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Tom,
You asked what phase of flight a HUD would be mostly used. Let me offer
how I use the HUD I have in the 737-800 I fly at work.
Basically, my HUD is a pull down glass plate called a combiner that
rotates up and out of view when not in use. The projection unit and
combiner are mounted over my head. They're large and very heavy, so
reducing them to a useful size is critical. I've seen the NASA HUD display
that's a small lens mounted to a headband, so I know it can be done. I have
the HUD down all the time below 18,000' and often I'll use it whenever I'm
hand flying the plane up to cruise altitude. The one I use has, I suspect,
far more cues in it than we'd ever see in a Lancair application.
Of primary use is the flight director cue, which is driven by what we set
on our flight mode control panel. It's essentially a repeater of the F/D on
our PFD, only in a different format. There are several ways to display the
flight director cues, but what we have is a small moving circle that
indicates the F/D guidance. We also display a larger fixed circle, which
represents the aircraft. such that the small circle is inside the larger
one. It's like playing the old game "Operation"- keep the small circle from
touching the edges of the larger one and all is well.
Primarily, we have pitch and roll modes, though we also have throttle cues
which are driven by whatever airspeed or mach we set as well. We can set
pitch for VSI, airspeed , approach (which indicates G/S) or VNAV mode
(derived from our flight management system computer) and roll can come from
heading, LNAV (driven by our GPS's, much like GPSS is on my S-Tec A/P), LOC
or approach modes.
Along the sides of the horizon display (which includes a moving compass
card on the horizon line)are airspeed tapes on the left and altitude and V/S
on the right. Above the altitude tape is the AOA display and below it is a
readout of the radio freq selected in the NAV radio and DME. A small bank
indicator is at the top of the display and radio altitude up to 2500' is
shown on the bottom. Finally, we have a wind arrow which shows direction
and velocity- very handy on landing. There are several other modes and cues
that aren't germane to the discussion, such as TCAS displays, windshear
display, unusual attitude cues, airspeed and throttle position, yaw, etc.
While it would be great to have all of this info in front of me when I'm
flying my ES, what I'd like to see is essentially a repeater of the Chelton
PFD. Anything beyond the PFD info would be gravy. I'd imagine that finding
a way to feed existing info like that onto a HUD would help keep the cost
lower. A display like that would allow me to fly IFR without taking my eyes
off the HUD, a real plus when you're looking for a runway on an ILS
approach. In VFR, you could keep your scan outside while looking for
traffic.
What's it worth? That's a tough one. To me it would depend on what was
on it and whether I felt I'd get enough use out of it. Most of my flying in
Southern Calif is VFR, so I don't know if I could justify an expensive
addition like that. I would very much like to have a flight director, which
I don't have at present.
I feel the technology is close enough that cost will decide when the
market's ready for it, much like the glass cockpit stuff that's common now.
I hope guys like you will keep working on it!
Skip Slater
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