SixDOF Flight Control System Definition

The flight control definitions are significantly different between WSF_RIGID_BODY_SIX_DOF_MOVER and WSF_POINT_MASS_SIX_DOF_MOVER.

The PM6 flight control system assumes a very limited set of controls. For stick-and-rudder controls, a mapping between control position and rotation rate command (degrees/second) must be provided. For lift and drag devices, a first-order-lag time constant can be provided for more realistic deployment.

PM6 Controls

flight_controls

    stick_back ... end_stick_back
    stick_right ... end_stick_right
    rudder_right ... end_rudder_right

    speedbrakes ... end_speedbrakes
    flaps ... end_flaps
    spoilers ... end_spoilers

 end_flight_controls

stick_back … end_stick_back

This defines the mapping between stick-back control, from -1 to +1, in the left column and pitch-up rate command, in degrees/second, in the right column.

stick_right … end_stick_right

This defines the mapping between stick-right control, from -1 to +1, in the left column and roll-right rate command, in degrees/second, in the right column.

rudder_right … end_rudder_right

This defines the mapping between rudder-right control, from -1 to +1, in the left column and yaw-right rate command, in degrees/second, in the right column.

rudder_right … end_rudder_right

This defines the mapping between rudder-right control, from -1 to +1, in the left column and yaw-right rate command, in degrees/second, in the right column.

speedbrakes … speedbrakes

This defines properties for speedbrake deployment. The only property currently available is lag_time_constant, which must be defined with a time value.

flaps … end_flaps

This defines properties for flaps deployment. The only property currently available is lag_time_constant, which must be defined with a time value.

spoilers … end_spoilers

This defines properties for spoilers deployment. The only property currently available is lag_time_constant, which must be defined with a time value.

A control system for a bank-to-turn aircraft might look like:

flight_controls

   stick_back
      -1.0  -4.0   # Full stick-fore requests 4 deg/s in pitch-down
       0.0   0.0   # Neutral stick requests 0 deg/s in pitch rate
       1.0   8.0   # Full stick-back requests 8 deg/s in pitch-up
   end_stick_back

   stick_right
      -1.0  -30.0  # Full stick-left requests 30 deg/s in roll-left
       0.0   0.0   # Neutral stick requests 0 deg/s in roll rate
       1.0   30.0  # Full stick-right requests 30 deg/s in roll-right
   end_stick_right

   rudder_right
      -1.0  -2.0   # Full rudder-left requests 2 deg/s in yaw-left
       0.0   0.0   # Neutral stick requests 0 deg/s in yaw rate
       1.0   2.0   # Full rudder-right requests 2 deg/s in yaw-right
   end_rudder_right

   speedbrakes
      lag_time_constant  1.0 sec
   end_speedbrakes

   flaps
      lag_time_constant  5 sec
   end_flaps

   spoilers
      lag_time_constant  1.0 sec
   end_spoilers

end_flight_controls

RB6 Controls

The RB6 flight control system determines how control inputs from the active pilot object are routed/mixed to move control surfaces, throttles, or other components/controls (such as landing gear, speed brakes, etc.). Many of the control surfaces serve as inputs into aero_component objects.

flight_controls … end_flight_controls

The flight_controls block defines various control surfaces/values (control_surface, control_value, and control_boolean) that control the vehicle and/or effect its performance. The flight_controls block also defines various input/signal modifiers which are referenced within the control surfaces/values (control_surface, control_value, and control_boolean) blocks. It is important to define Control Signal Modifiers before they are referenced in the Control Surfaces and Components blocks.

flight_controls

   // Control Signal Modifiers
   mapping_table ... end_mapping_table
   gain_table ... end_gain_table
   scalar_gain ... end_scalar_gain
   clamp_gain ... end_clamp_gain

   // Control Surfaces and Components
   control_surface ... end_control_surface
   control_value ... end_control_value
   control_boolean ... end_control_boolean

end_flight_controls

Control Signal Modifiers

The control signal modifiers provide a means to modify control input “signals” from the active pilot object. The modifiers can be used repeatedly within the control_surface, control_value, and control_boolean blocks, as needed.

mapping_table … end_mapping_table

Mapping tables are used to modify a control input signal by modulating with a control value source. The control value can be a range of sources such as mach, alpha, g-load, etc. A table defines the relationship between the control value

mapping_table <string>
   type ...
   table_data ... end_table_data
end_mapping_table

type <string>

This sets the type of the mapping table. Valid types include:

mach_mapping

Uses mach as the control_value

ktas_mapping

Uses ktas as the control_value

alpha_mapping

Uses alpha as the control_value

beta_mapping

Uses beta as the control_value

g_x_load_mapping

Uses g-load-x (Nx) as the control_value

g_y_load_mapping

Uses g-load-y (Ny) as the control_value

g_z_load_mapping

Uses g-load-z (Nz) as the control_value

alt_mapping

Uses altitude as the control_value

q_mapping

Uses dynamic pressure as the control_value

signal_mapping

Uses a signal as the control_value

table_data

This table maps a signal/input to an output/value). A typical table is like this:

table_data
   irregular_table
       independent_variable control_value precision float
       independent_variable input         precision float
       dependent_variable                 precision float
       control_value 0.0
           input   -1.0 -0.5  0.0  0.5  1.0
           values  -0.8 -0.4  0.0  0.4  0.8
       control_value 1.0
           input   -1.0 -0.5  0.0  0.5  1.0
           values  -0.8 -0.4  0.0  0.4  0.8
       control_value 2.0
           input   -1.0 -0.5  0.0  0.5  1.0
           values  -0.8 -0.4  0.0  0.4  0.8
   end_irregular_table
end_table_data

gain_table … end_gain_table

This table maps a signal/input to an output/value). A typical table is like this:

gain_table <string>

   type ...

   simple_table
    # value   gain
      -12.0   0.0
      -10.0   1.0
      0.00    1.0
      10.0    1.0
      12.0    0.8
      20.0    0.1
      30.0    0.0
   end_simple_table

end_gain_table

scalar_gain … end_scalar_gain

The scalar gain consists of a name and a gain value. Once defined, a scalar gain can be used repeatedly within the control_surface, control_value, and control_boolean blocks to scale a control signal.

scalar_gain <string>
   gain ...
end_scalar_gain

gain <real-value>

This sets the gain of the scalar gain.

clamp_gain … end_clamp_gain

Clamp gains are used to limit a signal between min/max values. The output of signal will be “clamped” to the minimum and maximum values.

clamp_gain <string>
   min_clamp ...
   max_clamp ...
end_clamp_gain

min_clamp <real-value>

This sets the minimum value that will be allowed to pass the clamp gain.

max_clamp <real-value>

This sets the maximum value that will be allowed to pass the clamp gain.

Control Surfaces and Components

The control_surface, control_value, and control_boolean represent control surfaces and other components on the platform that produce forces and moments or control actions on the vehicle.

control_surface … end_control_surface

This defines a “control surface” or other component that can produce aerodynamic effects on the platform. Control surfaces include ailerons, elevators, elevons, rudders, spoilers, speedbrakes, etc. but also include things like landing gear, which can produce drag. See Sample Control Surface for an example of a control_surface block.

Each control_surface is given a name that must be unique and must “map” to an aero_component that will produce the effect of the control_surface.

Warning

The key concept is that each control_surface in the flight_controls block should be “connected” to a corresponding aero_component.

The control_surface name and the aero_component type must match exactly and are case-sensitive.

control_surface <name-string>

   min_angle ...
   max_angle ...
   current_angle ...

   inputs ... end_inputs

   angle_mapping_table ... end_angle_mapping_table

   actuator ... end_actuator

end_control_surface

min_angle <angle-value>

This sets the minimum angle of this control surface.

max_angle <angle-value>

This sets the maximum angle of this control surface.

current_angle <angle-value>

This sets the current angle of this control surface.

inputs … end_inputs

Inputs provide a means to modify a “control input/signal” from the active pilot object. If multiple inputs blocks are used, the output from each block is summed with the other inputs for a given control_surface. This can provide a means to “mix” control inputs/signals to drive a particular control surface. For example, an elevon may mix signals from stick_right and stick_back inputs to allow the elevon to be used for both pitch and roll forces/moments.

inputs
   control_input.. end_control_input
end_inputs

control_input … end_control_input

control_input <string>
   modifier ...
end_control_input

modifier <string>

This indicates which of the Control Signal Modifiers should be used. If multiple modifier entries are present,

they are performed in succession with the result from the previous modifier serving as the input of the next, forming a “chain” of modifiers.

Warning

The key concept is that each control_input in flight_controls should be “connected” to a control_name in control_inputs.

The names must match exactly and are case-sensitive.

angle_mapping_table … end_angle_mapping_table

This table provides a means to “shape” the mapping of input to control surface angle. In many situations, a non-linear mapping will be used, with a reduced slope near zero and increased slope near the endpoints. This often improves the “feel” of controls and provides more control sensitivity near the zero point. Data in the table is normalized input mapping to a control surface angle in degrees.

Sample mapping table:

angle_mapping_table
   #input        angle_deg
   -1.00         -20.0
   0.00          0.0
   1.00          20.0
end_angle_mapping_table

In this example, a normalized input of +/- 1 results in a linear mapping to +/- 20 degrees.

actuator

This allows an simple model of an actuator.

actuator
   max_positive_rate ...
   max_negative_rate ...
   max_angle ...
   min_angle ...
   current_angle ...
end_actuator

max_positive_rate <angle-rate-value>

This is the maximum rate that the actuator can move in the positive direction.

Default: 0.0

max_negative_rate <angle-rate-value>

This is the maximum rate that the actuator can move in the negative direction.

Default: 0.0

max_angle <angle-value>

This is the maximum angle to which the actuator can move.

Default: 0.0

min_angle <angle-value>

This is the minimum angle to which the actuator can move.

Default: 0.0

current_angle <angle-value>

This is the current angle of the actuator.

Default: 0.0

Sample Control Surface

This is a sample control surface listing:

control_surface   RightElevator_TEUp
   min_angle            -20.0 deg
   max_angle            20.0 deg
   current_angle        0.0 deg

   inputs
      control_input     StickRight
         modifier       Gain_40Percent
         modifier       Clamp_PosNegOne
      end_control_input
   end_inputs
   inputs
      control_input     StickBack
         modifier       Gain_80Percent
         modifier       Clamp_PosNegOne
      end_control_input
   end_inputs

   angle_mapping_table
      #input  angle_deg
      -1.00   -20.000
      -0.90   -12.812
      -0.80   -8.744
      -0.70   -5.920
      -0.60   -3.958
      -0.50   -2.596
      -0.40   -1.650
      -0.30   -0.993
      -0.20   -0.537
      -0.10   -0.220
      -0.05   -0.100
      0.00    0.000
      0.05    0.100
      0.10    0.220
      0.20    0.537
      0.30    0.993
      0.40    1.650
      0.50    2.596
      0.60    3.958
      0.70    5.920
      0.80    8.744
      0.90    12.812
      1.00    20.000
   end_angle_mapping_table

   actuator
      max_positive_rate  60.0 deg/sec
      max_negative_rate  -60.0 deg/sec
      max_angle          20.0
      min_angle          -20.0
      current_angle      0.0
  end_actuator

end_control_surface

control_value

This defines a “control value” that can be used to drive controls such as throttles and thrust reversers or control other objects on the platform. A control value provides a range of values, constrained by the specified limits.

control_value <string>

   min_value ...
   max_value ...
   current_value ...

   inputs ... end_inputs

end_control_value

min_value <real-value>

This is the minimum value of the control value.

Default: 0.0

max_value <real-value>

This is the maximum value of the control value.

Default: 0.0

current_angle <real-value>

This is the current angle of the control value.

Default: 0.0

control_boolean

This defines a “control boolean” that can be used to drive “button”, “trigger”, and “switch” types of controls on the platform. A control boolean’s output is either true (on) or false (off).

control_boolean <string>

   current_value ...
   threshold_value ...

   inputs ... end_inputs

end_control_boolean

current_value <integer-value>

This should be ‘0’ if the control boolean is false (off) or ‘1’ if the control boolean is true (on).

Default: 0

threshold_value <real-value>

This sets the value above which a signal will be considered to be true (on).

Default: 0.5

Return to six_dof_object_types, rigid_body_vehicle_type, point_mass_vehicle_type