forum search & barometric pressure setting limited to 28.10

[fitness88]

The barometric pressure setting seems to be limited to a low of 28.10 what do you do when in NTTR and Syria the barometric pressure given by the tower is 27.XX?

 

Also how do you narrow a search to a specific forum like F/A-18, I'm getting results from all forums?

 

 

Thank you.

Edited January 2, 2021 by fitness88

[rob10]

In answer to your 2nd question, if you start to type in the SEARCH box upper right, it has tick boxes below to allow you narrow your search.  You want "This Forum" ticked assuming you're in the F-18 subforum when you start the search.

[fitness88]

1 hour ago, rob10 said:

In answer to your 2nd question, if you start to type in the SEARCH box upper right, it has tick boxes below to allow you narrow your search.  You want "This Forum" ticked assuming you're in the F-18 subforum when you start the search.

Thanks, I see what the problem is, I have zoom set above 100% which hides this option.

[Tholozor]

Ignore the QFE settings that ATC gives you, that's for field elevation. Use the QNH setting in the briefing.

[Swift.]

The US for the most part use QNH, which sets the 0 at mean sea level. So your altimeter at Nellis AFB should be about 1850ft. This corresponds to all the approach and departure charts you will find that assume you are touching down at about 1850ft.

[VIXEN413]

landed once in Poland with the 737-400 where the qnh was 1052mb. the standby altimeter we had could be set only to max 1050mb. 

We just added 60ft to what he was saying. lol

[fitness88]

Thanks for all your comments, to clarify...

At Nellis, airdrome data F10 indicates elevation=1841m which = 6040ft?

In briefing weather info QNH=760 is this mmHg?/29.92 indicates

In briefing take off and departure, QFE=711.53 mmHg/28.01 inHg

In cockpit I see the standby altimeter is mission set to 29.92Hg indicating 2000ft, I'm assuming this is QNH so where does the elevation 6040ft in F10 fit in?

 

Is there a reason why the standby altimeter only records the 1000 wheel indicator movement, the other counter wheels do not?

Edited January 2, 2021 by fitness88

[Tholozor]

1 hour ago, fitness88 said:

At Nellis, airdrome data F10 indicates elevation=1841m which = 6040ft?

In briefing weather info QNH=760 is this mmHg?/29.92 indicates

Nellis sits at 1840 feet MSL, not meters.
760mm = 29.92 inches.

[fitness88]

2 hours ago, Tholozor said:

Nellis sits at 1840 feet MSL, not meters.
760mm = 29.92 inches.

In that case the mistake should be corrected.

When calling inbound pilots are always given QFE by the tower, if it's below 28.10 what procedure is used for calculating?

[Balion]

25 minutes ago, fitness88 said:

When calling inbound pilots are always given QFE by the tower, if it's below 28.10 what procedure is used for calculating?

You may add ~1 inHg per each 1000 ft of airport elevation. So if tower says QFE 27,5 inHg for Nellis, you can add 1840 ft/1000 ft = 1.840, so QNH = ~29.34 inHg. Or just use online calculator like this: http://www.hochwarth.com/misc/AviationCalculator.html

[fitness88]

1 hour ago, Balion said:

You may add ~1 inHg per each 1000 ft of airport elevation. So if tower says QFE 27,5 inHg for Nellis, you can add 1840 ft/1000 ft = 1.840, so QNH = ~29.34 inHg. Or just use online calculator like this: http://www.hochwarth.com/misc/AviationCalculator.html

Thanks for that info I get the math.  Is 1 inHg per each 1000 ft of airport elevation always a constant regardless of weather/baro pressure?

[Balion]

52 minutes ago, fitness88 said:

Thanks for that info I get the math.  Is 1 inHg per each 1000 ft of airport elevation always a constant regardless of weather/baro pressure?

Strictly speaking it doesn't equal to 1 inHg per each 1000 ft even in standard conditions. It's just an approximation for fast math. Actual formula is more complex: https://en.m.wikipedia.org/wiki/Barometric_formula (for humidity = 0%).

Edited January 3, 2021 by Balion

[fitness88]

Paying more attention to baro pressure, it occurred to me that QNH in DCS is always stated as 29.92 in all the game missions with the exception when I 'create fast mission' with stormy weather.

[Mistermann]

Resurrecting this thread a bit.  My search of the forum brought me here and I figured I'd post here instead of creating a new thread.

I am working on a mission that lands at Groom Lake.  The mission generates the QFE automatically and it looks as follows:

I am gathering from the commentary earlier in this thread the QFE block doesn't mean anything.  When using the website posted by@Balion a few threads above, I get this information for Groom Lake (4500ft ASL).

So ... here's my question.  In the Hornet, I should update the Altimeter to 3003 from 2992 to properly establish the pressure at Groom Lake and therefore the altimeter will read properly on approach (before I switch to Radar Alt).  Right now, when on approach, the BALT is showing an altitude that's much too high.

Correct?  

Thanks for the help!

[Tholozor]

You shouldn't need to use an external calculator to obtain the QNH, it should be provided in the mission briefing in the Weather data block. The calculator you linked also doesn't take atmospheric temperature into account, which does create a disparity between QFE and QNH (i.e. with OAT at 30°C at Groom Lake, QNH at 29.92 changes the QFE to 25.60 instead of 25.46 at 20°C).

[Mistermann]

2 hours ago, Tholozor said:

You shouldn't need to use an external calculator to obtain the QNH, it should be provided in the mission briefing in the Weather data block. The calculator you linked also doesn't take atmospheric temperature into account, which does create a disparity between QFE and QNH (i.e. with OAT at 30°C at Groom Lake, QNH at 29.92 changes the QFE to 25.60 instead of 25.46 at 20°C).

Thanks - but I am still not following.  Looking at the QNH from the Weather portion of the briefing shows this:

"2992" is what my barometric pressure is already set to on the Altimeter.  When I approach the runway to land, my Altimeter is showing too high an Altitude.  I am making an "assumption" here (dangerous, I know).  That assumption is I need to dial in the proper numbers into the Altimeter in order to display the proper altitude above ground.  

So ... using that site mentioned in the previous message I used real world numbers to bring back a QNH as a test to see if that works.

Maybe I need to ask my question a different way.

How do I know the proper Barometric Pressure setting to dial into the Altimeter so my HUD (BARO) displays the proper altitude when above radar altimeter altitude? 

Or do I just forget about that and turn on the Radar Altimeter and disregard the HUD altitude when it flips from Radar to Baro?  I recognize I may be pushing the boundaries of DCS and simply should not worry about it.

Thanks.

 

Edited February 9, 2022 by Mistermann

[Sarge55]

It’s unfortunate that ATC doesn’t give you QNH on approach. This would solve this issue once and for all. 
 

Probably see a 10% drop in forum posts alone. 

[Tholozor]

@Mistermann Are you trying to dial the altimeter to read barometric altitude as 0 when on the ground (e.g. set the altimeter to the QFE pressure)?

Western aircraft/altimeters aren't designed to use QFE, only QNH. Approach plates are written to use MSL, not AGL.

[Bunny Clark]

20 minutes ago, Mistermann said:

I am making an "assumption" here (dangerous, I know).  That assumption is I need to dial in the proper numbers into the Altimeter in order to display the proper altitude above ground.  

This is incorrect. The barometric altimeter should be set up to show your altitude above mean sea level. Since all it can do is measure barometric pressure, any attempt to set it up to show altitude above the ground will only be accurate for that one specific spot. Setting the altimeter for altitude above sea level allows multiple aircraft flying from different areas to all coordinate altitudes using a fixed common reference. 

If you want to see your altitude above the ground when landing, switch your HUD to show radar altitude, using the ALT BARO / RDR switch below the UFC. 

[Ourorborus]

Simplest way is to ignore the QFE on DCS ATIS, and just adjust your altimeter to read the airfield altitude on startup. That will give you QNH.

Unless the mission has a very dynamic pressure system, that QNH will hold true for most 2 hour (or less) sorties. Particularly if you are operating in VMC below the LSALT.

In real world application, you would set Airfield QNH, for arrival/departure, area qnh outside the terminal area, Force QNH within the AO, and if complying with ATC, 1013/29.92 above the transition altitiude. (Fighters tend to ignore this unless transiting/cruising outside the AO). These figures will update throughout the day as weather progresses (but not THAT frequently)

However, unless the MIZ designer has provided all this info for you (either in briefing or by a script), setting QNH as indicated above before takeoff should suffice for 99% of missions in VMC, and probably 90% of missions in IMC.

 

 

[Mistermann]

Wow - thanks for all the helpful responses!  After all these years (30+) flying virtual jets, I clearly never fully understood what that adjustment on the altimeter was all about. 

13 hours ago, Sarge55 said:

It’s unfortunate that ATC doesn’t give you QNH on approach. This would solve this issue once and for all. 

Yeah, my mission is using some real radio chatter from Groom Lake as background ambiance when entering the landing pattern.  ATC provides all landing aircraft with the Altimeter setting which got me thinking about my mission and IF the 2992 setting was correct.  That lead me down the rabbit hole.  I tried mimicking the ATC calls with VO work to maintain the immersive illusion of other planes in the airspace. 

 

13 hours ago, Tholozor said:

@Mistermann Are you trying to dial the altimeter to read barometric altitude as 0 when on the ground (e.g. set the altimeter to the QFE pressure)?

Western aircraft/altimeters aren't designed to use QFE, only QNH. Approach plates are written to use MSL, not AGL.

That's what I was trying to do, yes.  I mistakenly thought the Baro Altimeter should be set to read 0 at the highest point of the runway.  

 

13 hours ago, Bunny Clark said:

This is incorrect. The barometric altimeter should be set up to show your altitude above mean sea level. Since all it can do is measure barometric pressure, any attempt to set it up to show altitude above the ground will only be accurate for that one specific spot. Setting the altimeter for altitude above sea level allows multiple aircraft flying from different areas to all coordinate altitudes using a fixed common reference. 

If you want to see your altitude above the ground when landing, switch your HUD to show radar altitude, using the ALT BARO / RDR switch below the UFC. 

Lightbulb moment, @Bunny Clark 

The switch to radar is definitely something I always do.  I mistakenly thought the difference between my RALT and BALT was the improper setting of my Altimeter.  I NEVER bother thinking about that setting, but when I heard all the REAL ATC calls, it made me wonder if I was doing it all wrong.  Your comment nailed it for me, thanks!!

 

13 hours ago, Ourorborus said:

Simplest way is to ignore the QFE on DCS ATIS, and just adjust your altimeter to read the airfield altitude on startup. That will give you QNH.

(snipped some real good details)

However, unless the MIZ designer has provided all this info for you (either in briefing or by a script), setting QNH as indicated above before takeoff should suffice for 99% of missions in VMC, and probably 90% of missions in IMC.

Most appreciated, @Ourorborus.  

Okay, so I consider myself more dangerously educated at this point.  I can go back to the notion that I can really fly a Hornet.