Re: pressure vs. altitude

[brian whatcott <inet@intellisys.net>]

There is no fixed relation between height and pressure.
It is convenient to make some assumptions so that all aircraft will read
the same altitude when flying at the same flight level.
 In order for this to occur, the ICAO has made the following explicit
assumptions, suited to latitudes round 40 degN in Europe and US.

Temperature decreases uniformly with height: the lapse rate is 6.5K per km
(below 11000 meters)
Air is dry and of constant composition
g = 9.8062 m/s^2
T0 = 288K
p0 = 1013.2 millibar

To 11000 meters: Troposphere
Height (in meters) = 44307 {1-(p/p0)^0.1902}

Above 11000 meters: Stratosphere
Height (in meters) = 11000 + 14600 log(pk/p)
where pk is pressure at 11000 meters
and p is the pressure at the altitude of interest.

Ref:
Physical & Mathematical Tables
Yarwood & Castle
Macmillan

Brian Whatcott   Altus OK



at 10:52 5/25/98 -0500, Jason Powell wrote:
> ...
> At a local high power rocket launch this weekend I was asked a question
> ...
> A fellow is designing an onboard computer for his rockets that has a
> pressure sensor onboard.  He wants to know how to turn his pressure readings
> into altitude readings as the rocket is accelerating up, decelerating up,
> and returning back to earth via a chute.
....
> Jason (and Kim and Jacob) Powell
> Kenosha, WI
> Our Webpage:  http://www2.wi.net/~fizzx/
> ==========================
> Physics Dept
> ZionBenton HS
> Zion, IL