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Altimeter Question



 
 
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  #1  
Old April 17th 08, 10:20 AM posted to rec.aviation.piloting,rec.aviation.student
terry
external usenet poster
 
Posts: 215
Default Altimeter Question

I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.

Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that

a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. The atmospheric pressure at the aerodrome has not changed.

Terry
PPL Downunder



  #2  
Old April 17th 08, 12:29 PM posted to rec.aviation.piloting,rec.aviation.student
Mortimer Schnerd, RN[_2_]
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Posts: 597
Default Altimeter Question

terry wrote:
I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.

Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that

a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. The atmospheric pressure at the aerodrome has not changed.



Their answer confuses me too. It seems that if the altimeter setting wasn't
changed from day 1 to day 2, yet it reads a lower altitude, the barometric
pressure must have risen. The altimeter will translate lower pressure to higher
altitude and higher pressure to lower altitude. So I think the answer should be
"a". And if I accept "a", I have to accept "c" as well, as you did.

I'm probably going to regret posting this because I'm going off the top of my
head but it wouldn't be the first time a test guide had the wrong answer posted.

Alright guys.... pile on!




--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com


  #3  
Old April 17th 08, 12:30 PM posted to rec.aviation.piloting,rec.aviation.student
Barry
external usenet poster
 
Posts: 70
Default Altimeter Question

I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.

Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that

a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. The atmospheric pressure at the aerodrome has not changed.


I agree with you - answers a and c are both correct. Day 2 QNH is about 1026.


  #4  
Old April 17th 08, 12:42 PM posted to rec.aviation.piloting,rec.aviation.student
terry
external usenet poster
 
Posts: 215
Default Altimeter Question

On Apr 17, 9:29*pm, "Mortimer Schnerd, RN" mschnerdatcarolina.rr.com
wrote:
terry wrote:
I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.


Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
* * * * ( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that


a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. *The atmospheric pressure at the aerodrome has not changed.


Their answer confuses me too. *It seems that if the altimeter setting wasn't
changed from day 1 to day 2, yet it reads a lower altitude, the barometric
pressure must have risen. *The altimeter will translate lower pressure to higher
altitude and higher pressure to lower altitude. *So I think the answer should be
"a". *And if I accept "a", I have to accept "c" as well, as you did.

I'm probably going to regret posting this because I'm going off the top of my
head but it wouldn't be the first time a test guide had the wrong answer posted.

Alright guys.... pile on!


No, its not the first time I have come across wrong answers either,
but it is the first time I have come across a wrong answer, pointed it
out to the author and was still told I was wrong. ( I dont want to
name the said author because I think he otherwise has published some
very good material and I am sure he will soon realise his mistake.. I
just wanted to be absolutely sure I was right before I responded to
his response!)
Thanks Mort


  #5  
Old April 17th 08, 12:42 PM posted to rec.aviation.piloting,rec.aviation.student
terry
external usenet poster
 
Posts: 215
Default Altimeter Question

On Apr 17, 9:30*pm, "Barry" wrote:
I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.


Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
* * * * ( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that


a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. *The atmospheric pressure at the aerodrome has not changed.


I agree with you - answers a and c are both correct. *Day 2 QNH is about 1026.


Yep, thats what I get
Thanks
  #6  
Old April 17th 08, 01:57 PM posted to rec.aviation.piloting,rec.aviation.student
Larry Dighera
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Posts: 3,953
Default Altimeter Question

On Thu, 17 Apr 2008 02:20:46 -0700 (PDT), terry
wrote in
:

I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.

Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale


http://en.wikipedia.org/wiki/Mbar
Atmospheric air pressure is often given in millibars where
"standard" sea level pressure is defined as 1013.25 mbar (hPa),
equal to 1.01325 bar. Despite millibars not being an SI unit, they
are still used locally in meteorology in some countries to
describe atmospheric pressure. The SI unit is the pascal (Pa),
with 1 mbar = 100 Pa = 1 hPa = 0.1 kPa. Meteorologists worldwide
have long measured air pressure in millibars. After the
introduction of SI units, others use hectopascals (which are
equivalent to millibars) so they could stick to the same numeric
scale. Similar pressures are given in kilopascals in practically
all other fields, where the hecto prefix is hardly ever used. In
particular, Canadian weather reports use kilopascals (which could
also be called centibars).


( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that

a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. The atmospheric pressure at the aerodrome has not changed.

Terry
PPL Downunder



http://www.acronymfinder.com/acronym.aspx?rec={8F1A7DDE-89E8-11D4-8351-00C04FC2C2BF}
What does QNH stand for?
Atmospheric Pressure (Q) at Nautical Height (aviation)
  #7  
Old April 17th 08, 02:29 PM posted to rec.aviation.piloting,rec.aviation.student
Stefan
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Posts: 578
Default Altimeter Question

Larry Dighera schrieb:

http://en.wikipedia.org/wiki/Mbar


Mbar would be a tad much. You certainly meant mbar.

What does QNH stand for?
Atmospheric Pressure (Q) at Nautical Height (aviation)


Bull****. QNH is *not* an acronym. It's one of over hundred Q-Codes
which were defined in the stone age of radio telephony. The letters were
randomly chosen, think of it as a numeration. Most of those Q-Codes are
forgotten today, but a few still live. In aviation, I mean in aviation
in all coutries except the USA, QNH, QFE and QNH are used to define
different altitude settings (roughly spoken).

QNH stands for the pressure you must tune in the kollmans window to have
the altimeter display the airport elevation when the airplane sits on
the ground. (As opposed to QFE, which ist the pressure to set for the
alitmeter to display zero on the ground and QNE, which is the altitude
which the alitmeter shows on the ground when it is set to standard
atmosphere.)

For those who believe in Wikipedia: http://en.wikipedia.org/wiki/Q-code
  #8  
Old April 17th 08, 02:38 PM posted to rec.aviation.piloting,rec.aviation.student
Stealth Pilot[_2_]
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Posts: 846
Default Altimeter Question

On Thu, 17 Apr 2008 07:30:56 -0400, "Barry" wrote:

I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.

Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that

a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. The atmospheric pressure at the aerodrome has not changed.


I agree with you - answers a and c are both correct. Day 2 QNH is about 1026.


playing with an altimeter here in my lap.
simulating 1390 by setting 390. the qnh reads as 1032.

moving the needle lower sees the qnh values going lower.

so to correct for the reduced reading I would need to move the qnh the
other way.(increase it)
I agree a is correct from playing with an actual altimeter.
c is correct just from reading the data in the question.

fwiw
Stealth pilot
  #9  
Old April 17th 08, 02:45 PM posted to rec.aviation.piloting,rec.aviation.student
WingFlaps
external usenet poster
 
Posts: 621
Default Altimeter Question

On Apr 18, 1:29*am, Stefan wrote:
Larry Dighera schrieb:

*http://en.wikipedia.org/wiki/Mbar

Mbar would be a tad much. You certainly meant mbar.

* What does QNH stand for?
* Atmospheric Pressure (Q) at Nautical Height (aviation)

Bull****. QNH is *not* an acronym. It's one of over hundred Q-Codes
which were defined in the stone age of radio telephony. The letters were
randomly chosen, think of it as a numeration. Most of those Q-Codes are
forgotten today, but a few still live. In aviation, I mean in aviation
in all coutries except the USA, QNH, QFE and QNH are used to define
different altitude settings (roughly spoken).

QNH stands for the pressure you must tune in the kollmans window to have
the altimeter display the airport elevation when the airplane sits on
the ground. (As opposed to QFE, which ist the pressure to set for the
alitmeter to display zero on the ground and QNE, which is the altitude
which the alitmeter shows on the ground when it is set to standard
atmosphere.)

For those who believe in Wikipedia:http://en.wikipedia.org/wiki/Q-code


QNH means query Newquay Harbour which was the British reference for
sea level.
It should give the atmospheric pressure at that dtaum -but I doubt
that the met offices bother to check what the actual height of that
datum is...

Cheers
  #10  
Old April 17th 08, 02:51 PM posted to rec.aviation.piloting,rec.aviation.student
terry
external usenet poster
 
Posts: 215
Default Altimeter Question

On Apr 17, 11:38*pm, Stealth Pilot
wrote:
On Thu, 17 Apr 2008 07:30:56 -0400, "Barry" wrote:
I am confused by this practice commercial nav question. ( at least I
am confused by the answer in the book which was b. but I think both a
and c are correct), but I appreciate some other opinions.


Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
subscale
* * * * ( thats equivalent to 29.92 inches of Hg for the US folks)
Day 2 Altimeter reads elevation of 1000 feet
Assuming the altimeter subscale was not changed between day 1 and day
2 it could be said that


a. The QNH is higher on day 2
b. The QNH is lower on day 2
c. The pressure altitude at the airport is lower on day 2
d. *The atmospheric pressure at the aerodrome has not changed.


I agree with you - answers a and c are both correct. *Day 2 QNH is about 1026.


playing with an altimeter here in my lap.
simulating 1390 by setting 390. the qnh reads as 1032.

moving the needle lower sees the qnh values going lower.

so to correct for the reduced reading I would need to move the qnh the
other way.(increase it)
I agree a is correct from playing with an actual altimeter.
c is correct just from reading the data in the question.

fwiw
Stealth pilot- Hide quoted text -

gday Stealth,
I just think of an altimeter as being a inverse pressure guage cos
pressure decreases with altitude, so for altitude reading to have gone
down , atmospheric pressure has to have gone up.
I gotta ask, why have you got an altimeter in your lap?
Terry

 




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