Ideal watch?

On 17-Dec-2003, "Michael 182" wrote:

How does an electronic altimeter work? Is there some kind of pressure
sensor?


Yes. The sensing element is in essence a solid-state strain gauge that
detects atmospheric pressure. This is similar to the mechanisms used in
many blind encoders. The Casio watch and similar electronic altimeters
include means for correcting for variations in barometric pressure.
(However, in the case of the Casio the adjustment is unfortunately not in
terms of sea level pressure but is rather just a means to adjust the
altitude readout. For aviation use you set it on the ground to the airport
elevation and adjust it in flight by setting it against the airplane's
altimeter.

While there are some very sophisticated piezoelectric pressure sensors that
allow for an electronic altimeter to be as sensitive as the good old
expanding bellows mechanical kind, the inexpensive strain gauge mechanism is
not quite as good. Adequate for blind encoding or an altitude watch where
required resolution is on the order of 50-100 feet, but not good enough for
use on an instrument approach to low minimums.
______
Elliott Drucker

wrote in message
Of course, it won't work in a
pressurized airplane.


I've always been curious about this: Wouldn't the altimeter still read an
increase/decrease in altitude? No, the altitude would not be correct but
for a backup to keeping the shiny side up in IMC it would have some value,
right?

--
Jim Fisher

Jim Fisher wrote:

I've always been curious about this: Wouldn't the altimeter still read an
increase/decrease in altitude? No, the altitude would not be correct but
for a backup to keeping the shiny side up in IMC it would have some value,
right?

It will show the altitude you've pressurized your cabin to -- nothing to do
with what's going on outside.


All the best,


David

"David Megginson" wrote in message
le.rogers.com...
Jim Fisher wrote:

I've always been curious about this: Wouldn't the altimeter still read
an
increase/decrease in altitude? No, the altitude would not be correct
but
for a backup to keeping the shiny side up in IMC it would have some
value,
right?

It will show the altitude you've pressurized your cabin to -- nothing to
do
with what's going on outside.

You are right, of course. So is 8000 feet a standard pressure for all
pressurized aircraft or are there some that keep 5000 or perhaps 10,000?

--
Jim Fisher

Jim Fisher wrote:

wrote in message
Of course, it won't work in a

pressurized airplane.



I've always been curious about this: Wouldn't the altimeter still read an
increase/decrease in altitude? No, the altitude would not be correct but
for a backup to keeping the shiny side up in IMC it would have some value,
right?


My wife gave me one of these watches for my birthday. Its altitude is
pretty much dead one if I set it right in a non-pressurized airplane.

I took it on a B737 business trip, figuring that since airlineres are
pressurized to 8000 feet it should work up to 8000 feet, and it's at
those lower altitudes that I really wanna know how high we are since
that's when theymake you turn off GPS receivers and such. I naively
thought that the cabin was not pressurized until 8000 and then the
pressurization was turned on at that point to keep it constant.

Imagine my disappointment when on takeoff roll our "altitude" dropped
over 100 feet and stayed there until we were several thousand feet up,
only gradually easing up to 8000. Learn something new every day about
how airlines work.

How do you think your ears would feel if they only started preasurization
upon reaching 8000'?

Mike
MU-2


"TTA Cherokee Driver" wrote in message
...
Jim Fisher wrote:

wrote in message
Of course, it won't work in a

pressurized airplane.



I've always been curious about this: Wouldn't the altimeter still read
an
increase/decrease in altitude? No, the altitude would not be correct
but
for a backup to keeping the shiny side up in IMC it would have some
value,
right?


My wife gave me one of these watches for my birthday. Its altitude is
pretty much dead one if I set it right in a non-pressurized airplane.

I took it on a B737 business trip, figuring that since airlineres are
pressurized to 8000 feet it should work up to 8000 feet, and it's at
those lower altitudes that I really wanna know how high we are since
that's when theymake you turn off GPS receivers and such. I naively
thought that the cabin was not pressurized until 8000 and then the
pressurization was turned on at that point to keep it constant.

Imagine my disappointment when on takeoff roll our "altitude" dropped
over 100 feet and stayed there until we were several thousand feet up,
only gradually easing up to 8000. Learn something new every day about
how airlines work.

"Mike Rapoport" wrote:
How do you think your ears would feel if they only started preasurization
upon reaching 8000'?

Your ears would feel just fine. Although the climb to 8000' can
happen pretty quickly, your ears can tolerate quick decreases
in pressure much easier than quick increases. Then as the plane
climbed above 8000' the pressure inside the cabin would remain
constant so you ears would think the plane is still at 8000'.
(I believe the reason the pressure profile is not controlled
that way during ascent has more to do with the practical aspects
of the pressurizing system). Now if the same profile were
reversed on the way down, that could cause significant discomfort
esp. for those with colds or for those who can't quickly equalize
their ear pressure. A more logical profile for the cabin pressure
would be to keep the cabin effective altitude at some multiple
of the outside altitude (perhaps around 1/4). So when the plane
is at 4000 feet, your ears would think you are at 1000ft. When
the plane got up to 32000 feet, your ears (and lungs) would think
you are at 8000 feet. I don't know how the system actually works
but I'm guessing it is some approximation of what I described.
(My plane is not pressurized, so I never had to learn about
that stuff).

~Paul

Mike Rapoport wrote:

How do you think your ears would feel if they only started preasurization
upon reaching 8000'?



Judging from my experience, I would be fine. But I have noticed other
people are more sensitive. I took my brother for a flight in the
Cherokee and when we leveled off at 5500 I told him we were at cruising
altitude, and he said "good, my ears will probalby stop bugging me now".
Taht surprised me, as I have never felt any ear discomfort climbing or
descending in an unpressurized GA airplane.

I've been off looking for a good aviation watch. I've looked at Citizen
Skyhawk watches, which look cool, but they don't have a backlight, which I
thought would be bad (good?) for flying at night. And I've seen some
others that are all digital, but I like having the hands for a timer. And I
found one that vibrates, which I thought would be really handy for switching
tanks and things, but it didn't have hands. So, I was wondering, what would
everyone like to see as a minimum set of features in an ideal watch? Here's
my list -

1) Analog hands and second hand for timing things
2) Digital clock set to Zulu time so I don't have to bother my small brain
with those pesky conversions
3) Backlight so I can see it when I'm flying at night
4) Vibrating alarm so I remember to do routine things like switch tanks.
5) Nifty E6B ring around the outside that I really can't see, but really
impresses the chicks at the bar

What say you?

For my two cents worth: I use a TIMEX
ATLANTIS 200. Not analog, but for 38 Bucks, it has two times, Timer, Light,
Alarm, but no vibrate mode. I can hear
it go off even with headsets. This is in a Grumman AA5 by the way. Cheers.

Bill Oparowski
N10SX

"Brinks" writes:

I've been off looking for a good aviation watch. I've looked at Citizen
Skyhawk watches, which look cool, but they don't have a backlight, which I
thought would be bad (good?) for flying at night. And I've seen some
others that are all digital, but I like having the hands for a timer. And I
found one that vibrates, which I thought would be really handy for switching
tanks and things, but it didn't have hands. So, I was wondering, what would
everyone like to see as a minimum set of features in an ideal watch? Here's
my list -

1) Analog hands and second hand for timing things
2) Digital clock set to Zulu time so I don't have to bother my small brain
with those pesky conversions
3) Backlight so I can see it when I'm flying at night
4) Vibrating alarm so I remember to do routine things like switch tanks.
5) Nifty E6B ring around the outside that I really can't see, but really
impresses the chicks at the bar

What say you?

Q: What do you get if you cross a pilot with a gorilla?
A: An ape with a big watch

In the middle of my instrument training, I bought a $40 Casio watch
which had analog hands that I set to local time, and a digital readout
which I set to UTC. I eventually switched back to the Seiko analog
watch I got as a high school graduation present from my parents, which
is the watch I still wear.

So, let me answer your questions:

1) Yes, got that
2) The panel clock in my Skylane has two time zones and a timer with an alarm
3) You should have some cockpit lighting to look at charts, etc, no?
4) See (2) (It's a Davtron M-800)
5) Hm

-jav