QNH???

Bryan Martin wrote:

Try http://www.auf.asn.au/groundschool/umodule3.html on the second page.


in article , Marlbra at
wrote on 2/22/05 3:17 AM:

my instructor told me not to worry about what "qnh" actually
means......... can someone here enlighten me please? i know it has
something to do with the barometric pressure and setting alt meter,
but what does QNH stand for...... as always thanks for your patience
guys and gals.....Im new here


From the above mentioned web page.
John


Q-codes

Note: the letters in the Q-code nomenclature have no literal significance,
these are remnants of an extensive notation system from the days of
wireless-telegraphy. There were some 200 three letter Q-codes each
representing a sentence, a phrase or a question, for instance QRM "I am
being interfered with"!. Some 30 Q-codes are still used by amateur radio /
morse code enthusiasts and the four below, plus QDM (the magnetic bearing
to a station), still survive in aviation. For a full listing of Q-codes try
www.cbug.org.uk/allqcodes.htm


QNE: is the ISA Standard Pressure altimeter setting of 1013.2 hPa. The term
QNE is now rarely encountered but if you set 1013.2 on the altimeter
pressure-setting scale while parked the altimeter will indicate the current
ISA pressure altitude of the airfield - which is the first step in
calculating density altitude. QNE is also the standard factory setting for
altitude encoding.

my instructor told me not to worry about what "qnh" actually
means......... can someone here enlighten me please? i know it has
something to do with the barometric pressure and setting alt meter,
but what does QNH stand for...... as always thanks for your patience
guys and gals.....Im new here

Marlbra wrote:
my instructor told me not to worry about what "qnh" actually
means......... can someone here enlighten me please? i know it has
something to do with the barometric pressure and setting alt meter,
but what does QNH stand for...... as always thanks for your patience
guys and gals.....Im new here

QNH is the pressure that the air would be at sea level, if it wasn't for
the land all being above sea level. If you were to bore a hole down to
sea level, and lower a barometer down the hole to the bottom, then QNH
is what pressure the barometer would read. Theoretically.

If you set your altimeter to QNH, then it will accurately show you
altitude above sea level, so you can avoid busting into someone's
controlled airspace. It will also show the airfield elevation when
you're on the ground at the airfield.

Frank

In article ,
Marlbra wrote:
my instructor told me not to worry about what "qnh" actually
means......... can someone here enlighten me please? i know it has
something to do with the barometric pressure and setting alt meter,
but what does QNH stand for...... as always thanks for your patience
guys and gals.....Im new here

It means do it "Quietly, No Hu-hu".


Well, you *asked* grin


Seriously, it is just a "code". an *arbitrary* symbol to which a particular
meaning has been assigned.

"Q" codes date from the days of Morse-code communications, where there was
a definite performance advantage to be gained by having "short-cut' symbols
for many "common" messages/phrases. example: it is *much* faster to
send the 3 Morse-symbols for "QRU" than it is to transmit "I have no traffic
for your station".

Yes but...

"QNH is a calculated number that makes your altimeter read
correctly (true altitude = pressure altitude) "

True alt is above sea or land in true feet or meter.
Pressure alt. is alt above the Std 29.92/1013.25 level, and that surface can
be above or below SL depending on atmosphere pressure.

Jan Carlsson
www.jcpropellerdesign.com


"T o d d P a t t i s t" skrev i meddelandet
news
Frank van der Hulst wrote:

QNH is the pressure that the air would be at sea level, if it wasn't for
the land all being above sea level. If you were to bore a hole down to
sea level, and lower a barometer down the hole to the bottom, then QNH
is what pressure the barometer would read. Theoretically.

I think "Theoretically" is the important part of this. When
you set QNH at the local airport, the altimeter reads
correctly only at the altitude of that local field (unless
the atmospheric temp and pressure changes with altitude in
the standard way, which it almost never does.) So, just
like there is a difference between true altitude and
pressure altitude when flying above the airport, the
imaginary barometer-in-the-hole won't really read QNH when
at the true altitude of the sea.

QNH is a calculated number that makes your altimeter read
correctly (true altitude = pressure altitude) at the
altitude/elevation of the reporting station. Everywhere
else (including at the true altitude of the sea) it's wrong,
but as long as we're all wrong by the same amount, we don't
run into each other.

T o d d P a t t i s t
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

QNH, QFE, QFF, QNE
When an airport measures the local air pressure, then this pressure is
called QFE. An airplane which has set the altimeter to the QFE value will
read zero feet on the altimeter when it is on the ground at this airport.

The QFE can be transformed into QNH by calculations and/or tables or
diagrams. In fact what happens is that the measured QFE is being corrected
for non-standard temperature, non-standard-humidity etc.

The resulting value is called QFF. This QFF value is then corrected for
field elevation, that means that it is transformed into a pressure as it
would have been at mean sea level (MSL) under standard conditions QNE (29.92
inches or 1013.2 mb of mercury at 59 degrees fahrenheit or 15 degrees
centigrade).

The resulting value is a local pressure value which we call QNH. An
airplane which has set the altitude to QNH value will read the field
elevation on the altimeter when it is standing at this airport!

Samm
I fly because it releases my mind from the tyranny of petty things . . . -
Antoine de St-Exupéry


"Marlbra" wrote in message
...
my instructor told me not to worry about what "qnh" actually
means......... can someone here enlighten me please? i know it has
something to do with the barometric pressure and setting alt meter,
but what does QNH stand for...... as always thanks for your patience
guys and gals.....Im new here

I agree, but you sat tru alt=Pressure alt, that will only happend if QNH is
1013.25 if flying with any other QNH setting pressure alt will not be what
you see on the altimeter, it will be the alt above SL (with its errors from
dif. temp. and other factors)

Jan

"T o d d P a t t i s t" skrev i meddelandet
...
Aside from the fact that you snipped off the last part of my
sentence - what was the "but" part. Did you disagree with
me? Looks to me like a case of contentious agreement :-)


"Jan Carlsson" wrote:

Yes but...

"QNH is a calculated number that makes your altimeter read
correctly (true altitude = pressure altitude) "

True alt is above sea or land in true feet or meter.
Pressure alt. is alt above the Std 29.92/1013.25 level, and that surface
can
be above or below SL depending on atmosphere pressure.

Jan Carlsson
www.jcpropellerdesign.com


"T o d d P a t t i s t" skrev i
meddelandet
news
Frank van der Hulst wrote:

QNH is the pressure that the air would be at sea level, if it wasn't
for
the land all being above sea level. If you were to bore a hole down to
sea level, and lower a barometer down the hole to the bottom, then QNH
is what pressure the barometer would read. Theoretically.

I think "Theoretically" is the important part of this. When
you set QNH at the local airport, the altimeter reads
correctly only at the altitude of that local field (unless
the atmospheric temp and pressure changes with altitude in
the standard way, which it almost never does.) So, just
like there is a difference between true altitude and
pressure altitude when flying above the airport, the
imaginary barometer-in-the-hole won't really read QNH when
at the true altitude of the sea.

QNH is a calculated number that makes your altimeter read
correctly (true altitude = pressure altitude) at the
altitude/elevation of the reporting station. Everywhere
else (including at the true altitude of the sea) it's wrong,
but as long as we're all wrong by the same amount, we don't
run into each other.

T o d d P a t t i s t
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.



T o d d P a t t i s t
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

Back when I worked at Boeing one of the test pilots told me that QFE and QNE
stood for Queen's Field Elevation (altimeter reference to the field so it
read zero on the runway) and Queen's Normal Elevation (altimeter referenced
to sea level). I don't know if this was just a memory aid, or if QFE and
QNE are actually acronyms for Queen's Field Elevation and Queen's Normal
Elevation.... anyone know?

Dean

In article ,
Dean Wilkinson wrote:
Back when I worked at Boeing one of the test pilots told me that QFE and QNE
stood for Queen's Field Elevation (altimeter reference to the field so it
read zero on the runway) and Queen's Normal Elevation (altimeter referenced
to sea level). I don't know if this was just a memory aid, or if QFE and
QNE are actually acronyms for Queen's Field Elevation and Queen's Normal
Elevation.... anyone know?

Yup. *NOT* true. 'Q codes' are just that _codes_. Not Acronyms.

Furthermore, "logic" shoots down both your 'memory aid' interpretations.
an "elevation" is a _distance_ measurement above a reference point, not
a 'pressure' reference. One can trust the "Queen's English" to use words
properly. grin

On top of that... manned flight was invented HERE in the US... not in that
dental-challenged, pompus, take credit for everything, dung-hole!


"Robert Bonomi" wrote in message
...
In article ,
Dean Wilkinson wrote:
Back when I worked at Boeing one of the test pilots told me that QFE and
QNE
stood for Queen's Field Elevation (altimeter reference to the field so it
read zero on the runway) and Queen's Normal Elevation (altimeter
referenced
to sea level). I don't know if this was just a memory aid, or if QFE and
QNE are actually acronyms for Queen's Field Elevation and Queen's Normal
Elevation.... anyone know?

Yup. *NOT* true. 'Q codes' are just that _codes_. Not Acronyms.

Furthermore, "logic" shoots down both your 'memory aid' interpretations.
an "elevation" is a _distance_ measurement above a reference point, not
a 'pressure' reference. One can trust the "Queen's English" to use words
properly. grin