Baro Altimeter precision

[Rudel_chw]

Hello,

 

I'm having trouble getting the altimeter to show the correct altitude ... there is always a difference between the instruments reading and the altitude value that I get on my triggers.

 

Here, I placed my MiG-29 on Active Pause and check the different readings, the HUD shows 1730 meters:

 

 

The analog instruments show about the same:

 

 

The altimeter is properly calibrated:

 

 

BUT .. the outside reading is higher:

 

 

Does anyone know why is this or how to correct it?

Thanks,

 

Eduardo

[Ironhand]

https://forums.eagle.ru/showthread.php?p=2549028#post2549028

 

Hopefully some answers here. It’s been awhile.

Edited July 10, 2019 by Ironhand

[Rudel_chw]

https://forums.eagle.ru/showthread.php?p=2549028#post2549028

 

Hopefully some answers here. It’s been awhile.

 

Thanks a lot for the help .. you are totally right, this altimeter error varies with the air Temperature than one sets on the Editor .. I made a quick test and found this:

 

 

My initial mission was at 20º and thus I was getting a very noticeable difference .. for some reason, on the Persian Gulf (where this particular mission was set) the ME doesnt allow me to go below 14.3 Cº

 

As a workaround, I will set my mission to 15º ... not very realistic for the zone, but this is a practice mission where I rate the player for his flying precision, so the error I was getting was a no-no

 

Thanks again, you've saved my mission :D

 

 

 

Cheers!

 

 

Eduardo

Edited July 11, 2019 by Rudel_chw

[draconus]

... for some reason, on the Persian Gulf (where this particular mission was set) the ME doesnt allow me to go below 14.3 Cº

 

As a workaround, I will set my mission to 15º ... not very realistic for the zone, but this is a practice mission where I rate the player for his flying precision, so the error I was getting was a no-no

Temperature limits in ME depend on the month set (or season) and the region (map). Check with this:

https://www.climatestotravel.com/climate/iran

for the South.

 

 

Also you can use the real temp and check the altitude multipied by difference in the scripts.

[Rudel_chw]

Temperature limits in ME depend on the month set (or season) and the region (map).

 

Didnt knew that, thanks for pointing it out :)

[Ironhand]

Although using 15° helps with your mission altitude issues, it masks the effects that the high temperatures in that part of the world have on engine thrust. So in that sense, it makes them less realistic, too. :) Right now it's something like 36°C in Qeshm. Try dialing that in and see the difference it makes just in the takeoff run.

[bbrz]

Unfortunately any temp deviation from ISA still has zero effect on aircraft performance in DCS.

[Rudel_chw]

Although using 15° helps with your mission altitude issues, it masks the effects that the high temperatures in that part of the world have on engine thrust. So in that sense, it makes them less realistic, too. :)

 

I understand .. I will leave the navigation practice on 15º, but the weapon practice missions will be at 30º .. it is a shame having to take this workarounds to solve issues that shouldnt be there on the first place :)

 

Thanks a lot for the help.

[Ironhand]

Unfortunately any temp deviation from ISA still has zero effect on aircraft performance in DCS.

If that's the case, then it's been lost. It did a few years ago but I haven't tested since they announced that it did back in 2017. Back in Dec of '17 it did.

[draconus]

Didnt knew that, thanks for pointing it out :)

To be more specific:

Caucasus - 4 seasons - all with different temp limits.

NTTR - all year limit

Don't own any more maps to test but I suspect only year round limits.

[Fri13]

I thought that the ATC will inform you the correct barometric value that you adjust in the aircraft. And that value is measured by the ATC based the temperature, moisture and all other variables so when you are flying in that general area, you will have the correct barometric altitude value.

[yufighter]

I noticed that on the planes MIG 29 and 21 it is not possible to adjust the zero altitude on a barometer altimeter if they are located at airports at a higher altitude. What is the reason for this?

 

Sorry for the bad "Google" English!

[bbrz]

I noticed that on the planes MIG 29 and 21 it is not possible to adjust the zero altitude on a barometer altimeter if they are located at airports at a higher altitude. What is the reason for this?

This works in no airplane in DCS and IRL it doesn't either.

Altimeters have only a small adjustment range and in 90% of the world you are not setting the altimeter to zero at the airfield (QFE) but you are setting the actual field elevation (QNH).

DCS still uses QFE since day 1 and at high altitudes the main drawback when trying to use QFE becomes obvious ;)

[bbrz]

If that's the case, then it's been lost. It did a few years ago but I haven't tested since they announced that it did back in 2017. Back in Dec of '17 it did.

Nice to know. Just a few weeks ago I wanted to start new takeoff performance calibration flights and found out that a different temperature doesn't change anything.

[bbrz]

I thought that the ATC will inform you the correct barometric value that you adjust in the aircraft. And that value is measured by the ATC based the temperature, moisture and all other variables so when you are flying in that general area, you will have the correct barometric altitude value.

Barometric altitude is just that. It has nothing to do with temp correction etc.

IRL you have to use correction tables if the temperature is significant below ISA, since you will be flying too low if you don't 'manually' apply the temperature correction.

[Ironhand]

Nice to know. Just a few weeks ago I wanted to start new takeoff performance calibration flights and found out that a different temperature doesn't change anything.

 

Perhaps it depends on the aircraft. Or, maybe, the effect isn't all that dramatic. Just double checked with my trusty steed--Su-27. Max mil takeoff with full fuel and weapons @ 0°C: 346km/hr liftoff speed reached in 42 sec and took 1.49km of runway. Same track file with temp altered to 35°C took 49 sec to reach that same speed and 1.83km of runway.

[bbrz]

Interesting. Maybe FM related? Have to recheck ASAP!

I'm always testing with AI aircraft, so this might be the reason.

Since the AI planes already outperform their human controlled counterparts, this would make matters even worse in hot and high conditions :(

[Rudel_chw]

I thought that the ATC will inform you the correct barometric value that you adjust in the aircraft. And that value is measured by the ATC based the temperature, moisture and all other variables so when you are flying in that general area, you will have the correct barometric altitude value.

 

 

 

Check the 1st post ... the barometric altitude is correctly calibrated, BUT the real aircraft alttitude is different.

[Rudel_chw]

I'm always testing with AI aircraft, so this might be the reason.

 

 

On DCS AI aircrafts use a Simple Flight Model .. the human player only, gets to use the Professional Flight Model.

[bbrz]

On DCS AI aircrafts use a Simple Flight Model .. the human player only, gets to use the Professional Flight Model.

I know, but I didn't know that the simple FM isn't affected by temperature.

Furthermore I can do the performance tests only with the AI planes, since most of them are only available as AI.

[bbrz]

Check the 1st post ... the barometric altitude is correctly calibrated, BUT the real aircraft alttitude is different.

Have you checked if the difference changes with altitude?

[Rudel_chw]

Have you checked if the difference changes with altitude?

 

 

No, only checked for chnages with ambien Tº ... to be honest, I just wanted a way to have the instruments altitude match the real altitude that DCS uses on its triggers calculations .. setting the Tº to 15º achieves that, so I'm happy now :)

[Ironhand]

Interesting. Maybe FM related? Have to recheck ASAP!

I'm always testing with AI aircraft, so this might be the reason.

Since the AI planes already outperform their human controlled counterparts, this would make matters even worse in hot and high conditions :(

 

I think it might only apply to the Su-27 & Su-33. They are the only aircraft that I could find this applicable to in the update notes, when I looked a few minutes ago. My recall isn’t what it used to be. I thought it applied to all. I’ll have to try it with the MiG-29 when I get a chance.

[bbrz]

Totally forgot about my own 'proficiency check' mission in the F-5.

Take off from Mozdok with full internal fuel, 3 275gal tanks, 2 AIM-9s and 100% gun rounds. TOW 21900lbs.

Left or right throttle idle and fuel cut off at 200kts.

Reland at Mozdok (without jettisoning anything of course)....OAT +25°C....noticable more difficult than at 0°C or even 15°C.

Edited July 12, 2019 by bbrz

[draconus]

I think it might only apply to the Su-27 & Su-33. They are the only aircraft that I could find this applicable to in the update notes, when I looked a few minutes ago. My recall isn’t what it used to be. I thought it applied to all. I’ll have to try it with the MiG-29 when I get a chance.

 

It's so basic feature that all PFM aircraft are affected. 29 too - just tested.