On 03/24/2010 08:14 AM, David Joyce wrote:
> Tony, The thought occurs to me to wonder why anyone would want a full
> width panel these days?
I would actually reverse the question: Why would anyone trade panel
space for a silly picknick tray? ;-)
I can give you a few reasons:
1) Versatility. There are very few (if any?) "we can do it all"-EFIS &
engine management systems which are very good in *everything* they are
supposed to do. With separate instruments, you can simply pick the
instruments that best suit you. For instance, I have a dual electrical
system, is there any glass panel thing that can cope with that and
display two battery monitors? With separate instruments, you don't have
to worry about these things.
If I want to replace an instrument later on, because there is a new and
better system, I can just do so, and am not bound to the EFIS I'm using
(which manufacturer might have gone out of business by then).
2) Reliability. Most solid state gyro systems are simply lying. They
don't display the real attitude, but compute that from a number of
sources and play a nice game of averaging, which seems to work well as
long as you fly VFR. But fly uncoordinated for 15 minutes or so, with
one wing lower than the other, and most of these systems quickly adapt
to it and start to tell that you are actually flying straight and level.
3) Redundancy. Apart from the obvious facts that with these systems you
put all your eggs in one basket, again the attitude indicator is the
main danger. Instead of being an independant instrument, it computes the
attitude from a number of sources, like static pressure for instance.
(Gravity sensors have too much drift, so the instrument calibrates
itself with other sources: "If static pressure increases, we are
descending, so let's display a nose down attitude.") Now, if you loose
your static port in IMC conditions, with conventional instruments you
loose a few instruments, but the attitude indicator (horizon) can help
you out. Not so with a glass panel, because if the static port is gone,
the horizon is gone too. Same with the pitot.
And of course, if you hit the display in turbulence, you don't loose a
single instrument, but everything you have. I wouldn't dare to fly in
IMC with such a thing.
4) Readability. Steam instruments are easy to read. You get used to a
certain needle position, and even the smallest deviation, or vibration
will attract your attention. With a digital representation the
resolution is often to course. A numerical output is then better, but
numerical outputs are horrible for the brain, consuming much more
resources to interpret, compared to just reading the angle of a needle.
Then of course we all know how easily computers lie to us. If the
display shows some parameter climbing in the red line, it is always a
question whether it is real, or just a sensor or data cable problem,
interference, or whatever.
Here in the Netherlands (and probably a lot of other countries as well)
we are required to have a TSO'd altimeter, airspeed indicator, and a
compass. So, we already need three separate instruments of the standard
six pack, besides the EFIS. Now add a separate gyro instrument to the
stack to partly solve the redundancy problem. Now also add an autopilot
to it, which comes with a turn indicator built in. What are we actually
saving with our EFIS? Just the vertical speed indicator!
I did the math while I was designing my panel, and discovered that with
any EFIS, I would actually add weight (considering my desire for
redundancy), add costs, loose some flexibility, and decided that it is
not worth it.
I also decided that I don't need a picknick tray. My lunch can wait
until I'm done flying. Packages can be put in the bagage bay. The
picknick tray is not the best place to keep loose stuff, and put
anything white or shiny in it and it affects the vision. And then I also
just disliked it. I'm building an airplane, and it should look like an
airplane. ;-)
Keeping the picknick tray would simply mean, even with an EFIS, that I
would have to scramble for panel space and probably trade off a few
desirable features.
Frans
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