Flight Gear - from History to Future

• A.R. Perry
  • alex.perry@ieee.org
  • Presenter and Developer

a FORUM presentation
(page 1)

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Project focus

• To create high quality simulation that
  • minimises short cuts and runs on ordinary computers
  • extensible and encourages local modifications

• Started April 1996 by David Murr
  • Open source (GPL) - No commercial backing as yet
  • Curt Olson made a multiplatform release in July 1997
• Since then, it expanded beyond flight aerodynamics
  • improving graphics, clouds and fog,
  • a shaded sky with sun, moon and stars correctly drawn,
  • automated worldwide scenery, network play,
  • electronic navigation systems, airports and runways,
  • head up display and instrument panel and much more ...

• Scales up from commodity computers
  • For commercial and research applications
  • Fairly easy using Linux on various targets

(page 2)

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Custom airport 2000



(page 3)

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Custom airport 2001



(page 4)

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Portability between Operating Systems

• Portable across operating systems (Mac, IRIX, etc)
  • For sound, 3D graphics, menus, joystick and keyboard
  • Implementation may be equivalent, yet very different
  • The PLIB project offers a simple API
  • http://plib.sourceforge.net

• Generally, the Windows binaries are portable
  • This is critical for most Win32 users
  • Few of them have developer tools installed

• Linux-based operating systems are very similar
  • Compared to Windows, MacOS and Irix, etc
  • Most problems affect PLIB first
  • When PLIB runs, FlightGear is generally ok
• With joysticks, for example:
  • Two ioctl()s, /dev/js0 or /dev/input/js0
  • Devices detected early and not consistently numbered

(page 5)

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Simulator Execution

• FlightGear can be running in less than an hour ...

• 1. Install Linux normally
  • Ensure zlib and its headers are present
• 2. Install and test 3D support
  • On video card, maximum of 25% of memory for 2D display
  • Then enable hardware accel (may need XFree86 3 and Utah)
  • Verify at least 100fps using gears (or play glTron)
• 3. Install PLIB 1.2 or later with headers
  • Already packaged in many distributions
  • Test with the supplied examples to ensure working
• 4. Install SimGear and FlightGear
  • Prepackaged in SuSE, Mandrake and Debian unstable
  • Or download SimGear, FlightGear source and base
  • Compile and install SimGear, then FlightGear, then
  • Finish installing the base and added scenery

• 5. Type "runfgfs" and enjoy

(page 6)

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Features beyond minimal install

• It's lonely being alone in the sky
  • Network play support is built-in
  • Each aircraft has to be reported to all others
  • Considerable network load, can degrade performance
  • The FlightGear Daemon is a standalone program
  • Runs on separate computer to do coordination

• View is more like passenger portholes on airlines
  • Not the wraparound windows of general aviation aircraft
  • Especially when the simulated aircraft has an open cockpit
  • Use multiple displays, as shown on next slide

• Base package only has a small area
  • San Francisco and adjacent Bay area, California
  • New pilots soon want to go somewhere else
  • The scenery server has the whole world, see later

(page 7)

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Multiple displays for the pilot




(page 8)

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Multiple displays implementation

• Multiple cards in one computer is slow
  • They compete for the limited bus bandwidth

• Use network socket communications
  • One machine runs FDM, and exports FDM data
  • Others use dummy FDM and import that data
  • No intrinsic limit to number of displays

• runfgfs --fov=45.0 --view-offset=0
  • --native=socket,out,60,s1,5500,udp
  • --native=socket,out,60,s2,5500,udp
• runfgfs --fov=45.0 --view-offset=-50
  • --native=socket,in,60,,5500,udp --fdm=external
• runfgfs --fov=45.0 --view-offset=50
  • --native=socket,in,60,,5500,udp --fdm=external

(page 9)

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Simulating the Aircraft

• The aerodynamic simulation is only one part
  • Of the whole environment being simulated
  • Its performance is critical to the user's experience
  • Errors in Flight Dynamics Model (FDM) are distracting
• Other simulator components such as the autopilot
  • Are designed to expect a realistic aircraft
  • May respond incorrectly as a result of FDM errors
  • Provide additional pilot distractions
• Can ruin the user's immersive experience

• The FDM is created as an object abstraction
  • Allows multiple FDMs to be installed
  • Permits R&D use and future expansion

(page 10)

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Simulating - Flight Dynamics Model

• LaRCsim, models a Cessna 172 or Navion
  • Dedicated C source with coefficients hard coded
  • Supports all normal flight maneuvers

• University of Illinois, parametric derivative
  • Simplified the models for cruise flight regimes
  • A configuration file is loaded at simulation start
  • Supports many different light aircraft choices

• JSBSim, completely parametric FDM
  • All the information is retrieved from XML format files
  • Can run independently of a full environmental sim
  • As of this year, supports the Cessna 172 fairly well and
  • The X-15 (a hypersonic rocket propelled research vehicle)

(page 11)

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XML appearing everywhere ?

• This year, most configuration files are XML
  • The engine models,
  • The instrument panel layouts, instrument designs,
  • The head up display layout,
  • The user preferences and the saved state

• The real benefit of using XML here ?
  • For people with no software development background
  • Pilots, instructors, maintenance techs, researchers
  • They can easily and effectively contribute
  • All have in-depth technical knowledge of value
  • How an aircraft and hence the simulator should behave

• Previously, Windows binary users were excluded
  • Much system configuration was done at compile-time

• Everyone must have direct access to the internals

(page 12)

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Simulating Instruments and Radios

• All real-life instruments have errors

• Note that the HUD is computer generated
  • The computer can do the physics modelling too
  • Real-life HUDs generally don't have these errors

• Navigation radios have been implemented this year
  • Errors are not (they make real-life use challenging)

• Communication radios are not implemented
  • Pilots cannot use their microphone inputs to interact
  • Radio usage is a large part of aviation complexity

(page 13)

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Simulator Structure - Properties

• Core is directly interacting objects
  • High level state is also generalized out of them

• Property database is new this year
  • Relates a hierarchical name: /position/latitude
  • To an object with getter and setter methods
  • Ideal for user interface needs and saved state
  • Used for parametric graphics elements, configuration files

• Properties are network accessible
  • runfgfs --props=socket,bi,20,,5555,tcp
  • telnet localhost 5555
  • Especially useful for Flight Instructor activities
  • Independent programs can interact with the simulation

(page 14)

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Simulating the World - TerraGear

• Open-source tools and rendering libraries
  • Collect free data for building 3D representations
  • The whole earth usable in real time rendering

• Much freely available GIS data on the internet
  • Core data for FlightGear has to be unrestricted
  • So many sources of raw data cannot be incorporated

• Three categories of data are in use
  • Digital Elevation Model (DEM), 1 km grid worldwide
  • Polygon outlines for lakes, islands, towns
  • New this year, we also use vegetation and land usage
  • Landmarks such as lighthouses, radio and water towers

• Individual users and groups can rebuild
  • Generate larger, slower files for faster computers
  • Use locally available, restricted, data sources
  • Optimize scenery quality for specific application

(page 15)

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TerraGear - Screen dump



(page 16)

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TerraGear - Storage size

• Clearly a synthetic image, but sufficient
  • Navigate by pilotage - comparing view to a chart
• Compact, about one kilobyte per square kilometer
  • Necessary, since about 10000 sq km may be in view

• Stored in a 4 level hierarchy, each 10-100 smaller
  • One planet, currently only the Earth
  • 10 deg x 10 deg rectangle
  • 1 deg x 1 deg, approx 100 km x 60 km
  • A rectangular tile of 100 km^2 approximately

• Tiles are demand loaded and unloaded
  • Runs slower when the visibility is better
  • Needs more memory to store tiles too

(page 17)

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National data limitations

• Poor worldwide data already being used
• Good data is often country specific
  • Need special code to read and process file format
  • A lot of effort to do this for every country
  • Rapidly reaches the point of diminishing returns

• Many organizations collect/transform the data
  • Creates a standardized format, for these applications
  • There is a huge amount of effort involved
  • So their prices are extremely high to fund it
  • They cannot give the data away for us to use

• Maybe those organization will sell us scenery
  • Run their data through TerraGear and burn some CDs
  • You can expect a high price tag for such reliable data

(page 18)

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Mismatched Charts - Atlas

• Public domain data is generally of reduced quality
  • or out of date, or selective, or local coverage, etc
• The scenery generated from that data is actually wrong
  • Compared to the real world out there

• Synthetic charts - Atlas project
  • Automatic translation of TerraGear files
  • Generates usable aviation style charts
  • Inaccurate compared to the real world
  • Therefore useless for flight in an aircraft

• The Atlas application is for browsing
  • This year, it connects directly to FlightGear
  • Display aircraft current location on moving map
  • Most small aircraft do not have moving map GPS

• Invaluable to the flight instructor

(page 19)

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Synthetic chart - example



(page 20)

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Worldwide detail within airports

• This year, added support for various databases
  • These list worldwide airport details
  • And their runway positions, lengths, etc
  • With hints on surface type and markings
  • This is sufficient to generate all runways

• What about the rest of the airport
  • Taxiways and ramp areas available in CVS version
    • Courtesy of Robin Peel's taxiway database
  • Control tower, hangars, terminals and similar
    • Not available, users can add them manually using PPE
  • Surface navigation signs and markings
    • No general support available, a lot of work with PPE

• Clearly, realism is poor below stalling speed
  • No central government control of those areas
  • Thus, no convenient data archive we can use

(page 21)

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Standard landing screenshot 2001



(page 22)

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Example of future support for signs



(page 23)

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Simulator Applications

• A wide range of people interested
  • Building a realistic home simulator out old airplane parts
  • Simply having a viable alternative to commercial sims
  • A platform for icing research at Smart Icing Systems Project
  • Control algorithms for an autonomous aerial vehicle
  • Retrofit some older sim hardware with FGFS based software
  • Renew an old Agwagon single seat, single engine simulator
  • Image generator for eval of ski-jump launch
    • and arrested recovery from an aircraft carrier
  • Scenery and out-the-window view for the Genesis 3000 sim
  • Airport familiarization to avoid runway incursions

• ... and many more
  • How about selling it ?

(page 24)

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Shrinkwrap sale

• Reselling open source software ?
  • It has not been a good revenue source for other companies
  • Partly because of the rapid version changes
  • And because of the low cost of bandwidth for the consumer
• Yet, several organizations are considering it
  • Can FlightGear be a viable profit center?

• It is being repackaged by many distributions
  • To ensure a painless installation for the community
  • There appears to be little benefit in making a product here
  • Closed source flight sim games are available at under $20

• Separate the database of visual scenery
  • Everything else user needs is only few megabytes
  • Which easily fits into a corner of a scenery CD
  • Will readily be downloaded when new versions available

(page 25)

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Shrinkwrap sale - Scenery

• The scenery needs lots of space
  • About a gigabyte for each continent currently
  • Is unlikely to get any smaller in future
  • This still represents a significant download
• The scenery is relatively stable over time
  • Old versions are usually useful with newer binary software
  • Upgrades only add detail to an existing and viable database

• There is clearly a retail opportunity
  • Probably a DVD or a dozen CDs of the world
  • Trivial marginal cost of adding a few dozen binaries
    • for popular distros and driver combinations
  • Thus, this retail package is likely to be fully functional

(page 26)

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Streaming scenery - concept

• Consider general aviation aircraft
  • Cruise usually below 200 knots, often only 120 knots
  • Flight visibility is (in real life) usually below 20 miles
  • For lower altitudes used by non-turbocharged piston engines
• Maximum of 8000 square miles per hour
  • Even when flying in a straight line (worst case)
  • This is new terrain that will come into view
  • Currently, database uses 1 MB/ 600 sq miles
• Streaming rate 12 megabytes/hour will be sufficient
  • That will fit through a normal 56K modem link
  • An airliner at cruising altitude needs all your DSL

• Bandwidth is often much lower
  • Because some scenery may already be downloaded
  • Will be zero in your favorite flight areas
  • Then there is no need to be on-line while flying

(page 27)

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Streaming scenery - implementation

• No change to FlightGear source is needed
  • The latitude and longitude of the aircraft are exported
  • Scenery is stored in convenient 100 sqkm pieces
  • An independent program can make directed requests
  • For example, by spawning "wget" calls
• Still any need for retail scenery packages ?

• Multiply this bandwidth by worldwide community
  • That is a sizeable traffic impact on the servers
  • Latency is critical; we must keep ahead of the pilot
  • Is the total still low enough to be supported for goodwill ?
  • Will free servers transition to monthly access fees ?
  • Would they then start delivering proprietary content ?

• Who knows ... until we try it

(page 28)

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Flight Training

• Could also be helpful when learning to fly
• Flight training is carefully regulated by government
  • To ensure that aircraft generally stay in the sky
  • Until their pilot intends for them to come down safely
  • There are real concerns, before authorities can approve a system

• What does the U.S. government want ?
  • Any pilot can sit down and immediately use it
  • It isn't dangerously different or deceptively easy
  • The instructor can specify the flight environment

• Flight Gear Avation Training Device
  • http://fgatd.sourceforge.net
  • Goal is to implement requirements to achieve approval
  • Most of the work is documentation and testing
  • Actual simulation is a minor part of the whole
  • Finding sources of suitable controls is a challenge

(page 29)

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Flight training - OverRegulated ?

• The FAA is responding to human nature
  • That doesn't go away just because it's inconvenient
• The things learnt first
  • Leave an almost unshakeable impression
  • At times of severe stress, will over-rule later training
  • Any false impressions are learned by a beginning student
  • Tend to remain hidden until a potentially lethal situation
  • At that time the pilot may react wrongly
• An excessively optimistic opinion
  • Of piloting skills will result if simulator is easy
  • Or if it does not exhibit common instrument flaws
  • A pilot will willingly fly into dangerous situations
  • that are beyond their skill proficiency and be at risk
• Only a trained instructor can judge
  • Whether the learning experience is beneficial
  • The documentation materials are essential to that

(page 30)

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What's in the future?

• FDMs are not (yet) accurate enough
  • Only suitable for conservative flights
  • Don't reflect the challenges of acrobatic maneuvering

• Higher performance human input devices
  • Beyond the 8-bit joystick resolution limit
  • Rugged and rigid, like real aircraft controls

• New consumer technologies for immersion
  • Surround projectors, head mounted displays
  • Directional sound and cockpit motion effects
  • Users will fly safe, forgetting they're not in danger

• Recent radar and visual satellite surveys
  • Enough detail to be used as photorealistic scenery
  • First, we must manipulate terabytes in real time
  • Data volume is about a million times larger than now

(page 31)

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Conclusions

• FlightGear is a simple Open Source project
  • Builds on many existing projects
  • In the community tradition

• Due to the subject it addresses
  • It has many issues and concerns
  • Are raised that rarely inconvenience other projects

• These elements are providing the exciting challenges
  • And variety of associated activities
  • Enjoyed by the developers

• Thank you for your interest.
  • Questions ?

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