Jim Yanik
January 30th 04, 02:22 AM
Alan Dicey > wrote in
:
> B2431 wrote:
>> I notice some HUDs have 2 glasses. How does this work without
>> reflections from the second one and interferance from the first?
>>
>> Dan, U. S. Air Force, retired
>
> Put simply, a dual combiner increases the vertical field of view of
> the HUD symbology.
>
> The sheets of glass in front of the pilot are called combiners: they
> combine the HUD display symbology (projected from beneath by a very
> bright CRT and some big lenses) with the pilots forward view by
> reflecting the symbols projected from a very bright CRT under the
> glareshield.
>
> http://www.cmcelectronics.ca/En/Prodserv/Milav/milav_dcs_hud_nthawk_faq
> _en.html
>
> http://www.mikesflightdeck.com/head_up_displays.htm
>
> The combiners are cleverly-engineered partial reflectors. The
> simplest design is just a semi-silvered mirror. The pilots view of
> the outside world is dimmed a little, but the HUD symbology is
> overlaid onto the pilots Field of View (FoV), reflected from below.
>
> More advanced combiners use dichroic coatings to partially reflect
> only the narrow set of wavelengths emitted by the (usually green) crt
> tube. All other light is passed straight through, resulting in a
> brighter real-world view (important in bad weather, dusk or night
> operations).
>
> The surfaces that are not meant to reflect are given anti-reflection
> coatings to minimise the ghost images.
>
> From the pilots point of view, the two combiners are one on top of
> the
> other, hence the increase in the vertical FoV. A single combiner
> would need too much space above the glareshield and behind the
> windscreen, and need a truly enormous final condensing lens in the CRT
> projection optics.
>
>
I wonder if LCD projection optics will replace the vacuum tube CRT?
And maybe LEDs for a light source?
--
Jim Yanik
jyanik-at-kua.net
:
> B2431 wrote:
>> I notice some HUDs have 2 glasses. How does this work without
>> reflections from the second one and interferance from the first?
>>
>> Dan, U. S. Air Force, retired
>
> Put simply, a dual combiner increases the vertical field of view of
> the HUD symbology.
>
> The sheets of glass in front of the pilot are called combiners: they
> combine the HUD display symbology (projected from beneath by a very
> bright CRT and some big lenses) with the pilots forward view by
> reflecting the symbols projected from a very bright CRT under the
> glareshield.
>
> http://www.cmcelectronics.ca/En/Prodserv/Milav/milav_dcs_hud_nthawk_faq
> _en.html
>
> http://www.mikesflightdeck.com/head_up_displays.htm
>
> The combiners are cleverly-engineered partial reflectors. The
> simplest design is just a semi-silvered mirror. The pilots view of
> the outside world is dimmed a little, but the HUD symbology is
> overlaid onto the pilots Field of View (FoV), reflected from below.
>
> More advanced combiners use dichroic coatings to partially reflect
> only the narrow set of wavelengths emitted by the (usually green) crt
> tube. All other light is passed straight through, resulting in a
> brighter real-world view (important in bad weather, dusk or night
> operations).
>
> The surfaces that are not meant to reflect are given anti-reflection
> coatings to minimise the ghost images.
>
> From the pilots point of view, the two combiners are one on top of
> the
> other, hence the increase in the vertical FoV. A single combiner
> would need too much space above the glareshield and behind the
> windscreen, and need a truly enormous final condensing lens in the CRT
> projection optics.
>
>
I wonder if LCD projection optics will replace the vacuum tube CRT?
And maybe LEDs for a light source?
--
Jim Yanik
jyanik-at-kua.net