Question, are you going to be able to enter the QNH or is 1013 going to be
the default? It won't be to accurate if you always use 1013 as the presure
changes all the time and you don't always take off at sea level.
Standard formula used by pilots for presure height is 1 bar = 30 ft of
altitude.
eg Take off Sea level at 1000 bar
Cruise at 3000 ft then presure will be about 900 bar

But if you going to this extent why not calcutate desity height too.
International Standard is 1013.2 bar at +15 deg C.
Stick in a temperature probe and calculate your density height. Rough
calculation is every 1000ft you climb you loss 2 deg C
Check out a Privat Pilot training manual at an aero club.

Regards Jason.


William M. Smithers wrote:
>
> On Fri, 13 Nov 1998, Richard Parsons wrote:
>
> >
> > Who knows how to calculate the altitude using a pic. I have built all
the circuitry for all, just the altitude stuff now...
> >
> > I have a fancy formula (email me if you want it) but I am looking for an
easy one that even a pic can do......  I have to enter the QNH (corrected
air preasure for a given altitude, typically 1.013 bar at
> > sea level) and it must spew out the height in feet (or meteres...)
whatever is easier.
> > I am using a PIC73 with two Differental preasure transducers (one for
air speed and the other for altitude)
>
> For altitude (in PSI):
>
> alt = 14.7-((feet*(52.85 - (0.000673*feet)))/100000.0);
>
> This is only good to about 12,000ft though, but I use it
> for diving decompression, and most people don't scuba dive
> higher than that.  It sounds like your doing avionics, so
> this won't help.

Yes - he's doing a crash-course in microlight flying!
(Hi Richard!)

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