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ENGINE COOLING

Good cooling is important but ideally we'd like to recover as much momentum as possible, exiting that cooling air at as close to free stream velocity as possible. An excellent system will exit the air at above the free stream velocity, offsetting cooling drag or even creating slight thrust.

We'll never get there with a flat air cooled installation, but let's get all we can.

Next step is to instrument your exit with a pitot tube and temp sensor to see what you have for exit velocity.

Might be a case of premature pitottemperaturation.
 
Here it is calculated. The classic equation is...

0.5 * density in slugs per cubic ft * velocity^2 in ft per second = q in lbs per sq ft

...but to make life easy there are spreadsheets or good online calculators which allow entries as pressure altitude, KTAS, choice of temperature unit, etc.


It's a baseline, the pressure available to push mass through the system. The point of interest is how much of it is captured as increased upper plenum static pressure.

This and the related replies all bump around my original question. I'm not at the baffle stage of the build. I'm getting my a$$ whipped by other issues.

I wanted to know where/how the dynamic pressure was being measured. Cowl inlet? Post inlet ramp? etc. Measured by what? A test (not aircraft) pitot that utilizes it's own static port to provide a direct Pd reading? I'm trying to reconcile a test set-up I haven't seen. As many (probably most) tend to misunderstand Pt versus Ps versus Pd relationships/dynamics, I was trying to guess the integrity of the application and results.

Might add a General Thread on aforementioned relationship if the mods will allow.
 
Zaviston, in his S/A articles, presents his set up for measuring pressure, etc. in the cowl using piccolo tubes, etc.

The first article was in Dec, 2007.

[I have a copy in .pdf format but my attempt to attach was met with an "incorrect file extension" error message]
 
I think Dan has covered the method to measure pressures here several times over the years. Search function is your friend here.
 
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