I think we are saying the same thing here and thinking we aren't. The standard atmosphere and the international standard atmosphere are both 101.325 kPa. (the aviation version, ISA also specifies sea level temperature and lapse rate. The IUPAC value of 100 kPa is a standard pressure in a laboratory test for specifying material properties and is not a standard atmosphere. The value simply ISN'T the average pressure at sea level, based on data in spite of the "round value folks" wishing it were (they should use 760 mm Hg, that's pretty round).
--- On Sun, 9/4/11, Michael Payne <[email protected]> wrote: From: Michael Payne <[email protected]> Subject: [USMA:51074] Re: planes collide To: "U.S. Metric Association" <[email protected]> Date: Sunday, September 4, 2011, 7:33 PM I agree, but the International Standard Atmosphere is used every day in the aviation world. We even have a readout in the cockpit of the ISA temperature which is Celsius plus or minus the difference from Standard. It gives SAT, TAT and ISA. Because of the speed thru the air, the probe and leading edges heat up which gives Total Air Temperature. In Concorde this was around +90-100C, TAT was a limiting factor on speed. The SAT is the real outside air temperature (Static Air Temp), ISA generally varies between +20C to -20C at altitude based solely on what the temperature would be if it were a standard ISA day at that altitude. All of this is based solely on ISA temperature lapse rate and altitude. Plus every airspeed indicator, altimeter, vertical rate indicator, etc, has to be calibrated using ISA tables. Aircraft performance is based and changes, depending on whether it's hotter or colder than standard temperature and altitude. The takeoff run in say Aspen (2400 m altitude) is considerable longer because of the elevation, ISA standard temp -1C. If the temperature in Aspen is 27C as it is today, that's ISA plus 28C for takeoff, performance suffers and pilots need tables to figure out how much runway and performance the airplane will have if one engine quits at an inopportune time. All of this data is based on the ISA. Mike Payne On 04/09/2011, at 17:13 , John M. Steele wrote: The SI Brochure seems to distinguish (in nomenclature) between the "standard pressure" which I agree is 1 bar or 100 kPa, and the "standard atmosphere" which is Resolution 4 of 10th CGPM as 101.325 kPa. That decision has never been abrogated. It specifically says is is for general use, thus is not limited to thermometry or altimetry, although certainly important there. --- On Sun, 9/4/11, Michael Payne <[email protected]> wrote: From: Michael Payne <[email protected]> Subject: [USMA:51069] Re: planes collide To: "U.S. Metric Association" <[email protected]> Cc: "U.S. Metric Association" <[email protected]> Date: Sunday, September 4, 2011, 4:26 PM In 1999, the International Union of Pure and Applied Chemistry (IUPAC) said that for the purposes of specifying the properties of substances, “the standard pressure” should be defined as precisely 100 kPa (≈750.01 torr) or 29.53 inHg rather than the 101.325 kPa value of “one standard atmosphere” (From Wikipedia). I think we're talking about 2 different things here, the Standard Atmosphere and the International Standard Atmosphere. I know the latter is purely a set of units set up to calibrate and test things worldwide to the same standard. 15C, 1 Atmosphere of 1013,25 hPa. It's heavily used in the aerospace industry for calibration and performance. Everyone has to be on the same page for these two items. A bit more research is needed. Mike Payne On 04/09/2011, at 07:39 , John M. Steele wrote: One (standard) atmosphere is 101.325 kPa. However, properties for many chemicals are specified at 1 bar (100 kPa) rather than 1 atm. There is also a 'technical atmosphere" 98.0665 kPa (based on kilogram-force), which is now deprecated and rarely used.. --- On Sun, 9/4/11, Michael Payne <[email protected]> wrote: From: Michael Payne <[email protected]> Subject: [USMA:51064] Re: planes collide To: "U.S. Metric Association" <[email protected]> Date: Sunday, September 4, 2011, 6:58 AM I believe one atmosphere is still 100 kPa, the 1013,25 comes from the International Standard Atmosphere. Commonly referred to as the ISA it's what manufacturers use to calibrate instruments and what aircraft makers use to calibrate the performance of aircraft. In the aviation world we constantly refer to the temperature being below or above ISA, the lapse rate is fixed under ISA as 1.98 C up to 36090 (11000 m) where it's supposed to be constant. Obviously in the real world it changes which has an affect on performance. Mike Payne On 03/09/2011, at 13:57 , G. Stanley Doore wrote: The 1013.25 mbar (101.325 kPa) pressure for altimeter settings is NOT "arbitrary" as Kilopascal & Wiki write. The standard altimeter setting for worldwide altimeter settings was determined from the mean surface pressure level. Stan Doore On Sep 3, 2011 11:36 AM, "Michael Payne" <[email protected]> wrote:
