Quote:
Originally Posted by Piotrsko
Why not use a barometer or altimeter for air pressure, a temp gage and do real time calculations in some sort of density altitude app on your phone?
Use google maps or 5 sattelite gps for altitude corections
Isn't density altitude not the same as what you are creating?
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1) I've seen one laboratory-grade barometer in my life ( CAR and DRIVER ).
2) We need a 'raw' barometric pressure for online density altitude calculators.
3) An aneroid-type altimeter, calibrated at the beginning of a test section, would lose calibration if one traversed from one isobaric line to another, or if pressure changed during the session.
That would be the value of the NOAA isobaric contour maps. You'd know if the altimeter had drifted. And density can be derived directly from millipascals, inches, or millimeters of mercury reported.
4) GPS will give you an accurate elevation, but it won't inform about air density.
5) Contrary to popular belief, the gravitational constant used in the air density calculation varies with location on the planet. There's no onboard instrument to quantify that which is available to us.
6) A sling-psychrometer and a psychrometric chart would nail down dry-bulb, wet-bulb, relative humidity, etc. which would define the specific weight of local air, from which density could be derived. It's not something you can do on the fly though. Even with a co-pilot riding shotgun.