Avionics MCQs – Head Up Displays
1 - Question
Which of the following is true with respect to Head up display?
a) View and assimilate the flight data with his head up in a transparent display
b) Assimilate the flight data without looking at any kind of display panel
c) View and assimilate the flight data that is projected on the helmet
d) Using a head up display a pilot and view and assimilate the flight data in all 360°
Explanation: A major improvement in the man-machine interface is the HUD system. The major advantage in HUD is that the pilot is able to view and assimilate the important flight data parameters whilst head up and maintaining full visual concentration to the outside world. The area at which the flight parameters are displayed is only on the transparent display panel thus the pilot does not have a 360° display.
2 - Question
Which one of the following flight parameters are not present in a typical commercial head up display?
d) Throttle position
Explanation: A typical head up display system in a commercial aircraft consists of airspeed, altimeter, heading, slip/skid indicator, turn/bank indicator, artificial horizon lining, angle of attack indicator, vertical speed indicator, flight path vector and much more depending upon the customer requirements.
3 - Question
The main reason for using a collimated display in HUD is ________
a) More information can be displayed
b) Wide view of display
c) Information displayed is focused at infinity
d) Fast screen refresh rates
Explanation: A collimated display is a display in which the rays of light emitted/reflected is parallel to the display. Since the rays of light are parallel, its focus is at infinity, thus the pilot is able to view the information on the HUD without changing his focus from the outside world scene without parallax error. Also, the ray of light from a collimated display would not disperse with distance.
4 - Question
What are the sensors used in combination with a raster mode HUD?
c) Radar and FLIR (Forward Looking InfraRed)
d) Microwave radar
Explanation: In the raster mode HUD a video image of the outside world (generated from the FLIR sensors mounted in the aircraft) and the synthetic image of the outside world (generated from radar sensor) are combined to produce an enhanced vision system. The advantages of these enhanced vision system are that it enables the pilot to fly and land the aircraft in very low visibility conditions and in airports without ILS or MLS or for night flying.
5 - Question
Which of the following is the correct order for the path of light in a HUD?
a) CRT -> mirror -> collimating lens -> combiner glass -> pilot
b) CRT -> collimating lens -> mirror -> combiner glass -> pilot
c) CRT -> mirror -> combiner glass -> collimating lens -> pilot
d) Collimating lens -> CRT -> mirror -> combiner glass -> pilot
Explanation: The symbols and flight parameters are generated and magnified by the CRT (Cathode Ray Tube) and is reflected almost 90° by a mirror. The reflected rays are passed through a collimating lens which produces a parallel ray of light with focus at infinity. The collimated rays are then displayed in a combiner glass which combines the outside world picture with the flight parameters generated to be viewed by the pilot.
6 - Question
The Instantaneous FOV (Field Of Vision) changes with the position of view.
Explanation: The instantaneous FOV is the total angular coverage of the outside world scene which can be viewed by the pilot at any particular instant. IFOV=2tan-1 D/2L, where a D= diameter of collimating lens and L=length of pilot’s eyes to the collimating lens. Clearly, as the position of view changes, L changes resulting in a change in IFOV.
7 - Question
What is the IFOV for a collimating lens of diameter 100mm, the distance between the collimating lens and combiner glass=50mm, the distance between pilot eyes and combiner glass=400mm?
Explanation: D=100mm, L=50+400 =450mm (Since L is the distance from the observer to the collimating lens) IFOV = 2 x tan-1 (D/2L) =2 x tan-1( 100/2×450) = 12.6803° ≈ 12.6°
8 - Question
Which of the following are not controlled by the HUD processor?
a) Power supply to HUD
b) Brightness level and contrast level
c) Symbol and font generation
d) Computing flight parameters
Explanation: The flight parameters are computed by the air data computer. The various controls and functions carried out by the HUD processor are display formats, axis conversion, parameter conversion, format management, brightness and contrast control, power supply and calibration.
9 - Question
What is the contrast ratio of real world image to the CRT display image?
Explanation: A combiner allows 70% of the outside world light and 30% of the CRT produced collimated light to pass through it. Thus contrast ration= brightness of real-world light : brightness of CRT light = 70 : 30 = 7 : 3 .
10 - Question
What is the reason for using CRT used instead of LCD or LED displays?
a) To meet the required brightness level
b) Cheap to manufacture
c) Low energy of operation
Explanation: To clearly see the flight parameters displayed on the combiner glass against the bright sky, it is necessary to achieve a display brightness of 30,000 Cd/m2. This high brightness requirement is the reason why CRT is used instead of LCD or LED, even though CRT’s are heavier and require more power to run.