This is a short description of FlightGear's default Head-up display (HUD), it can be (de)activated with the [h]-key. To change the brightness, press [shift]+[h].
There are also two so called 'minimal' HUDs available which are accessible with [shift]+[i], to return to default HUD press [i].
Some of the HUDs options can be altered in the menu: View > Adjust HUD Properties
Features
Aileron
Monitors the bearing of the control input on the ailerons axis.
Airspeed
Current speed relating to the ambient air in knot/knots (kt/kts) (1 kt = 1.852 km/h).
Altitude
Current altitude relating to sea-level in feet (ft) (1 ft = 30.48 cm).
GPS
The active GPS waypoint identifier is displayed, as well as the distance and bearing to it. The GPS ground track and course-deviation are also displayed - for the course deviation, the distance off-course is displayed in nautical miles (nm), with an arrow indicating the direction to fly to regain the GPS course.
Elevation
Current altitude above ground in feet. Relating to the location of the aircraft's radio altimeter, therefore it's not zero if the aircraft is on the ground.
Elevator
Monitors the bearing of the control input on the elevators axis.
G-load
Displays the g-force to the pilot in g - to avoid black-/redout.
- The value riding on top of the Airspeed indicator.
Heading
Direction of the aircraft relating to the geographical North pole in degree (360 degree scale).
Location
To change the coordinates-system, go to Autopilot > Set Lat/Lon-format.
Pitch
Like set with [Home]/[End].
- It's the left marker of the Elevator indicator.
Pitch ladder
Displays the aircraft's pitch relating to the grounds level/horizontal in degree. It's used as an artificial horizon.
- The big ladder like looking indicator at the HUDs centre.
- Attitude indicator
Rudder
Monitors the bearing of the control input on the rudders axis.
Thrust
Monitors the thrust on airplanes or the collective of helicopters.
Turn-bank-indicator
Further Information
The basic setup of the above described default HUD is defined at $FG ROOT/Huds/Default/default.xml. There is also a 'Runway projection' available which is, because of some issues, disabled by default.
Documentation can be found at: $FG ROOT/Docs/README.xmlhud
Since FlightGear 0.9.10 there is also a newer and more flexibly HUD-system available. An example can be found at $FG ROOT/Huds/NTPS.xml and documentation at $FG ROOT/Docs/README.hud. Also have a look at $FG_ROOT/Huds/README.
preferences.xml
While the instruments and their behaviour are set in the Huds-directory, the basic settings and the look regarding to any HUD are set in $FG ROOT/preferences.xml. Search the file for <hud> and you will find a list of properties. For a short description of those have a look at property tree. But I'll give some of them a closer look:
Colour
The preferred thing one would like to customize is, I guess, the HUDs colour.
Discover your own settings is quite easy: Access the property tree via the Menu File > Browse Internal Properties ([/]-character) or via the Property server and your browser. Go to sim/hud/color, e.g. http://localhost:5500/sim/hud/color, edit a value and watch the result in FlightGears window instantly.
Once the decision is made head back to preferences.xml, copy the <color n="0">-tag and paste it on top of the colours within the <palette>-tag. Rename the existing tags in numeric order and finally put your discovered values in the new one. It should look like this, except your own values, of course:
<current-color type="int">0</current-color> <palette> <color n="0"> <transparent type="bool">true</transparent> <antialiased type="bool">false</antialiased> <brightness type="float">1</brightness> <alpha type="float">0.67</alpha> <red type="float">0.1</red> <green type="float">1.0</green> <blue type="float">0.3</blue> </color> <color n="1"><!-- day --> ... </color> <color n="2"><!-- night --> ... </color> </palette>
Font
<font> <name type="string">Helvetica.txf</name> <size type="float">8</size> </font>
To change font just enter another name out of the ones in $FG ROOT/Fonts (case sensitive!). For more information about those fonts and on .txf format peruse $FG_ROOT/Fonts/README.
Since the size is type 'float' values like '7.449' are allowed, too.
Path
/!\ Just a draft and maybe not correct.
<path>Huds/Default/default.xml</path> <path>Huds/NTPS.xml</path> <!-- new HUD -->
The first one is the default HUD mentioned above. It is for the old HUD only. The second is the first one of the 'minimal HUD's and it is for the new HUD only. The other 'minimal' one is called by the code (I guess), its path is Huds/Minimal/default.xml.
For each <path> are some more HUDs available, a complete list (except aircraft specific):
old HUD:
Huds/Custom/default.xml Huds/Default/default.xml Huds/Engineering/default.xml Huds/Minimal/default.xml
new HUD:
Huds/NTPS.xml Huds/default.xml
Property tree
More information about FlightGear's property tree and on how to access it can be found at its page: Property Tree.
Paths starting with '$FG ROOT/' apply to the file system, the others are intra-property tree.
/sim/hud current-color (0|1|2...) int One out of /sim/hud/palette enable3d (false|true) bool hud n=0 3D off|on enable3d[1] (false|true) bool hud n=1 3D off|on frame-stat-type (tris|???) ??? path (Huds/...) Path to hud n=0 path[1] (Huds/...) Path to hud n=1 visibility (false|true) bool hud n=0 hidden|visible visibility[1] (false|true) bool hud n=1 hidden|visible /sim/hud/color/ Contains settings of current-color alpha (0...1) float 0=invisible, 1=nontransparent alpha-clamp (???) ??? antialiased (false|true) bool Antialiasing off|on blue (0...1) float brightness (0...1) float 0=dark/black green (0...1) float red (0...1) float transparent (false|true) bool Transparency off|on /sim/hud/font/ name (*.txf) string One out of $FG_ROOT/Fonts size (8) float Size of font /sim/hud/palette/ /sim/hud/palette/color/ Settings of predefined colours, nearly /sim/hud/palette/color[n]/ the same options as in /sim/hud/color.
Additional HUD's
- HeliHUD
- Designed to fly helicopters in Helicopter View it is also handy for any craft with a not yet finished cockpit. The download contains instructions and specs.