According to http://ardupilot.org/dev/docs/setting-up-sitl-on-linux.html
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In the past ArduPilot required a special version of JSBSim. As of December 2018 that is no longer the case, and we can use the standard JSBSim releases.
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Moreover currently build-jsbsim.sh is failing with error:
../../src/models/propulsion/FGTurbine.h:297:3: error: ‘FGParameter’ does not name a type; did you mean ‘FGThruster’?
FGParameter *N1SpoolUp;
^~~~~~~~~~~