JSBSim in Flight Gear

[matheusdarocha]

Hello everyone,

I would like to ask if there is a way to insert a JSBSim maneuver in Flight Gear, for example:

event name="Trim with elevator"
condition> simulation/sim-time-sec ge 0.71 </condition
set name="ic/targetNlf" value="2.5"/
set name="simulation/do_simple_trim" value="3"/
notify/
/event

The goal is to see the aircraft doing this maneuver

Is that possible?

Thanks in advance

[seanmcleod]

Any reason you've asked pretty much the same question twice in two separate issues, this issue and issue https://github.com/JSBSim-Team/jsbsim/discussions/657 ?

[matheusdarocha]

Hello Sean, Before I asked to do this in python and then I thought it could be in any software. I will erase the previous question

[seanmcleod]

Yes you can script maneuvers in a script file and in general JSBSim output can be sent to FlightGear via an output element, take a look at:

https://github.com/JSBSim-Team/jsbsim/blob/375f5be0fdfeb210f4cf66f938e3e6fd426c2966/data_output/flightgear.xml

[matheusdarocha]

thanks a lot Sean, but I still have some difficulty to implement this

The step by step of what I did was:

1. tried to open Flight gear by cmd using the command
   fgfs.exe -fg-root="{your path}" -aircraft=c172p -native-fdm=socket,in,60,,5550,udp -fdm=external
   It didnt work and gave the answer that no -fg root or -aircraft is avaiable

then i put the cmd line in the Flight Gear correct path and opened it using
fgfs.exe

flight gear opened with C172P

then i download the folder at the link, and tried the command at cmd

src/jsbsim -realtime data_output/flightgear.xml scripts/c1723.xml

but it didnt work

I tried to go with cmd line to the folder where the script was, but it didnt work as well.

Do you have an example that i can use to try to do the maneuver?

Thanks a lot for the attention so far

Matt

[bcoconni]

There is a detailed tutorial in our FAQ.

Please follow the steps carefully, especially when asked to provide some options to the command line such as --native-fdm=socket,in,60,,5550,udp. If you skip any of them don't expect to get any working result.

If this example does not work correctly on your PC then please provide details about what is going wrong ; "it didnt work" is not very helpful.

[matheusdarocha]

thank you bcoconni, it work perfectly!

By the way, do you know any way to insert the maneuvers by python instead of a xml file?

[seanmcleod]

I posted some python based code examples in this disucssion - #519

[matheusdarocha]

Thanks Sean! I took a look at it, but i already have the python code, but i want to see the maneuver done in python at Flight gear, is there a way to do it?

[seanmcleod]

You have all the information at hand, just add this output element in the aircraft model's file which will output FlightGear packets as the model is run via python.

jsbsim/data_output/flightgear.xml

Lines 18 to 19 in 375f5be

	<output name="localhost" type="FLIGHTGEAR" protocol="UDP" port="5550" rate="60" version="24">
	</output>

[matheusdarocha]

Hello Sean, thanks for the answer
Unfortunatelly when I put this lines on my aircraft models, after run the python code, it doesn't move the flight gear model.

the script that i am trying to run is

fdm.do_trim(1)   

for t in np.arange(0,20,dt):
    fdm.run()
    if t < 0.01:
        fdm.do_trim(1)

trim the aircraft, and then loop through time.

When i run in prompt like the JSBSim:
python Filename.py data_output/flightgear.xml --realtime --nice

it does run JSBSim but doesn't make the simulation output goes to FG

[seanmcleod]

Unfortunatelly when I put this lines on my aircraft models,

If you do something that doesn't work please show exactly what you did and/or the output.

For example, here is an example (albeit commented out) of an output element in the C172p aircraft model file. Show us the equivalent version that you added for FlightGear output. Use the triple back-ticks ``` mechanism to format it as xml and/or python when pasting snippets.

jsbsim/aircraft/c172p/c172p.xml

Lines 916 to 941 in 33735db

	</aerodynamics>
	<!--
	<output name="JSBout172C.csv" type="CSV" rate="60">
	<property> aero/qbar-psf </property>
	<property> accelerations/udot-ft_sec2 </property>
	<property> accelerations/vdot-ft_sec2 </property>
	<property> accelerations/wdot-ft_sec2 </property>
	<property> accelerations/a-pilot-x-ft_sec2 </property>
	<property> accelerations/a-pilot-y-ft_sec2 </property>
	<property> accelerations/a-pilot-z-ft_sec2 </property>
	<property> accelerations/n-pilot-x-norm </property>
	<property> accelerations/n-pilot-y-norm </property>
	<property> accelerations/n-pilot-z-norm </property>
	<rates> ON </rates>
	<velocities> ON </velocities>
	<forces> ON </forces>
	<moments> ON </moments>
	<position> ON </position>
	<fcs> OFF </fcs>
	<propulsion> OFF </propulsion>
	<aerosurfaces> OFF </aerosurfaces>
	<fcs> OFF </fcs>
	<ground_reactions> OFF </ground_reactions>
	</output>
	-->
	</fdm_config>

Unless you Filename.py does something explicitly with the arguments data_output/flightgear.xml --realtime --nice nothing is going to be done to handle those arguments.

Which does bring up the point with regards to --realtime, so given your current Python example:

for t in np.arange(0,20,dt):
    fdm.run()

This is going to run as fast as your PC can run it, i.e. much faster than real-time, so who knows maybe it transmitted all 20*dt frames to FlightGear in less than a second and you didn't even notice the changes in FlightGear.

[matheusdarocha]

Thanks again for the attention and patience. I 'll try to explain what I did.

First I followed bcoconni instruction at a detailed tutorial in our FAQ. Using my script and my model, it worked really well and I can see the maneuver at flight gear as soon as it finishes.

The script that I used was:

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/xsl" href="http://jsbsim.sf.net/JSBSimScript.xsl"?>
<runscript xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="http://jsbsim.sf.net/JSBSimScript.xsd"
    name="Cruise flight with steady turn in 737.">

  <description>
    This is a very simple script that trims the aircraft with running
    engines at altitude and runs out to 100 seconds. Some state data
    is printed out at ten second intervals. 
  </description>

 <use aircraft="mb339pan" initialize="reset01"/>

  <run start="0" end="15" dt="0.008333">

    <property value="0"> simulation/notify-time-trigger </property>

    <event name="Set engines running">
      <condition> simulation/sim-time-sec le 0.1 </condition>
      <set name="propulsion/engine[0]/set-running" value="1"/>
      <set name="propulsion/engine[1]/set-running" value="1"/>
      <notify/>
    </event>

  <event name="Initialization 4">
   <description>Set the engine controls</description>
   <condition>
     simulation/sim-time-sec GE 0.0
   </condition>
   <notify/>
   <set name="fcs/advance-cmd-norm[0]"   value="1.0"/>
   <set name="fcs/advance-cmd-norm[1]"   value="1.0"/>
   <set name="fcs/throttle-cmd-norm[0]"  value="0.85"/>
   <set name="fcs/throttle-cmd-norm[1]"  value="0.85"/>
   <set name="propulsion/set-running" value="-1"/>
  </event>

    <event name="Trim">
      <condition>
        simulation/sim-time-sec le 3
      </condition>
      <set name="simulation/do_simple_trim" value="1"/>
      <notify>
        <property>velocities/vc-kts</property>
        <property>velocities/vc-fps</property>
        <property>velocities/vt-fps</property>
        <property>attitude/phi-rad</property>
        <property>attitude/theta-rad</property>
        <property>attitude/psi-rad</property>
      </notify>
    </event>

	  <event name="Trim with elevator">
		<condition>	simulation/sim-time-sec ge 10 </condition>
		<set name="fcs/TrimWithHTorEle" value="1"/>
		<set name="ic/targetNlf" value=".5"/>
		<set name="simulation/do_simple_trim" value="3"/>
	<notify/>
   </event>
  </run>
</runscript>

Now I want to do the same thing, but not with a script using xml, but a python code that represents the maneuver.
So i did the code below:

import jsbsim
import math
import numpy as np
import sys
sys.path.insert(1,'F:/OS/WORKING/200019_-_Turkish_Aerospace_Projeto_ASOJ/ENG/01_Aeronautics/09_Simulation/05_Tools/00_Python_library')
import akaer_aerolib_v7 as ak
import os


model_path = ('C:/tecnica/matheus.rocha')
modelpath = (model_path + '/200019_ASOJ_Green_FDM_V5_2')
model_name = '200019_ASOJ_aircraft'

Altitude = 6000
Veq= 400
Vtrue = math.sqrt(ak.Rho(0)/ak.Rho(Altitude))*Veq
Nlf = 1

MCA = '6J'
ak.WriteXml(modelpath + '//aircraft//', model_name, \
'MC' + MCA, 25, 'Green', False) ## comentar
fdm = jsbsim.FGFDMExec(modelpath)

fdm.load_model(model_name)
fdm['aero/blue'] = 1 ## comentar

dt = 0.001
fdm.set_dt(dt)

fdm['fcs/flap-pos-deg'] = 0
fdm['aero/alpha-max-rad'] = math.radians(20.0)
fdm['aero/alpha-min-rad'] = math.radians(-16.0)
fdm['ic/h-agl-ft'] = Altitude
fdm['ic/h-sl-ft'] = Altitude
fdm['ic/vt-kts'] = Vtrue

fdm.do_trim(1)   

for t in np.arange(0,20,dt):
    fdm.run()
    if t < 0.01:
        fdm.do_trim(1)   
        
print('end')

The aircraft model is the same, but I added the output line as you said.
It runs really well, just as the xml file, but the connection between python and FG does not work, it does not bring any error, just does not move to trim Nz = 1

[bcoconni]

@matheusdarocha, you need to specify the log directive data_output/flightgear.xml to your FDM. So your script should look like:

fdm = jsbsim.FGFDMExec(modelpath)

fdm.load_model(model_name)
fdm.set_output_directive('path/to/jsbsim_root/data_output/flightgear.xml')  # Tell JSBSim to send data to FlightGear.

fdm['aero/blue'] = 1 ## comentar

Note the additional code line:

fdm.set_output_directive('path/to/jsbsim_root/data_output/flightgear.xml')

Of course you should replace the path path/to/jsbsim_root by the appropriate path so that JSBSim can load the file data_output/flightgear.xml.

[matheusdarocha]

@bcoconni thanks for your attention

I tried to put the additional line as you said but the aircraft at FG didn't move.
What I did was:

start FG using command line at prompt:

fgfs --fdm=null --native-fdm=socket,in,60,,5550,udp --fdm=external --aircraft=mb339pan

run the code in python below

import jsbsim
import math
import numpy as np
import sys
sys.path.insert(1,'F:/OS/WORKING/200019_-_Turkish_Aerospace_Projeto_ASOJ/ENG/01_Aeronautics/09_Simulation/05_Tools/00_Python_library')
import akaer_aerolib_v7 as ak
import os

model_path = ('C:/tecnica/matheus.rocha')
modelpath = (model_path + '/200019_ASOJ_Green_FDM_V5_2')
model_name = '200019_ASOJ_aircraft'

Altitude = 6000
Veq= 400
Vtrue = math.sqrt(ak.Rho(0)/ak.Rho(Altitude))*Veq
Nlf = 1

MCA = '6J'
ak.WriteXml(modelpath + '//aircraft//', model_name, \
'MC' + MCA, 25, 'Green', False) ## comentar
fdm = jsbsim.FGFDMExec(modelpath)

fdm.load_model(model_name)

fdm.set_output_directive('data_output/flightgear.xml')  # Tell JSBSim to send data to FlightGear.

fdm['aero/blue'] = 1 ## comentar

dt = 0.001
fdm.set_dt(dt)

fdm['fcs/flap-pos-deg'] = 0

fdm['aero/alpha-max-rad'] = math.radians(20.0)
fdm['aero/alpha-min-rad'] = math.radians(-16.0)

fdm['ic/h-agl-ft'] = Altitude
fdm['ic/h-sl-ft'] = Altitude
fdm['ic/vt-kts'] = Vtrue

fdm.do_trim(1)   

for t in np.arange(0,20,dt):
    fdm.run()
    if t < 0.01:
        fdm.do_trim(1)   
        
print('end')

and then nothing happens on flight gear

[seanmcleod]

but I added the output line as you said.

Can you add a snippet of the xml to show exactly where and what you added to the aircraft's xml file?

What happens if you add an output element like the one I showed from the C-172p example, i.e. one that outputs a CSV file when you run your python script? Does the CSV file get created and populated?

[matheusdarocha]

@seanmcleod thanks for the attention

The xml that i put the addional line is below

<?xml version="1.0"?>
    <?xml-stylesheet type="text/xsl" href="http://jsbsim.sourceforge.net/JSBSim.xsl"?>
    <fdm_config name="m_ASOJ_global6000_green_v01" release="BETA" version="2.0"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="http://jsbsim.sourceforge.net/JSBSim.xsd">
        
        <fileheader>
            <author> Akaer </author>
            <filecreationdate> 2022-02-02 </filecreationdate>
            <version>$Revision: 1.00 $</version>
            <description> Bombardier Global 6000 - ASOJ Green Aircraft </description>
            <license>
                <licenseName>GPL (General Public License)</licenseName>
                <licenseURL>http://www.gnu.org/licenses/gpl.html</licenseURL>
            </license>
            <note>
                This model may contain confidential and proprietary material for the 
                sole use of the intended recipient and/or may be subject to export 
                control regulations. Any review or distribution by others is strictly 
                prohibited. If you are not the intended recipient, please contact 
                Akaer at +55 (12) 2139-1100 or https://www.akaer.com.br/eng/contact
          </note>
        </fileheader>
    	
    	<metrics file="metrics/200019_ASOJ_Green_Coeff_metrics"/>
    <!-- -->
    	<mass_balance file="mass_balance/200019_ASOJ_Green_CG25_MC6J"/>
    
    <!-- -->
    <!-- Include engine data and fuel mass configuration -->
    	<propulsion file="propulsion/200019_ASOJ_Green_Engine_BR710_CG25_MC6J"/>
    	
    		<!-- Include ground data -->
        <ground_reactions>
    		<!-- Include ground parameters-->
        </ground_reactions>
    	<system name="BlueAircraftActive">
    		<channel name="BlueAircraft">	
    			<switch name="aero/blue">
    				<default value="0.0"/>
    				<test value="aero/blue">
    					aero/blue eq 1.0
    				</test>	
    			</switch>
    		</channel>
    	</system>
    	
    	<system file="metrics/200019_ASOJ_Coeff_GeoParam"/>
    
    	<system file="200019_ASOJ_FCS_Flap"/>
    	
    	<system file="200019_ASOJ_FCS_Pitch"/>
    	
    	<system file="200019_ASOJ_FCS_Roll_v3_2"/>
    	
    	<system file="200019_ASOJ_FCS_Yaw"/>
    	
    	<system file="metrics/200019_ASOJ_Coeff_Arms_v04"/>
    	
    
    	<aerodynamics file="aerodynamics/200019_ASOJ_AerodynamicDB"/>
    	
        <output name="localhost" type="FLIGHTGEAR" protocol="UDP" port="5550" rate="60" version="24"> 
 </output> 
    </fdm_config>
    <!-- -->

start FG using command line at prompt:

fgfs --fdm=null --native-fdm=socket,in,60,,5550,udp --fdm=external --aircraft=mb339pan

run the code in python below

import jsbsim
import math
import numpy as np
import sys
sys.path.insert(1,'F:/OS/WORKING/200019_-_Turkish_Aerospace_Projeto_ASOJ/ENG/01_Aeronautics/09_Simulation/05_Tools/00_Python_library')
import akaer_aerolib_v7 as ak
import os

model_path = ('C:/tecnica/matheus.rocha')
modelpath = (model_path + '/200019_ASOJ_Green_FDM_V5_2')
model_name = '200019_ASOJ_aircraft'

Altitude = 6000
Veq= 400
Vtrue = math.sqrt(ak.Rho(0)/ak.Rho(Altitude))*Veq
Nlf = 1

MCA = '6J'
ak.WriteXml(modelpath + '//aircraft//', model_name,
'MC' + MCA, 25, 'Green', False) ## comentar
fdm = jsbsim.FGFDMExec(modelpath)

fdm.load_model(model_name)

fdm.set_output_directive('data_output/flightgear.xml') # Tell JSBSim to send data to FlightGear.

fdm['aero/blue'] = 1 ## comentar

dt = 0.001
fdm.set_dt(dt)

fdm['fcs/flap-pos-deg'] = 0

fdm['aero/alpha-max-rad'] = math.radians(20.0)
fdm['aero/alpha-min-rad'] = math.radians(-16.0)

fdm['ic/h-agl-ft'] = Altitude
fdm['ic/h-sl-ft'] = Altitude
fdm['ic/vt-kts'] = Vtrue

fdm.do_trim(1)

for t in np.arange(0,20,dt):
fdm.run()
if t < 0.01:
fdm.do_trim(1)

print('end')

and then nothing happens on flight gear

About the CSV file with the outputs, it is usually not created when run with python script, so it was not created

[seanmcleod]

Please use the triple back tick options, followed by the content type, e.g. python, xml, sh to format the relevant sections of your comment, makes it a lot easier to read.

About the CSV file with the outputs, it is usually not created when run with python script, so it was not created

The point was to confirm whether output elements in your FDM were working at all, i.e. replace the Flight Gear specific output element with a simple CSV one and confirm whether that works, i.e. when running your python script the CSV file is created with data logged etc.

[matheusdarocha]

I changed the output to get a csv and it worked.
Also, I discovered, I had to reset to initial conditions before the loop, now I can run python and see the maneuver at JSBSim

Thanks a lot for all the help

[seanmcleod]

now I can run python and see the maneuver at JSBSim

Do you mean you can see it in FlightGear now?

[matheusdarocha]

Yes I Can, it worked. Now i am working at @bcoconni comment to make it run in realtime
Thanks a lot

[bcoconni]

@matheusdarocha If you drive FlightGear from a Python script, you'll most likely notice that your aircraft flies much too fast. This is because JSBSim runs its computation as fast as possible i.e. much faster than real time.

If you want your simulation to run in real time, you'll need to wait that enough real time has elapsed since the last simulated time step. One means to achieve this result is the code below (the real time management is below the if args.realtime: instruction):

jsbsim/python/JSBSim.py

Lines 126 to 139 in a119eb2

	frame_duration = fdm.get_delta_t()
	sleep_nseconds = (frame_duration if args.realtime else sleep_period) * 1E9
	current_seconds = initial_seconds = time.time()
	result = fdm.run()
	while result and fdm.get_sim_time() <= args.end:
	if args.realtime:
	current_seconds = time.time()
	actual_elapsed_time = current_seconds - initial_seconds
	sim_lag_time = actual_elapsed_time - fdm.get_sim_time()
	for _ in range(int(sim_lag_time / frame_duration)):
	result = fdm.run()
	current_seconds = time.time()