presence of an obstacle is detected, i.e. if the distance
between the closest
obstacle from the source position is less than or equal to the length of the
line of sight
vector, then a recirculation induced airflow velocity is to be calculated and
steps 38 to 40
are performed.
It should be understood that an obstacle may correspond to a part of the
simulated terrain
stored in the database such as a hill and/or a simulated structure such as a
building.
It should also be understood that if more than one obstacle is identified as
having a positon
within the maximum range defined by the length of the line of sight vector
along the
direction of the line of sight vector, only the obstacle being the closest
form the source
position is considered and the distance determined at step 36 then corresponds
to the
distance between the source position and the closest obstacle from the source
position.
At step 38, a recirculation induced airflow velocity at the main rotor of the
simulated
helicopter is calculated using the distance between the simulated obstacle and
the simulated
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helicopter determined at step 36, the airspeed of the simulated helicopter and
the height
above ground of the helicopter. In one embodiment, the shortest the distance
between the
source position and the closest obstacle is, the greater the recirculation
effect on the
recirculation induced airflow velocity is.
In one embodiment, the method 30 further comprises a step of comparing the
airspeed of
the simulated helicopter to an airspeed threshold and performing steps 36-40
only when the
received airspeed of the simulated helicopter is less than the airspeed
threshold.
In the same or another embodiment, the method 30 further comprises a step of
comparing
the height above ground received at step 32 to a height threshold and
performing steps 36-
40 only when the received height above ground is less than the height
threshold.
Finally, the recirculation induced airflow velocity at the main rotor of the
simulated
helicopter is outputted at step 40. In one embodiment, the recirculation
induced airflow
velocity at the main rotor is stored in memory. In the same or another
embodiment, the
recirculation induced airflow velocity at the main rotor is sent to the
simulation engine
which uses the recirculation induced airflow velocity at the main rotor to
calculate an actual
airflow velocity at the main rotor which is used for controlling the simulated
helicopter.
The actual airflow velocity at the main rotor of the simulated helicopter is
calculated using
the initial airflow velocity at the main rotor and the recirculation induced
airflow velocity at
the main rotor calculated at step 38. In one embodiment, the actual airflow
velocity at the
main rotor of the simulated helicopter is obtained by adding the calculated
recirculation
induced airflow velocity at the main rotor to the initial airflow velocity at
the main rotor.
In one embodiment, the method 30 is executed in substantially real-time while
the user
interacts with the simulator to provide the user with a real-time effect of
the presence of an
obstacle on the simulated helicopter.
In one embodiment, the step 36 comprises sending to the simulation engine a
request for
receiving the distance of the closest obstacle from the source position of the
line of sight
vector. In this case, the request comprises at least the source position and
the direction of
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the line of sight vector such as the azimuth angle associated with the line of
sight vector.
The simulation engine receives the request and determines the distance of the
closest
obstacle from the source position along the direction of the line of sight
vector. In one
embodiment, the simulation engine transmits the determined distance to the
computer
machine that executes the method 30 and the computer machine compares the
received
distance to the length of the line of sight vector. If the distance is greater
than the length of
the line of sight vector, the computer machine determines that the execution
of the method
30 should be stopped and calculates no induced airspeed velocity. However, if
the received
distance is less than or equal to the length of the line of sight vector, the
computer machine
performs the steps 38-40 of the method 30 using the received distance. In an
embodiment in
which the request further comprises the length of the line of sight vector,
the simulation
engine may be further configured for comparing the determined distance to the
length of
the line of sight vector and transmits the determined distance to the computer
machine only
when it is less than or equal to the length of the line of sight vector.
In one embodiment, the method 30 further comprises iteratively varying the
direction of the
line of sight vector. It should be understood that the direction of the line
of sight vector may
iteratively take a plurality of different values. When the direction of the
line of sight vector
is represented by an azimuth angle, the value of the azimuth angle is changed.
In this case,
for each direction, the closest obstacle is identified and the distance to the
closest obstacle
is determined for each direction at step 36. A recirculation induced airflow
velocity
component is determined for each direction at step 38 using the respective
distance to the
closest obstacle. The actual airflow velocity is then calculated using the
recirculation
induced airflow velocity calculated for each direction.
In an embodiment in which the direction of the line of sight vector is
represented by an
azimuth angle, the value of the azimuth angle may be iteratively changed to
cover 360
degrees so that any obstacle present around the simulated may be detected
independently of
the particular location of the obstacle. For example, the value of the azimuth
angle may be
iteratively varied by 10 degrees from 0 degree to 360 degrees
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,
In one embodiment, the method 30 further comprises varying the source position
of the line
of sight vector and performing the steps 36-40 for each possible source
position for the line
of sight vector. It should be understood that the variation of the source
position may be
combined with the above-described variation of the direction of the line of
sight vector. For
example, the direction of the line of sight may be varied for a same first
source position for
the line of sight vector, then the source position of the line of sight vector
may be changed
from the first source position to a second and different source position and
the direction of
the line of sight is then varied again.
In one embodiment, the different source positions for the line of sight vector
may be chosen
to be on the simulated helicopter. In another embodiment, only some of the
different source
positions may be chosen to be on the simulated helicopter. For example, some
of the source
positions may be located on the simulated helicopter while other source
positions may be
located between the simulated helicopter and the ground.
In one embodiment, the different source positions are located along an axis
which is chosen
to be orthogonal to the azimuth plane of the simulated helicopter. For
example, the different
source positions may be located on the rotation axis of the main rotor of the
simulated
helicopter.
Figure 3 illustrates an embodiment in which a line of sight vectors may take
16 different
azimuth angle values. A single line of sight vector 50 and the source position
52 of the line
of sight vector 50 is constant and does not vary. In the illustrated example,
the source
position 52 of the line of sight vector 50 is positioned on the rotation axis
of the main rotor
54 of a simulated helicopter. The azimuth angle of the line of sight vector 50
is changed to
iteratively take one of the 16 possible values and for each azimuth angle
value, the distance
to the closest obstacle is determined. For example, the value of the azimuth
angle may be
changed at each simulation step. The distance to the closest obstacle for each
azimuth angle
value is then used for calculating the recirculation induced airflow velocity
and the actual
airflow velocity as described below.
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In the illustrated example, the line of sight vector is able to detect the
presence of an angled
wall 56 when it occupies the 7 right-most possible positions.
While in the above description, there is described that a single line of sight
vector is
generated at step 34, it should be understood that a plurality of line of
sight vectors may be
generated at step 34. In this case, the plurality of line of sight vectors may
have a same
source position and/or a respective and different direction such as a
different azimuth angle.
In this case, for each line of sight vector, the respective distance from the
closest obstacle is
determined at step 36 and the recirculation induced airflow velocity is
determined at step
38. At step 20, the actual airflow velocity is determined for direction using
the initial
airflow velocity and the recirculation induced airflow velocity.
In an embodiment in which a line of sight vector may iteratively occupy
several source
positions each positioned along an axis orthogonal to the azimuth plane of the
simulated
helicopter or the source position of a plurality of line of sight vectors is
positioned along an
axis orthogonal to the azimuth plane of the simulated helicopter, the
distances to the closest
obstacle obtained for a same given direction but different source positions
may be averaged
to provide a single distance which is then used in the calculation of the
recirculation
induced airflow for the given direction.
Referring back to Figure 3, 16 line of sight vectors 50 may be concurrently
generated at
step 34. The adjacent line of sight vectors 50 are then spaced apparat by an
angle of 12.5
degrees. The distance between the closest obstacle and the source position 52
is
concurrently determined for each one of the 16 line of sight vectors 50. The
recirculation
induced airflow velocity and the actual airflow velocity are each concurrently
determined
for the 7 right-most line of sight vectors 50 since the nine other line of
sight vectors
detected no obstacle.
While in Figure 3 the different line of sight vectors 50 are located within a
same plane,
Figure 4 illustrates an embodiment in which the line of sight vectors are
located within five
different parallel planes 70-78 which are each orthogonal to the rotation axis
80 of the main
rotor of a simulated helicopter 82. Each plane 70-78 may comprise a single
line of sight
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vector having its source position on the rotation axis 80 and of which the
azimuth angle is
iteratively varied to cover a circumference of 360 degrees. In another
example, each plane
may each comprise a plurality of line of sight vectors having different
azimuth angles. In
one embodiment, the line of sight vectors may be aligned form one plane 70-78
to another.
In this case, for a given line of sight vector belonging to a given plane 70-
78 and having a
given azimuth angle corresponds a line of sight vector having the same given
azimuth angle
and belonging to another plane 70-78. In this case, the distances to the
closest obstacle
obtained for the line of sight vectors sharing the same azimuth angle and
belonging to
different planes 70-78 may be averaged to obtain an average distance which is
subsequently
used for determining the recirculation induced airflow velocity for the given
azimuth angle.
In the illustrated embodiment, the line of sight belonging to the three bottom-
most planes
74-78 allows detecting the obstacle 84 while the line of sight vectors
belonging to the
planes 70 and 72 detect no obstacle.
In the following, there is described one exemplary method for calculating the
actual airflow
velocity when a plurality of line of sight vectors are generated each having a
respective
azimuth angle i. For each azimuth angle i, the respective recirculation
induced airflow
velocity wi at the rotor is defined by the following equation:
wi = '<Instructor Height fAirSpeed(KLocal f(di) + KAverage f(C11)) Vinduced
where:
di is the local distance between the main rotor disk extremity and the nearest
obstacle
detected along the azimuth angle i. and is obtained from the diameter or
radius of the main
rotor and the distance between the source position and the nearest obstacle
determined at
step 34;
fHeight is a function of height above ground, as defined below;
fAirspeed is a function of the aircraft airspeed, as defined below;
f(di) is a function of the local distance di, as defined below;
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f(di) is the average of f(di) for all the azimuth angles i;
'<Instructor is a slider gain that may be adjusted by a flight instructor
during a training
session;
'<Local is a tuning gain used to adjust the effect of the recirculation at an
azimuth angle i;
KAverage is a tuning gain used to adjust the induced velocity effect on the
whole main rotor;
and
Vinduced is the main rotor induced average velocity (downwash) under the
helicopter
calculated by the simulation engine.
In one embodiment, the height function 'Height is a tuning function that fades
out the
recirculation effect when the helicopter is out of ground effect. The height
function may be
defined as follows:
fHeight = min max ,' HOGE -h
T T , 0.0) 4.0)
HOGE ¨ nIGE
where h is the height of the main rotor above the ground and HIGE and 1-10GE
are the
parameterizable limit points in and out of ground effect for the application
of the
recirculation effects.
The airspeed function f
Airspeed is defined as follows:
min max (VMax VAirspeed
=
fAirspeed 0.0), 1.0)
VMax Mm
where VAirspeed is the helicopter airspeed (including the wind component)
tangential to the
ground, Vmin is the minimum airspeed from which full recirculation effect is
present and
Vmax is the maximum airspeed where no recirculation effect is present.
The local distance function f(di) is defined as follows:
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. .
RC= min (max (Dm"¨ ____________________________ di , 0.0) 4.0)
Dmax¨Dmin
where Dmin is the minimum distance for full recirculation effect and Dmax is
the maximum
distance where no recirculation will occur. Tuning the gain KLocal on this
function affects
the local effect of the obstruction at the main rotor grid point corresponding
to the azimuth
angle i, resulting in un-commanded pitch and roll effects on the helicopter.
The function KC is defined as follows:
= f(di) /n
The airflow velocity induced by the recirculation may be seen as a gain on the
initial
airflow velocity produced by the main rotor disk Vinduced = Since this
recirculation induced
airflow velocity is a function of the helicopter main rotor downwash intensity
(resulting
from its thrust), it can be understood that the recirculation has no effect
when the helicopter
is on the ground with no thrust and that a larger effect occurs as the power
is increased and
the helicopter takes off near an obstruction.
Once the recirculation effects have been calculated at the extremities of the
main rotor disk,
they can be interpolated at the main rotor blade elements (along the radius of
the main rotor
and to the current azimuthal angle of each actual main rotor blades) or in the
center of the
main rotor. This recirculation is then added to the vertical velocity
component of airflow
induced by the main rotor at each blade element k as it is shown in equation
7:
VInducedTotal,k = Vinduced,k wk
Where:
VInducedTotal,k = Vertical airflow velocity at the main rotor blade element k
including the
recirculation
VInduced,k
= Vertical airflow velocity at the main rotor blade element k without the
recirculation
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. .
NAik = Recirculation velocity at blade element k, after interpolating
the values at the
relevant azimuth at the main rotor disk to the blade elements.
As a result of the added recirculation induced airflow velocity at the blade
elements, the
main rotor effectiveness is reduced, which adversely affects the helicopter
performance.
Local effects can also create a moment on the main rotor that will affect the
helicopter roll
and pitch attitudes.
In one embodiment, the actual forces and moments resulting from the
aerodynamic effect
applied on the rotor disk may have a time delay. Since the main rotor is
turning at a high
rate, this time delay results in an azimuthal shift of the force being applied
on the rotor disk.
This azimuth difference is called a phase angle. In one embodiment, a
provision to adjust
the phase angles based on the pilot's feedback can be added by offsetting the
azimuths of
the recirculation induced airflow velocity solution. With this tuning
parameter, the pitch
and roll behaviour of the aircraft can be adjusted when it is hovering near an
obstruction.
It should be understood that other models may be used for calculating the
recirculation
induced velocity at the main rotor using the distance to the closest obstacle.
It should be understood that the method 30 may be embodied as a computer
machine
comprising at least one processing unit or processor, a communication unit and
a memory
having stored thereon statements and/or instructions that, when executed by
the processing
unit, executes the steps of the above-described method.
Figure 5 illustrates one embodiment of a system 100 for calculating the
recirculation
induced velocity at the main rotor of a simulated helicopter. The system 100
comprises a
line of sight vector generator 102 and a first or induced airflow velocity
calculator 104
which is in communication with second or actual airflow velocity calculator
106.
The line of sight vector generator 102 is configured for generating at least
one line of sight
vector as described above. In one embodiment, the line of sight vector
generator 102 is
configured for generating a single line of sight vector and varying the source
position
and/or the direction of the single line of sight vector, as described above.
In another
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. .
embodiment, the line of sight vector generator 102 is configured for
generating a plurality
of line of sight vectors each having a different direction and/or a different
source position,
as described above.
The line of sight vector generator 102 is further configured for transmitting
information
about the generated line of sight vector to a distance calculator 108. The
transmitted
information contains at least the source position and the direction of the
line of sight vector,
for each generated line of sight vector. The distance calculator 108 is
configured for
calculating the distance between the source position and the closest obstacle
along the
direction and transmitting the calculated distance to the first calculator
104, for each line of
sight vector, as described above.
In one embodiment, the line of sight vector generator 102 may further transmit
the length of
the line of sight vector to the distance calculator 108. In this case, the
distance calculator
108 may be configured for comparing the determined distance to the length of
the line of
sight vector and transmit the determined distance to the attenuation gain
calculator only
when the determined distance is less than or equal to the length of the line
of sight vector. It
should be understood that, if it receives no distance from the distance
calculator 108, then
the first calculator 104 calculates no recirculation induced airflow velocity.
In another embodiment, the line of sight vector generator 102 may further be
configured for
transmitting the length of the line of sight vector to the first calculator
104. In this case, the
first calculator 104 may be configured for comparing together the determined
distance
received from the distance calculator 108 and the received length of the line
of sight vector
and calculating the attenuation gain only when the distance received form the
distance
calculator 108 is less than or equal to the length of the line of sight
vector.
For each line of sight vector, the first calculator 104 is configured for
calculating the
recirculation induced airflow velocity using the respective distance received
from the
distance calculator 108, as described above. The first calculator 104 is
further configured
for transmitting the calculated recirculation induced airflow velocity to the
second
calculator 106 which determines the actual airflow velocity at the rotor of
the simulated
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helicopter using the initial airflow velocity and the recirculation induced
airflow velocity,
as described above.
In one embodiment, the distance calculator 108 is separate from the system
100. In this
case, the distance calculator 108 may correspond to the simulation engine
configured for
generating the simulation of the helicopter.
In another embodiment, the distance calculator 108 is part of the system 100.
In one embodiment, each one of the modules 102-108 is provided with a
respective
processing unit such as a microprocessor, a respective memory and respective
communication means. In another embodiment, at least two of the modules 102-
108 may
share a same processing unit, a same memory and/or same communication means.
For
example, the system 100 may comprise a single processing unit used by each
module 102-
106, a single memory and a single communication unit.
Figure 6 is a block diagram illustrating an exemplary processing module 120
for executing
the steps 32 to 40 of the method 30, in accordance with some embodiments. The
processing
module 120 typically includes one or more Computer Processing Units (CPUs)
and/or
Graphic Processing Units (GPUs) 122 for executing modules or programs and/or
instructions stored in memory 124 and thereby performing processing
operations, memory
124, and one or more communication buses 126 for interconnecting these
components. The
communication buses 126 optionally include circuitry (sometimes called a
chipset) that
interconnects and controls communications between system components. The
memory 124
includes high-speed random access memory, such as DRAM, SRAM, DDR RAM or other
random access solid state memory devices, and may include non-volatile memory,
such as
one or more magnetic disk storage devices, optical disk storage devices, flash
memory
devices, or other non-volatile solid state storage devices. The memory 124
optionally
includes one or more storage devices remotely located from the CPU(s) 122. The
memory
124, or alternately the non-volatile memory device(s) within the memory 124,
comprises a
non-transitory computer readable storage medium. In some embodiments, the
memory 124,
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or the computer readable storage medium of the memory 84 stores the following
programs,
modules, and data structures, or a subset thereof:
a vector module 130 for generating at least one line of sight vector;
a distance module 132 for calculating the distance between the source
position of the line of sight vector and the closest obstacle along the
direction of the line of
sight vector;
an induced airflow velocity module 134 for calculating the recirculation
induced airflow velocity at the rotor using the calculated distance; and
an actual airflow velocity module 136 for calculating the actual airflow
velocity at the rotor using the initial airflow velocity and the recirculation
induced airflow
velocity.
It should be understood that the distance module 132 and/or the actual airflow
velocity
module 136 may be omitted.
Each of the above identified elements may be stored in one or more of the
previously
mentioned memory devices, and corresponds to a set of instructions for
performing a
function described above. The above identified modules or programs (i.e., sets
of
instructions) need not be implemented as separate software programs,
procedures or
modules, and thus various subsets of these modules may be combined or
otherwise re-
arranged in various embodiments. In some embodiments, the memory 84 may store
a
subset of the modules and data structures identified above. Furthermore, the
memory 84
may store additional modules and data structures not described above.
Although it shows a processing module 120, Figure 6 is intended more as
functional
description of the various features which may be present in a management
module than as a
structural schematic of the embodiments described herein. In practice, and as
recognized by
those of ordinary skill in the art, items shown separately could be combined
and some items
could be separated.
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. ,
While the above-described methods and systems refer to a simulated helicopter,
it should
be understood that the above-described methods and systems may apply to any
simulated
rotorcraft such as a simulated cyclogyro, a simulated cyclocopter, a simulated
autogyro, a
simulated gyrodyne, a simulated rotor bike, or the like.
The embodiments of the invention described above are intended to be exemplary
only. The
scope of the invention is therefore intended to be limited solely by the scope
of the
appended claims.
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