FGInitialCondition

class jsbsim.FGInitialCondition

Initializes the simulation run.

Takes a set of initial conditions (IC) and provide a kinematically consistent set of body axis velocity components, euler angles, and altitude. This class does not attempt to trim the model i.e. the sim will most likely start in a very dynamic state (unless, of course, you have chosen your IC’s wisely, or started on the ground) even after setting it up with this class.

Usage Notes

With a valid object of FGFDMExec and an aircraft model loaded:

FGInitialCondition* fgic = FDMExec->GetIC();

// Reset the initial conditions and set VCAS and altitude
fgic->InitializeIC();
fgic->SetVcalibratedKtsIC(vcas);
fgic->SetAltitudeAGLFtIC(altitude);

// directly into Run
FDMExec->GetPropagate()->SetInitialState(fgic);
delete fgic;
FDMExec->Run();

//or to loop the sim w/o integrating
FDMExec->RunIC();

Alternatively, you can load initial conditions from an XML file:

FGInitialCondition* fgic = FDMExec->GetIC();
fgic->Load(IC_file);

Speed

Since vc, ve, vt, and mach all represent speed, the remaining three are recalculated each time one of them is set (using the current altitude). The most recent speed set is remembered so that if and when altitude is reset, the last set speed is used to recalculate the remaining three. Setting any of the body components forces a recalculation of vt and vt then becomes the most recent speed set.

Alpha,Gamma, and Theta

This class assumes that it will be used to set up the sim for a steady, zero pitch rate condition. Since any two of those angles specifies the third gamma (flight path angle) is favored when setting alpha and theta and alpha is favored when setting gamma. i.e.

  • set alpha : recalculate theta using gamma as currently set

  • set theta : recalculate alpha using gamma as currently set

  • set gamma : recalculate theta using alpha as currently set

The idea being that gamma is most interesting to pilots (since it is indicative of climb rate).

Setting climb rate is, for the purpose of this discussion, considered equivalent to setting gamma.

These are the items that can be set in an initialization file:

  • ubody (velocity, ft/sec)

  • vbody (velocity, ft/sec)

  • wbody (velocity, ft/sec)

  • vnorth (velocity, ft/sec)

  • veast (velocity, ft/sec)

  • vdown (velocity, ft/sec)

  • latitude (position, degrees)

  • longitude (position, degrees)

  • phi (orientation, degrees)

  • theta (orientation, degrees)

  • psi (orientation, degrees)

  • alpha (angle, degrees)

  • beta (angle, degrees)

  • gamma (angle, degrees)

  • roc (vertical velocity, ft/sec)

  • elevation (local terrain elevation, ft)

  • altitude (altitude AGL, ft)

  • altitudeAGL (altitude AGL, ft)

  • altitudeMSL (altitude MSL, ft)

  • winddir (wind from-angle, degrees)

  • vwind (magnitude wind speed, ft/sec)

  • hwind (headwind speed, knots)

  • xwind (crosswind speed, knots)

  • vc (calibrated airspeed, ft/sec)

  • mach (mach)

  • vground (ground speed, ft/sec)

  • trim (0 for no trim, 1 for ground trim, ‘Longitudinal’, ‘Full’, ‘Ground’, ‘Pullup’, ‘Custom’, ‘Turn’)

  • running (-1 for all engines, 0 … n-1 for specific engines)

Properties

  • ic/vc-kts (read/write) Calibrated airspeed initial condition in knots

  • ic/ve-kts (read/write) Knots equivalent airspeed initial condition

  • ic/vg-kts (read/write) Ground speed initial condition in knots

  • ic/vt-kts (read/write) True airspeed initial condition in knots

  • ic/mach (read/write) Mach initial condition

  • ic/roc-fpm (read/write) Rate of climb initial condition in feet/minute

  • ic/gamma-deg (read/write) Flightpath angle initial condition in degrees

  • ic/alpha-deg (read/write) Angle of attack initial condition in degrees

  • ic/beta-deg (read/write) Angle of sideslip initial condition in degrees

  • ic/theta-deg (read/write) Pitch angle initial condition in degrees

  • ic/phi-deg (read/write) Roll angle initial condition in degrees

  • ic/psi-true-deg (read/write) Heading angle initial condition in degrees

  • ic/lat-gc-deg (read/write) Latitude initial condition in degrees

  • ic/long-gc-deg (read/write) Longitude initial condition in degrees

  • ic/h-sl-ft (read/write) Height above sea level initial condition in feet

  • ic/h-agl-ft (read/write) Height above ground level initial condition in feet

  • ic/sea-level-radius-ft (read/write) Radius of planet at sea level in feet

  • ic/terrain-elevation-ft (read/write) Terrain elevation above sea level in feet

  • ic/vg-fps (read/write) Ground speed initial condition in feet/second

  • ic/vt-fps (read/write) True airspeed initial condition in feet/second

  • ic/vw-bx-fps (read/write) Wind velocity initial condition in Body X frame in feet/second

  • ic/vw-by-fps (read/write) Wind velocity initial condition in Body Y frame in feet/second

  • ic/vw-bz-fps (read/write) Wind velocity initial condition in Body Z frame in feet/second

  • ic/vw-north-fps (read/write) Wind northward velocity initial condition in feet/second

  • ic/vw-east-fps (read/write) Wind eastward velocity initial condition in feet/second

  • ic/vw-down-fps (read/write) Wind downward velocity initial condition in feet/second

  • ic/vw-mag-fps (read/write) Wind velocity magnitude initial condition in feet/sec.

  • ic/vw-dir-deg (read/write) Wind direction initial condition, in degrees from north

  • ic/roc-fps (read/write) Rate of climb initial condition, in feet/second

  • ic/u-fps (read/write) Body frame x-axis velocity initial condition in feet/second

  • ic/v-fps (read/write) Body frame y-axis velocity initial condition in feet/second

  • ic/w-fps (read/write) Body frame z-axis velocity initial condition in feet/second

  • ic/vn-fps (read/write) Local frame x-axis (north) velocity initial condition in feet/second

  • ic/ve-fps (read/write) Local frame y-axis (east) velocity initial condition in feet/second

  • ic/vd-fps (read/write) Local frame z-axis (down) velocity initial condition in feet/second

  • ic/gamma-rad (read/write) Flight path angle initial condition in radians

  • ic/alpha-rad (read/write) Angle of attack initial condition in radians

  • ic/theta-rad (read/write) Pitch angle initial condition in radians

  • ic/beta-rad (read/write) Angle of sideslip initial condition in radians

  • ic/phi-rad (read/write) Roll angle initial condition in radians

  • ic/psi-true-rad (read/write) Heading angle initial condition in radians

  • ic/lat-gc-rad (read/write) Geocentric latitude initial condition in radians

  • ic/long-gc-rad (read/write) Longitude initial condition in radians

  • ic/p-rad_sec (read/write) Roll rate initial condition in radians/second

  • ic/q-rad_sec (read/write) Pitch rate initial condition in radians/second

  • ic/r-rad_sec (read/write) Yaw rate initial condition in radians/second

load(rstfile: str, useAircraftPath: bool = True) → bool

Loads the initial conditions.

Parameters:

  • rstname – The name of an initial conditions file

  • useAircraftPath – true if path is given relative to the aircraft path.

Returns:

true if successful

trim_requested() → TrimMode

Does initialization file call for trim ?

Returns:

Trim type, if any requested (version 1).