So,

starting SU5 there's something weird happening to the Altitude (A) and how it is influenced at least by the value of Temperature (T), for a constant pressure setting in the barometric altimeters - haven't checked with radio altimeters.

With MFS's latest update if you use manually set weather, define the QNH for the situation, place your aircraft say at the threshold of one of the runways at a given airfield and set the mean sea level T to it's ISA value ( 15 ºC ), you can then read the correct altitude of that point in your barometric altimeter, but if you vary T up or down from ISA, you will see your altitude varying as well in your altimeter 😕

Whazzzzup ? What did Sebastien do this time 🙂 ?

Well, I have mixed feelings about this :

.) I can see that if I increase the value of T, the altitude being read in the baro altimeter decreases;

.) I can see that if I decrease the value of T, the altitude being read in the baro altimeter increases;

Is this bad ? Well... yes, and no...

Yes because with a given QNH setting, varying T alone shouldn't have any impact on your baro altimeter altitude reading, yet !

It appears that for the first time they're either trying to find QFF or, even better, to model geopotential height and how it is affected by the temperature / density of an air mass.

The effect is essentially going in the right direction. At  considerably higher than ISA values of T the pilot has to bear in mind that the same adagio - "from high to low ... / from low to high ..." - applies just as with pressure, so you will actually be flying at a higher height above ground than the one read in your altimeter, and the way around ( and that's the problem for precision approaches in cold winter time ) if the values of T drop well bellow ISA.

Meteoblue feeds MFS with their model data, and their data accounts for geopotential height, so, for the first time in the history of flight simulator, and actually the first time in mass civil flightsims, although Aerowinx PSX, Flight Gear, and in some way even DCS World and IL-2 already model it, we are probably walking in the good direction towards a more realistic and useful - for training - representation of theses effects.

Let's hope for a fix, but not for them - ASOBO - to drop this track !

I you'd like to know more about this subject you can check, for instance:

- https://www.metpod.co.uk/calculators/pressure/

- https://www.quora.com/What-is-the-basic-difference-among-QNH-QFE-QFF-pressure-altitude-and-density-altitude

- https://www.youtube.com/watch?v=mXn8R7mXIv0

 

Edited July 29, 20214 yr by jcomm
typos

When changing temperature in CAE's simulator, we can see it shows BOTH temperature and pressure are changing, so the inputted QNH would stays where you set. so I guess MSFS it just lack this little balancing tune.