not a bug QFE question... possible bug ?

[Droning_On]

just flew mission 6 (maybe 7 cant remember now) on the red flag campain, and the ATC told me to set my QFE at 27.8,  but the Viper would only go down to 28.1 ????

Am i doing something wrong ?

cheers J

[AlexCaboose]

Most countries use QNH, not QFE. To expand on this, QFE is altitude above the field, whereas QNH is altitude above sea level below transition level (usually 18000ft). QNH should give you a better understanding of your aircraft’s performance for TOLD.

Edited September 5, 2022 by AlexCaboose

[Droning_On]

thanks but QNH is referancing sea level not airfield level.    The ATC specificaly notes runway QFE at a Barometric Pressure level below what I can set on the F-16C Altimeter control knob??   Runway in Question was Nellis btw !!

Just seemed strange 

 

Edited September 5, 2022 by Droning_On

[Droning_On]

Found my answer here..... its a DCSism

 

[Yurgon]

1 hour ago, Droning_On said:

the ATC told me to set my QFE at 27.8,  but the Viper would only go down to 28.1 ????

Am i doing something wrong ?

No, it's DCS being... outdated.

The DCS in-game ATC is still extremely rudimentary, best ignore it altogether.

As AlexCaboose already said, the US usually prefer QNH over QFE (General Aviation may do it differently).

Nellis is at roughly 1850 feet MSL (give or take, and depending on the exact location on the base), so naturally the air pressure there is going to be significantly lower than at sea level, and can easily go lower than the Kollsman window allows for.

With the static weather that is currently in use in almost every DCS mission, QNH will be steady over time and over the entire map, so if you set QNH before takeoff and never touch the altimeter again, you're safe. (And you can transition to standard pressure above the transition altitude and later transition back to the same QNH as before below the transition level.)

I'm sure we'll eventually get an improved ATC who will issue QNH/QFE based on local procedures, or maybe also based on pilot preference, or who can be queried for either of these. For now, just forget that the ATC exists; he'll deny entry to empty runways and then clear you into approaching traffic anyway. 

[AlexCaboose]

20 minutes ago, Droning_On said:

thanks but QNH is referancing sea level not airfield level.    The ATC specificaly notes runway QFE at a Barometric Pressure level below what I can set on the F-16C Altimeter control knob??   Runway in Question was Nellis btw !!

Just seemed strange 

 

 

That doesn't give you anything useful for TOLD at 1850 feet.

[Droning_On]

Cheers Yurgon,  makes perfect sense......  Kollsman window ??? looks like I have some googling to do later

Wasnt sure how it effected flight characteristics as the F-16 wobbles about in flight if you play about with it on landing 

[Frederf]

Kollsman window and knob is just the name of the dispay that says 29.92 (or whatever number) and the knob that changes the value shown in the window.

F-16 and really most modern Western jets aren't designed for QFE altimeter reference. Even Soviets which commonly used it and have special altimeters that could be adjusted really low sometimes couldn't set 0 height at high airports.

[Yurgon]

50 minutes ago, Droning_On said:

Kollsman window ??? looks like I have some googling to do later

You should! It's one of those topics that aren't usually covered in any DCS manual, but since it applies to all of aviation, air pressure and altimeter settings are something all pilots should definitely know about.

"Kollsman window" is just another name for the small subscale-window inside of every barometric altimeter, also known simply as the "altimeter subscale".

This subscale has its limits, which is why QFE can't always be set. QNH, well, if the sea level air pressure was extremely high or extremely low, it might not be possible to set QNH either, but under normal circumstances, QNH shouldn't be a problem, whereas QFE totally depends on the elevation of the airfield in question (or rather, it depends on the density altitude, which in turn depends on elevation and local air pressure).

56 minutes ago, Droning_On said:

Wasnt sure how it effected flight characteristics as the F-16 wobbles about in flight if you play about with it on landing 

That may depend on the autopilot or hold modes that are currently active. When you change the altimeter subscale, to the aircraft that looks like it just lost or gained dozens of feet in altitude, and with some modes it may now try rather violently to correct that and "get back" to the desired altitude.

To avoid any such problem, the altimeter subscale should be set well before landing. And the other reason is, you really want to have a good altitude reference before beginning the approach, so you don't accidentally fly straight into terrain in bad visibility, just because the altimeter wasn't adjusted for local air pressure and you ended up 1200 feet lower than planned.

[Yurgon]

2 minutes ago, AvroLanc said:

The most important lesson here is that under NO circumstances should you ever listen to, or indeed bother to use, DCS ATC. It really sucks.

Supercarrier ATC is actually pretty good.

But yeah, land based ATC leaves a thing or two to be desired. Or three. Actually, let's call it "many".

[AlexCaboose]

It's definitely many. ATC rework was promised years ago, and I hope it's in the works.

[Lace]

Yeah, QFE not really that relevant when you have a RAD Alt.  QNH more important for performance figures, deconfliction, etc.

[Phantom711]

Am 5.9.2022 um 16:24 schrieb Yurgon:

No, it's DCS being... outdated.

The DCS in-game ATC is still extremely rudimentary, best ignore it altogether.

As AlexCaboose already said, the US usually prefer QNH over QFE (General Aviation may do it differently).

Nellis is at roughly 1850 feet MSL (give or take, and depending on the exact location on the base), so naturally the air pressure there is going to be significantly lower than at sea level, and can easily go lower than the Kollsman window allows for.

With the static weather that is currently in use in almost every DCS mission, QNH will be steady over time and over the entire map, so if you set QNH before takeoff and never touch the altimeter again, you're safe. (And you can transition to standard pressure above the transition altitude and later transition back to the same QNH as before below the transition level.)

I'm sure we'll eventually get an improved ATC who will issue QNH/QFE based on local procedures, or maybe also based on pilot preference, or who can be queried for either of these. For now, just forget that the ATC exists; he'll deny entry to empty runways and then clear you into approaching traffic anyway. 

#As you stated, QFE has very little relevence in real life aviation...including Genaral Aviation. As a pilot you have to know the field elevation and you just take it from there. 

There might be countries, that use QFE to some extent... The only country I have definitely heard of that does it, is the UK....but as you said, probably at smaller airfields...not London Heathrow...

[Dragon1-1]

I think Russians use QFE, and some other European countries probably too. 

[Machalot]

The Viggen uses QFE all the time, including to sight bombs on target.