29.92 popping up on the HUD...?

Recently I started to see the barometric pressure reading of 29.92 appear once on the HUD for just a few seconds as I was preparing to land. I assume it is the current barometric pressure at the runway?

Thank you.

It displays the barometric pressure setting on your altimeter, not the airfield. I don't remember the exact trigger, but you need to be in landing configuration.

I believe it serves as a way to easily see your current setting and remember to change it accordingly, based on what the ATC tells you.

When landing you set you altimeter to radar from barometric once under 5000 ft to give correct altitude

Red

When landing you set you altimeter to radar from barometric once under 5000 ft to give correct altitude

 

Red

I am not so sure about that...

Rad Alt shows height, not altitude. It may be OK for landing on a carrier or a perfectly flat plain, but not for normal approaches.

Recently I started to see the barometric pressure reading of 29.92 appear once on the HUD for just a few seconds as I was preparing to land. I assume it is the current barometric pressure at the runway?

 

 

Thank you.

IIRC the barometric sub scale setting will flash in the HUD when first decelerating through 300kts, or descending through 10000ft, whichever is later.

Or something similar, I forget the exact trigger.

Thanks for the info on 29.92 in the HUD.

Don't you set the radar alt. to warn you when your height AGL is less than what you set it too?

Baro radar is what I thought you reference when landing and pretty much most of the time since all map items reference Baro.

Yes Baro for airfields for sure as rad alt would fluctuate constantly.

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When landing you set you altimeter to radar from barometric once under 5000 ft to give correct altitude

 

Red

That’s not how it’s really done.

It displays the barometric pressure setting on your altimeter, not the airfield. I don't remember the exact trigger, but you need to be in landing configuration.

 

I believe it serves as a way to easily see your current setting and remember to change it accordingly, based on what the ATC tells you.

Harker,

Just curious but I would be interested to see what your rig does on Heavens benchmark? It is close to mine but I have newer products, I7-9700K OC 4.4, RTX 2070 OC , Z390, 32 GB RAM.

I get 230 FPS on HIGH settings, thanks.

BTW not sure about baro pressure, I'm just getting back into DCS with new rig.

Thanks for the info on 29.92 in the HUD.

Don't you set the radar alt. to warn you when your height AGL is less than what you set it too?

Baro radar is what I thought you reference when landing and pretty much most of the time since all map items reference Baro.

This is my limited understanding, I may be wrong and am happy to be corrected.

Baro alt = altitude based on air pressure. Pressure changes with weather conditions, hence you having to dial in the correct baro pressure every single time, so you're aligned and get a valid readout that won't fly you into a mountain. This is ASL altitude, you need it because those airport charts tell you the altitude you're supposed to be at in the approach/pattern etc. They're supposed to give you enough clearance over obstacles that rad alt can't warn you about. Take a city, for example. If you fly into a factory chimney, radalt would tell you about the problem about 2 feet into the chimney...

Rad alt = altitude based on an actual radar pinging the ground. This is AGL. The air force uses it to not fly into mountains and as a backup altitude indicator. The navy additionally uses it for carrier recoveries, because it's simpler, more precise and above all, the ocean doesn't have mountains or buildings to worry about. Just ships (that you know are there). Also, there are no airport charts that you need to reference. The pattern and landing altitudes are, ideally, the same every single time (or close to). Rad alt becomes unreliable pretty quickly, that's why your radalt stops at what, 3k feet? 5k for the F-14.

That 29.92 is actually the standard baro alt you're supposed to set above a certain altitude. Every a/c does it. The main reason for that is because nobody knows the current weather conditions at 30k feet precisely, because nobody has a weather station up there (usually). So to coordinate with other planes, everyone agreed to this standard baro setting so when you're near someone else, they'll have the same setting as you and when you're supposed to fly at 30k and they're supposed to be at 28k, you don't accidentally collide because you have the altimeter set to whatever your respective starting points used to have.

Having it blink in your HUD is the friendly reminder to set it from the high altitude standard to whatever the airport tells you to use for landing.

Having said that, weather simulation in DCS is kinda crappy and most people ignore it, because it's a pain in the ass and also... most servers are locked in on perfect flying weather, so who gives a **** about instruments, it's all VFR free style, baby! :D

This is my limited understanding, I may be wrong and am happy to be corrected.

 

Baro alt = altitude based on air pressure. Pressure changes with weather conditions, hence you having to dial in the correct baro pressure every single time, so you're aligned and get a valid readout that won't fly you into a mountain. This is ASL altitude, you need it because those airport charts tell you the altitude you're supposed to be at in the approach/pattern etc. They're supposed to give you enough clearance over obstacles that rad alt can't warn you about. Take a city, for example. If you fly into a factory chimney, radalt would tell you about the problem about 2 feet into the chimney...

 

Rad alt = altitude based on an actual radar pinging the ground. This is AGL. The air force uses it to not fly into mountains and as a backup altitude indicator. The navy additionally uses it for carrier recoveries, because it's simpler, more precise and above all, the ocean doesn't have mountains or buildings to worry about. Just ships (that you know are there). Also, there are no airport charts that you need to reference. The pattern and landing altitudes are, ideally, the same every single time (or close to). Rad alt becomes unreliable pretty quickly, that's why your radalt stops at what, 3k feet? 5k for the F-14.

 

That 29.92 is actually the standard baro alt you're supposed to set above a certain altitude. Every a/c does it. The main reason for that is because nobody knows the current weather conditions at 30k feet precisely, because nobody has a weather station up there (usually). So to coordinate with other planes, everyone agreed to this standard baro setting so when you're near someone else, they'll have the same setting as you and when you're supposed to fly at 30k and they're supposed to be at 28k, you don't accidentally collide because you have the altimeter set to whatever your respective starting points used to have.

 

Having it blink in your HUD is the friendly reminder to set it from the high altitude standard to whatever the airport tells you to use for landing.

 

Having said that, weather simulation in DCS is kinda crappy and most people ignore it, because it's a pain in the ass and also... most servers are locked in on perfect flying weather, so who gives a **** about instruments, it's all VFR free style, baby! :D

You're pretty much right here. However, the barometric pressure you set is the pressure at 0ft ASL. You're essentially telling the altimeter "when your pressure is the same as the pressure I dial in, the altitude is 0ft." From that it will know the altitude above sea level (or technically below; there are some places a few hundred feet in negative altitude).

The reason they set standard pressure (29.92) above the transition altitude (in the USA it's 18,000ft, in Europe it's more variable) is not because of there not being weather readings at that altitude. All you need to know is the pressure at sea level. Pressure decreases at a fixed pattern as altitude increases. The reason they do this is simply so the altimeter doesn't have to be continuously updated during cruise. You could continue updating the altimeter if you wanted (technically speaking that is; setting standard pressure is a requirement).

Only going by Chuck's guide,,feel free to tell him it's wrong

Red

Harker,

 

Just curious but I would be interested to see what your rig does on Heavens benchmark? It is close to mine but I have newer products, I7-9700K OC 4.4, RTX 2070 OC , Z390, 32 GB RAM.

 

I get 230 FPS on HIGH settings, thanks.

 

BTW not sure about baro pressure, I'm just getting back into DCS with new rig.

Sure thing. But what do you mean HIGH settings? I have Heaven 4.0 and there are only 2 basic presets, Basic and Extreme. You mean the Extreme preset?

Only going by Chuck's guide,,feel free to tell him it's wrong

 

 

Red

It's a tricky subject.

Your altimeter calculates your current altitude with pitot-static air pressure sensors located on the aircraft's fuselage.

Normally, the way to perform an approach at any airport is to consult the ATC (or carrier) to get the proper barometric pressure setting. This way, you know that the altimeter will give you a reliable reading since the altitude you see on the HUD in BARO mode will always be correct.

However, in the tutorial I didn't bother with the barometric setting. 29.92 inches of Mercury (Hg) (or 1013,2075 HPa) is what we call the "Standard Pressure", which is a reference pressure used above the "Transition Altitude", which is yet another altitude reference as explained by Jak525. Instead, I used the Radar Altimeter mode in the groove since in that particular situation it gave a more accurate reading. You could've totally landed with the Barometric mode, but for that you absolutely need to get the right Barometric Pressure Setting from the Carrier Controller. Otherwise, fly the ball and forget about the Baro Altitude reading.

The Radar Altimeter mode has the advantage of being more accurate when flying straight, but the reading gets completely wrong when performing bank manoeuvers since the radar altimeter sends radar beams perpendicular to your fuselage, which is problematic when the wings are not level. Performing approaches over uneven terrain gives erratic readings as well.