Timeline for If left stationary at a specific height, would altimeter change the displayed value over time?
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
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| Jul 15, 2015 at 19:35 | comment | added | casey | @jamesqf that is still a reference pressure, though you are inferring it from field elevation (you adjust the reference pressure input until you get the output you want) | |
| Jul 15, 2015 at 19:27 | comment | added | jamesqf | @casey: Though what you use to set the altimeter will vary. If you're at a towered field or controlled airspace, you use the reference pressure. At a small field - say in the Idaho backcountry - you set the altimeter to the field elevation. (Though sometimes it matters which end of the field you're on :-)) | |
| Jul 15, 2015 at 17:57 | history | tweeted | twitter.com/#!/StackAviation/status/621378186882981888 | ||
| Jul 15, 2015 at 12:44 | comment | added | casey | @Alexus the inputs to the altimeter are actual local pressure and a reference pressure. The difference between the two pressures determines the altitude of the local pressure level (approximately, it does not take temperature into account). An altimeter actually tracks constant pressure levels, not true altitudes. | |
| Jul 15, 2015 at 6:07 | answer | added | Skip Miller | timeline score: 2 | |
| Jul 15, 2015 at 4:32 | vote | accept | Alexus | ||
| Jul 15, 2015 at 4:30 | comment | added | Terry | @Alexus You don't have to know the height of the local station you're passing because the setting they give is adjusted to mean sea level. For example, if the station reports 30.00 inches, that's what you would set in the Kollsman window. If the station were at 2,000 ft msl, the actual pressure there would be approximately 28 inches given the standard pressure lapse rate of approx 1 inch per 1,000 ft. However, a barometer at the station would typically read 30.00 inches because it would be adjusted to read relative to mean sea level. | |
| Jul 15, 2015 at 2:36 | comment | added | jamesqf | The variation is not necessarily slight, but can be several hundred feet or more. | |
| Jul 15, 2015 at 0:40 | answer | added | UnrecognizedFallingObject | timeline score: 10 | |
| Jul 15, 2015 at 0:23 | comment | added | Alexus | So it also takes an input of local pressure at a known height? | |
| Jul 15, 2015 at 0:20 | comment | added | Terry | Yes, an altimeter based on atmospheric pressure will change over time. If you, say, park your airplane at an airport with an elevation of 400 feet msl and your altimeter is reading 400 feet, when you come back a day later, for example, it will read differently. If a low pressure system has come in, it will read higher. If a high pressure system has come in, it will read lower. And that is why there's a knob on the altimeter to allow you to change what it reads, and also why you should change the setting to match local pressure when you're enroute and below 18,000 feet in the U.S. | |
| Jul 14, 2015 at 23:56 | history | asked | Alexus | CC BY-SA 3.0 |