Cannot set QFE low enough for Sinai map

[HPLsCat]

In the cold and dark instant action, you can't roll your QFE down low enough to match the airfield elevation. Doesn't strike me as a bug per-se, or a Sinai problem, the Viper just needs a bit more low end range.

[razo+r]

Modern western aircraft usually dont use QFE and thus are not allowing to set such low pressures. Use and set QNH instead. 

Also, to make sure, if your altimeter matches the airfield altitude, thats QNH not QFE. QFE is when you are on the ground and the altimeter shows 0.

Edited June 25, 2023 by razo+r

[Lace]

QFE is mostly for circuit work or visual rejoins, and as razor correctly states, will read zero on the ground, and your height above the airfield when in the air.  As a result it is only really of any value in the immediate vicinity of the airfield.  The jets modelled in DCS mostly have a RADAR altimeter, which will only read height (not altitude), and therefore is the primary reference for low-level flight.   QNH will read your altitude above MSL.  Each airfield will have an elevation value from a datum point (which may or may not be where you are parked).  With QNH set your altimeter should read the same as the airfield elevation.  QNH is usually the same as the Regional Pressure Setting, and will give you an accurate altitude over a greater area of land.  On a low level cross-country flight you will receive several RPS en-route and will adjust your altimeter accordingly (if you didn't adjust and were flying towards an area of low pressure, then your altimeter would begin to overread, i.e. you would be lower than you think - which could lead to CFIT).  For high level flying, once you cross the transition altitude (varies by country, USA 18000 ft, UK much lower at around 3000ft - we don't have any high mountains) you will set 1013mb.  This will ensure all aircraft are at the correct Flight Level.  At these heights it is more important to harmonise traffic than to know your exact altitude above MSL.  With everyone working with the same std pressure setting, then deconfliction is made easier.  FL is reported in 100s of feet, so FL300 is 30,000ft.

The issue with some of the Sinai map, is that some of it is below MSL, which makes accurate altimeter setting difficult (or impossible).  However, as stated, use your RADALT for low down work, and a standard pressure setting for high level and you'll be fine.

[darkman222]

But given the fact that the ground around the airfield is not flat you could not use your RADALT for flying a circuit approach reliably. So you need to calculate the airfield elevation from your QNH altitude. If you dont have the aerodrome chart, approach or someone else needs to give it to you then. Is that right @Lace ?

[Lace]

The three things, QHN, QFE and field elevation are linked, and knowing any two you can calculate the other.  1mb of pressure is approx 27ft, but to make the maths easier we can call it 30ft.  If you know QNH and QFE then the difference in mb x 30 will give you the field elevation. 

If you know the field elevation and QNH (arriving from a cross-country, un-manned tower, no ATIS, paper chart in your grubby mitt), then QFE is QNH - (field elevation/30).  For example, if the field elevation is 600ft, and QNH 1021mb, then QFE is QNH-(600/30) or about 1001mb.  Setting this should give you an accurate 1000ft AGL circuit and will read zero on the ground.

If you have no chart or QFE, but a RADALT, then either do a run and break at 1000ft AGL along the runway and make a mental note of the pressure altitude, and use this as your circuit height, or do a standard overhead join with 2000ft on the RADALT over the departure end of the runway, and again, make a mental note of the pressure altitude, then subtract 1000ft for circuit height.  You can use these methods with any pressure setting, as you are simply flying a constant altitude, through the circuit. 

I hope that makes sense.

[Lee1]

On 6/25/2023 at 9:45 AM, Lace said:

QFE is mostly for circuit work or visual rejoins, and as razor correctly states, will read zero on the ground, and your height above the airfield when in the air.  As a result it is only really of any value in the immediate vicinity of the airfield.  The jets modelled in DCS mostly have a RADAR altimeter, which will only read height (not altitude), and therefore is the primary reference for low-level flight.   QNH will read your altitude above MSL.  Each airfield will have an elevation value from a datum point (which may or may not be where you are parked).  With QNH set your altimeter should read the same as the airfield elevation.  QNH is usually the same as the Regional Pressure Setting, and will give you an accurate altitude over a greater area of land.  On a low level cross-country flight you will receive several RPS en-route and will adjust your altimeter accordingly (if you didn't adjust and were flying towards an area of low pressure, then your altimeter would begin to overread, i.e. you would be lower than you think - which could lead to CFIT).  For high level flying, once you cross the transition altitude (varies by country, USA 18000 ft, UK much lower at around 3000ft - we don't have any high mountains) you will set 1013mb.  This will ensure all aircraft are at the correct Flight Level.  At these heights it is more important to harmonise traffic than to know your exact altitude above MSL.  With everyone working with the same std pressure setting, then deconfliction is made easier.  FL is reported in 100s of feet, so FL300 is 30,000ft.

The issue with some of the Sinai map, is that some of it is below MSL, which makes accurate altimeter setting difficult (or impossible).  However, as stated, use your RADALT for low down work, and a standard pressure setting for high level and you'll be fine.

QNH is not the same as RPS. QNH and RPS can be different and usually are in my experience. The QNH as you rightly state is where the altimeter reads the airfield altitude AMSL when sat on the airfield. RPS is the setting one would use whilst poling along low level but outside the airfield environs so that everyone flying around VFR iis using the same pressure setting when not relying on Radalt and is a forecast for the whole area. Makes life easier when GA traffic is flying around using quadrantals! Don't imagine the military stuff these days has much use for RPS anymore what with either flying around high level to get somewhere economically or else tearing around low level and just looking outside making sure not to hit the ground or antyhing in the air   Transition level as you correctly say is when one changes from QFE/QNH/RPS to the standard setting 1013mb/29.92inches.

Edited July 7, 2023 by Lee1

[Lace]

9 hours ago, Lee1 said:

QNH is not the same as RPS. QNH and RPS can be different and usually are in my experience. The QNH as you rightly state is where the altimeter reads the airfield altitude AMSL when sat on the airfield. RPS is the setting one would use whilst poling along low level but outside the airfield environs so that everyone flying around VFR iis using the same pressure setting when not relying on Radalt and is a forecast for the whole area. Makes life easier when GA traffic is flying around using quadrantals! Don't imagine the military stuff these days has much use for RPS anymore what with either flying around high level to get somewhere economically or else tearing around low level and just looking outside making sure not to hit the ground or antyhing in the air   Transition level as you correctly say is when one changes from QFE/QNH/RPS to the standard setting 1013mb/29.92inches.

 

I didn't say it is the same, I said it is often the same - obviously it depends on local weather conditions, but it is generally within one or two mb of your departure field, because that is the pressure setting for that region.  Over longer distances it can diverge further from your initial setting, but your final setting should again be quite close to your arrival QNH.

I'm not sure where you fly, but in the UK we don't use quadrantals, it is a semi-circular rule for VFR deconfliction, with 000-179MTrack being odd+500, and 180-359 even+500.  However, IME most people don't use it and compliance is not mandatory.

I'm sure some readers might find this interesting, but we are drifting well away from the OP question now.

[Lee1]

5 hours ago, Lace said:

I didn't say it is the same, I said it is often the same - obviously it depends on local weather conditions, but it is generally within one or two mb of your departure field, because that is the pressure setting for that region.  Over longer distances it can diverge further from your initial setting, but your final setting should again be quite close to your arrival QNH.

I'm not sure where you fly, but in the UK we don't use quadrantals, it is a semi-circular rule for VFR deconfliction, with 000-179MTrack being odd+500, and 180-359 even+500.  However, IME most people don't use it and compliance is not mandatory.

I'm sure some readers might find this interesting, but we are drifting well away from the OP question now.

I stand corrected!