Technology
While conceptually simple, implementation of aircraft HMDs is quite complex. There are many variables:
- precision - the angular error between the line-of-sight and the derived cue. The position of the helmet is what is used to point the missile, it thus must be calibrated and fit securely on the pilot's head. The line between the pilot's eye and the reticle on the visor is known as the line of sight (LOS) between the aircraft and the intended target. The user's eye must stay aligned with the sight – in other words, current HMDs cannot sense where the eye is looking, but can place a "pipper" between the eye and the target.
- latency or slew rate - how much lag there is between the helmet and the cue.
- field of regard - the angular range over which the sight can still produce a suitably accurate measurement.
- weight and balance - total helmet weight and its center of gravity, which are particularly important under high "g" maneuvers. Weight is the largest problem faced by fighter aircraft HMD designers. This is much less a concern for helicopter applications, making elaborate helicopter HMDs common.
- safety and cockpit compatibility, including ejection seat compatibility.
- optical characteristics – calibration, sharpness, distant focus (or 'Collimation', a technique used to present the images at a distant focus, which improves the readability of images), monocular vs. binocular imagery, eye dominance, and binocular rivalry.
- durability and ability to handle day to day wear and tear.
- cost, including integration and training.
- fit and interfacing the aviator's head to the aircraft – head anthropometry and facial anatomy make helmet fitting a crucial factor in the aviator's ability to interface with the aircraft systems. Misalignment or helmet shift can cause an inaccurate picture.
Read more about this topic: Helmet Mounted Display
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