GPS altitude vs altimeter altitude

I suggest that you contact the FAA before you launch a robot
airplane and kill somebody.



--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Chris W" wrote in message
news:TKB0g.933$9c6.344@dukeread11...
| It seems as though those who actually read what I was
really asking
| didn't think it was important to find or know the answer
so let me get a
| little more specific. I am going to launch a remote
control airplane
| that has an autopilot. The autopilot has an altitude hold
function that
| is based on barometric pressure sensor. I will also have
a GPS used for
| guidance. The data from that GPS will be transmitted
using APRS on
| 144.39 mhz to any amateur station listening. Once the
autopilot is
| turned on it will hold the pressure altitude it is at, so
as it flies
| along it's route (maybe as many as a few hundred miles)
and the
| barometric pressure changes the plane will climb and
descend to maintain
| the same pressure altitude. However the only data I will
be getting
| back is the GPS altitude. I need a way to do a reality
check so if I
| see the plane is descending or climbing I will know it is
because of
| changes in the barometric pressure and not the something
that has gone
| wrong. The plan is to get the latest METAR data from the
closest
| observation point to the current position of the plane and
then do the
| math compared to what it was where and when it launched so
I will know
| about what the GPS altitude should be reading as that is
all I will be
| able to see. For those who want to know why I don't just
have it
| transmit the pressure altitude back, I have four good
reasons; cost,
| weight, size, complexity. My first flights will be only
20 miles or
| so. For safety I will be sure it steers clear of any
class B, C, and D
| air space. I'm not sure what pressure altitude I will
have it fly at
| .... probably somewhere between 1500' and 6000' AGL
depending on the
| distance for it to cover.
|
| --
| Chris W
| KE5GIX
|
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