Head-Up Displays (HUD) appeared in the 1960s. Relatively long time HUDs were used exclusively in military aviation. Nowadays, because of the numerous benefits HUDs began to be used on modern civil aircraft.
HUD is an information display system of projection type that projects image onto the glass in front of the pilot. HUD screen is placed in direct line of sight between pilot and the windshield (Fig. 174).
Fig. 174. The principle of operation of B-787 HUD
Special projection equipment is projected monochrome image on the glass. Reflecting from glass the image falls into the eye of pilot. Since the display is almost transparent, displayed information is perceived by pilot on the background of surrounding situation.
During flight, eyes of the pilot are focused at the infinity, so if the image will be projected on the screen, the pilot could not clearly perceive information in flight. To prevent this visual effect and exclude the need for refocusing projected images are collimated. Because of special optics, radiation from projector is modified so that all the rays are parallel. In this configuration, pilot will perceive the image as if it remote from the aircraft.
The use of HUD is important because the information displayed on it is in sight all the time. Pilot do not need to be distracted and observe instruments, which is important for safety, especially during take-off and landing.
One of the HUD advantages is the possibility to provide pilot with means of artificial vision. Initial data for displaying may be the image from infrared vision system or radar images. In addition HUD can display synthesized image from the terrain base. Displaying of such information using HUD considerably facilitates takeoff and landing in adverse weather conditions and at night.
Another important feature is that HUD display basic navigational information (Fig. 175, 176). HUD displays are used to display information from SVS. Example of display of underlying surface and artificial obstacles on HUD display is shown on Fig. 177. Fig. 175. Displaying of aeronautical information during take-off (HGS, RocwellColins) Fig. 176. Displaying of aeronautical information during approach (HGS, RocwellColins) Fig. 177. Displaying of the terrain from SVS (HGS, RocwellColins)
This information may be issued on its own or together with a graphical representation of the means of artificial vision (Fig. 178). Also, during movement at the airport HUD displays electronic chart of the airport pointing the desired direction, which facilitates the orientation of pilot on the ground. Fig. 178. Combining of information delivery by system of night vision with aeronautical information (HGS, RocwellColins)