Altimeter settings: QNH versus QFE

I also know the classical arguments like "a nautical mile
equals a minute of latitude", but how often do you fly true north or
south?)

Airplane pilots like to look at the length of a course line, compare it
to the minutes latitude and know exactly the distance without the use of
any other tools. I understand that there are other tools. I was raised
as a Dutch man and brought up with the metric system - and prefer it.
But, to me nautical miles make sense, YMMV.

On another topic, why have horizontal speed in km/h and vertical speed
in meters/sec? To me, this is odd. If the units were the same, you could
simply divide one into the other and get the L/D - again, YMMV.

Tony V.

"Tony Verhulst" wrote in message
...
I also know the classical arguments like "a nautical mile
equals a minute of latitude", but how often do you fly true north or
south?)

Airplane pilots like to look at the length of a course line, compare it
to the minutes latitude and know exactly the distance without the use of
any other tools. I understand that there are other tools. I was raised
as a Dutch man and brought up with the metric system - and prefer it.
But, to me nautical miles make sense, YMMV.

On another topic, why have horizontal speed in km/h and vertical speed
in meters/sec? To me, this is odd. If the units were the same, you could
simply divide one into the other and get the L/D - again, YMMV.

Tony V.

Knots, MPH, KPH, meters/sec are just numbers. Just read the POH and fly the
numbers.

However, I have a beef with metric altimeters. The large hand reads 1000
meters per rev. An imperial units altimeter reads 1000 feet per rev. 1000
meters = 3281 feet so the metric altimeter is less than 1/3 as sensitive as
the one based on feet. To me, that seems inadequate.

I like to see the altimeter hand move with small changes in altitude.
That's confirmation that all is well in the instrument panel. I've seen
haywire varios insistently reading up while the altimeter was winding down.
I'm not sure I would have spotted that as quickly with a metric altimeter.

I suppose there is no reason that a metric altimeter could not be more
sensitive. With today's digital technology, 100 meters per rev should be
possible. I've never seen one that sensitive.

Bill Daniels

Bill Daniels wrote:

I like to see the altimeter hand move with small changes in altitude.
That's confirmation that all is well in the instrument panel. I've seen
haywire varios insistently reading up while the altimeter was winding down.
I'm not sure I would have spotted that as quickly with a metric altimeter.

I suppose there is no reason that a metric altimeter could not be more
sensitive. With today's digital technology, 100 meters per rev should be
possible. I've never seen one that sensitive.

Actually, even yesterday's digital technology already provides very
sensitive altimeters in our varios, GPS units, or flight computers.
These are digital readouts, of course, not hands, but I find myself
looking at my Cambridge 302 altimeter reading much more than the
mechanical one. You can use it in feet or meters, and have plenty of
sensitivity.

The next mechanical altimeter I buy will likely be an INsensitive unit,
like one of the 0-10,000' or 0-20,000 single hand units for less than $150.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

In article ,
"Bill Daniels" wrote:

However, I have a beef with metric altimeters. The large hand reads 1000
meters per rev. An imperial units altimeter reads 1000 feet per rev. 1000
meters = 3281 feet so the metric altimeter is less than 1/3 as sensitive as
the one based on feet. To me, that seems inadequate.

Some gliders I have flown have altimeters marked in feet, but 3000 ft
per revolution rather than 1000.

Presumably it's possible to design a single unit for either metric or
imperial use and tweak the calibration by the 10% difference.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

On Fri, 03 Jun 2005 03:43:36 +1000, Graeme Cant
wrote:

309 wrote:

All of the aruguing aside, can anybody out there tell me a little of
the history of QNH, QFE, and QNE (etc.), specifically, WHAT does the
"Q" stand for??? The "F"? The "N", the "H" or the "E"???

The three letter "Q" codes date back to W/T, radio operators and Morse
code. They were a shorthand way of requesting/passing information and I
don't recall any where the other letters have any significance.

I don't know, but wonder with the thought in creating Morse (most
common letters easiest to send), if the letters for the most common
(at the time?) were the least confusing and/or shortest sent in
combination?

Funny to get exactly the reactions one could foresee. OK, I admit I
don't have much hope of getting the ISU units accepted in aviation, but
the "nautical mile/minute of latitude" story has been dealt with long
ago, shortly after the French Revolution. There still are French (I'm
Belgian, please don't mix us up) survey maps with longitude and
latitude in grades, not degrees (400 grades = 360 degrees). You then
have: 1 hundredth of a grade = 1 kilometre (UK) / kilometer (USA). Just
as efficient (or inefficient), and decimal, but it hasn’t been able to
replace the 360 degree system, not even in the ISU. Oh, by the way,
this geodetic system uses the Paris meridian as zero, not the Greenwich
one.
why have horizontal speed in km/h and vertical speed in meters/sec? To
me, this is odd. If the units were the same, you could simply divide
one into the other and get the L/D
Odd, yes, but I’m not really in favour of calculating the L/D by
dividing indicated speed by sink anyhow: the value will vary wildly in
a relatively short time, and wind can play havoc with this kind of
calculation.


--
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stephanevdv wrote:

Just
as efficient (or inefficient), and decimal, but it hasn’t been able to
replace the 360 degree system,

Just to add confusion to the discussion: The decimal system has been
about the dumbest idea which has happened to mankind. The phoenicians
got it right by using the duodecimal system (actually, they used even
the 60-system), which is much more suited for most real life situations.
But some dimmer folks replaced it by the decimal system, because they
couldn't do the math without using their fingers. So I fear we have to
live with that.

Stefan

And what about computer folks?
They can't go further than 0 and 1!


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stephanevdv
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'duodecimal system' -- We use that all the time in libraries in the
USA.

Larry

"Stefan" wrote in message
:

stephanevdv wrote:

Just
as efficient (or inefficient), and decimal, but it hasn't been able to
replace the 360 degree system,

Just to add confusion to the discussion: The decimal system has been
about the dumbest idea which has happened to mankind. The phoenicians
got it right by using the duodecimal system (actually, they used even
the 60-system), which is much more suited for most real life situations.
But some dimmer folks replaced it by the decimal system, because they
couldn't do the math without using their fingers. So I fear we have to
live with that.

Stefan

Get rid of feet, knots and NM???

That may work for gliders, but not necessarily for other type aircraft. The
math is simple using the nautical system with lots of shortcuts to do the
math simply. Mach number means nothing to glider pilots (save the shuttle
dudes), but it does to us jet jocks.


"stephanevdv" wrote in
message ...

Just another point in this discussion: when I look at an approach map of
an airfield, the pattern altitude is expressed as a height above
ground. To me, this means the easiest way of complying is to fly QFE
when entering the pattern (no mathematics needed) - providing of course
you can get the necessary information.

If you want to fly QNH, pattern altitudes should be expressed AMSL.

By the way, here in Europe (except UK, of course) glider altimeters are
in meters, not feet, thereby conforming to ICAO annex 5 whose purpose
it is to standardize units of measurement to the ISU. As the approach
maps (and other aviation maps) usually are in feet, we already have to
make computations anyhow.

It's high time we got rid of feet, knots and nautical miles! Their only
real purpose in aviation seems to be to make it more difficult to get a
pilot's licence, as you have to adjust to a new set of units. (Yes, I
know there are certain countries where they like to use outdated unit
systems. I also know the classical arguments like "a nautical mile
equals a minute of latitude", but how often do you fly true north or
south?)


--
stephanevdv
------------------------------------------------------------------------
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fly -