Improving Glider Realism
This section lists the areas that have a significant impact on soaring realism. This wiki has additional relevant information in the Soaring area.
Gliders
This section reviews the design issues affecting the user aircraft.
Flight Model
Of course, gliders need a custom-designed flight model.
Glider external 3D models
This is the best understood bit of glider simulation... designing a decent 3D model. You can tell if it's any good just by looking at it, although performance plays a part too. For the current FG glider state of the art, here's the ASK21:
Glider cockpit 3D models
Less well understood, but still not rocket science, gliders need a good 3d model for the cockpit with the panel and the various levers (joystick, flaps, airbrakes, water ballast, landing gear). The ASK21 panel is displayed below - functional but a bit sparse compared to real gliders:
Gauges
Unfortunately it is not possible to create a decent glider by simply copying across existing instruments from a power aircraft. The minimum instrument set is an altimeter, air speed indicator, and variometer. The variometer (vario) is unique to soaring.
Variometer
At its simplest, a variometer is a rate of climb indicator. However, this pure (uncompensated) indication of vertical speed is very poor for climbing effectively in thermals as the effect of the vertical movement of the air is swamped by the pilot's actions with the control column (so called 'stick thermals'). Since the 1930's, real gliding variometers have used some method to compensate for the climb rate induced by the pilot pushing or pulling on the control column.
- Total energy compensation. If the glider is climbing, a factor can be subtracted from the indicated lift if the glider is decelerating, and the reverse during descent. So if the glider is neither accelerating or decelerating the absolute rate of climb (or sink) will be shown.
- Potential energy = mass x G x height (or height = energy / (mass x G))
- Kinetic energy = 0.5 x mass x velocity squared
- if in time period 't' the glider goes from height 'h1'..'h2' and speed 'v1'..'v2':
- uncompensated vario reading = (h2-h1)/t
- TE adjustment = height the glider would have gained if it hadn't accelerated
- = (change in kinetic energy / (mass x G))
- = (0.5 * mass * v2^2 - 0.5 * mass * v1^2) / (mass x G)
- = (v2^2 - v1^2) / 2G where G = 9.81 meters per second per second
- TE reading = uncompensated reading + TE adjustment
- TE reading = (h2-h1)/t + (v2^2 - v1^2) / 19.62
- (all units meters, seconds, meters per second)
- Netto compensation. The design sink rate of the glider at the current airspeed is added to the total energy vario reading, so the variometer actually displays the vertical rate of the air outside the glider. For a perfectly compensated instrument, the vario will show zero in still air regardless of the airspeed of the aircraft
IGC file logger
To compare flights with others, it helps to have a log of your flight in the 'IGC format'. This is a text file with an agreed format, with some header rows and then one-row-per-timestamp for the lat/long/alt.
The specification for the IGC format log file is available on the FAI website.
The full specification has become unbelievably tortuous, but most of the records are optional and an example of a working file would be:
AXXXb21_sim_probe 2.55 HFDTE070608 HFFXA035 HFPLTPILOTINCHARGE: not recorded HFCM2CREW2: not recorded HFGTYGLIDERTYPE:DG HFGIDGLIDERID:B21 HFDTM100GPSDATUM: WGS-1984 HFRFWFIRMWAREVERSION: 2.55 HFRHWHARDWAREVERSION: 2008 HFFTYFRTYPE: sim_probe by Ian Forster-Lewis HFGPSGPS:Microsoft Flight Simulator HFPRSPRESSALTSENSOR: Microsoft Flight Simulator HFCIDCOMPETITIONID:B21 HFCCLCOMPETITIONCLASS:Microsoft Flight Simulator I013638FXA B1658174040958N07737022WA0094000940000 B1658214040875N07737069WA0095200952000 B1658254040811N07737136WA0095300953000 ... and more B records for the rest of the file G123456789
IGC files can be uploaded to everytrail.com or can be converted by gpsvisualizer.com for viewing in Google Earth.
Enviroment lift modelling
This section reviews the requirements for the environment modelling, in particular the simulation of the vertical component of air movement on which gliders depend for soaring flight.
Thermals
Ridgelift
A paper on the efficient calculation of ridge lift is available from Ian Forster-Lewis.
Wave
Multiplayer
Solo soaring is all about admiring the scenery, and multiplayer soaring is predominantly about comparing times to complete the same cross-country task.