That process is exactly what a pilot is doing (below transition to flight level) when he enters altimeter correction so the airfield will read the correct height above sea level for landing and takeoff (particularly in landing, as you aim at the blue in takeoff, and you aim at the hard in landing).
However, it seems odd you would encode the pressure in the boat as altitude. Why not use an aneroid barometer and record "station pressure." Your process memorizes local sea level pressure at an instant, but it will surely be different the next time you raise the mast in another time and place. NWS uses two processes to calculate a "sea level pressure." One uses the altimeter equation and directly yields the altimeter correction, the other uses a different assumption about temperature of the air column between sea level and the station and is preferred for analysis of highs, lows, weather patterns. ________________________________ From: James R. Frysinger <j...@metricmethods.com> To: U.S. Metric Association <usma@colostate.edu> Sent: Sun, April 18, 2010 9:50:39 PM Subject: [USMA:47171] Re: Air flight altitudes in meters Thanks, John. Your knowledge obviously exceeds my faint acquaintance with this matter. Now, I HAVE had personal experience with aneroid altimeters, the pneumo-mechanical sort where the big hand spun a complete circle for every "one thousand feet" (I think that was the number). We used them on submarines to measure the "pressure in the boat". (Non-submariners should call 'em "ships".) Whenever we raised the induction mast to ventilate (an extremely infrequent event on some missions) we would "zero" our altimeter readout by adjusting the base pressure knob. As air bank pressures bled down due to air usage or rose when compressors charged them back up, that readout would change. Your experience undoubtedly was ABOVE sea level, though. Jim John M. Steele wrote: > Actually, it is nominally based on height above sealevel. Sitting on the > runway, with altimeter correction dialed in, it will read the published > height of the runway above sealevel. > At cruise levels, no altimeter correction is used and reading is called >flight level. It is the height above sea level IF sea level were at 15 °C, >101.325 kPa, and a lapse rate of -6.5 K/km to the stratosphere (11 km), and >zero lapse rate above that to 20 km. Further it it uses a height variable >called geopotential height, the height that would be true if gravity were >constant with height. There is a transformation between that and geometric >height in the standard. > > ------------------------------------------------------------------------ > *From:* James R. Frysinger <j...@metricmethods.com> > *To:* U.S. Metric Association <usma@colostate.edu> > *Cc:* U.S. Metric Association <usma@colostate.edu> > *Sent:* Sun, April 18, 2010 8:47:07 PM > *Subject:* [USMA:47168] Re: Air flight altitudes in meters > > > Altimeters work off of atmospheric pressure readings, Pat. But the readout is > in terms of height above terrain. So assignments and reports are always in > length units. No human pressure to altitude correlation procedures are used. > > Jim > > Pat Naughtin wrote: > > Dear John, Jim, and All, > > > > My understanding is that air craft actually measure pressure in something >like kilopascals and that this pressure measurement is then changed (dumbed >down ?) to a measure that implies that a measure of length has been made >somehow. > > > > I suppose you could dangle a mass tied on a piece of string out the window >of the plane so that it drags along the ground, but it sounds impractical! > > > > By the way, some approximate conversions from pressure to height might go >something like this: > > > > Pressure > > > > > > > Altitude > > > > kilopascal > > > > > > > metres > > > > 100 > > > > > > > 0 > > > > 90 > > > > > > > 1 000 > > > > 80 > > > > > > > 2 000 > > > > 70 > > > > > > > 3 000 > > > > 65 > > > > > > > 4 000 > > > > 60 > > > > > > > 5 000 > > > > 45 > > > > > > > 6 000 > > > > 40 > > > > > > > 8 000 > > > > 22 > > > > > > > 10 000 > > > > 19 > > > > > > > 12 000 > > > > 15 > > > > > > > 14 000 > > > > 10 > > > > > > > 16 000 > > > > 7 > > > > > > > 18 000 > > > > 4 > > > > > > > 20 000 > > > > 3 > > > > > > > 25 000 > > > > 1 > > > > > > > 30 000 > > > > > > Cheers, > > Pat Naughtin > > Author of the ebook, /Metrication Leaders Guide,/ that you can obtain from >http://metricationmatters.com/MetricationLeadersGuideInfo.html PO Box 305 >Belmont 3216, > > Geelong, Australia > > Phone: 61 3 5241 2008 > > > > Metric system consultant, writer, and speaker, Pat Naughtin, has helped >thousands of people and hundreds of companies upgrade to the modern metric >system smoothly, quickly, and so economically that they now save thousands >each year when buying, processing, or selling for their businesses. Pat >provides services and resources for many different trades, crafts, and >professions for commercial, industrial and government metrication leaders in >Asia, Europe, and in the USA. Pat's clients include the Australian Government, >Google, NASA, NIST, and the metric associations of Canada, the UK, and the >USA. See http://www.metricationmatters.com ><http://www.metricationmatters.com/>for more metrication information, contact >Pat at pat.naugh...@metricationmatters.com ><mailto:pat.naugh...@metricationmatters.com> ><mailto:pat.naugh...@metricationmatters.com ><mailto:pat.naugh...@metricationmatters.com>> or to get the free '/Metrication >matters/' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe. > > > > On 2010/04/19, at 05:57 , John M. Steele wrote: > > > >> It is my understanding that European air space is controlled in feet. > >> The Wikipedia article on "flight level" shows a metric structure for >Russia, China, Mongolia, North Korea and various CIS States (non-European >former USSR satellites). Everybody else flies in feet (I think). > >> > >> ------------------------------------------------------------------------ > >> *From:* James R. Frysinger <j...@metricmethods.com ><mailto:j...@metricmethods.com> <mailto:j...@metricmethods.com ><mailto:j...@metricmethods.com>>> > >> *To:* U.S. Metric Association <usma@colostate.edu ><mailto:usma@colostate.edu> <mailto:usma@colostate.edu ><mailto:usma@colostate.edu>>> > >> *Sent:* Sun, April 18, 2010 3:13:10 PM > >> *Subject:* [USMA:47149] Air flight altitudes in meters > >> > >> > >> My impression had been that all air flight altitudes were given and >heeded in terms of feet. But this article implies flight altitudes in meters. > >> >http://www.foxnews.com/world/2010/04/17/european-skies-largely-remain-fly-zone/ > >> > >> Jim > >> > >> -- James R. Frysinger > >> 632 Stony Point Mountain Road > >> Doyle, TN 38559-3030 > >> > >> (C) 931.212.0267 > >> (H) 931.657.3107 > >> (F) 931.657.3108 > >> > > > > -- James R. Frysinger > 632 Stony Point Mountain Road > Doyle, TN 38559-3030 > > (C) 931.212.0267 > (H) 931.657.3107 > (F) 931.657.3108 > -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
