Altimeter Question

On Apr 18, 4:06*am, Gig 601Xl Builder
wrote:
WingFlaps wrote:
On Apr 18, 2:40 am, Gig 601Xl Builder
wrote:
terry wrote:

I wasnt aware you dont use the QNH term in the States. *So what do you
call the number you dial up to make the altimeter read airport
elevation?
altimeter

Nope. If you dial up the local barometric pressure the altimeter may
not read airfield elevation....

Cheers

GO away no fly boy.

I see you don't know. In fact an altimeter is calibrated to the
standard atmosphere so if the temp. is not standard it will not read
field elevation when local QNH is applied.

Pretty basic knowlege for a PPL, Oh I forgot, I'm not supposed to be a
pilot.

Cheers

WingFlaps schrieb:

I see you don't know. In fact an altimeter is calibrated to the
standard atmosphere so if the temp. is not standard it will not read
field elevation when local QNH is applied.

Wrong.

From The ICAO Manual of Radiotelephony (ICAO Document 9432) Glossary:
QNH: Altimeter sub-scale setting to obtain elevation when on the ground

So an altimeter set to local QNH will always read field elevation *by
definition*.

Pretty basic knowlege for a PPL

Indeed.

On Apr 18, 4:43*am, Stefan wrote:
WingFlaps schrieb:

I see you don't know. In fact an altimeter is calibrated to the
standard atmosphere so if the temp. is not standard it will not read
field elevation when local QNH is applied.

Wrong.

*From The ICAO Manual of Radiotelephony (ICAO Document 9432) Glossary:
QNH: Altimeter sub-scale setting to obtain elevation when on the ground

So an altimeter set to local QNH will always read field elevation *by
definition*.

* Pretty basic knowlege for a PPL

Indeed.

Yes it may say that but it's being loose because it forgt to include
the "barometric pressure reduced to MSL by application of the ISA".
Alltimeters are calibrated for the standard atmosphere. -right?
Think about it, if an ARFOR gives QNH how could it be correct for all
terrain if local temperatures differed? I covered this in my PPL tech
course -was this not covered in your manuals?
just in case you still don't see it, from Wiki:

"The altimeter is calibrated to show the pressure directly as an
altitude above mean sea level, in accordance with a mathematical model
defined by the International Standard Atmosphere (ISA)... An altimeter
cannot, however, be adjusted for variations in air temperature.
Differences in temperature from the ISA model will, therefore, cause
errors in indicated altitude."

OK?

Cheers

WingFlaps schrieb:

So an altimeter set to local QNH will always read field elevation *by
definition*.

Yes it may say that but it's being loose because it forgt to include
the "barometric pressure reduced to MSL by application of the ISA".
Alltimeters are calibrated for the standard atmosphere. -right?

Right.

Think about it, if an ARFOR gives QNH how could it be correct for all
terrain if local temperatures differed? I covered this in my PPL tech
course -was this not covered in your manuals?

Think about it, nobody said it would be correct for all altitudes, but
just for one altitude: the airfield elevation.

just in case you still don't see it, from Wiki:

Wiki, the ultimate authoritative source.

Hint: Look up the difference between QNH and QFF.

On Apr 18, 7:55*am, Stefan wrote:
WingFlaps schrieb:

So an altimeter set to local QNH will always read field elevation *by
definition*.
Yes it may say that but it's being loose because it forgt to include
the "barometric pressure reduced to MSL by application of the ISA".
Alltimeters are calibrated for the standard atmosphere. -right?

Right.

Think about it, if an ARFOR gives QNH how could it be correct for all
terrain if local temperatures differed? *I covered this in my PPL tech
course -was this not covered in your manuals?

Think about it, nobody said it would be correct for all altitudes, but
just for one altitude: the airfield elevation.



Perhap we are at crossed purposes but an ARFOR does not refer to an
airfield -that's a METAR and not all fields issue them. So in this
case how can QNH give field elevation unless it's an ISA day?

Cheers

Cheers

Cheers

WingFlaps schrieb:

Perhap we are at crossed purposes but an ARFOR does not refer to an
airfield -that's a METAR and not all fields issue them. So in this
case how can QNH give field elevation unless it's an ISA day?

Again: QNH gives *by definition* the field elevation. If an ARFOR gives
you a QNH, then it is related to one well defined spot on the surface.

On Apr 18, 7:10*am, Stefan wrote:
WingFlaps schrieb:

Perhap we are at crossed purposes but an ARFOR does not refer to an
airfield -that's a METAR and not all fields issue them. So in this
case how can QNH give field elevation unless it's an ISA day?

Again: QNH gives *by definition* the field elevation. If an ARFOR gives
you a QNH, then it is related to one well defined spot on the surface.


As I understand it ( In Australia) the QNH in an ARFOR must be within
5 mbar of the "real QNH" - ie what gives you field elevation for any
place within that area. otherwise the area will be broken up into sub
areas and no 2 adjacant sub areas must differ by more than 5 mbar.
That way the errors which Wing flap alludes to, and must certainly
exist in non ISA atmosphere, would result in errors of no more than
150 feet between aircraft using either the correct AFROR QNH or the
airfield set QNH

Stefan wrote in news:c9458$4807bcae$54487328$4551
@news.hispeed.ch:

WingFlaps schrieb:

Perhap we are at crossed purposes but an ARFOR does not refer to an
airfield -that's a METAR and not all fields issue them. So in this
case how can QNH give field elevation unless it's an ISA day?

Again: QNH gives *by definition* the field elevation.

Only at the airport ref point, so, no, it doesn't.


Bertie

On Apr 18, 9:10*am, Stefan wrote:
WingFlaps schrieb:

Perhap we are at crossed purposes but an ARFOR does not refer to an
airfield -that's a METAR and not all fields issue them. So in this
case how can QNH give field elevation unless it's an ISA day?

Again: QNH gives *by definition* the field elevation. If an ARFOR gives
you a QNH, then it is related to one well defined spot on the surface.

BINGO! That's right, setting QNH on an altimeter DOES NOT does give
field elevation UNLESS it's issued for that field :-)

Cheers

Stefan wrote in news:680f0$48077e23$54497f6b
:

WingFlaps schrieb:

I see you don't know. In fact an altimeter is calibrated to the
standard atmosphere so if the temp. is not standard it will not read
field elevation when local QNH is applied.

Wrong.

From The ICAO Manual of Radiotelephony (ICAO Document 9432) Glossary:
QNH: Altimeter sub-scale setting to obtain elevation when on the
ground

So an altimeter set to local QNH will always read field elevation *by
definition*.


No, it will read the elevation where you are. UIt will read field
elevation at the reference point.


Pretty basic knowlege for a PPL

Indeed.


Indeed indeed.


Bertie