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QNH, QFE, QNE and QFF explained! :)


Slothface

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QNH is used exactly the same as QFE the difference being that your altimeter will read a silly number on touchdown (yes i know it's airfield elevation but who wants to land at 397ft when you could just easily land at 0ft)

 

My home field is 5665'. Good luck using QFE. :music_whistling:

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QNH is used exactly the same as QFE the difference being that your altimeter will read a silly number on touchdown (yes i know it's airfield elevation but who wants to land at 397ft when you could just easily land at 0ft)

 

In DCS every airfield QNH will be the same due to the weather modelling.

 

I know that's a late reply to this post, but I suppose better late than never ;)

 

Just to weigh in on the QNH: the "silly number" is shared with other aircraft even if they come from neighbour airfields or from far away, which is important. It's also the (virtual) height from MSL and is used to determine at which altitude you should fly depending on your heading (circular rule), and the transition altitude to switch to FL. All that is meant to avoid collisions, remain in the appropriate airspace, facilitate the control and other air traffic services, any of which would be more awkward with QFE.

 

When you land somewhere, you must know the airfield / aerodrome data anyway (you must plan for alternates), and the altitude is a good indication of your aircraft performance, important for landing distances for ex. so it's nice to know. In the worst case, height is pretty easy to estimate in VFR.

 

Arguably, SAS would be even better, if not for the fact we have to land at some point ;) So I find the QNH to be a good compromise.

 

However, QNH has probably even more sense for general aviation than airliners or military aircraft, which are less concerned with the above since they can quickly change to FL (at least in Europe).

 

Well spotted for the QNE! :)

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In DCS every airfield QNH will be the same due to the weather modelling.

 

This isn't true even with a uniform atmosphere distribution. QNH is a calibration for altimeter to read a certain value when at a certain elevation (and in a certain location but we're talking about DCS uniform atmosphere so every location is the same).

 

The issue comes that the altimeter is built with a certain assumed atmosphere "shape" which is not equal to the real atmosphere. This can be any reason in real life but in DCS from temperature. Cold air makes the shape more compact and hot air larger. Since the atmospheres are different shapes it's impossible to make the altimeter reading and true altitude match up everywhere. QNH chooses to have the curves cross at the elevation being calibrated. At all other altitudes there is an error.

 

"QNH" given for static weather briefing is calibrated for a mythical airport at 0m ASL, not for the particular airport your mission happens at. This "QNH for a theoretical sea-level airfield" has a different Q-code in real meteorology: QFF.

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