> FWIW, the CAFE Foundation's research has shown that using a cooling
> exit shape very similar to Finn's cheek exits might be the most
> efficient way to get air out of the cowl.
>
> Charlie

Interesting, but what about cooling drag? Right now I have way more
cooling than I need. I was hoping to reduce cooling drag by closing off
those exits - potentially with the few inches of the cone removable for
hot summer days.

Finn

This is all very interesting.  On the rev-1 version, I was planning to try to use the cheek extension area as the only air exit, because it looked to me to be the lowest pressure area.  Traditionally, the bottom of the cowl is used, but I can't believe that's a low pressure area.  The top of the fuselage would get into high pressure due to the front of the canopy, not to mention the ramifications of an oil or water leak.  To me, the sides of the fuselage seem to be the natural choice for air exit. 

This did work, but only to a point.  I found that I had too much cooling with the bottom, and cheeks open, so I blocked off the bottom opening.  That would have been much better in cruise, but was too little for climb.   The new cheek exits are noticeably smaller than the old ones, so I'm sure it wouldn't work as the only exit.   Of course I also have a muffler coming out the bottom now, so I don't have the option to close that off anyway.   It would have been easy to block off the cheeks on the old cowl, since I already had those bulkheads, but for some reason, I never tried it.   

I'm also interested in the drag penalty for leaving the cowl cheeks open.  I don't mind the look of the open cheeks (hold the proctologist jokes)  and they do allow for easy inspection of most of the engine.  For now, I'll be happy to leave them open for the extra cooling, and inspections ability, but once I start cleaning up the airframe, they'll have to get closed and faired if they're causing me any significant drag.  

Do we have any aerodynamics folks who could comment on this (in plain English <g>) ?