Including Atmospheric Winds in JSBSim Simulation via Python

[viniciusrottolo]

Hello everyone,

I'm trying to include synthetic winds in a JSBSim simulation using Python, but I'm facing some difficulties.

I'd like to know the correct way to include synthetic winds in the simulation via Python, especially when I'm trying to trim the aircraft in the presence of these winds.

Here's the code I'm using:

import jsbsim, math

# Global variables that must be modified to match your particular need
# The aircraft name
# Note - It should match the exact spelling of the model file
AIRCRAFT_NAME = "737"
# Path to JSBSim files, location of the folders "aircraft", "engines" and "systems"
PATH_TO_JSBSIM_FILES = "../.."

# Avoid flooding the console with log messages
jsbsim.FGJSBBase().debug_lvl = 0

fdm = jsbsim.FGFDMExec(PATH_TO_JSBSIM_FILES)

# Load the aircraft model
fdm.load_model(AIRCRAFT_NAME)

# Set engines running
fdm['propulsion/engine[0]/set-running'] = 1
fdm['propulsion/engine[1]/set-running'] = 1

# Set alpha range for trim solutions
fdm['aero/alpha-max-rad'] = math.radians(12)
fdm['aero/alpha-min-rad'] = math.radians(-4.0)

# Trim results
results = []

# Atmosphere conditions
fdm['atmosphere/psiw-rad'] = math.pi/2
fdm['atmosphere/wind-mag-fps'] = 10

# Initial Conditions
fdm['ic/h-sl-ft'] = 15000
fdm['ic/vc-kts'] = 300
fdm['ic/gamma-deg'] = 0

# Initialize the aircraft with initial conditions
fdm.run_ic()

# Trim
try:
    fdm['simulation/do_simple_trim'] = 1
    print(f" psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
            f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")
except jsbsim.TrimFailureError:
    pass  # Ignore trim failures

However, I noticed that both atmosphere/psiw-rad and atmosphere/wind-mag-fps were not changed.

Here's the answer I got:

psiw-rad: 3.142
wind-mag-fps: 0.000

Does anyone have any suggestions on how to correctly set up initialization to include atmospheric winds in the simulation?

Thank you in advance for any help!

[seanmcleod]

Hmm, I wondered whether the fdm.run_ic() to run the initial conditions was possibly resetting the wind. And it looks it is, plus the trim is as well. Will need to double-check whether trim re-runs the initial conditions internally. Also whether

# Atmosphere conditions
fdm['atmosphere/psiw-rad'] = math.pi/2
fdm['atmosphere/wind-mag-fps'] = 10

print(f"BIC psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
        f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

# Initial Conditions
fdm['ic/h-sl-ft'] = 15000
fdm['ic/vc-kts'] = 300
fdm['ic/gamma-deg'] = 0

# Initialize the aircraft with initial conditions
fdm.run_ic()

print(f"AIC psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
        f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

# Atmosphere conditions
fdm['atmosphere/psiw-rad'] = math.pi/2
fdm['atmosphere/wind-mag-fps'] = 10

# Trim
try:
    print(f"BT: psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
            f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

    fdm['simulation/do_simple_trim'] = 1
    
    print(f"AT: psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
            f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

BIC psiw-rad: 0.000
 wind-mag-fps: 10.000

AIC psiw-rad: 0.000
 wind-mag-fps: 0.000

BT: psiw-rad: 0.000
 wind-mag-fps: 10.000

AT: psiw-rad: 3.142
 wind-mag-fps: 0.000

Now there are some initial condition properties for wind, however it looks like a setter for the magnitude is missing?

jsbsim/src/initialization/FGInitialCondition.cpp

Lines 1521 to 1525 in 56c6662

	PropertyManager->Tie("ic/vw-mag-fps", this,
	&FGInitialCondition::GetWindFpsIC);
	PropertyManager->Tie("ic/vw-dir-deg", this,
	&FGInitialCondition::GetWindDirDegIC,
	&FGInitialCondition::SetWindDirDegIC);

[viniciusrottolo]

Would this be simple to modify?

[seanmcleod]

Should be fairly easy, busy testing it out - seanmcleod@190c060

If my further testing is successful then I'll submit a pull request.

[seanmcleod]

So for my testing I took the script 737_cruise.xml and noted the trim results, then I added the following to execute just before the trim operation.

	<event name="Set wind">
		<condition> simulation/sim-time-sec le 0.1 </condition>
		<set name="ic/vw-mag-fps" value="10"/>
		<set name="ic/vw-dir-deg" value="30"/>
		<notify/>
	</event>

And then compared the trim results with wind present and noted that the trim results are slightly different, as well as most of the properties being reported every 5 seconds.

I also had the atmosphere/wind-mag-fps and atmosphere/psiw-rad properties reported every 5s to confirm that they matched the initial wind conditions I'd set, i.e. that they weren't reset as part of the trim process etc. and they do match the initial wind conditions.

    <event name="Repeating Notify" persistent="true">
      <description>Output message at 5 second intervals</description>
      <notify>
....
....
		  <property>atmosphere/psiw-rad</property>
		  <property>atmosphere/wind-mag-fps</property>          
      </notify>

So I'll submit a pull request now.

[viniciusrottolo]

I am testing this in Python, and it seems that fdm.run_ic() does not load the value of fdm['ic/vw-dir-deg']. See the example below:

# Initial Conditions
fdm['ic/h-sl-ft'] = 15000
fdm['ic/vc-kts'] = 300
fdm['ic/gamma-deg'] = 0

fdm['ic/vw-dir-deg'] = math.degrees(math.pi/4)
fdm['ic/vw-mag-fps'] = 25

# Initialize the aircraft with initial conditions
fdm.run_ic()

print(f"AIC psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
        f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

# Trim

try:
    print(f"BT: psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
            f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")

    fdm['simulation/do_simple_trim'] = 1
    
    print(f"AT: psiw-rad: {fdm['atmosphere/psiw-rad']:.3f} \n",
            f"wind-mag-fps: {fdm['atmosphere/wind-mag-fps']:.3f} \n\n")
    
    print("Trim \n\n",
            f"elev: {fdm['fcs/elevator-pos-deg']:.3f} \n",
            f"l_ail: {fdm['fcs/left-aileron-pos-deg']:.3f} \n",
            f"r_ail: {fdm['fcs/right-aileron-pos-deg']:.3f} \n",
            f"rud: {fdm['fcs/rudder-pos-deg']:.3f} \n\n")
            
except jsbsim.TrimFailureError:
    pass  # Ignore trim failures

BIC psiw-rad: 0.000 
 wind-mag-fps: 0.000 


AIC psiw-rad: 0.000 
 wind-mag-fps: 25.000 


BT: psiw-rad: 0.000 
 wind-mag-fps: 25.000 


AT: psiw-rad: 0.000 
 wind-mag-fps: 25.000 
 
 Trim 

 elev: -2.210 
 l_ail: 0.000 
 r_ail: -0.000 
 rud: 0.000 
 

If we set fdm['ic/vw-dir-deg'] after fdm.run_ic(), we get:

# Initial Conditions
fdm['ic/h-sl-ft'] = 15000
fdm['ic/vc-kts'] = 300
fdm['ic/gamma-deg'] = 0

fdm['ic/vw-dir-deg'] = math.degrees(math.pi/4)
fdm['ic/vw-mag-fps'] = 25

# Initialize the aircraft with initial conditions
fdm.run_ic()

fdm['ic/vw-dir-deg'] = math.degrees(math.pi/4)

 BIC psiw-rad: 0.000 
 wind-mag-fps: 0.000 


AIC psiw-rad: 0.000 
 wind-mag-fps: 25.000 


BT: psiw-rad: 0.000 
 wind-mag-fps: 25.000 


AT: psiw-rad: 0.785 
 wind-mag-fps: 25.000 


 Trim 

 elev: -1.937 
 l_ail: -2.712 
 r_ail: 2.712 
 rud: -2.282 

[seanmcleod]

There is an order dependence here. In order to set the wind direction you need to have wind that has a magnitude > 0.

jsbsim/src/initialization/FGInitialCondition.cpp

Lines 619 to 638 in e26d03b

	//******************************************************************************
	// Modifies the wind direction while keeping its velocity unchanged. The vertical
	// component (in local NED frame) is unmodified. The aircraft velocity with
	// respect to the ground is not changed but the true airspeed is.
	void FGInitialCondition::SetWindDirDegIC(double dir)
	{
	const FGMatrix33& Tb2l = orientation.GetTInv();
	FGColumnVector3 _vt_NED = Tb2l * Tw2b * FGColumnVector3(vt, 0., 0.);
	FGColumnVector3 _vWIND_NED = _vt_NED - vUVW_NED;
	double mag = _vWIND_NED.Magnitude(eU, eV);
	FGColumnVector3 _vHEAD(mag*cos(dir*degtorad), mag*sin(dir*degtorad), 0.);
	_vWIND_NED(eU) = _vHEAD(eU);
	_vWIND_NED(eV) = _vHEAD(eV);
	_vt_NED = vUVW_NED + _vWIND_NED;
	vt = _vt_NED.Magnitude();
	calcAeroAngles(_vt_NED);
	}

[viniciusrottolo]

Thanks.