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Enter Barometric pressure on altimeter?


joebloggs
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I just read this somewhere, but I'm not sure what it means. That you are supposed to enter the barometric pressure on the altimeter before take off. Unfortunately, it didn't tell you how to do this and it's the first time I have come across it. What I read tells you to ask for permission to take off and be sure to enter the barometric reading before doing so, but that's all it says.

 

Could someone please explain explain how to do this and what it means? Thanks!

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there is a knob at the lower right of altimeter, set it to 10 ft before you takeoff. And you should set it to 29.92 inch after you takeoff

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the BP should always be set prior for take off and landing

the information of the correct value obtain by the ATC as wind heading and other informations:)

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So always set it to 10ft and nothing more first? Cheers!

 

Nope.

It depends if you want to se QFE or QNH.

If QFW - just set 0 on your altimeter (or pressure given by ATC)

If QNH - set runway elevation on your altimeter.

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As long as you do not use dynamic wether, in DCS it is enough to set you altimeter so that is shows elevation of the airport you are taking off from. You should not set you altimeter back to standard pressure (29.92) just after takeoff. You should do it at specific FL (e.g. FL100) and remember to reverse it to previous setting when you descent below that altitude.

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Nope.

It depends if you want to se QFE or QNH.

If QFW - just set 0 on your altimeter (or pressure given by ATC)

If QNH - set runway elevation on your altimeter.

 

What does QFW and QNF stand for? Also, where do I find out the runway elevation? Sorry for sounding thick, but I have never come across this before. Thanks for the replies.

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What does QFW and QNF stand for? Also, where do I find out the runway elevation? Sorry for sounding thick, but I have never come across this before. Thanks for the replies.

 

I think he hit W instead of E. It should be QFE.

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What does QFW and QNF stand for? Also, where do I find out the runway elevation? Sorry for sounding thick, but I have never come across this before. Thanks for the replies.

 

Watch the speling ;)

QNH - pressure at an airport or place at sea level

QFE - pressure at an airport or place on its surface (that is, at its elevation)

 

They are part of the Q code but used in aviaton. Those letters actually mean nothing, it is not initials or something like that.

 

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

 

The airport elevation and header elevations are in the airport charts. Look into DCS directories for a PDF with that info or in the kneeboard.

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Actually, take the time and watch this:

 

 

For me, all this QFE and QNH nonsense suddenly became totally clear and obvious by just watching that. ;)

 

To the best of my knowledge, the information in that film is still accurate, with the exception of the ICAO Standard Atmopshere now being defined as 1013.25 mb instead of 1013.20 mb.

 

USAF fighters use a different scale: they use Inches of Mercury instead of millibars, so the numbers in the video are off by a large margin, but all the same rules and principles apply, you'll just have to mentally replace 1013.25 mb with 29.92 inHG.

 

I hope this helps with the "why". :thumbup:

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1) So, just to sum up.. I put the QFE the ATC gives me after I request takeoff into the altimiter? He just gave me a QFE of 30.16, so I move the gauge to 3016 on the altimeter? This will give me the altitude over the runway yes?

 

2) Where do I get the elevation numbers from for the airfield if I want to do it that way?

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1) So, just to sum up.. I put the QFE the ATC gives me after I request takeoff into the altimiter? He just gave me a QFE of 30.16, so I move the gauge to 3016 on the altimeter? This will give me the altitude over the runway yes?

 

Yes, you put 30.16 in the little window in the altimeter, and as you are on the ground, the altimeter should read 0 ft.

QFE on takeoff is just a check, you can already figure it out turning the altimeter knob until it reads 0 ft: the pressure displayed in the window is the QFE. It is more useful for landing.

Pretty similar with QNH.

 

 

2) Where do I get the elevation numbers from for the airfield if I want to do it that way?

 

Already told you: from the airport charts. You have them in this file and also in the kneeboard. Or you can download DCS manager for Android, but those charts are a bit outdated:

C:\Program Files\Eagle Dynamics\DCS World\Doc\Charts\DCS_GND_Charts.pdf

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