There is a great deal of publicity about development of flat panel displays,
driven by the market need for advertising, brighter laptops, tv etc. Those
that have been applied in military and commercial aviation cockpits are have
so far been outside the price range suited to light aircraft, and are usually
mounted in far more shielded environments. However things are improving.
You can now buy a display for a few hundred uk pounds which will be about 3
times brighter than your typical computer monitor.
Unfortunately this is not good enough to compete with uniform skylight
reflected around a small cockpit by day, let alone direct sunlight. A low
wing configuration is clearly much worse than a high wing for this. The
standard Europa tinted plexiglass helps a bit (factor of 2), but you really
need to add an opaque film above your head, wear dark clothing (even blacken
your face), and then add a shroud to mask light from the side.
Here are some measurements from an unscreened 250 cd/sqm display system in
the Europa cockpit (G-EMIN). It should be noted that the screen cannot be
mounted flat against the face of the cockpit module, as the contrast falls
when the viewing line is away from the perpendicular. However a tilted
screen has the advantage of allowing air to circulate around it, which is
important as they are limited at the top end to around 50C.
Pointing at uniform blue sky at midday as reference .....................1000.
Scattered light along pilot's eyeline from screen with display OFF... 15
Typical light received from screen (in dark)........ with display ON.... 8
So there is around twice as much scattered light as there is light from the
screen and the effective contrast falls to around a third. It is very
difficult to read a map display at such a contrast. 1000+ cd/sqm screens can
be bought at a price, but this would still be diluted down to 66% , and of
course direct sunlight rather than skylight washes even these out. At the
present therefore it is necessary to add a screening tunnel to use such
displays reliably by day. Even then, the time taken to for the eye to adapt
---From viewing outside brightness is a problem, bearing in mind that attention
should not be directed to a display for more than brief time.
This situation will improve with more brightness per buck, but we really need
a reasonably priced colour version of the b/w reflective technology already
existing on gps screens, palmtops etc., which just love more illumination on
them.
Graham Clarke G-EMIN
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