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**rotor_wash** · 07-30-2005, 02:06 PM

You are nearly correct with the 1 atmosphere of pressure; however that applies to ONLY underwater. Standard pressure decreases approximately 1" Hg (mercury) per 1000' above sea level increase given a "standard day". The change from slightly below sea level at Death Valley to 8000' pressure altitude is a change from 30.21" Hg to ~22.21" Hg. At 18,000' pressure altitude, you are roughly above 1/2 of the atmosphere.
Temperature is another matter with ~3.5 degrees Fahrenheit (2deg C) change per 1000 '. 125F at Death Valley becomes ~96F at 8000'.
I'll continue to put the correct tire pressure when recorded cold - regardless of the temp/altitude. I'll leave Boyles Law to the 'Rocket Surgeons' out there.
R_W

07-30-2005, 02:06 PM	#5
rotor_wash Site Sponsor Join Date: Sep 2003 Location: Gainesville, VA Posts: 94	1 atm pressure differs under water. You are nearly correct with the 1 atmosphere of pressure; however that applies to ONLY underwater. Standard pressure decreases approximately 1" Hg (mercury) per 1000' above sea level increase given a "standard day". The change from slightly below sea level at Death Valley to 8000' pressure altitude is a change from 30.21" Hg to ~22.21" Hg. At 18,000' pressure altitude, you are roughly above 1/2 of the atmosphere. Temperature is another matter with ~3.5 degrees Fahrenheit (2deg C) change per 1000 '. 125F at Death Valley becomes ~96F at 8000'. I'll continue to put the correct tire pressure when recorded cold - regardless of the temp/altitude. I'll leave Boyles Law to the 'Rocket Surgeons' out there. R_W __________________ Rotor_Wash HEMS (Helicopter Emergency Medical Service) Pilot (ret) Northern VA 2002 3124KS 2007 Tahoe Solar