There's already a problem at least at VATSIM stemming from the fact that when the clients are used by different flight simulation platforms, and one is in MFS with Live Weather, discrepancies arise between the "true" altitudes due to the fact that MFS unlike XP or FSX / P3D is modelling te non ISA pressure lapse rates due to Tempretaure variation.

It would be good to find out if LR is considering this in their new version ...

Why is this important ? Well, I can think of different reasons, but a good example of how differing models can be disruptive is well described here at the flightsim.com ( MFS Support Forums ) General board by one of the developers from VATSIM:

https://forums.flightsimulator.com/t/vatsim-ivao-pilotedge-users-be-aware-of-an-important-bug/426142/363?u=jcommflight

I've sent LR a message with this "hint", just as Alexis did regarding Magnetic Variation...

Edited August 12, 20214 yr by jcomm

Agree, I think that would be one of those details that would be nice to have. Even considering that it shouldn't be too hard to implement, since it only requires writing a new formula for the calculation of pressure (and then derive indicated altitude from local pressure).

But then you would have the likes of jarmstro complaining that "Meyer has no respect for his customers and only panders to the professionally obsessed." 🤣

Anyway, XP already does a good job correctly modeling the failure of pitot/static and their different effects on indicated altitude/aispeed (I don't know to what extent the competitor sim models that), so it might as well improve things further by modeling non standard pressure lapse rate.

 

2 hours ago, jcomm said:

There's already a problem at least at VATSIM stemming from the fact that when the clients are used by different flight simulation platforms, and one is in MFS with Live Weather, discrepancies arise between the "true" altitudes due to the fact that MFS unlike XP or FSX / P3D is modelling te non ISA pressure lapse rates due to Tempretaure variation.

It would be good to find out if LR is considering this in their new version ...

Why is this important ? Well, I can think of different reasons, but a good example of how differing models can be disruptive is well described here at the flightsim.com ( MFS Support Forums ) General board by one of the developers from VATSIM:

https://forums.flightsimulator.com/t/vatsim-ivao-pilotedge-users-be-aware-of-an-important-bug/426142/363?u=jcommflight

I've sent LR a message with this "hint", just as Alexis did regarding Magnetic Variation...

Ok, time to confess.  Are you in the Hot Start discord?  Because we were literally talking about that very thing yesterday, and how the Challenger 650 has this implemented.

 

19 minutes ago, GoranM said:

Ok, time to confess.  Are you in the Hot Start discord?  Because we were literally talking about that very thing yesterday, and how the Challenger 650 has this implemented.

 

Nope - just use Discord to talk to a few friends ...  Hunpty-Dumpty included 🙂 

I believe Alexis / Alec @ Avsim is, though, and he is in the "Loop" also with LR  🙂

 

Edited August 12, 20214 yr by jcomm

Ok, well X-Plane, as a default sim, doesn't have temperature variation.  Mainly because not many people actually know about it.  Including Vatsim controllers.  But it is possible to code it into add on aircraft.  As I said, the 650 has it.  This has already caused some vatsim controllers a headache, because some of our testers are climbing to reported altitudes, but due to temperature variation, the altitude on vatsim controllers screens are showing different altitudes.

But anyway, to answer your question, in its default state, making a basic add on, there is no altimeter temperature variation in X-Plane.  But the SDK does allow for it.

Edited August 12, 20214 yr by GoranM

Yep, that can indeed be done, and other details like a more realistic navaid model accounting for the various specificities of some of the transmitters and the bands they work with, or accounting for Magnetic Variation even if the base sim does not, etc...

I just hope this is not going to clash with model data being used by the simulation platforms when in "Live Weather" mode and what the simulator is fetching from it.

I saw Austin talking about the next version of XP and that he intends to do something more for the weather engine. OTOH we now know ASOBO is doing it already when MFS is used in "Live Weather" mode, and using ISA lapse rates otherwise.

Now, if different sims use different sources / models for the forecast weather data, and they opt for taking pressure level height from the model, instead of from the generic formulas like those I linked above in the OP, we can always end up running into discrepancies 😕

It would be great to know what ASOBO is really using to make their calculations, and then check with LR since Aiustin is working on the next generation of XP and see if they plan to use the same approach.

Edited August 12, 20214 yr by jcomm

I know everyone (and some especially so!) is excited and clamoring to get his favourite "nitpick" resolved in XP12...but if you bust a certain level of being obnoxious and spammy with your emails Austin will probably simply delete all further mails from you without even reading them 😄. Call your shots carefully.

As for the altitude indication error for non-isa temperature gradients:

A birdie told me that it would not be a good idea to spend a ton of time coding around this or get on Austin´s nerves with sending a ton of messages. I would rather wait for XP12.

Edited August 12, 20214 yr by Janov

3 hours ago, jcomm said:

MFS unlike XP or FSX / P3D is modelling te non ISA pressure lapse rates due to Tempretaure variation.

https://forums.flightsimulator.com/t/vatsim-ivao-pilotedge-users-be-aware-of-an-important-bug/426142/363?u=jcommflight

I read that post. Are you sure that MSFS is actually modeling different pressure lapse rates due to temperature deviations? In the post there's no mention of temperature deviations, and I suspect the issue is that MSFS models different pressure lapse rates due to _sea level pressure_ deviations.

Can someone check if indicated altitude in MSFS changes when changing sea level temperature (but keeping sea level pressure the same)?

EDIT: of course the aircraft must be at altitude while changing the sea level temperature.

Edited August 12, 20214 yr by Murmur

Good question!

Have to check !

Probably the problem should be rather solved on MFS side... because it will bring more problems than advantages for other platforms - not only XP - when used with VATSIM.

 

Edited August 12, 20214 yr by jcomm

The whole concept of pressure altitude, ISA deviation error and QNH/altimeter setting to compensate for flying over high altitude terrain is very complex.

For real and online ATC the only thing that matters is the altitude that is transmitted from the altitude encoder of the transponder. The encoder will transmit "pressure altitude" - so it will not even "know" about temperature deviations.

I assume there is a problem in MSFS where the altitude "transmitted" to VATSIM is not the indicated pressure altitude, but the temperature corrected pressure altitude. So on a hot day all MSFS pilots appear to be flying too high - or something to that effect.

Examples:

An aircraft flying on a hot day at FL200 will show 20.000 on the altimeter, and transmit 20.000 on the Mode-C altitude. It will be higher than 20.000 feet MSL, though (high temperature).

An aircraft flying on an ISA day at 5000 feet with the QNH of 1020 will show 5.000 on the altimeter and transmit 5210 on the Mode-C altitude. It will be at 5.000 feet MSL. (The ATC controller can see 052 for altitude on his screen, but knows that it is due to high pressure).

Edited August 12, 20214 yr by Janov

51 minutes ago, Murmur said:

Can someone check if indicated altitude in MSFS changes when changing sea level temperature (but keeping sea level pressure the same)?

EDIT: of course the aircraft must be at altitude while changing the sea level temperature.

@Murmur, That part I already tested, and yes - it changes.

Problem is, how they're doing it...

It is rising a problem for people flying on VATSIM and probably other virtual atc networks, described on the post I linked above.

@ Janov has summarized it above very well and concisely for those not willing to spend a few minutes reading the linked thread on my OP !

It still has to be determined how MFS is calculating that "temperature compensation". We need further clarification from ASOBO, I believe. I have asked at their public forums but haven't received an answer so far.

This being said, if the modelling of such effects makes it's way into the next version of X-Plane it will be nice for the nitpicky chasers 🙂

 

 

isnt it a confirmed bug that msfs has temperature at altitude borken - and therefore by implication pressure altitude also borken?

AFAIK the only important thing is that all aircraft in the same vacinity have the same simulated pressure, which makes this a vatsim/msfs issue rather than anything for LR to worry about.

Vatsim already provide a live weather source to unify platforms afaik, its up to MS to use it (which they dont plan on afaik)

Edited August 12, 20214 yr by mSparks

7 minutes ago, mSparks said:

isnt it a confirmed bug that msfs has temperature at altitude borken - and therefore by implication pressure altitude also borken?

AFAIK the only important thing is that all aircraft in the same vacinity have the same simulated pressure, which makes this a vatsim/msfs issue rather than anything for LR to worry about.

They ( ASOBO ) are fixing it, in steps.

Right now it's fixed within the simulator, so that, irrespective of Temperature you get the proper arfield reference altitude reading when you set the proper QNH being at the aerodrome reference point for that data. Previously, when you varied "T" the altitude reading would also vary. They fixed that already.

The other part is fixing the data that is sent to clients like VATSIM. That, I believe, will get fixed with SU6.

OFC it would be great if somewhere along the next version of X-Plane we could have this modelled as well.

Edited August 12, 20214 yr by jcomm

21 minutes ago, jcomm said:

The other part is fixing the data that is sent to clients like VATSIM. That, I believe, will get fixed with SU6.

"Open up the weather system to 3rd party devs" aka "use vatsim weather" is marked under "not planned".

For xplane you can already select "vatsim" as the source with the NOAA weather plugin afaik (which may end up needing a new version when they overhaul the weather)

Edited August 12, 20214 yr by mSparks

5 minutes ago, mSparks said:

"Open up the weather system to 3rd party devs" aka "use vatsim weather" is marked under "not planned".

For xplane you can already select "vatsim" as the source with the NOAA weather plugin afaik.

Yes, this is one of the advantages, among other ( like being available for 3 desktop platforms ) of X-Plane over other sims.

Anyway, MFS is vatsim-ready from the ATC pov. Only "problem" results from presently there being no other wildly used desktop civil flight simulation platform that models the effect of "T" in non-ISA pressure lapse rates., and yet all having VATSIM ( an other ) ATC clients and getting out-of-sync altitude information among them when MFS aircraft are in play.