Talk:Altimeter

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Aviation: Aircraft

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Technology

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74.140.133.110 (talk) 02:14, 7 May 2008 (UTC) =((Po/Psl)^0.19026-1)*288.15/-0.0065 what is this? It needs to be defined with a physics formula and explained.[reply]

Untitled[edit]

I brought in the altimetry/bathymetry reference because it is a prime in-reference for altimetry, which is referred here. Feel free to rearrange as you see fit.--Natcase 03:17, 17 November 2006 (UTC)[reply]

See also the hillwalking article linked under "See also", which has an explanation of the barometric equation in a purer form. Galltywenallt 22:18, 16 April 2007 (UTC)[reply]

'an altimeter is an instrument that shows height above sea level, especially one mounted in an aircraft and incoporating an aneroid barometer that senses differences in pressure caused by changes in altitude.

New thread (Sept 2022): As a newcomer I found this entire article to be unbalanced. There is a heavy (excessive) emphasis on skydiving, which is an area which deserves a mention but not 25% of the whole article. There is a rather bizarre reference to ground effect vehicles. It is also light on other important aspects. I would suggest an article structure as follows:

- Definition

- Altimetric technologies: barometric, radar/Lidar, satellite receivers, ground-based technologies - the pros and cons of each type and when they are used

- Detail on the common aneroid barometric altimeter: its construction, operation, calibration and use. Mandated equipment for many aircraft types. Sources of measurement errors.

- The vertical datum: the various common reference levels and when they are used; QFE/QNH/QNE settings. The ISA standard atmosphere. Mean sea level definition for inland locations; the models in use for this

- Specific altimeter applications: air navigation; climbing and hiking; skydiving

- Related applications: the variometer; the airspeed indicator

- References and links

I could write this if there is agreement that it would be an improvement. However I don't want to jump in with a whole-article change. — Preceding unsigned comment added by Harcourt Stanton (talk • contribs) 11:12, 5 September 2022 (UTC)[reply]

False readings?[edit]

Does an altimeter ever give false readings?

If it is only a special kind of barometer, is it ever resynchronized in the middle of a flight? I am assuming that altimeters are initialized to a particular known state, usually at the time of takeoff. If the barometer is electronic in nature, would a power failure cause it to resynchronize to a patently false state, even in midflight? If lightning strikes a plane, how can you tell if the altimeter went through a reset sequence? —Preceding unsigned comment added by 216.99.219.134 (talk) 19:36, 20 August 2009 (UTC)[reply]

How to read?[edit]

The article didn't give any pictures depicting how to read an altimeter. This might get confusing. —Preceding unsigned comment added by 64.219.120.5 (talk) 15:36, 23 August 2009 (UTC)[reply]

Related, The diagram at the upper left is incorrect. The text states it is indicating 10,180 ft, which is sort of true, with outside/3rd marker at 1 for 10,000 ft, and the "clock hands" showing 180ft. However, the diagonal lines at the bottom of the altimeter are still showing, which means the display is 180 feet. The diagonal lines turn black once over 10,000 ft to prevent pilots from misreading the 3rd indicator and flying into the ground. I'm unsure how to edit the picture. 8r455 (talk) 02:31, 5 February 2015 (UTC)[reply]

Calibration formula[edit]

Why calibration formula has been changed?

Modification of "10:11, 31 January 2010" introduce an error, correct formula is 1-(...), not (...)-1 —Preceding unsigned comment added by Wbigger (talk • contribs)

Opening sentence[edit]

I think this opening sentence needs to be changed, because it is not quite accurate:

"An altimeter is an instrument used to measure the altitude of an object above a fixed level."

Typical altimeters in aircraft, measure to MSL (Mean Sea Level), so it is a misnomer to say "above a fixed level." That is because MSL is not a "fixed level."

"Mean sea level does not remain constant over the surface of the entire earth. Mean sea level at the Pacific end of the Panama Canal stands 20 cm higher than at the Atlantic end." here

My suggestion, then, is that the sentence be changed to read thus:

"An altimeter is an instrument used to measure the altitude of an object above Mean Sea Level."

Will appreciate further comments from other editors. 66.81.53.160 (talk) 11:26, 25 October 2011 (UTC)[reply]

Sounds like a reasonable argument, but it's original research until you find a ref to support this definition.Socrates2008 (Talk) 12:17, 25 October 2011 (UTC)[reply]

Temperature Correction[edit]

The section on altimeters in aircraft contains the statement "An altimeter cannot, however, be adjusted for variations in air temperature". Years ago an article in Summit Magazine (a climbing journal) carried an article on temperature correction. Some factoids I recall: the scale on an altimeter assumes an FAA standard adiabatic lapse rate, or change in pressure with altitude. It assumes a specific T_{sea level}. If the actual T_{sea level} is known, then (to the extent that an adiabat is appropriate) you can indeed correct for temperature. In effect, you have to correct for the fact that a column of air, say 300m high, weighs less when warm than when cold. As you ascend, the error is in delta-H; you can't fix it by using a single known elevation. A correction would no doubt be difficult for a mechanical altimeter, but surely it would be a piece of cake for a 21^st century microchip? Is it done? Captain Puget (talk) 05:25, 30 November 2012 (UTC)[reply]

In Pilot School, the saying is "From High to Low or Hot to Cold, look out below." Meaning if moving from a high temperature area to a lower temperature, the altimeter will indicate a higher altitude than the plane is actually at. The same happens if flying into a low pressure area. There is no automatic correction, but a rule of thumb is 100ft per 10 degrees of temperature change. 8r455 (talk) 02:35, 5 February 2015 (UTC)[reply]