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TK PRES LO above 20k feet with empty centerline tank


Nealius

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  • 1 month later...

This is not magic 😉

Maybe you forgot to close the fueling probe? At leat i get this warning every time, i forget this. Espacially at night ofc.

On 1/19/2022 at 11:29 PM, Foka said:

And also it's not "above 20k" but it goes off exactly on 20k, and shut off few hundret feet above, like it is some magic layer of different pressure.

 

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Yes, this happens always at 20k true (world) altitude in DCS. Funnily enough I can't manage to reproduce this in SP to submit a track, but I get it always in our group's MP server.


Edited by Ahmed
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On 1/20/2022 at 12:06 AM, Tholozor said:

According to the NATOPS (section 2.2.2.1), the TK PRES LO caution should display when the internal tanks are depressurized above 20kft. So the 20kft portion is correct, but I guess the question would be why is the system thinking the internal tanks are being depressurized. Depressurization should occur with the probe extended or the hook & gear handles down.

 

I think TK pressure automatically means external tanks

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32 minutes ago, Rissala said:

I think TK pressure automatically means external tanks

Directly from the NATOPS FM:

IN FLIGHT  

•  Internal fuel tank pressure low above 20,000 feet.

Possible fuel pump cavitation above 40,000 feet
High rates of descent may damage fuel cells

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On 3/9/2022 at 5:19 PM, norman99 said:

Directly from the NATOPS FM:

IN FLIGHT  

•  Internal fuel tank pressure low above 20,000 feet.

Possible fuel pump cavitation above 40,000 feet
High rates of descent may damage fuel cells

I don't remember getting the warning without external tanks but I rarely fly without them so I could be wrong.

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Hey guys,

I found out that I experience this issue only if I set the barometric pressure on the altimeter differently than is the default value (29.92 inHG?). If my mission briefing says, that the pressure near the Carrier is e.g. "30.12 inHG", I usually modify the barometric pressure value during the cold start procedure. After that I pretty often get the "TK PRES LO" message after I climb to the 20.000 ft and it lasts only for a second or so. It doesn´t seem to me related to my current fuel state (in DCS).

Goliathus

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  • 2 weeks later...

If there is any problem for the ED to reproduce this issue, I can do this anytime I want. It is very simple. Just fly straight to the altitude 20.000 ft and don´t exceed 20.100 ft. Then just change the altimeter pressure setting and voila - you get the TK PRES LO message. Then change it back to the default pressure setting and the message is gone instantly. This can be done multiple times if you stay flying between 20.000 - 20.100 ft.

I fly the liberation campaign missions and set the altimeter pressure to the value in my briefing page. And it seems like the only way to avoid this warning message is not to set the altimeter pressure, but then it is not showing the correct barometric altitude, which can be an issue during landing approach on a carrier.

If the ED still can´t reproduce this issue, I can upload one of my liberation missions to help checking if it is not related only to the Liberation campaign messing something in the mission editor´s settings. To be honest, I din´t try if this issue persists in any of the ED´s original missions.

I hope this helps to investigate this issue.

Thx,

Goliathus

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On 4/2/2022 at 11:29 PM, Devastator said:

by the way, it happens also if you have a centerline and open the fuel probe for refueling (tried with a speed of ~320knots). 

Open fuel probe is afaik correct, it has to depressurise the tanks for refueling so you'll get a press low caution.

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22 hours ago, Goliathus said:

If there is any problem for the ED to reproduce this issue, I can do this anytime I want. It is very simple. Just fly straight to the altitude 20.000 ft and don´t exceed 20.100 ft. Then just change the altimeter pressure setting and voila - you get the TK PRES LO message. Then change it back to the default pressure setting and the message is gone instantly. This can be done multiple times if you stay flying between 20.000 - 20.100 ft.

I fly the liberation campaign missions and set the altimeter pressure to the value in my briefing page. And it seems like the only way to avoid this warning message is not to set the altimeter pressure, but then it is not showing the correct barometric altitude, which can be an issue during landing approach on a carrier.

If the ED still can´t reproduce this issue, I can upload one of my liberation missions to help checking if it is not related only to the Liberation campaign messing something in the mission editor´s settings. To be honest, I din´t try if this issue persists in any of the ED´s original missions.

I hope this helps to investigate this issue.

Thx,

Goliathus

Usually above a certain altitude ( in real life 10000ft or 18000ft, I’ve seen both depending the area) you reset barometric pressure to 2992 (1013) so all planes have same reference. Upon return to airbase you receive new barometric from ATC. 

I had the TK PRES LO indication last time I flew and forgot to put 2992 back. ( I had 3031 at the time) 
 


Edited by diamond26

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59 minutes ago, diamond26 said:

Usually above a certain altitude ( in real life 10000ft or 18000ft, I’ve seen both depending the area) you reset barometric pressure to 2992 (1013) so all planes have same reference. Upon return to airbase you receive new barometric from ATC. 

I had the TK PRES LO indication last time I flew and forgot to put 2992 back. ( I had 3031 at the time) 
 

 

For civil aviation you are correct. Transition level/altitude is where you set 29.92/1013.

For combat operations in theatre, this is not the case. Use the altimeter setting provided in the brief. You’re no exactly going to be changing your altimeter halfway through a surface attack, as you dive through 10k.
 

Whether a single altimeter setting is applied theatre wide depends on the situation, geographic area, current weather etc. Sometimes the theatre may be split into 2 or 3 different areas if it’s more appropriate. As long as everyone in the briefed area is on the same setting, altitude separation can be assured. As an example, the NTTR exclusively uses Nellis QNH at all levels.

Local QNH would only be used for takeoff/landing and possibly low level CAS type operations where JTACs can provide the QNH.

But that’s digressing…

There is definitely a bug with the warning as air pressure is irrelevant, it’s internal fuel tank pressure that the warning is referencing. Note this isn’t fuel pressure, but the pressure of the air that is fed into the fuel tank from the engine bleed air, as the fuel quantity reduces. This pressurised air is what helps maintain fuel pressure regardless of the attitude flown or the Gs pulled.


Edited by norman99
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3 minutes ago, norman99 said:

For civil aviation you are correct. Transition level/altitude is where you set 29.92/1013.

For combat operations in theatre, this is not the case. Use the altimeter setting provided in the brief. You’re no exactly going to be changing your altimeter halfway through a surface attack, as you dive through 10k.
 

Whether a single altimeter setting is applied theatre wide depends on the situation, geographic area, current weather etc. Sometimes the theatre may be split into 2 or 3 different areas if it’s more appropriate. As long as everyone in the briefed area is on the same setting, altitude separation can be assured. As an example, the NTTR exclusively uses Nellis QNH at all levels.

Local QNH would only be used for takeoff/landing and possibly low level CAS type operations where JTACs can provide the QNH.

I guess each country has its own standards on this one. In my experience we used to change barometric altitude at 10000ft. 

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This thread is still marked as "investigating", "can not reproduce" and "need track replay", so I did some testing and made a track replay of the issue. 

Please ED, look at this way to reproduce this issue anytime you want:

1. You must change the value on the barometric altimeter to different value than is the default value (29.92 inHG) BEFORE you reach the 20.000 ft altitude

2. Level at alt. between 20.000 - 20.100 ft 

3. You get the TK PRES LO warning instantly

4. Then you can play with the barometric altimeter settings as you wish and see that returning to the default value (forcing the altimeter to show less than 20.000 ft) clears the "TK PRES LO" warning. 

 

I tried this in the free flight mission in the Presian Gulf map and in other instant missions as well. You get this issue all the time, but only if you change the barometric altimeter value before you reach the 20.000 ft. If you don´t change the barometric value on the altimeter at first, leveling at the 20.000 ft and playing with the values won´t work to reproduce this issue. 

Here is link to the track replay: 

 

Please note that I´m aware of the fact, that in this mission the briefing says that QFE is 29.86 inHg, not 29.92 inHg. 

 

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By "track replay" they meant a .trk file from DCS, not a video.

To me, this looks like a variable error. It appears to occur in a small band when your aircraft is between "world" 20kft and "altimeter" 20kft (it doesn't occur at 29.92 because then, they correspond exactly). This suggests that the "world" altitude is incorrectly used instead of "altimeter" one, and the warning trips when one altitude check passes and the other doesn't. This is a theory, but that's where I'd look first if I was the one coding it (no actual experience coding avionics in DCS, but I did some pretty advanced avionics stuff for KSP in LUA, and it involves a lot of boolean checks like that). 


Edited by Dragon1-1
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Hi BIGNEWY,

On 1/19/2022 at 11:41 AM, BIGNEWY said:

I have tried again today to reproduce this but no luck so far. 

If anyone does have a short as possible track replay showing it please attach it. 

thanks

I can see this post is still tagged as if the trackfile was still missing and as if it was not a reproducable issue.

I´m sure that issue mentioned in our posts isn´t a high priority case, because it´s not affecting gameplay that much. But I´d just like to ask you to confirm if we lately provided enough information for the ED dev team, so it can dive deeper into this issue somewhere in the future. In my previous posts there is a video track, steps how one can reproduce this issue, and there is also a short trk. file. 

Thx.

Goliathus

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On 4/6/2022 at 7:58 AM, norman99 said:

Even in a combat theatre such as Iraq, Afghanistan, Syria etc?

From Carrier ops manual for DCS:

"Use of Radar altimeter during Carrier operations:
In real life the “RADALT is set to HUD” the entire time the aircraft is at sea. The switch on the HUD control panel does not move all deployment. The Flashing B that will appear on the right side of the
altimeter above 5,000 ft is accepted."

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About carrier ops: "The younger pilots are still quite capable of holding their heads forward against the forces. The older ones have been doing this too long and know better; sore necks make for poor sleep.'

 

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23 minutes ago, fagulha said:

From Carrier ops manual for DCS:

"Use of Radar altimeter during Carrier operations:
In real life the “RADALT is set to HUD” the entire time the aircraft is at sea. The switch on the HUD control panel does not move all deployment. The Flashing B that will appear on the right side of the
altimeter above 5,000 ft is accepted."

I’m not sure the relevance? Above 5,000ft, Baro altitude is still displayed, and hence the altimeter setting still needs to be set according to local/theatre procedures.

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23 hours ago, Goliathus said:

Hi BIGNEWY,

I can see this post is still tagged as if the trackfile was still missing and as if it was not a reproducable issue.

I´m sure that issue mentioned in our posts isn´t a high priority case, because it´s not affecting gameplay that much. But I´d just like to ask you to confirm if we lately provided enough information for the ED dev team, so it can dive deeper into this issue somewhere in the future. In my previous posts there is a video track, steps how one can reproduce this issue, and there is also a short trk. file. 

Thx.

Goliathus

Thanks for the PM I had not checked this for a while, I have asked the team to take a look.

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