<... My point is this:  At a 90 or 100 degree F day, at full throttle, sea
level, std day pressure (29.92), you won't be generating 100% power - because,
you are sucking in hot ambient air through the induction
system (lower density than standard) ...>
Would you entertain the notion that, although you're not generating quite as
much power/heat at 90-100F, you can't reject anywhere near as much heat at those
temperatures as you could at 50-60F.  If what you imply was the case, hot days
would be great for cooling.  Actually just the opposite is true.
We need to look at both sides of the coin ... Jim S.


David Carter wrote:

> Great post, Al.
>
>  Just a comment on one of the "assumptions" we all start with when
> discussing estimation of cooling system sizes for hot weather:  How much hp
> is being developed, i.e., how much heat is to be rejected?
>    - I wonder if everyone is "assuming" that they must calculate radiator
> areas based on heat being generated/to be rejected while generating 100%
> power, i.e., 160 or up to 180-205 for a n/a rotary, depending on what you
> think you will be getting?
>         --  My point is this:  At a 90 or 100 degree F day, at full
> throttle, sea level, std day pressure (29.92), you won't be generating 100%
> power - because, you are sucking in hot ambient air through the induction
> system (lower density than standard) and, without looking up the equations
> for normalizing measured performance to "std day", I guess we'll be
> generating only 90% of the 160 or so hp.
>             ---  So, when we are analyzing or talking about cooling in hot
> weather, we need to state a percentage of "std day hp" that we estimate to
> be generating in the stated "non std hot day" we are designing for.  I'll
> try to dig out that info, unless someone else beats me to it.
>         -  We should be able to post a two column table with "Outside Air
> Temp (OAT)" & "% of hp at full throttle".
>             --  And, while we are at it, we ought to be factoring in the
> manifold pressure drop across the air filter:
>                 ----  My Cessna 182 or 172 with the oiled foam induction air
> filter drops 2" - that's what I always see.
>                 ----  A friends Mooney with dry paper filter drops 1".  That
> is consistent with what others have observed on takeoff and posted.