FA18C Hornet barometric altitude incorrect reading?

[tityus]

Howdy

I`m not sure if this is from a recent update or I haven`t noticed it before, but the baro alt int the hornet appears to be slightly incorrect.

With the Kollsman window showing the 29.92 adjust for the mission I briefly created (QNH 29.92),

I`ve followed these steps: 

• At 5000ft RDR, over the ocean, I switched ALT source from RDR to BARO - there was a significant difference in reading and +0.07 inHg was needed to to correct it
• I repeated the situation at 1000ft RDR and +0.01 inHG was needed to correct
• at 40000ft, 680ft difference from altitude displayed in F2 screen (that`s more than 1 inHg correction).
• Just to make sure, I got another plane (F15E) and, at 40k, difference was insignificant.

An altimeter that much off would be a No GO.

I`ve searched the forum before posting, but did not locate a thread about it.

Does anyone have the same problem?

 

Edited August 24, 2023 by tityus

[Hulkbust44]

1in is equal to 1000ft. 0.07 is a 70ft difference.
Also, what was the temperature...

Sent from my moto g stylus 5G (2022) using Tapatalk

[Fresh]

Hi there.

DCS correctly implements temperature effects. That means when it is cold your are lower than shown on the barometric altimeter. In summer you are higher. Roughly 4% difference per 10 degrees deviation from standard ISA temperature. Try your test again but make sure the sea level temperature is 15 degrees celcius.

Good luck!

 

Fresh

[tityus]

I guess I've failed on exposing the problem clearly.

the issue is: under the same conditions, with the mission QNH adjust, my hornet displays baro alt different from other modules.  (and from what is displayed at the F2 or F10 view)

On 8/23/2023 at 10:10 PM, Hulkbust44 said:

1in is equal to 1000ft. 0.07 is a 70ft difference.
Also, what was the temperature...

Thanks Hulkbust. yes 1in is equal to 1000ft, but don't focus too much attention to it - I inserted that info to illustrate the gradual offset of the altimeter | the gist is: same atmospheric conditions, same QNH setting -> the Hornet is displaying different altitude than other modules flying under the same conditions.

On 8/25/2023 at 4:12 AM, Fresh said:

DCS correctly implements temperature effects. That means when it is cold your are lower than shown on the barometric altimeter. In summer you are higher. Roughly 4% difference per 10 degrees deviation from standard ISA temperature. Try your test again but make sure the sea level temperature is 15 degrees celcius.

Thanks for the reply, Fresh. DCS trying to simulate the real "conditions" is one of the things that we like so much. I know that, same as the real world counterparts, the altimeters in DCS can be adjusted for pressure, but not for temperature variation and this is a risk factor. Up north, you will find approach plates indicating the need to "Apply altitude corrections for cold temperatures."  However, the issue I`m pointing is, regardless of the mathematical model used to simulate atmospheric effects, every plane altimeter, at the same conditions, using the same altimeter setting, should indicate the same altitude. (unless altimeter error is modeled differently from aircraft to aircraft)

It could be intentional or not, but IMO, this bug* could cause vertical separation issues between packages containing different type of planes.

*or not

 

Anyways, let's see if there are other points.

-------

I tested flying with a friend and the conclusion is that the issue is not the hornet - it`s the MudHen

F16, F14 and FA18C are all showing acceptable altitude under the conditions above. The F15E is not - since it is a relative new module they will probably fix that in a future patch.

Thanks for the input Hulkbust and Fresh.

Edited August 26, 2023 by tityus

[Fresh]

Thanks for testing! Good to know that the F-15E is deviating.

Fresh

[SickSidewinder9]

It kinda seems like the backup analog altimeter and the HUD are different.  The gauge seems to show some whacky number that is way off even though the gauge is where the QNH is set and where the HUD should be getting its data from, I'd think.

[CBStu]

I read all the above explanation but still, it seems DCS has some problems w/ this. Contact a tanker and he tells you altitude and speed. It is never correct. It is in the ball park alt is + or - 500, speed is + or - 20-30. Look at F10 map and read the altitude of other planes. It is never correct. Click one of those planes and look at the speed in the popup window. Never correct. I just live w/ it but do wonder sometimes why. OTOH, I have no idea how they make DCS as super as it is so I fly on and enjoy.

[Tholozor]

F10 map gives you the DCS engine's "true" altitude, it doesn't account for inherent errors in barometric pressure systems or atmospheric deviation.

The editor works off the "true" altitude, as do voice callouts for tankers, AWACS, and player reporting (e.g. CV recovery).

[SickSidewinder9]

On 9/23/2023 at 6:53 PM, Tholozor said:

F10 map gives you the DCS engine's "true" altitude, it doesn't account for inherent errors in barometric pressure systems or atmospheric deviation.

The editor works off the "true" altitude, as do voice callouts for tankers, AWACS, and player reporting (e.g. CV recovery).

The second part of that is the problem, though.  It should read off the altimeter.  If fact, above 18k the altitude should be reported as a flight level with a setting of 29.92, but obviously, calculating that isn't built in.  And the military probably doesn't do it that way.  Don't they use angles when not talking to civi ATC?  Still annoying to hear my guy call his position to the carrier and not use the indicated altitude.