Modeling of VTOl fixed UAV

[prashant19012002]

I am new to JSBSim i tried it with few fuel based models. but when i tried to run it with a electric based UAV i am not able to test for any scripts. are their any electric aircraft xml files along with scripts files for cruise condition or any other which i can use as a reference for my model.
It would be very helpful if someone helps me with this.

[bcoconni]

are their any electric aircraft xml files along with scripts files for cruise condition or any other which i can use as a reference for my model.

Hi @prashant19012002,

Yes, you can check the FDM of DJI F450 quadcopter in https://github.com/JSBSim-Team/jsbsim/tree/master/aircraft/F450

[prashant19012002]

Hi @bcoconni i tried running this particular model with Test_F450_Launch.xml script. but i got the error as

  Propulsion:

In file aircraft/F450/Propulsion.xml: line 4
 Unknown engine type

Aircraft propulsion element has problems in file Path "aircraft/F450/F450.xml"
Script file Path "scripts/Test_F450_Launch" was not successfully loaded

Its because the kind of engine this particular model uses
which is defined as a bldc motor

<?xml version="1.0"?>
<!--bldc_engine name="DJI E305"-->
  <brushless_dc_motor name="DJI E305">
  <velocityconstant> 960 </velocityconstant>
  <coilresistance>0.117</coilresistance>
  <noloadcurrent>0.45</noloadcurrent>
  <maxvolts> 14.63 </maxvolts>
</brushless_dc_motor>

This is exactly what i need but i am not able to execute the final trim script and get the results.

[seanmcleod]

@prashant19012002 where did you download/install your JSBSim from? I'm guessing you have a very old version.

I'm using the current JSBSim repo source, built it locally and was able to run the script without any issues. Note it executes a ground trim.

.C:\source\jsbsim> .\Debug\JSBSim.exe --script=scripts\Test_F450_Launch.xml
...
....
  Body Rates (relative to given frame, expressed in body frame)
    ECI:   4.348681968941312e-20, -0.002968449199997751, -0.002940172240112663 (p,q,r in deg/s)
    ECEF:  0, 0, 0 (p,q,r in deg/s)

---- JSBSim Execution beginning ... --------------------------------------------

Repeating Notify (Event 10) executed at time: 0.002000
    fcs/ScasEngage = 0.000000
    fcs/throttle-cmd-norm = 0.000000
    fcs/throttle-cmd-norm[1] = 0.000000
    fcs/throttle-cmd-norm[2] = 0.000000
    fcs/throttle-cmd-norm[3] = 0.000000
    propulsion/engine[0]/propeller-rpm = 0.000000
    propulsion/engine[1]/propeller-rpm = 0.000000
    propulsion/engine[2]/propeller-rpm = 0.000000
    propulsion/engine[3]/propeller-rpm = 0.000000
    propulsion/engine[0]/thrust-lbs = 0.000000
    propulsion/engine[1]/thrust-lbs = 0.000000
    propulsion/engine[2]/thrust-lbs = 0.000000
    propulsion/engine[3]/thrust-lbs = 0.000000
    position/h-agl-ft = 935.731957
    velocities/vc-kts = 0.000000
    attitude/phi-rad = 0.000000
    attitude/theta-rad = 0.000000
    attitude/psi-rad = 1.570796

Start: Tuesday October 03 2023 11:46:10 (HH:MM:SS)
  Ground Trim

  Trim successful
  Trim Results:
          Altitude AGL:   0.49  wdot:  7.28e-04 Tolerance: 1e-03  Passed
           Pitch Angle:  -0.01  qdot: -4.34e-05 Tolerance: 1e-04  Passed
            Roll Angle:  -0.00  pdot:  3.82e-05 Tolerance: 1e-04  Passed

Trim (Event 1) executed at time: 0.004000
    position/h-agl-ft = 0.494346

GEAR_CONTACT: 0.004000 seconds: Front_Center 1
GEAR_CONTACT: 0.004000 seconds: Aft_Left 1
GEAR_CONTACT: 0.004000 seconds: Aft_Right 1

Repeating Notify (Event 10) executed at time: 1.000000
    fcs/ScasEngage = 0.000000
    fcs/throttle-cmd-norm = 0.000000
    fcs/throttle-cmd-norm[1] = 0.000000
    fcs/throttle-cmd-norm[2] = 0.000000
    fcs/throttle-cmd-norm[3] = 0.000000
    propulsion/engine[0]/propeller-rpm = 0.000000
    propulsion/engine[1]/propeller-rpm = 0.000000
    propulsion/engine[2]/propeller-rpm = 0.000000
    propulsion/engine[3]/propeller-rpm = 0.000000
    propulsion/engine[0]/thrust-lbs = 0.000000
    propulsion/engine[1]/thrust-lbs = 0.000000
    propulsion/engine[2]/thrust-lbs = 0.000000
    propulsion/engine[3]/thrust-lbs = 0.000000
    position/h-agl-ft = 0.494346
    velocities/vc-kts = 0.000031
    attitude/phi-rad = 0.000000
    attitude/theta-rad = -0.005774
    attitude/psi-rad = 1.570796

GEAR_CONTACT: 1.134000 seconds: Aft_Left 0
GEAR_CONTACT: 1.134000 seconds: Aft_Right 0
GEAR_CONTACT: 1.138000 seconds: Front_Center 0

Repeating Notify (Event 10) executed at time: 2.000000
    fcs/ScasEngage = 1.000000
    fcs/throttle-cmd-norm = 0.500000
    fcs/throttle-cmd-norm[1] = 0.500000
    fcs/throttle-cmd-norm[2] = 0.500000
    fcs/throttle-cmd-norm[3] = 0.500000
    propulsion/engine[0]/propeller-rpm = 6001.089805
    propulsion/engine[1]/propeller-rpm = 6000.600891
    propulsion/engine[2]/propeller-rpm = 6001.089660
    propulsion/engine[3]/propeller-rpm = 6000.601036
    propulsion/engine[0]/thrust-lbs = 1.025826
    propulsion/engine[1]/thrust-lbs = 1.026302
    propulsion/engine[2]/thrust-lbs = 1.025826
    propulsion/engine[3]/thrust-lbs = 1.026302
    position/h-agl-ft = 4.819809
    velocities/vc-kts = 5.832503
    attitude/phi-rad = -0.000013
    attitude/theta-rad = 0.046461
    attitude/psi-rad = 1.570796
.....
.....

Repeating Notify (Event 10) executed at time: 29.002000
    fcs/ScasEngage = 1.000000
    fcs/throttle-cmd-norm = 0.489997
    fcs/throttle-cmd-norm[1] = 0.489996
    fcs/throttle-cmd-norm[2] = 0.490004
    fcs/throttle-cmd-norm[3] = 0.490004
    propulsion/engine[0]/propeller-rpm = 6012.074369
    propulsion/engine[1]/propeller-rpm = 6012.070768
    propulsion/engine[2]/propeller-rpm = 6012.153097
    propulsion/engine[3]/propeller-rpm = 6012.150476
    propulsion/engine[0]/thrust-lbs = 0.806391
    propulsion/engine[1]/thrust-lbs = 0.806391
    propulsion/engine[2]/thrust-lbs = 0.806418
    propulsion/engine[3]/thrust-lbs = 0.806418
    position/h-agl-ft = 598.069851
    velocities/vc-kts = 18.232151
    attitude/phi-rad = -0.000040
    attitude/theta-rad = 0.047818
    attitude/psi-rad = 1.570800

End: Tuesday October 03 2023 11:46:13 (HH:MM:SS)
(base) PS C:\source\jsbsim>

[prashant19012002]

Hi @seanmcleod yeah this seems to be the issue i am facing from many days. I Cloned the current JSBSim repo from GitHub and built it using visual studio and was using that. But after seeing your command i ran that

C:\jsbsim> .\Debug\JSBSim.exe --script=scripts\Test_F450_Launch.xml


     JSBSim Flight Dynamics Model v1.2.0.dev1 Oct  3 2023 10:21:35
            [JSBSim-ML v2.0]

earlier my command was

C:\jsbsim>JSBSim --script=scripts/Test_F450_Launch


     JSBSim Flight Dynamics Model vcompiled from FlightGear 2020.3.18 Mar 14 2023 06:05:46
            [JSBSim-ML v2.0]

I used this command for most of my scripts early.
Thank you for the help.

[LucasJSch]

I was trying to add VTOL capabilities to a Cessna C310R . The way I found to solve this was adding a section in <external_reactions> like the following:

<force name="vtol_force" frame="INERTIAL">
        <location unit="IN">
            <x> 0 </x>
            <y> 0 </y>
            <z> 0 </z>
        </location>
        <direction>
            <x>1</x>
            <y>0</y>
            <z>0</z>
        </direction>
</force>

The upper lift worked like charm. But the aircraft ended up pointing upwards, I guess because of the aerodynamics. My question is: How can I model this so that the aircrafts maintains its attitude, and doesn't point upwards like a rocket?

[seanmcleod]

Not really due to aerodynamics. Look at the location at which you've positioned this, basically on the nose of the aircraft. So there is a torque given by the force multiplied by the distance from the nose to the cg.

[LucasJSch]

000 is the nose? Where is the CoG ?

[seanmcleod]

Take a look at - https://jsbsim-team.github.io/jsbsim-reference-manual/user/concepts/frames-of-reference/

The empty weight CoG is defined in the FDM, once fuel etc. is added the actual CoG will differ, you can query it via the property tree and/or depending on how you're running JSSim it's also printed out to the console.