Re: Flight Computers and Temperature

That's true. I thought it worth mentioning, though. If you
can correct that much error with one reading...

Regards,
-Larry C.


"Robert DeHate" <robert@xxxxxxxxxx> wrote in message
news:dhd1gm$3oq$1@xxxxxxxxxxxxxxxxxxxxxxx
> That is for absolute readings.
> But altimeters report a difference between one reading and another.
>
> Robert
> "Larry Curcio" <lcurcio@xxxxxxxxxxx> wrote in message
> news:W8wZe.6702$L15.4171@xxxxxxxxxxx
> > I agree with you, David, and I don't think it's overkill at all.
> > Even in a tropospheric flight, ground temperature alone can
> > make a remarkable difference.
> >
> > The altitude reading is proportional to the absolute base altitude
> > temperature. For planes, base altitude is normally sea level. For
> > HPR, it is normally ground level. The assumed temperature in
> > the U.S. standard atmosphere is 15 degrees C or 59 degrees F.
> > The correction would therefore be actual absolute temperature
> > over assumed absolute temperature:
> >
> > CorrectedAltitude =
> > AltitudeReading*(273.15+TempC)/288.15
> >
> > On hot days, the altimeter underestimates; on cold days it
overestimates.
> > At 12 degrees F (-10 degrees C), an altimeter reading of 1000 feet
> > would therefore denote an corrected altitude of 905 feet.
> >
> > There is also an assumed temperature lapse rate of 6.5 degrees per km,
> > but it turns out that errors in this rate do not have huge effects.
> >
> > Bottom line: For most flights, ground temperature alone would be a
> > big help.
> >
> > Regards,
> > -Larry Curcio
> >


.

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