QNH

[Taproot]

Heya

 

Ok. So in mission editor you have this QNH option. I guess it is for the altimeter setting in the aircraft. As it seems like now I can enter any number between 720 and 790.

 

But. What number should I use to have the default "2992" number that's entered in the altimeter on the A-10?

 

I really dont get this QNH stuff..

[82nd-Sweet]

Standard QNH is 1013 but only a number between 720 and 790 I don't know I'll have to check in the editor when I get back home.

[Taproot]

hooookey.. THen why cant I enter 1013 in? 790 is the highest I can. Is this cause of weather settings?

[mhe]

QNH is the calculated pressure at sea level with the base of the calculation being a measurement at the airfield giving you the QNH. So if you enter the QNH correctly, your altimeter will display the elevation of the airfield above sea level.

 

The 29.92 you enter into the A-10C's altimeter is a setting in inches of mercury (29.92"Hg is equal to 1013.25 hPa or millibars). This value can be either QNH or QFE.

 

So when an airfield measures let's say 1000hPa locally and it knows it is 1000ft above sea level, it then calculates the QNH by using it's known elevation as steps for hPas. In lower altitudes you can assume 27-30ft altitude per hPa (it depends on many factors like temperature as well). Let's take 30ft per hPa. So if you are at 1000ft from sea level, your pressure should drop 1000/30 hPa -> 33.33hPa. So if you add this to your local measurement, you end up with 1033hPA as your QNH. If a pilot enters this into his altimeter, it will read the field elevation. 1000is your QFE, meaning that when the pilot enters QFE into his altimeter, the altimeter will read zero when on the ground.

 

Don't know why there is only 720 from 790 as choosable value, I assume that depends on the airfield elevation you work with. I don't play around much with the mission editor, so can you assign QNHs to each airfield or is it a global setting?

 

Also, the values would suggest to me that these are rather QFE than QNH values for higher airfields, as QNHs are typically values from approx. 980 to about 1030. At least that's how it is in civilian aviation in the real world.

[winz]

it's 720-790 because it's in torrs aka mm of mercury. :)

[Eddie]

The value in the ME is to set the air pressure for the static weather system.

 

It uses mmHg, not inHg or Mb. So 1013 Mb/29.92 inHg = 760 mmHg.

[Taproot]

Sweet, ty all :)