 | |
| Original author(s) | David Murr, Curt Olson, Michael Basler, Eric Korpela[1] |
|---|---|
| Developer(s) | FlightGear developers & contributors |
| Initial release | July 17, 1997; 27 years ago (1997-07-17) |
| Stable release | |
| Repository | |
| Written in | C++,C[3] |
| Engine |
 |
| Operating system | Linux macOS Windows FreeBSD Solaris or IRIX |
| Platform | Cross-platform |
| Size | 1.54 GB (Main files) |
| Available in | 5 languages |
| Type | Flight simulator |
| License | GNU General Public License |
| Website | www |
FlightGear Flight Simulator (often shortened toFlightGear orFGFS) is afree,open sourcemulti-platformflight simulator developed by theFlightGear project since 1997.[4]
David Murr started this project on April 8, 1996. This project had its first release in 1997 and continued in development. It has specific builds for a variety of differentoperating systems includingMicrosoft Windows,macOS,Linux,IRIX, andSolaris.
FlightGear is anatmospheric andorbital flight simulator used in aerospace research and industry. Its flight dynamics engine (JSBSim) is used in a2015 NASA benchmark to judge new simulation code to the standards of the space industry.
FlightGear started as an online proposal in 1996 by David Murr, living in the United States. He was dissatisfied withproprietary, available, simulators like theMicrosoft Flight Simulator, citing motivations of companies not aligning with the simulators' players ("simmers"), and proposed a new flight simulator developed by volunteers over the Internet.[5][6] The flight simulator was created using custom 3D graphics code. Development of anOpenGL based version was spearheaded by Curtis Olson starting in 1997.[6]FlightGear incorporated other open-source resources, including the LaRCsim flight dynamics engine fromNASA, and freely available elevation data. The first working binaries using OpenGL came out in 1997. By 1999 FlightGear had replaced LaRCsim withJSBSim built to the sims' needs, and in 2015 NASA usedJSBSim alongside 6 other space industry standards to create a measuring stick to judge future space industry simulation code.[7]
FlightGear reached 1.0 in 2007, 2.0 in 2010, and there were 9 major releases under 2.x and 3.x labels, with the final one under the previous numbering scheme being "3.4", since "3.6" was cancelled. The project moved to a regular release cadence with 2-4 releases per year since 2016, with the first version under the new naming scheme being "2016.1". Around that time, the graphical front end "FlightGear Launch Control", also known as "FGRun", was replaced by ahard-codedQt launcher.[8]FlightGear'ssource code is released under the terms of theGNU General Public License and isfree and open-source software.
TheFlightGear project has been nominated by SourceForge, and subsequently chosen as project of the month by the community, in 2015, 2017, and 2019.[9][10][11]
Forces experienced by a flying aircraft depend on the time-varying state of atmosphericfluid flow along the flight path - the atmosphere being a fluid that can exchange energy, exchange moisture orparticles, changephase orother state, and exert force withboundaries formed by surfaces. Fluid behaviour is often characterised byeddies(Videos:aircraft,terrain) orvortices on varying scales down to themicroscopic, but is harder to observe as the air is clear except for moisture phase changes likecondensation trails or clouds. The atmosphere-terrain boundaryinteraction follows fluid dynamics, just with processes on hugelyvarying scales and 'weather' is theplanetary boundary layer. The aircraft surface interaction works with thesame dynamics, but on a limitedrange of scales. Forces experienced at any point along a flight path, therefore, are the result of complicated atmospheric processes on varying spatial scales, and complex flow along the craft's surface. Craft also experience varying gravitational force based on the 3d shape of the potential well and thenon-spherical shape of the Earth.
FlightGear can simulate the atmosphere ranging fromenergy inputs/outputs to the system, like energy from the sun or volcanic sources, through to fluid flow on various scales and changes of state.FlightGear is able to model different surface characteristics such as heating or cooling, and the exchange of heat and moisture with the atmosphere depending on factors like windflow or dew point.FlightGear models the continuously evolving life-cycle of phenomena on various scales, driven by interaction of fluid with terrain. They range from turbulence on different scales to, individual thermals, thunderstorms, through to moving air layers, and depicting air-masses on the scale of thousands of kilometers. Atmospheric water is modeled byFlightGear ranging from state changes such as condensing into cloud or haze layers, along with energy provided from latent heat to drive convective fluid flow, through to precipitation as rain droplets, snow, or hail.[12][13][14][15]
The process of generating lift creates turbulence with vortices, andFlightGear models wake turbulence withshedding of wingtip vortices by flown craft as well as AI craft.[16][17]
FlightGear also has a less physically accurate model that usesMETAR weather updates of differing frequency, designed for safe operation ofaerodromes, todis-continuously force atmosphere based on attempted guesses of processes that are fundamentally constrained by the closeness or density of observation stations, as well as thesmall-scale, limited, rounded off,non-smoothly varying, and need-to-know precision of information.[18] Aloft waypoint settings modelling high altitude behaviors of wind can be synced to updates from Jeppeson.[19]
Flightgear has a simulation of planetary bodies in the solar system which is used for purposes like driving latitude dependent weather from solar radiation, as well as the brightness and position of stars forcelestial navigation. There is a model of gravity based on a non-spherical Earth, and craft can even experience differing gravity across their bodies which will exerttwisting force.[20] A model of the observedvariation in the Earth'scomplex magnetic field, and the option to simulate, to an extent, the propagation of radio wave signals due to interaction with different types of terrain, also exists inFlightGear.[21][22]
FlightGear uses an exact,non-spherical, model of Earth, and is also able to simulate flight inpolar regions and airports (arctic orantarctic) without simulator errors due to issues with coordinate systems.
FlightGear supports multipleflight dynamics engines with differing approaches, and external sources such asMATLAB/Simulink, as well as custom flight models for hot air balloons and spacecraft.[23][24]
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'sLaRCSim, and integrated intoFlightGear as the default from 1999.[25] Flight characteristics are preserved despite low frame rate, as JSBSim physics are decoupled from rendering and tick at 120 Hz by default.[26] This also supports high time-acceleration as rendering does not have to be done faster causing theGPU to be a bottleneck.
Mass balance, ground reactions, propulsion, aerodynamics, buoyant forces, external forces, atmospheric forces, and gravitational forces can be utilized byJSBSim, the current default flight dynamics engine supported byFlightGear, to determine flight characteristics.[27]JSBSim supports non-terrestrial atmospheres and has been used to model unmanned flight in the Martian atmosphere by NASA.[28][29][25]
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 in6-degrees-of-freedom for simulations like JSBSim[30] 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[31][32] were anonymous[33] 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.[32][20]
YASim's approach to flight dynamics uses the geometry of the aircraft present in the 3D model at startup, conceptually similar toBlade 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 intransonic to hypersonic regimes.[34] By contrast, offline approaches like JSBSim can incorporatewindtunnel data. They can also incorporate the results ofcomputational fluid dynamics which can reach computable accuracy onlylimited by the nature of the problem and present daycomputational resources.
FlightGear also supports LaRCsim and UIUC.[35][36]
FlightGear is able to accelerate and decelerate time, speeding up or slowing down the simulation. Time acceleration is a critical feature for simulating longer flights and space missions. For all interactions with the simulator, it allows people to speed up uneventful parts, and gain more experience (decisions and problem solving). It also means automated simulations used for research finish faster - this is helped byFlightGear'sheadless mode.
FlightGear is able to support high time accelerations by allowing parts of the simulation to run at different rates. This allows saving of CPU and GPU resources by letting unimportant parts of the simulation, like visuals or less time-sensitive aircraft systems, run at slower rates. It also improves performance. Separate clocks are available for JSBSim physics, different parts of aircraft systems, as well as environment simulations at large scale (celestial simulation) and small scale (weather physics).
Flightgear's atmospheric rendering is able to provide constantly changing visual cues of processes affecting atmospheric fluid flow and their likely evolution and history - to make prediction of conditions ahead or when returning at a later time possible. Simulation of directionallight scattering by the Advanced Light Scattering framework in the atmosphere shows the 3d distribution, layering, geometry, and evenstatistical orientation of particles in differentscattering regimes like Mie or Rayleigh. This ranges from different moisture droplets, to smog, toice crystals of different geometry in clouds or halos.[13][12][37][38]
The 3d density distribution of cloud (orcondensation trail) moisture rendered byFlightGear acts as a cue to the corresponding 3d structure of fluid flow, such as theup and down draft loop of storm cell,internal gravity waves formingundulating cloud bands signalling a sweeping cold front, or windshearshaping cirrus clouds at higher altitude.[12][13][15][37][38]
FlightGear is able to render rain falling from specific clouds in rain volumes containing the correct droplet size to determine the properties like thickness and intensity of rainbows.[12][14][38] Perceptual phenomena like rain streaks are rendered with streak length shortening as time is slowed. Rain and water spray streaks on canopy glass provides cues to the relative air flow, while frost and fog with correct light scattering provide cues to temperature.[39][37][38]
FlightGear is able to render specified historical accumulation levels of water and snow accounting for flatness on the surfaces of for both terrain and buildings. This provides cues to surface moisture or friction, and weather driven by surface heating that reduces with snow thickness.FlightGear can render gradual snow and ice cover on inland and ocean water.[12][38]
Layering of hazes is rendered byFlightGear, such as low lyingground haze with 3d structure, smog related to human activity, and dust.FlightGear renders varioushalos due to ice crystals in the atmosphere, or due to Mie scattering in fog by artificial lights such as landing lights.[13][37]
FlightGear is able to render day/night visuals of Earth from orbit at high detail with scattering due to clouds, dust, and moisture, as well as effects such as lightning illuminating storm cells. Orientation cues in cockpit are provided by changing colour of light from Sun, Earth, and Moon for craft such as the Space Shuttle. The gradual transition in lighting for spacecraft, between upper and lower atmosphere regimes, is handled by dedicated rendering code. Auroras are simulated with varying intensity and varying penetration of magnetic flux tubes into the atmosphere. They are visible from both space and ground.[20][40][37]
Accurate rendering of planets, moons, and stars with correct phases/brightness based onFlightGear's celestial simulation allows cues or data forcelestial navigation - without reliance on vulnerable ground aids, including of pre-GPS era craft. The celestial simulation allows craft such as the Space Shuttle[20][41] to usestar tracker instruments.
Flightgear's Advanced Light Scattering framework simulates locations in time as well as space. The environment simulation renders seasonal change as leaves of different species of trees, bushes, and grass change colour or fall.[42] Simulated swaying of grass, trees and windsocks provide cues to processes changing the windfield near the ground, while wave simulation provides cues near water.[13][12][38] Cloud shadows and the general state of the atmosphere affect light traveling to each point of the environment and then traveling in the atmosphere to reach the eye - the cloud setup and particle spread in the atmosphere changes the colour of the light cast on the environment.[13] Water colour therefore changes based on atmosphere overhead, and also depends on water impurites in a region.FlightGear is capable of rendering a variety ofvolcanic activity of different intensity that, from v2019.2, responds to the windfield, as well as smoke.
The combination of rendering of the state of atmospheric processes, Aurora, simulation of celestial bodies, ground accumulation of rain or snow or dust, ice cover of water, and the environment simulation produces visualisations with a vast number of permutations.[13][12][40][37]
Severalnetworking options allowFlightGear to communicate with other instances ofFlightGear. Amultiplayerprotocol is available for usingFlightGear on alocal network in a multi aircraft environment. This can be used forformation flight orair traffic control simulation. Soon after the original Multiplayer Protocol became available, it was expanded to allow playing over the internet. It is possible to see other players in the simulator if they have the same aircraft models and viewing their flight path is possible with the simulator's online multiplayer map.[43]
SinceFlightGear version 2020.1 it is possible to connect toVATSIM by using the open-source swift pilot client.[44]
Several instances ofFlightGear can be synchronized to allow for amulti-monitor environment.
FlightGear usesmetar data to produce live weather patterns in real time.[45] Detailed weather settings allow for 3d clouds, a variety ofcloud types, and precipitation. Precipitation and terrain affect turbulence and cloud formations.[46] Aloft waypoint settings allow high altitude behaviors of wind to be modeled from live weather information, and thermals can also be modeled.[47]
Although not developed or typically analyzed solely as a game in the traditional sense,FlightGear has nevertheless undergone reviews in a number of online and offline publications, and received positive reviews as a flight simulator game.[48]FlightGear 1.0.0 was noted as being impressive for a game over a decade in the making, with a wide variety of aircraft and features.
PC Magazine noted how it is designed to be easy to add new aircraft and scenery.[49]Linux Format reviewed version 2.0 and rated it 8/10.[50]
In June 2014Honda lawyers issued atakedown request in which it was claimed that theHondaJet model in the simulator infringes on Honda'strademarks. Subsequently, HondaJet became the first model removed from the simulator for legal reasons.[51]
Games journalist Tim Stone, in his simulation column The Flare Path, criticized the practice of third-parties attempting to profit from the work of community volunteers to the project, pointing to deceptive practices of stealing media available online from other sims to misrepresent VirtualPilot3d, as well as highlighting allegedly fake customer testimonials.[52] Following up in 2018, Tim Stone wrote a second column in which he again criticized the "ethical standards" and "extraordinary willingness to lie in the pursuit of sales" displayed by the advertisements for another game which used screenshots from FlightGear.[53]
FlightGear has been used in a range of projects in academia and industry (includingNASA).[54] The application has also been used for pilot training and as a research and development platform by various agencies and universities.
The simulator has been used by numerous institutes and companies, such as NASA/Ames Human Centered System Lab.[55][56] Pragolet s.r.o.[57] and the Endless Runway Project; a consortium of several European aerospace institutes.[58][59]
Endless Runway Project, consortium of several European aerospace institutes.[67][68]
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