http://naca.larc.nasa.gov/reports/1948/naca-report-920/

Alan,

 

Consider the following table for the approximate theoretical rise in inches of Hg versus KIAS:

 

KIAS Hg"

100   0.5

150   1.1

200   2.0

250   3.0

300   4.5

 

Ram air is free.

 

All I got from the NASA report is:

 

1. Keep the leading edge of the opening rounded with a large radius.  Done.

 

2. Stick it out from the body so that there is no surface flow interference at the entry.  Something like the Lancair 300 series.

 

3. It is all somewhat dimensionless. I.E. Hole must be big enough, shape is less important.

 

Note: Some testing was done at .3 to .4 Mach or approximately 200 to 260 Kts.  Our kind of speeds.

 

Also note: A well sealed cooling plenum may possibly give  1" Hg rise for induction air taken from the plenum at 200 KIAS.  Of course, 1" Hg is worth what? About 3.5% power (ROP)?