December 18, 20214 yr 3 minutes ago, jcomm said: Wrong... QFF does change Sparks. You can have the exact same pressure level intercepting your "airfield ground level", and widely varying temperatures, and while QNH stays put, QFF does vary... In XP weather settings, you're setting QFF, that's why QNH (and altimeter reading) changes if temperature changes (but QFF is kept the same). Edited December 18, 20214 yr by Murmur "Society has become so fake that the truth actually bothers people".
December 18, 20214 yr 7 minutes ago, jcomm said: Wrong... QFF does change Sparks. You can have the exact same pressure level intercepting your "airfield ground level", and widely varying temperatures, and while QNH stays put, QFF does vary... Give a loo at your ATPL Sylabus / Exams... they'll give you the basic theory on that.... kinda. I think the difference is though that your altimeter doesnt care about any of that, its a pressure gauge calibrated for ISA. temperature differences (away from ISA) screw with that. Edited December 18, 20214 yr by mSparks AutoATC Developer
December 18, 20214 yr 6 minutes ago, Murmur said: In XP weather settings, you're setting QFF, that's why QNH (and altimeter reading) changes if temperature changes (but QFF is kept the same). Then, it's wrong 🙂 It doesn't matter what they use for their weather settings reference provided the end result is correct. If for a given airport and meteorological situ you have on a given day QNH set at 1010 hPa, and on another day where you're at ISA-20 you also have QNH reported as 1010 hPa, then your altimeter will have to show the exact same altitude ( the reference airfield altitude ) to you...., right ? QFF and actually QFE will vary of course. If a simulator references it's weather model to QFF, then it has to be coherent for QNH / QFE settings too... Even QFF is not bullet proof, and there are actually differing methods to calculate it ... Edited December 18, 20214 yr by jcomm Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
December 18, 20214 yr 2 minutes ago, jcomm said: Then, it's wrong 🙂 Well, the physics behind are actually correct. If it lets you set QFF, then it's correct that QNH will change (if temperature changes). The problem is that QFF is not actually used in aviation. So, if XP internally corrects for that, and for example the ATIS gives the correct QNH, then there would be no problem. But the best thing of course would be setting directly the QNH in the weather screen, instead of the QFF. Edited December 18, 20214 yr by Murmur "Society has become so fake that the truth actually bothers people".
December 18, 20214 yr 5 minutes ago, mSparks said: Soooo None of us really knows what XP does now.... True, but we do have Janov's experiment, and it shows that as it is right now it's as wrong as ASOBO did it on MSFS... They - ASOBO - had to drop the effect simulation while they try to find a better way to implement it... Edited December 18, 20214 yr by jcomm Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
December 18, 20214 yr Just now, jcomm said: True, but we do have Janov's experiment, and it shows that as it is right now it's as wrong as ASOBO did it on MSFS... They had to drop the effects while they try to find a better way to implement it... Uhm... If the setting in XP is QFF, then it's not wrong (physics is correct). "Society has become so fake that the truth actually bothers people".
December 18, 20214 yr 4 minutes ago, jcomm said: True, but we do have Janov's experiment, and it shows that as it is right now it's as wrong as ASOBO did it on MSFS... They had to drop the effects while they try to find a better way to implement it... afaik If you keep the qnh (set on your altimeter) the same and change the temperature your altitude reading on the altimeter will change. Edited December 18, 20214 yr by mSparks make less ambiguous. AutoATC Developer
December 18, 20214 yr 2 minutes ago, mSparks said: afaik If you keep the qnh the same and change the temperature your altimeter will change. The altimeter will read the same (by definition, it always reads airfield elevation above MSL). But in XP, you set the QFF, so the QNH and altimeter reading (correctly) change. Edited December 18, 20214 yr by Murmur "Society has become so fake that the truth actually bothers people".
December 18, 20214 yr 1 minute ago, Murmur said: reads airfield elevation it reads the pressure. but the scale is for ISA. if the pressure is changing at a different rate than the ISA (due to temp not being 15 degrees at msl) your altimeter must change. AutoATC Developer
December 18, 20214 yr Sparks, IF the reported QNH is the same, then you have to read the same alt... irrespective of T... Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
December 18, 20214 yr The pressure lapse compression or expansion only happens above field altitude. How will a temperature offset from ISA affect the pressure below elevatioj? There is no air mass to be influenced there, so the effect only happens beginning above AGL. At field elevation, it doesnt matter Alexis Mefano
December 18, 20214 yr 14 minutes ago, jcomm said: Sparks, IF the reported QNH is the same, then you have to read the same alt... irrespective of T... Im not talking about qnh/qff/qne etc. the altimeter is a pressure gauge, where feet is millibars difference from 1013 (or whatever the altimeter is set to) on an ISA day. I forget, its something like 30 feet per millibar. if there is xx feet per millibar instead of 30 because its a cold day for the same altimeter setting the altimeter will read half the altitude it would on an isa day. (nb I always always get then the wrong way round) Edited December 18, 20214 yr by mSparks AutoATC Developer
December 18, 20214 yr seems i dont have dementia yet. https://skybrary.aero/articles/international-standard-atmosphere-isa Pressure is taken to fall at about 1 millibar per 30 feet in the lower atmosphere (up to about 5,000 feet). AutoATC Developer
December 18, 20214 yr 12 minutes ago, Alec said: The pressure lapse compression or expansion only happens above field altitude. How will a temperature offset from ISA affect the pressure below elevatioj? There is no air mass to be influenced there, so the effect only happens beginning above AGL. At field elevation, it doesnt matter The temperature offset changes the QFF (pressure reduced to sea level). So, if you keep the QFF constant (in XP you actually set the QFF), then the QNH (and altimeter reading) changes. The problem is that using the QFF is not pratical. Austin should replace the entry in XP12 weather screen to modify QNH instead, not QFF. Edited December 18, 20214 yr by Murmur "Society has become so fake that the truth actually bothers people".
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