gertd57 4 Posted March 3, 2022 Share Posted March 3, 2022 Hi all, During my last flights I observed the following: I allways push "B"before taking off, to set the baro for the altimeter. After this the altimeter should show the corrected altitude. (measured above sea = 0 ft altitude) When flying, I observe different readings on the Altimeter and the radio-altimeter. The radio-altimeter has only the same reading when the altimeter is set to 1013 Mb!! I don't know if this is a bug, something in the twotter or something in msfs?? As I understand it the RA and the normal altimeter should show the same altitude when the correct pressure is set in the altimeter. Hope you can help, Gert Link to comment Share on other sites More sharing options...
MarkHurst 173 Posted March 3, 2022 Share Posted March 3, 2022 1 hour ago, gertd57 said: As I understand it the RA and the normal altimeter should show the same altitude when the correct pressure is set in the altimeter. Surely the Radio Altimeter shows the actual measured distance from the terrain? The regular altimeter shows an approximate height above a fixed datum (generally sea level) based on the estimated local barometric pressure. Link to comment Share on other sites More sharing options...
gertd57 4 Posted March 3, 2022 Author Share Posted March 3, 2022 Hi Mark, Thats right. So when flying above sea the altimeter and radio altimeter should show the same altitude. Or am I wrong?? On the twotter that happens only at 1013 mbar. In my opinion it should allways be more or less the same, if the correct barometric pressure is put into the altimeter. Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted March 4, 2022 Aerosoft Share Posted March 4, 2022 And how far is it off now? The two gauges both read the variables from the sim, there is no calculations being done on them so it could indicated what the sims has is not correct. I did a quick test and could not see a difference (but seeing 50 feet on a altimeter is next to impossible) Link to comment Share on other sites More sharing options...
gertd57 4 Posted March 4, 2022 Author Share Posted March 4, 2022 Hi Matthijs, flying from EGPL to EGPR Altimeter set with pressing B on 1022mbar, reading 1500ft radio altimeter reading a bit over 1300 ft. 1022 mbar is right pressure from noaa info. flying above the sea, so to mee readings should be abt the same. Hope you can help? Greetings, Gert Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted March 4, 2022 Aerosoft Share Posted March 4, 2022 Interesting... I'll try a few things this weekend. But as said, we use the simvars. Link to comment Share on other sites More sharing options...
gertd57 4 Posted March 4, 2022 Author Share Posted March 4, 2022 Hi Mathijs, I think the problem is in msfs. I tried anothe flight over the sea, near Lands End ad teh Scilly Islands. There the difference between the altimeter and radio altimeter was only some 20ft!! So my conclusion is that something strange is going on, I think in the live weather of msfs!! Sincerely yours, Gert Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted March 8, 2022 Aerosoft Share Posted March 8, 2022 I tend to agree with you. I think the issue is that the base altitude of the sim is set in a not to fine grid. Link to comment Share on other sites More sharing options...
UnsealedKarma 52 Posted March 10, 2022 Share Posted March 10, 2022 On 3/4/2022 at 3:29 PM, gertd57 said: I think the problem is in msfs. I tried anothe flight over the sea, near Lands End ad teh Scilly Islands. There the difference between the altimeter and radio altimeter was only some 20ft!! The problem seems related to live weather and is perhaps a variation of the infamous MSFS live weather pressure bug. I loaded up the Twin Otter at Barra with live weather (see screenshot). The difference between the radar altitude indicator in the shot (c. 1300 feet) and the barometric altitude indicator (c. 1500 feet) is caused by a discrepancy between the simvars they reflect. The barometric Altimeter in the Twotter uses (A:INDICATED ALTITUDE, feet). If the barometer is calibrated to the correct sea level pressure (A:INDICATED ALTITUDE, feet) should equal (A:INDICATED ALTITUDE CALIBRATED, feet). The value the simulator projects is c. 1500 feet for both. The Radar altimeter uses (A:PLANE ALT ABOVE GROUND, feet). Above water (A:PLANE ALT ABOVE GROUND, feet) should be equal to (A:PLANE ALTITUDE, feet). The value the simulator projects is c. 1300 feet. Flying with live weather at the same place in the stock 172 give me the same results. I changed the weather to the 'clear' preset and then - exact match between the two. Please login to display this image. Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted March 11, 2022 Aerosoft Share Posted March 11, 2022 Good find! Link to comment Share on other sites More sharing options...
UnsealedKarma 52 Posted March 11, 2022 Share Posted March 11, 2022 5 hours ago, Mathijs Kok said: If Asobo is reluctant or unable to solve the bug (that affects all planes) I suppose the barometric altimeter could be changed to display PLANE ALTITUDE multiplied by INDICATED ALTITUDE divided by INDICATED ALTITUDE CALIBRATED (to get the uncalibrated altimeter errors). Then the two altimeters will correspond. The solution is neither ideal nor elegant, however. Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted March 13, 2022 Aerosoft Share Posted March 13, 2022 On 3/11/2022 at 11:19 PM, UnsealedKarma said: If Asobo is reluctant or unable to solve the bug (that affects all planes) I suppose the barometric altimeter could be changed to display PLANE ALTITUDE multiplied by INDICATED ALTITUDE divided by INDICATED ALTITUDE CALIBRATED (to get the uncalibrated altimeter errors). Then the two altimeters will correspond. The solution is neither ideal nor elegant, however. I stored that suggestion. Thanks. Link to comment Share on other sites More sharing options...
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