Metric Instruments

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 |

The digital/analog argument was put to me thus. A digital
watch tells you what time it is, an analog watch tells
you what time it isn't as well. The same applies to
analog instruments, in the case of the ASI it tells
you your speed if you study it and at a glance if you
are above or below your target. It's a question of
what you need to know. Digital needs study and calculation,
analog is instant.

At 19:24 25 August 2005, wrote:
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

At 22:06 24 August 2005, Ian Strachan wrote:

snip

Bill Daniels wrote:

snip

GPS provides highly accurate, although not ATC compliant,
altitude.

I am afraid that the claim that GPS altitude is recorded
'highly
accurately' in IGC files from IGC-approved GPS recorders,
is
unfortunately not true.



This is not an attack on the accuracy of the GPS system
or even its
altitude recording capability. It is a reporting of
results of GPS
altitude recording in IGC flight data files derived
from a number of
low-cost GPS boards made by a number of different companies
from
different parts of the world. I guess that in more
expensive
'professional aviation standard' GPS boards, and in
differential-GPS
systems with local beacons, the GPS altitude figures
are more accurate
and with less anomalies. But such (expensive) systems
do not apply to
the current 27 types of GNSS flight recorders that
are IGC-approved
(from 11 manufacturers) and whose IGC-approval documents
appear on the
IGC gliding/gnss web site:

http://www.fai.org/gliding/gnss/igc_approved_frs.pdf

The truth is that it is possible to record altitude
very accurately with GPS, suyveyors who produce our
maps use GPS both for lat/long and elevation with a
resolution in height of less that 15mm over 10Km. Perhaps
the reason that the manuafacturers mentioned above
do not upgrade their equipment is that there is no
demand as the IGC refuse to consider using GPS altitude.
However good a baro recorder is it can never approach
the accuracy of GPS.