Default head-up display

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Note  The HUD system will one day be replaced by a Canvas HUD system.
Huds/default.xml
Huds/minimal.xml
Huds/NTPS.xml

The default head-up display (HUD) of FlightGear is available for any craft which does not include its own. A head-up display This is a link to a Wikipedia article is an important instrument in modern, mostly military, cockpits.

Activate the HUD with h. Pressing it repeatedly moves through the configured colours and turns it off again. To change the brightness, press Shift+H. Press Shift+I to go through the available HUDs. Press i to switch back to the first one at any time. Have in mind that some aircraft do assign one or more of those keys differently and therefore some functions may be missing from them.

Some of the head-up options of the HUD can be altered in the menu: View > Adjust HUD Properties

In addition custom HUDs for aircraft such as the F-14B and F-16 can relatively easily be created through an XML-based system FlightGear provides. Have a look at Further Information if you are planning to create a HUD.

Features

Control inputs

Aileron
Displays the aileron control axis input. Attached along the upper side is the indicator for the trim input on that axis.
Properties: /controls/flight/aileron and /controls/flight/aileron-trim
Elevator
Displays the elevator control axis input. Attached to the left the trim on this axis.
Properties: /controls/flight/elevator and /controls/flight/elevator-trim
Rudder
Displays the rudder control axis input. Attached to the bottom the trim input.
Properties: /controls/flight/rudder and /controls/flight/rudder-trim
Throttle
Displays the throttle control axis input.
Property: /controls/engines/engine/throttle

Instruments

AMSL (Altitude above Mean Sea Level)
Current altitude above mean seal level in feet (ft) (1 ft = 30.48 cm).
Property: /position/altitude-ft
g-load
The G-force This is a link to a Wikipedia article applied to the pilot - to avoid black-/redout.
Property: /accelerations/pilot/z-accel-fps_sec with factor -0.03108095
Gyrocompass
This is an ideal version of a gyrocompass without the drawbacks of a real one. It shows heading of the aircraft relative to the geographical north pole (true north) in degree (360 degree scale).
Property: /orientation/heading-deg
KIAS (Knots Indicated Airspeed)
Current speed relative to the ambient air in knots (kt) (1 kt = 1.151 mph = 1.852 km/h).
Property: /velocities/airspeed-kt
Latitude / Longitude
Current location according to the geographic coordinate system This is a link to a Wikipedia article.
To change the format of the displayed coordinates, go to Autopilot > Set Lat/Lon-format.
Properties: /position/latitude-string and /position/longitude-string
Pitch ladder
Displays the pitch and roll of the aircraft relative to the horizontal plane in degrees. It is used as an artificial horizon (Attitude indicator).
Properties: /orientation/roll-deg and /orientation/pitch-deg
Radio altimeter
Shows current altitude above ground level (AGL) in feet. Relating to the location of the radio altimeter of the aircraft, it is not zero if the aircraft is on the ground.
Property: /position/altitude-agl-ft
Turn-bank-indicator
Turn Coordinator
Properties: /orientation/roll-deg and /orientation/side-slip-deg

Autopilot

HUD autopilot

If the autopilot is active the HUD displays its settings. For each active function (heading, altitude and speed) a box will appear below the gyrocompass containing information on its mode and, if existent, the associated value.

Heading control
Whether it is active or not and on which mode it operates is determined by the content of the /autopilot/locks/heading property.
The values are taken from /autopilot/settings/heading-bug-deg and /autopilot/settings/true-heading-deg.
Altitude control
Active mode: /autopilot/locks/altitude
Their values: /autopilot/settings/target-altitude-ft, /autopilot/settings/vertical-speed-fpm and /autopilot/settings/target-agl-ft.
Speed control
Active mode: /autopilot/locks/speed
Their values: /autopilot/settings/target-speed-kt and /autopilot/settings/target-speed-mach

GPS

HUD GPS

The upper left hand corner shows the most important information on the current state of the GPS. Namely these are (line by line):

GPS operating mode Active waypoint
D: Distance in nautical miles (NM) to active waypoint TTW: Calculated time to active waypoint
BRG: Bearing to next waypoint XTR: Cross track deviation, deviation from the track between the previous and active waypoint in nautical miles (NM)
GS: Ground speed, the speed relative to the ground

Big fat arrow

Remains of a going to be useful instrument.

To get rid of it, remove or comment runway.xml from $FG_ROOT/Huds/default.xml.
To make it point to the airport selected by menu item "Tower Position", apply patches as shown here.

Further Information

HUDs may be replaced or added by changing or adding their paths in preferences.xml or by setting the paths as command line options. To change the order of the existing ones the options would be: --prop:/sim/hud/path[1]=Huds/minimal.xml --prop:/sim/hud/path[2]=Huds/default.xml

If you consider to create your own HUD have a look at Canvas HUD first.

The basic settings regarding to any HUD are set in flightgear/fgdata/next/defaults.xml. Search the file for the <hud> tag and you will find a list of properties.

The setup of the default HUD is defined at flightgear/fgdata/next/Huds/default.xml and documentation can be found at $FG_ROOT/Docs/README.hud.

Additional HUDs

HeliHUD
The HeliHUD is designed for fly helicopters in Helicopter View it is also handy for any craft with a not yet finished cockpit. It also contains a minimalistic HUD only showing some navigational information such as compass and GPS. The download contains instructions and specs.