Message-ID: <3B21267F.AAA110CA@regandesigns.com>
Date: Fri, 08 Jun 2001 12:24:47 -0700
From: "Hamid A. Wasti" <hamid@regandesigns.com>
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To: lancair.list@olsusa.com
Subject: Re: Blue Mountain Avionics
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Resonance Research" <DR.RESONANCE@next-wave.net> wrote:

> I would like to
> share my panel plan with regarding to inexpensive electronic display panel
> design.

I would like to share some concerns with regard to your plan.  Let me start
with some background & disclaimers.  Brent & I are the hardware designers of
Sierra Flight Systems EFIS2000 and Northstar CT-1000 as well as other
products.  That allows me to talk about this stuff with practical experience
while it allows others to dismiss my opinion as biased.

> Our aircraft is a Lancair IV-P in its last 10 months of
> construction (the 99.9% phase).

I am glad to see that you are realistic about how long it takes to go through
the the last 0.1%.  Wish more people were this realistic.

> We used a Sony Vaio computer and removed the display from the computer.  A
> simple 7 conductor shielded cable allows 30 inches of separation from the
> main computer body which we placed in a small fabricated pullout "box"
> under the right side of the panel.

The 7 conductor cable is most probably some flavor of LVDS cable.  LVDS
requires all the drive pairs to be twisted pair and impedance matched.  Failure
to do so may result in erratic performance depending upon mutual conduction,
cable position and ambient temperature.  30" is quite short for LVDS, so you
may be able to get away with it without meeting all these requirements.

>  The Vaio screen which is 12 x 14 inches
> in size is on the right side of the panel and tilts toward the pilot 30
> degrees.

The real problem with any LCD in the cockpit is the backlight.  How bright is
the LCD?  Will you be able to see it in daylight?  Most laptops are in the 70
to 140 nits range.  With tat large a screen, I would bet that it is in at the
low end of the range.  Daylight readability is defined as 800 nits.  If the
display is not bright enough, it will wash out in bright light and be
unreadable.  The other and bigger problem is night time readability.  How dim
does backlight get?  If it is more than about 2nits your night vision will be
compromised to the point where having the LCD on will be a hazardous
condition.  I doubt the laptop will get much below 20 nits at its dimmest
setting.  Systems designed for outdoors operation use special high intensity
backlights to achieve sunlight readability.  Systems specifically designed for
cockpit use have to have the additional feature of a very high dimming ratio.
You are not going to get either of those on a laptop backlight.

A second potential problem is viewing angle.  Laptops are not designed for a
wide viewing angle.  In fact, a narrow angle is considered "better" by many due
to privacy concerns when using the laptop in a crowded setting.  Will you be
able to see the laptop from the pilot's seat.  What about the co-pilot's seat?
Again, this is very dependent on the actual LCD you are using and may or may
not be a problem in your case.

> The small fingertouch pad was also removed and placed just in
> behind the flight control stick on the left armrest.  A pushbutton in this
> same area allows mouse "clicks" on selected screen programs.

That is great if you are operating the touch pad on the ground or while not
flying the airplane.  It will be a pretty hard place to reach with your right
hand while your left hand is holding the stick.  Also, if you are right handed,
you may want to play with that setup.  Unless you are more coordinated than I
am, you may have a hard time operating a mouse with your weak hand (I have a
very hard time using my wife's computer which is set up with a left hand
mouse).

> Our plane is 28 VDC so we used a small LM317 electronic
> regulator in a metal box to drop the voltage to the correct voltage level
> for the Vaio (10 VDC).

I am surprised that the VAIO runs at 10V.  Most laptops run at 18V and require
about 40W of power to operate and charge the battery, about 20W to operate when
the battery is charged.  I doubt that the VAIO's power requirement would be
significantly less.  If you are putting out only 20W from your 10V regulator,
that will be 2A.  With an input voltage of 28V and an output voltage of 10V,
the LM317 is dropping 18V or 36W.  The absolute maximum rating for a LM317 is
1.5A and 20W with proper heat sinking.  In the best case, your regulator is
going to spend much of its life shut down because of the built in over-current
and over-temperature protection.  In the worst case it will self distract.
Even if you gang two regulators together (that requires special matching
circuitry, you can not just put the two in parallel) you are still looking at
dissipating 40W of power from the heat sink.  That is a non-trivial task and
requires proper heat sink design.

> I have used the Jepp/Mentor Graphics Flitestar and Flightmap program...

Another problem that you may or may get hit with is rotating media operation.
Will the hard drive and the CD ROM tolerate the vibration of in flight use?
What is the game plan if the hard drive starts giving you seek errors in
flight?  Again, this is very installation dependent and may or may not affect
you.

Do think about these issues.  I have pointed out some hard numbers here, not
just a "it won't work because I did not design it" statement.   Best of luck.

Hamid


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