Patent
1982-12-28
1985-04-02
Henry, Jon W.
G02B 2710
Patent
active
045084246
DESCRIPTION:
BRIEF SUMMARY
This invlention relates to apparatus for displaying information, and especially, although not exclusively, to apparatus for displaying information to the pilot of an aircraft.
The most commonly used method of displaying information to an aircraft pilot is to arrange information-providing instruments in front of the pilot, out of the field of view which he has when observing the outside world through his cockpit window. As the instruments are generally arranged below that field of view, this system is known as the head-down display (HDD) system. In the simpler type of HDD system, the uncollimated HDD system, the instruments are of the type having an instrument display face (dial (analog) or counter (digital) or other (symbolic) or image forming device such as a cathode ray tube CRT) on which it is necessary for the pilot to focus, as in simple dial display devices or CRT display devices, for example. If a pilot who is observing the outside world wishes to study information displayed by such a system, he has to avert his gaze in the direction of the relevant instrument (this will take, say, one tenth of a second), refocus his eyes from infinity to the distance of the relevant instrument display face (this will take about 1/2 second), absorb the relevant information, move his gaze back to the outside world (another tenth of a second, say), and then re-focus at infinity (about 1/2 second, again). Thus, in addition to the time taken to study the instrument display and the relatively small period of the order of one fifth of a second in gaze movement, the time which the pilot partly loses in his study of the outside world includes a total period of about 1 second in re-focussing time.
The only extensive use of collimated HDD systems to date has been in the field of moving maps where, because the image is necessarily optically developed, it has been found convenient to produce a collimated image. Otherwise, even the use of modern CRT displays in the HDD mode have been in the uncollimated form. In recent years certain display systems have been developed with a view to overcoming this drawback.
A system known as the HUD (head-up display) system has been developed for use in fixed-wing aircraft. In this system a collimated image of a graticule is presented in the pilot's normal field of view, i.e. in the pilot's normal field of view when observing the outside world. The system works in the following way: a combiner (a "half-silvered mirror", i.e. a transparent sheet having a partially transparent, reflective coating) is mounted in front of the pilot in his normal field of view at such an orientation that the pilot can simultaneously see (a) the outside world, through the combiner, and (b) a reflected image of a suitably positioned optical device which presents to the combiner a collimated image of a graticule; the collimated image is produced in the same manner as in the above-described collimated HDD system. Thus, the pilot can study the information presented by the HUD information at the same time as studying the outside world.
There are certain problems inherent in the use of the HUD system in fixed-wing aircraft. Firstly, there are limitations on how close to the point the device can be mounted, since it is necessary to maintain both the crash clearance (the clearance which must be maintained in front of the pilot to protect him from colliding with equipment when thrown forward against his strapping in a crash) and, where the aircraft is fitted with an ejector seat, the `ejector seat clearance` (for parts of the pilot's body such as knees, feet, etc.). It will be appreciated that the further away the HUD apparatus is from the pilot, the larger must be the size of both the combiner and the collimated optical device in order to produce an image of a required size (as perceived by the pilot) of the reticule. The space envelope in the nose of the aircraft, where the collimated optical device is mounted, is at a very high premium, especially in a jet-fighter type of aircraft, so that it is necessary to limit the size
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Henry Jon W.
Hinds William R.
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