<... How do the Mass Air requirements change with altitude ...>
They don't, except as the heat rejection requirements change.
You get the same mass airflow at 180 kias at sea level or 15 k ft. Of course
your TRUE airspeed at 15k is a lot higher and that's what pumps more of the
thinner air through the system.  Also, to the extent that fuel flow is less at
15 k ft, so you have less heat rejection requirements and therefore less mass
flow requirements.

<... if the fuel burn was 8.5gph and altitude was 25K ...>
.... you'd be making about 300 kts TAS and would no doubt have the same mass
airflow as at SL 8.5 gph.

Mass airflow is a function of indicated airspeed which is dynamic pressure which
is how many molecules are going past a point in a unit of time.

Just a theory ... Jim S.

Eric Ruttan wrote:

> Ed
> How do the Mass Air requirments change with altitude.  For example, if the
> fuel burn was 8.5gph and altitude was 25K would the mass air requirements
> change do to thiner air?  Would the lower temp make a difference?
>
> Thanks for your help.
>
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