Editing FlightGear (section)

==== Flight Dynamics ====
''FlightGear'' supports multiple [[flight dynamics]] engines with differing approaches, and external sources such as [[MATLAB]]/[[Simulink]], as well as custom flight models for hot air balloons and spacecraft.<ref name=":122">{{Cite web|title=Flight Dynamics Model - FlightGear wiki|url=http://wiki.flightgear.org/Flight_Dynamics_Model|access-date=2019-07-23|website=wiki.flightgear.org}}</ref><ref>{{Cite web|title=Flight Simulator Interface - MATLAB & Simulink|url=https://www.mathworks.com/help/aeroblks/introducing-the-flight-simulator-interface.html|archive-url=https://web.archive.org/web/20130704083155/http://www.mathworks.com/help/aeroblks/introducing-the-flight-simulator-interface.html|archive-date=2013-07-04|url-status=live|access-date=2021-03-15|website=Mathworks - Makers of MATLAB and Simulink - MATLAB & Simulink}}</ref>

===== JSBSim =====
''JSBSim'' is a data driven flight dynamics engine with a C++ core built to the needs of the FlightGear project from 1996 to replace NASA's ''LaRCSim'', and integrated into ''FlightGear'' as the default from 1999.<ref name=":14">{{Citation|last=Berndt|first=Jon|title=JSBSim: An Open Source Flight Dynamics Model in C++|url=https://arc.aiaa.org/doi/abs/10.2514/6.2004-4923|work=AIAA Modeling and Simulation Technologies Conference and Exhibit|year=2004|publisher=American Institute of Aeronautics and Astronautics|doi=10.2514/6.2004-4923|isbn=978-1-62410-074-1|access-date=2019-09-01|url-access=subscription}}</ref> Flight characteristics are preserved despite low frame rate, as JSBSim physics are decoupled from rendering and tick at 120&nbsp;Hz by default.<ref>{{Cite web|last=|first=|date=|title=Howto:Methods to replace the NASAL code with JSBSim code - FlightGear wiki|url=http://wiki.flightgear.org/Howto:Methods_to_replace_the_NASAL_code_with_JSBSim_code#Performance_of_JSBSim_.28or_data-driven_languages.29_in_a_real-time_.28RT.29_context|url-status=live|archive-url=https://web.archive.org/web/20190903092718/http://wiki.flightgear.org/Howto:Methods_to_replace_the_NASAL_code_with_JSBSim_code|archive-date=2019-09-03|access-date=2019-09-03|website=FlightGear wiki}}</ref> This also supports high time-acceleration as rendering does not have to be done faster causing the [[Graphics processing unit|GPU]] to be a bottleneck.

Mass balance, ground reactions, propulsion, aerodynamics, buoyant forces, external forces, atmospheric forces, and gravitational forces can be utilized by ''JSBSim'', the current default flight dynamics engine supported by ''FlightGear'', to determine flight characteristics.<ref>{{Cite web|title=JSBSim - FlightGear wiki|url=http://wiki.flightgear.org/JSBSim|access-date=2019-07-23|website=wiki.flightgear.org}}</ref> ''JSBSim'' supports non-terrestrial atmospheres and has been used to model unmanned flight in the Martian atmosphere by NASA.<ref>{{Cite web|last=|first=|date=|title=JSBSim Open Source Flight Dynamics Model|url=http://jsbsim.sourceforge.net/links.html|url-status=live|archive-url=https://web.archive.org/web/20190901135809/http://jsbsim.sourceforge.net/links.html|archive-date=2019-09-01|access-date=2019-09-01|website=jsbsim.sourceforge.net}}</ref><ref>{{Citation|last1=Kenney|first1=P. Sean|title=Simulating The ARES Aircraft In The Mars Environment|url=https://arc.aiaa.org/doi/abs/10.2514/6.2003-6579|work=2nd AIAA "Unmanned Unlimited" Conf. and Workshop & Exhibit|publisher=American Institute of Aeronautics and Astronautics|doi=10.2514/6.2003-6579|access-date=2019-09-01|last2=Croom|first2=Mark|year=2003|isbn=978-1-62410-094-9|hdl=2060/20040034718|s2cid=13269363 |hdl-access=free}}</ref><ref name=":14" />

====== Benchmark testing by NASA ======
JSBSim was used by NASA in 2015 with other space industry simulation code, both to establish a ruler to judge future code for the requirements and standards of the space industry, as well as check agreement. The verification tested both atmospheric and orbital flight in [[Six degrees of freedom|6-degrees-of-freedom]] for simulations like JSBSim<ref>{{Cite web|date=January 2015|title=Check-Cases for Verification of 6-Degree-of-Freedom Flight Vehicle Simulations - Volume II|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150001264.pdf|url-status=live|archive-url=https://web.archive.org/web/20170227123110/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150001264.pdf|archive-date=2017-02-27|access-date=|website=NASA Technical Reports Server|at=See Section B.6.7 JSBSim|last1=Murri|first1=Daniel G.|last2=Jackson|first2=E. Bruce|last3=Shelton|first3=Robert O.}}</ref> that supported both. The results from 6 participants consisting of NASA Ames Research Center (VMSRTE), Armstrong Flight Research Center (Core), Johnson Space Center (JEOD), Langley Research Center (LaSRS++, POST-II), Marshall Space Flight Center (MAVERIC), and JSBSim<ref name=":83">{{Citation|last1=Murri|first1=Daniel G.|title=Check-Cases for Verification of 6-DOF Flight Vehicle Simulations - Volume I|date=2015|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150001264.pdf|volume=|pages=|publisher=NASA|language=en|doi=|access-date=2019-09-03|last2=E. Bruce Jackson|last3=Shelton|first3=Robert O.}}</ref><ref name=":62">{{Cite web|last=|first=|date=|title=Check-Cases for Verification of 6-Degree-of-Freedom Flight Vehicle Simulations - Volume I|url=https://nescacademy.nasa.gov/src/flightsim/Reports/NASA-TM-2015-218675-EOM_checkcase_summary.pdf|access-date=|website=NASA Engineering and Safety Center Academy|at=See Section 7.4 - Summary of Comparisons}}</ref> were anonymous<ref>{{Cite web|last=|first=|date=2015|title=Further Development of Verification Check-cases for Six-Degree-of-Freedom Flight Vehicle Simulations|url=https://nescacademy.nasa.gov/src/flightsim/Reports/aiaa-15-1810-EOM_chkcases-II.pdf|url-status=live|archive-url=https://web.archive.org/web/20210310134926/https://nescacademy.nasa.gov/src/flightsim/Reports/aiaa-15-1810-EOM_chkcases-II.pdf|archive-date=10 March 2021|access-date=|website=NASA Engineering and Safety Center|at=See Section II G}}</ref> as NASA wanted to encourage participation. However, the assessment found agreement for all test cases between the majority of participants, with the differences being explainable and reducible for the rest, and with the orbital tests agreeing "quite well" for all participants.<ref name=":62" /><ref name=":732"/>

===== YASim =====
YASim's approach to flight dynamics uses the geometry of the aircraft present in the 3D model at startup, conceptually similar to [[Blade element theory]] used by some software, to calculate a rough approximation of fluid dynamics - with the conceptual problems that each "element" is considered in isolation therefore missing affecting fluid flow to other elements, and the approximation breaking down for craft in [[Mach number#Classification of Mach regimes|transonic to hypersonic regimes]].<ref>{{Cite web|last=Neely|first=Gary|date=|title=What is YASim?|url=http://www.buckarooshangar.com/flightgear/yasimtut_introduction.html|url-status=live|archive-url=https://web.archive.org/web/20190902085249/http://www.buckarooshangar.com/flightgear/yasimtut_introduction.html|archive-date=2019-09-02|access-date=2019-09-02|website=www.buckarooshangar.com}}</ref> By contrast, offline approaches like JSBSim can incorporate [[Wind tunnel|windtunnel]] data. They can also incorporate the results of [[computational fluid dynamics]] which can reach computable accuracy only [[Numerical methods in fluid mechanics|limited]] by the nature of the problem and present day [[Supercomputer#Performance measurement|computational resources]].

''FlightGear'' also supports LaRCsim and UIUC.<ref name=":132">{{Cite web|title=Flight Dynamics Model - FlightGear wiki|url=http://wiki.flightgear.org/Flight_Dynamics_Model|access-date=2019-07-23|website=FlightGear wiki}}</ref><ref>{{Cite book|last1=Zhang Jingsha|last2=Geng Qingbo|last3=Fei Qing|title=International Conference on Automatic Control and Artificial Intelligence (ACAI 2012) |chapter=UAV Flight Control System Modeling and Simulation Based on FlightGear |date=2012 |url=http://mr.crossref.org/iPage?doi=10.1049/cp.2012.1443 |pages=2231–2234|publisher=Institution of Engineering and Technology|doi=10.1049/cp.2012.1443|isbn=978-1-84919-537-9}}</ref>