DAMN IT. I JUST DONT GET QFE 2 QNH SETTINGS in F-5E - Page 5 - ED Forums
 


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Old 02-13-2018, 11:19 AM   #41
Hamilton
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Quote:
Originally Posted by shagrat View Post

(...)"Minumum QNH? altmeter setting on DCS:F-5E is 2810."(...)

So if the barometric pressure in the F-5E cannot be set lower than 28.10 it is not possible to set a QNH or QFE below 28.10...

Thanks Shagrat
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Old 02-13-2018, 11:22 AM   #42
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AHH... Thank you. But I do not understand what you are describing.
I get a QFE of say 25.53. 58 + 25.53 = 93.53 which already sounds wrong.

"QFE is given X'' Hg then X+55 hPa is X+0.162''Hg. (1 hectopascal = 0.029529... inch of mercury)." ????? What does this mean?
58 * 0.029529 = 1.712682
So bligh me! I am not understanding what in the bloody heck you are describing. Where is .162 coming from?
I am just amazed that this is that complicated.
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Old 02-13-2018, 11:34 AM   #43
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Quote:
Originally Posted by DaveRindner View Post
... = 93.53 which already sounds wrong.

...
I am just amazed that this is that complicated.

Yes that is wrong. Forget the 58. That is hPa. Your altimeter is in inHg. Do not waste time converting hPa to inHg.

Answers were given here https://forums.eagle.ru/showpost.php...42&postcount=8

and here https://forums.eagle.ru/showpost.php...7&postcount=40

It is really simple.

Last edited by dolfo; 02-13-2018 at 11:35 AM. Reason: spelling
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Old 02-13-2018, 11:37 AM   #44
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Have you tried googling "qfe to qnh conversion"? The first hit (stackexchange) explains it pretty well. As long as you are able to find the airfield elevation and have a calculator (for dividing by 30 or 900), the conversion is pretty straight forward.
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Old 02-13-2018, 12:57 PM   #45
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Thanks for linking to my post Dolfo, I was starting to think no one actually read it haha. Rep inbound for the PHAK reference. And +1 to not worrying about hPa in this case.

Last edited by tom_19d; 02-13-2018 at 02:10 PM.
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Old 02-13-2018, 02:30 PM   #46
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The original problem was DCS ATC gives pressure in QFE. The F-5 altimeter cannot set QFE for high elevation .airports.

There is no solution to this problem that results in the F5 altimeter reading zero at touchdown at a high elevation airfield.

All other remedies require that you know the field elevation and math.

QNH is QFE plus field elevation. The field elevation becomes your new zero when QNH is set.

It is that simple.

What is required are accurate charts and the ability to correctly apply them, same as the real world.

DCS has no cartography department. Trying to fly IFR in a simulation that has no accurate charts is why this thread seems so confounding.

If you cannot set QFE then you MUST know field elevation and derive and set QNH and convert everything accordingly. There is no “easy” solution.
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Old 02-13-2018, 02:53 PM   #47
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The OP never asked how to make the altimeter show zero when the aircraft is on the ground. He asked how to convert QFE to QNH, just look at the very title of the thread. "DAMN IT. I JUST DONT GET QFE 2 QNH SETTINGS in F-5E"

Also from the first post...

Quote:
Originally Posted by DaveRindner View Post
DAMN IT. I JUST DONT GET QFE 2 QNH SETTINGS in F-5E

So how in the bloody hell do I take ATC QFE of 25.23 and turn it into correct QNH altimeter setting of 2968 or 29.68 . I am not seeing any relationship where 27 or 30 goes into.
No cartography department so that means we have no plates? The 476th would disagree with you.

476 vFG Flight Info Pubs Their TACAN approaches and SIDs out of Vaziani are a riot.

Plus you don't need charts, even on a server with no own ship on the F10 map you can always see field elevation of the field you will be landing at.

To convert QFE to QNH there is an easy solution. Dolfo and I have both covered it. Field elevation in MSL of landing airport divided by 1000. Round this number to two decimal places, add it to QFE. Put this in the Kollsman window, you have QNH. Not simple? Move a decimal point three places left and add. I can do that in my head and I am terrible at mental math.

Two people have answered the OP's question and shown the math using the scenario posed by his original post. Our work is visible, if it is wrong please explain how. I'm not trying to be contentious but much like 33-DFTC I am floored that this thread can possibly still be going on.
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Old 02-13-2018, 03:08 PM   #48
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"QNH is QFE plus field elevation. The field elevation becomes your new zero when QNH is set."
OMG! OK I starting to beleive that, in fact, I am an idiot. But the above make no sense to me.
Pmiceli QFE is Quiery Field Elevation. Field elevevation is in feet or meters. QFE , as given by ATC is a pressure deviation. Lets say QFE, from ATC , as 25.53. Field Elevation is 1000'.
So per your formula its 25.53 + 1000 = 1025.23 which makes no damned sense whatsoever. That is my stumbling block, as reading on this on net and here, is that apple units of measurement + orange units of measurement = sour grapes. I am looking for a simple straightforward formula, to properly set Altimeter, and no explanations I have gotten so far makes any frigging sense to me.

Prior to the posting of Tbilisi approach chart, I understood procedure for setting Altimeter, prior to landing as;
((Elevation of field in feet) / 1000 ) + QFE as given from ATC.
So for field at elevation of 1000' above MSL with QFE from tower as 25.23.
(1000/1000) + 25.23 = 26.23. Then I find F-5E altimeter cannot go below 2810. So as I see it my understanding is deeply flawed.

Now back to the chart. Tbilisi airport is at elevation of 58 hPa. As soon I saw that , I had a WTF!! moment. Everything I thought I got, I did not. Becouse does it mean for elevation to in pressure units , hPa is heptapascals. What do I with number where does it go, what is it converted into. As per your explanation of QNH as QFE + field elevation . So for QFE of 25.25 + 58 = 93.25. An impossible setting.
So what do you mean when QNH=QFE + Field Elevation? This is a basic question and I am getting nowhere. Explanations and definitions do not make any sense to me.

" The field elevation becomes your new zero when QNH is set." As described it is incomprehensible. What new zero, what was old zero. Zero AGL?

Please take a look at this conversion table.
https://www.sensorsone.com/inhg-to-m...version-table/
I don't see anything usefull as it relates to setting altimeter.

Then there is this.
https://www.pprune.org/tech-log/2446...onversion.html
Likewise, the explanation yields impossible to set numbers.
(Field elevation in feet /30) + QFE = QNH altimeter setting. Does not work, or I am misunderstanding something basic.
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Old 02-13-2018, 03:15 PM   #49
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Quote:
Originally Posted by DaveRindner View Post

Prior to the posting of Tbilisi approach chart, I understood procedure for setting Altimeter, prior to landing as;
((Elevation of field in feet) / 1000 ) + QFE as given from ATC.
So for field at elevation of 1000' above MSL with QFE from tower as 25.23.
(1000/1000) + 25.23 = 26.23. Then I find F-5E altimeter cannot go below 2810. So as I see it my understanding is deeply flawed.
Hi Dave, please stop trying to do anything with hPa or anything that involves dividing anything by 27 or 30. You have the math correct in your above example. The problem with the scenario you pose is that if a field with an elevation of 1000 feet had a pressure setting that low it would be in one of the worst hurricanes ever recorded- that is the only way to get that low of a QNH setting. If you try your math again with a more reasonable QNH like 29.50 (QFE 28.50 in this example) you will see that you are doing it correct, you just chose an unrealistic QFE as a base point for that airport.

Last edited by tom_19d; 02-13-2018 at 03:23 PM. Reason: misspelling
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Old 02-13-2018, 03:16 PM   #50
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Quote:
Originally Posted by DaveRindner View Post
AHH... Thank you. But I do not understand what you are describing.
I get a QFE of say 25.53. 58 + 25.53 = 93.53 which already sounds wrong.

"QFE is given X'' Hg then X+55 hPa is X+0.162''Hg. (1 hectopascal = 0.029529... inch of mercury)." ????? What does this mean?
58 * 0.029529 = 1.712682
So bligh me! I am not understanding what in the bloody heck you are describing. Where is .162 coming from?
I am just amazed that this is that complicated.
It isnt complicated.

QNH is QFE plus field elevation. If you arent on the ground the only way to accurately set the difference is to know how to convert field elevation to its pressure equivilent.

You must know the field elevation and how to make the conversion accurately.

In the real world we relied on a chart such as the example and either an altimeter with dual windows (hPa and “ Hg) or a conversion chart. This was mostly a training exercise in the classroom because every weather station has QNH instantly available.

Your 58 hPa to “ Hg was wrong. If you do the math wrong, you will never understand what is going on.

58 hPa is 1.71 inches of Mercury not .162.

For enroute operations 100 feet per tenth of an inch of mercury is a close enough approximation. So if QFE is reported as 28.10 “Hg at an airport elevation of 2000 feet, QNH is approximately 30.10 “ Hg

For instrument approaches, that is not precise enough. In the real world, if you cant get the local altimeter setting you either can’t fly the approach or you use the altimeter setting from a nearby source and add a correction to the approach altitudes.

Places that use QFE ( no one anymore IIRC, even Russia is QNH) would provide QNH on request.

In DCS, you are going to need to have QNH or the ability to convert QFE accurately using known field elevation or the runway elevation for the instrument approach you plan to use.
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