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Head-Up Display Print E-mail
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Written by Sabc   
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Head-Up Display Controls
Basic Symbology
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The HUD is basically a piece of glass located on top of the pilot's dashboard, in the center of the pilot's forward view (see photos below). It is transparent to let the pilot look through it, but its inner surface is reflective and since the HUD is slightly tilted towards the pilot, important information can be projected to the HUD from under, and this projection reflects from the HUD surface and goes into the pilot's eyes, letting the pilot see this information transposed in his field of view (as if they were painted in the windshield). HUD is a basic instrument in modern fighter aircrafts which lets the pilot monitor important flight and targeting information without having to regularly glance down at the dashboard, thus losing visual contact with important objects in front of the aircraft.

argaiv1991

The F-15E HUD (Kaiser IR-2394/A) is much greater than the HUD in previous F-15 models (A, B, C, D), thus letting the system display more information. It provides a 21° x 28° field of view. Note that although the HUD glass is more or less rectangular, the limits of the maximal projected area are rounded (see photo below left), thus no image can be projected to the very edges of the HUD. Symbology projected to the HUD appear in green, its appearance can be controlled by the pilot, using the HUD controls (see next chapter) under the UFC (Up-Front Controller). HUD symbology is projected as if 'focused at infinity', thus letting the pilot see the symbology sharply while actually looking at objects far in front of the aircraft.

hud_face

So called 'stroke' and 'raster' symbology can be projected onto the HUD. Stroke symbology contains fixed font alphanumeric characters (i.e. letters and numbers) and simple geometric forms (lines, circles, rectangles, etc.). This symbology provides flight and targeting data as well as important visual cues for navigation and combat. Raster symbology means green monochrome video image. If a LANTIRN navigation pod is installed on the jet, the image of its FLIR camera can be viewed on the HUD. This feature enables the F-15E to be manually flown at low altitudes even in pitch dark, since the pilot sees the terrain in front of him on the HUD in green color.

Some symbology and data are always visible on the HUD, while the presence of other symbology and data on the HUD depends on which master mode the aircraft is in - this can be selected by the pilot using the master mode selector buttons located directly underneath the HUD controls. Note, that the pilot can declutter the HUD (clear it from symbology) at any time in order to have a clear view forward if necessary.

Head-Up Display Controls

The HUD control rack is located inthe middle of the pilot's dashboard, right below the UFC. The rack contains all the control switches and knobs necessary for managing the appearance of the HUD symbology. Note that this rack houses the master mode selector buttons as well, which too have effect on the informaton displayed on the HUD. The following picture illustrates the layout of the HUD control switches and knobs and their functions are exlained in detail below.

hud_control_panel

Brightness Knob controls the brightness of the stroke symbology. Note that due to its nature, stroke symbology is always displayed at a 'maximum contrast setting'.

Symbol Declutter Switch serves as a declutter switch for the HUD. When set to 'NORM', all stroke symbology appears on the HUD. When set to 'REJ1' or 'REJ2' some or all of the stroke symbology is removed from the HUD. Note that the pilot can program which symbology should be removed and which should remain in any of these settings. Brightness Knob #1 and Symbol Declutter Switch together are labeled as 'SYM', since they control the appearance of stroke symbology on the HUD.

Day/Night/Auto Switch sets the HUD display mode. When set to 'DAY', HUD symbology illumination goes to max power so information displayed on the HUD should be visible even in bright daylight. When set to 'NIGHT', symbology illumination is low, but still clearly visible against the dark sky. When set to 'AUTO', symbology illumination varies depending on ambient lighting. Note that oddly enough, in 'AUTO' mode, the HUD does not provide enough illumination in the dark.

BIT Button and BIT Indicator are used during maintenance when the HUD's built-in test function should be engaged.

Video Brightness Knob controls the brightness of the raster (video) symbology.

Contrast Knob controls the contrast of the raster symbology. Video Brightness Knob and Contrast Knob together are labeled as 'VID', since they control the appearance of video imagery on the HUD.

Basic Symbology

As it was mentioned above, HUD symbology largely depends on which master mode the aircraft is in. However, there is basic symbology always present on the HUD. This is illustrated on the following picture:

hud_basic_symbology

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- Available Gs
- Current Gs
- Mach Ratio
- True Airspeed
- Angle of Attack (AOA)
- Indicated Airspeed
- Pitch Ladder
- Command Heading Marker
- Heading Scale
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- Gun Cross
- Waterline Symbol
- Velocity Vector
- Barometric Altitude
- Radar Altitude
- Horizon Line
- Steering Data Block
- Ghost Velocity Vector
- Maximum Projected Area

HUD symbology changes when the aircraft is switched into different master modes. Explanations of symbols used in different master modes are coming soon. Please check back later.

Forum Discussion

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Last Updated on Tuesday, 07 September 2010
 


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