Head Up Display (HUD)

Wg Cdr Rajagopal

Head Up Display

Index

Components of Head Up Display

  • HUD presents flight information and guidance in a pilot’s visual line of sight
  • In critical phases of flight, like take off or landing the system is very useful
  • Head Up Display system consists of four components
  • Display controller to control various modes
  • Display guidance computer to generate symbology
  • Overhead unit which is a projector
  • Combiner which is a glass screen to reflect displays to pilot
  • Ambient light sensor controls brightness and adjusts display brightness
  • Display brightness is adjusted as per lighting in flight deck

Eye Box

  • Overhead unit uses a collimator to produce parallel light source
  • Collimator projects the display to an eye reference point
  • Eye reference point is the ideal position for image
  • Ideally the image must meet the eye at infinity
  • Parallax error must be avoided
  • Eye box is also called head motion box determines the head movement
  • HUD is visible in a 3 d box around his eye reference point
  • The box is normally 5 inches wide, 3 inches high and 6 inches deep

Bore Sighting

  • Head up display should project a conformal image
  • Conformity avoids disorientation when taking over visual
  • Real object its image on the combiner are aligned when real object is visible
  • Conformity is achieved by construction of a correct image
  • Correct image means it has at the correct perspective and size for object range
  • Bore Sighting is the process of correct alignment of object with its image
  • Object and its image must vary by less than half a degree

Advancements in Head Up displays

  • First generation displays used cathode ray tube with projectors and combiners
  • Fading problems and high voltage requirements were drawbacks
  • Solid state light source replaced cathode ray tubes in second generation
  • Lower voltage and lesser fade with wider field of view and sharp images
  • Third generation used optical wave guides instead of overhead projector
  • Eye box was increased considerably
  • Phosphor coated wind screen is being used to replace combiner
  • Windscreen is being used as a display in the fourth generation head up

Information Display

  • Mandatory information
  • Air Data Computer
  • Inertial Reference Unit
  • Radio Altimeter
  • Radio Navigation
  • Flight Management System

Tunnelling Effect in Head Up Display

  • Tunnelling is caused by attention capture and over dependence
  • Pilots tend to disregard external visual reference

Cluttering in Head Up Display

  • Cluttered display obscures visual information cues
  • Confuses the pilot at times

Enhanced Vision in Head Up Display

  • Enhanced vision system help in night flying
  • Forward looking infrared creates a heat map type image at night

Synthetic Vision in Head Up Display

  • Synthetic vision system helps during flight in instrument met conditions
  • Displays computer generated graphics on screen

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