Metric Instruments

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