Discrepancies about altitudes and speed

[thebeloved]

Hi everyone!

I noticed that speeds and altitudes have quite a major discrepancy compared to what is displayed in the HUD. As per images, my HUD altitude is about 15200' whereas in the sim it's reported about 1000' below (13900').

These screenshot are from Mission 4 and I can see clearly Hale 31 higher than me, despite the datalink indicates 15 (15000'). But that's an issue that happens overall in the campaign.

Has anyone experienced the same issue?

nullnull

[razo+r]

The altitude in the F2 bar is not pressure altitude (what your altimeter shows) but true altitude that includes the influence of temperature deviation from ISA.

Also it obviously depends on what your altimeter is set to. If you fly with standard altimeter setting or QFE, it will not show the same.

[thebeloved]

21 minutes ago, razo+r said:

The altitude in the F2 bar is not pressure altitude (what your altimeter shows) but true altitude that includes the influence of temperature deviation from ISA.

Also it obviously depends on what your altimeter is set to. If you fly with standard altimeter setting or QFE, it will not show the same.

Thanks, I imagined it was a different reference. Yet, despite setting the altimeter on STD QNH, I had to climb to 16400' in order to stay in formation with Hale 31. At that time the altitude in the reference bar is exacty 15000'. I wonder whether, by mission settings. the altitudes of the airplanes can be referenced all on QNH in order to have correct numbers.

[razo+r]

12 hours ago, thebeloved said:

Thanks, I imagined it was a different reference. Yet, despite setting the altimeter on STD QNH,

Standard QNH is not a thing, it's either standard or QNH but not both.

12 hours ago, thebeloved said:

I had to climb to 16400' in order to stay in formation with Hale 31. At that time the altitude in the reference bar is exacty 15000'. I wonder whether, by mission settings. the altitudes of the airplanes can be referenced all on QNH in order to have correct numbers.

That's where the limitations of DCS are. I am not sure, I would have to check, but DCS references true altitude as default. So by knowing the temperature difference from ISA and the QNH, you could calculate the altitude you would have to be to intercept XY at specified altitude.

But in real life you would switch to standard above a certain altitude so you are all on the same reference and thus can guarantee traffic seperation and coordination.

[thebeloved]

6 hours ago, razo+r said:

Standard QNH is not a thing, it's either standard or QNH but not both.

That's where the limitations of DCS are. I am not sure, I would have to check, but DCS references true altitude as default. So by knowing the temperature difference from ISA and the QNH, you could calculate the altitude you would have to be to intercept XY at specified altitude.

But in real life you would switch to standard above a certain altitude so you are all on the same reference and thus can guarantee traffic seperation and coordination.

Transition altitude in EFRO is 5000', therefore once passing that altitude I set Standard QNH (29.92inHg). We are not flying in US where TA is 18000'. Now I would assume that also the AI flies with my same instruments, therefore we should read the same pressure altitude. Calculating the true altitude is a no go and it's not real life procedure (imagine this in an RNAV approach, it would be a disaster). Anyway I understand this is a topic for another section of the DCS forum as it is not pertinent to the campaign. Cheers for your help.

[razo+r]

2 hours ago, thebeloved said:

Transition altitude in EFRO is 5000', therefore once passing that altitude I set Standard QNH (29.92inHg). We are not flying in US where TA is 18000'.

Thats for real life but irrelevant for DCS. Nothing (except you, the player) in DCS is using standard.

2 hours ago, thebeloved said:

Now I would assume that also the AI flies with my same instruments, therefore we should read the same pressure altitude.

AI for sure does not fly flight levels in DCS as you can only set AGL or AMSL in the editor. So by switching to standard you aren't improving the situation (specifically for DCS).

2 hours ago, thebeloved said:

Calculating the true altitude is a no go and it's not real life procedure (imagine this in an RNAV approach, it would be a disaster).

You do correct your altitude for non-precision approaches (RNAV and non-RNAV) below a certain temperature exactly because of the effect of temperature on your altimeter, as your true altitude becomes less and are at risk of flying below the obstacle protected zone.

2 hours ago, thebeloved said:

Anyway I understand this is a topic for another section of the DCS forum as it is not pertinent to the campaign. Cheers for your help.

Fair enough. Just remember that DCS AI and real life are two seperate things. They don't switch to standard like you would do, regardless where in DCS you fly. If you want to fly at the same altitude like the AI does, you would (I think) have to fly temperature compensated, but like you said that is not a thing that you do in cruise flight. It's just another area of DCS that is barely developed and fairly limited.