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Thread: QNH and QFE

  1. #1
    Member Dojo's Avatar
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    QNH and QFE

    I made a post about this in the private trainee forum, and I've gotten a lot of questions/messages about this, so hopefully I'm going to clear up any confusion. These terms get mixed up all the time in the DCS universe, and we often give each other bad information. I will not discuss QNE and QFF, you don't really need either of them in DCS. If you're academically curious about those, there are plenty of guides/calculators on the Internet. This will be focused on the DCS pilot.

    First, QFE. QFE means QField Elevation. What's TRICKY about that, is what "Field Elevation" refers to. It is NOT the elevation of the airfield above MSL, as is commonly mistaken. It is the elevation of your AIRFRAME above the particular field. If anyone or an ATC gives you the QFE, what they are giving you is the pressure value for your altimeter, that will make your altimeter read ZERO when you are on the ground at that particular airfield.

    This is also the value that AI ATC will give you when you are about to take off, and it is the value that the AI ATC will give you when you request inbound to a particular airfield. So it has lots of value with respect to the particular airfield you are at, but nothing else.

    This is NOT the value that the 476th uses, although DCS pilots will often ask each other "What's the QFE?". This is also NOT the value that the A10's systems are referenced to (the TAD, weapons, etc). Therefore, it has little value when you are not working at a particular airfield.

    The more useful value is QNH. QNH means QNautical Height. This is the elevation above Mean Sea Level (MSL). This is what your systems are referenced to, and it's what the 476th uses. Within DCS, you get this value by placing your aircraft on the runway at a given airfield, and turning the altimeter ALTITUDE and NOT the altimeter pressure to the airfield's elevation. You get the airfield's elevation from an airfield chart. (NOTE: runway's can have different elevations on each end).

    For example, suppose we're taxiing to runway 32 at Vaziani. The chart tells me the elevation is 1482ft, a fixed number. So I tune my altimeter's ALTITUDE to 1480ft (slightly lower is always better), and the resulting altimeter pressure MIGHT be 29.78. This resulting number is the QNH. In the real world, Atis or the ATC may supply this number. (it changes as the pressure changes, so it's not a constant, and neither is QFE for that matter).

    So if someone asks you for QNH in DCS world, the above is the proper procedure to get it. Remember that the AI ATC gives you QFE, not QNH.

    Also, QNH can be different in different regions, although the DCS modeling of this is questionable (i.e. it's roughly constant throughout the Georgia/Russia DCS map).

    There's nothing wrong with using QFE for VFR landings, it's just not otherwise as useful.

    (also note, when crossing above 10,000ft, it's common to set your altimeter to standard, or 29.92, and vice versa when descending below 10,000ft).

    I hope I've done a better job of clearing this up!
    Last edited by Dojo; 05Aug14 at 20:51.

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  3. #2
    76th vFS Pilot Griffin's Avatar
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    Good post Dojo, it certinaly is informative about the matter!

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