Metric Instruments

"Tim Ward" wrote in message
ink.net...

"Bill Daniels" wrote in message
...
Does it strike some of the digerati here that expensive mechanical
altimeters with easily mis-read clock-like hands locked into either the
metric or US measurement systems are archaic?

GPS provides highly accurate, although not ATC compliant, altitude.
Various
vendors provide electronic pressure altimeters with digital displays
that
can be switched between meters and feet with the push of a button.
Digital
pressure altitude sensors drive the "glass cockpits" of new GA aircraft.

I seems to me that clock-like altimeters designed 70 years ago and
maintained by watchmakers must be nearing their well-deserved
retirement.

Bill Daniels

Yeah, now if they can just make them so they don't need batteries.

Tim Ward


What's the big deal with batteries? IMHO, batteries are at worst a minor
inconvenience easily worth enduring for the benefits of the technology they
make possible.

Every portable gadget uses them. Most folks have a cell phone, PDA,
portable GPS, digital camera, maybe a camcorder and who knows what else.
Even your car, tug or winch won't start without a battery. They're cheap
and they work fine with a little TLC and regular replacement.

My glider uses a standard 7.5 AH 12V SLA that now sits on a shelf connected
to a charger that quietly maintains the charge. I know for sure that it
will work at least 10 hours and still show more than 12.5 volts while
transmitting. It has a three year "replace by" date written on it whereupon
I will plunk down $20 for another at "Batteries-R-Us" even if it still seems
OK. I don't trust old batteries.

Bill Daniels

"Bill Daniels" wrote in message
...

"Tim Ward" wrote in message
ink.net...

"Bill Daniels" wrote in message
...
Does it strike some of the digerati here that expensive mechanical
altimeters with easily mis-read clock-like hands locked into either
the
metric or US measurement systems are archaic?

GPS provides highly accurate, although not ATC compliant, altitude.
Various
vendors provide electronic pressure altimeters with digital displays
that
can be switched between meters and feet with the push of a button.
Digital
pressure altitude sensors drive the "glass cockpits" of new GA
aircraft.

I seems to me that clock-like altimeters designed 70 years ago and
maintained by watchmakers must be nearing their well-deserved
retirement.

Bill Daniels

Yeah, now if they can just make them so they don't need batteries.

Tim Ward


What's the big deal with batteries? IMHO, batteries are at worst a minor
inconvenience easily worth enduring for the benefits of the technology
they
make possible.

Every portable gadget uses them. Most folks have a cell phone, PDA,
portable GPS, digital camera, maybe a camcorder and who knows what else.
Even your car, tug or winch won't start without a battery. They're cheap
and they work fine with a little TLC and regular replacement.

My glider uses a standard 7.5 AH 12V SLA that now sits on a shelf
connected
to a charger that quietly maintains the charge. I know for sure that it
will work at least 10 hours and still show more than 12.5 volts while
transmitting. It has a three year "replace by" date written on it
whereupon
I will plunk down $20 for another at "Batteries-R-Us" even if it still see
ms
OK. I don't trust old batteries.

Bill Daniels


Upon reflection, Bill, I'm sure that an instrument could be built that could
satisfy both of us.
Digital, easily scalable, there's no reason it can't have both an analog
display (or quasi-analog, with LCD) for trends, and a 5 digit display for
accuracy. It could have a lithium cell recharged by the expansion and
contraction of an aneroid . Several "perpetual clocks" have used that
scheme to drive mechanical gear trains with far smaller pressure changes
than you'll get going up and down in a glider or airplane.
An update rate of twice a second should be plenty fast enough. With LCDs,
and CMOS circuitry running a few microamps at two volts or so, it's probably
not impossible to build. You could probably build one with a primary lithium
battery that would only need to be changed once every ten years or so.
That would be the cheapest way to go.
What will it cost to get it approved? How many people are going to buy it?
In the small market that is aviation, what will it cost to build? If you
could sell it cheaper than a mechanical altimeter, you might have a shot.
In enough volume, you might be able to do that. I don't know if the
altimeter market is large enough for that to be possible. The combined
output of all the altimeter manufacturers is probably not as big as a run
of, say, a cheap DVD player.

I dunno. I'm afraid good enough is the enemy of best.

If you don't care whether or not it's approved, or whether it takes
batteries, then you should look at the Flytec hang glider varios. They have
a lot of options as to what they display and how they display it, and I
believe they'll display altitude both digitally and analog. They'd take up
a bit more space on a panel, though.

Tim Ward

I have to fall firmly and loudly into the "digital is good, electrical
insturments can be reliable, mechanical varios belong in museums"
group.

I would love to see a serious study that shows that classic analog
airspeed and altimeters (as used in gliders) are easier to read and
less susceptible to misinterpretation than a properly designed (but
unfortunately, theoretical) replacement digital airspeed and altimeter.
With the advent of Head-up-Displays (HUDs), fighter planes have moved
to almost completely digital displays of most values - only those where
trend is crucial, such as vertical velocity and radar altitude,
continue to have a companion analog display. Otherwise, its a straight
number, usually rounded off to the nearest knot and 10 feet. Works
fine in an F-15E, should work pretty good in an LS6

By comparison, trying to interpret a three-needle altimeter is like
trying to read sanskrit! And then there are 1 1/2 revolution airspeed
indicators!

If you have a PDA in your cockpit, try setting it up to have a nice big
font altitude (and speed, if available) display on it and try it - you
might find that it is really easy to glance at and read.

I have two seperated battery systems, and no mechanical vario. I'm
stuck with a "steam-gauge" airspeed indicator and altimeter, but what I
would really like is a digital airspeed, digital altimeter, and an
accurate AOA indicator. For tradition, I'll keep the vario needles -
since there I'm looking for trend (to provide a value to the audio),
and read a digital averager for real decision making.

Heck, last year I took off on a fine day only to find my airspeed inop
(bug in the pitot) - but that didn't prevent me from flying a nice
little 500+ k XC with some friends of mine. The only time I really
missed the airspeed indicator was in the pattern. Just flew it a bit
faster than usual (that AOA indicator sure would have been nice to have
then...).

Now the huge caveat - this is all fine in a private ship - I don't see
how a the average club ship would manage.

Kirk
66

In message .com,
writes
I have to fall firmly and loudly into the "digital is good, electrical
insturments can be reliable, mechanical varios belong in museums"
group.

Must admit that my beliefs a Digital is good - for somethings - bad
for others - analogue is good - for somethings - bad for others.

Digital is very good for getting absolutes - fly at a particular flight
level - a specific temperature - or a rate of something. Analogue is
very good for trends and similar, horses for courses. Most of what we
do flying we just want a trend or rough peak - analogue - say (in my
personal opinion) thermal centering.For saying that a particular thing
is better or good enough, say is that thermal good enough to stay with
or is it falling off so we want to go to another, digital in the form of
an averager is the absolute best.

We don't need absolute altitude in an altimeter. Flight Levels are in
500 ft increments. We do absolutes in loggers.

Mechanical can break so can electric. You can get many more functions
out of electric which is good. However I am fully in favour of separate
and different technology systems in case something goes pop.

My own experience in club equipment is that electric goes wrong many
times more often than mechanical and it is far easier to get a poorly
installed mechanical system working than an electronic.

I would love to see a serious study that shows that classic analog
airspeed and altimeters (as used in gliders) are easier to read and
less susceptible to misinterpretation than a properly designed (but
unfortunately, theoretical) replacement digital airspeed and altimeter.
With the advent of Head-up-Displays (HUDs), fighter planes have moved
to almost completely digital displays of most values - only those where
trend is crucial, such as vertical velocity and radar altitude,
continue to have a companion analog display. Otherwise, its a straight
number, usually rounded off to the nearest knot and 10 feet. Works
fine in an F-15E, should work pretty good in an LS6

Well known fact, much publicised by the ergonomicist who sits next to
me, is that three needle altimeters are pure trouble from a reading
point of view. ASIs are less prone to missreading but it does happen.
(She once borrowed one of mine for a lecture on the fact).

Very fast ships (F15s and the like couldn't use foot or even hundred
foot needles as they would spin so fast that they would fall off) need
different technology. Actually, the best (from my opinion) ASI was the
one used in the lightning which was a horizontal tape that wound across
the top of the instrument panel.

They are using analogue in the same way that we are but the low values
are inappropriate. For this they use digital which is easier to control
at fast fates of change.

As you say they are using needles for trends, we do the same. I kinda
think that to do our job properly we need both (needle and digital), the
argument between electric and mech is different but again I think we
need both from a safety point of view.

By comparison, trying to interpret a three-needle altimeter is like
trying to read sanskrit! And then there are 1 1/2 revolution airspeed
indicators!

If you have a PDA in your cockpit, try setting it up to have a nice big
font altitude (and speed, if available) display on it and try it - you
might find that it is really easy to glance at and read.

And see what happens when the software goes pling which happens with
even the best systems.

I have two seperated battery systems, and no mechanical vario. I'm
stuck with a "steam-gauge" airspeed indicator and altimeter, but what I
would really like is a digital airspeed, digital altimeter, and an
accurate AOA indicator. For tradition, I'll keep the vario needles -
since there I'm looking for trend (to provide a value to the audio),
and read a digital averager for real decision making.

Heck, last year I took off on a fine day only to find my airspeed inop
(bug in the pitot) - but that didn't prevent me from flying a nice
little 500+ k XC with some friends of mine. The only time I really
missed the airspeed indicator was in the pattern. Just flew it a bit
faster than usual (that AOA indicator sure would have been nice to have
then...).

Now the huge caveat - this is all fine in a private ship - I don't see
how a the average club ship would manage.

Kirk
66

Robin
--
Robin Birch

On Thu, 25 Aug 2005 21:02:37 +0100, Robin Birch wrote:

In message .com,
writes
I have to fall firmly and loudly into the "digital is good, electrical
insturments can be reliable, mechanical varios belong in museums" group.

Most of what we do
flying we just want a trend or rough peak - analogue - say (in my personal
opinion) thermal centering.For saying that a particular thing is better or
good enough, say is that thermal good enough to stay with or is it falling
off so we want to go to another, digital in the form of an averager is the
absolute best.

Agree 100% I really like the vario display on an SDI C4 and a Tasmin
V1000 vario. Both use analogue for instant reading and digits for the
averager. Both are easy to use.

OTOH what are you doing looking at the vario in a thermal :-)
I find the sound from a C4 makes centring very easy and all I look at
is a glance at the averager from time to time to see if its time to leave
the thermal yet.

I very much like the idea of a B.40 as backup vario because it has its own
internal battery and switch-over circuitry. I just wish it used an LCD
analogue display rather than a needle for the instant rate display.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

In message s, Martin
Gregorie writes
On Thu, 25 Aug 2005 21:02:37 +0100, Robin Birch wrote:

In message .com,
writes
I have to fall firmly and loudly into the "digital is good, electrical
insturments can be reliable, mechanical varios belong in museums" group.

Most of what we do
flying we just want a trend or rough peak - analogue - say (in my personal
opinion) thermal centering.For saying that a particular thing is better or
good enough, say is that thermal good enough to stay with or is it falling
off so we want to go to another, digital in the form of an averager is the
absolute best.

Agree 100% I really like the vario display on an SDI C4 and a Tasmin
V1000 vario. Both use analogue for instant reading and digits for the
averager. Both are easy to use.

OTOH what are you doing looking at the vario in a thermal :-)
Flying club K8s that I keep forgetting to put the battery in and so the
mechanical is all I've got or my Astir when I've forgotten to charge
them and they've gone flat on me after 4 hours :-))

I find the sound from a C4 makes centring very easy and all I look at
is a glance at the averager from time to time to see if its time to leave
the thermal yet.

I very much like the idea of a B.40 as backup vario because it has its own
internal battery and switch-over circuitry. I just wish it used an LCD
analogue display rather than a needle for the instant rate display.


--
Robin Birch