You could just try duct taping a bent tab at the leading edge of the hole to act as a deflector and create low pressure at the hole. Then go fly it again. Quick and dirty.

 

 Wait a minute! Who am I to give advice to the master of all things rotary?

 

Mike Wills

RV-4 N144MW 

----- Original Message -----

From: Tracy Crook

To: Rotary motors in aircraft

Sent: Friday, September 18, 2009 5:00 PM

Subject: [FlyRotary] Re: Re RV-8 cooling test

Because it looked easy to modify the bottom cowl outlet on the RV-8 to a cowl flap configuration I decided to try that before installing some louvers in the same area.  Attached is a picture of the cowl after I cut out the area that would form the bottom of cowl flap. 

Couldn't resist the urge to test fly the plane with that big gaping hole in the bottom.   I was thinking that it would show if it was the small size of the stock opening that was causing the problem or if aerodynamic factors dominated.

The 'big hole' outlet ran about 10 degrees cooler than stock which was not nearly the improvement I'm looking for so I can't believe that the louvers would work in this location.  Back to working on the cowl flap in the hopes that the low pressure area behind it will extract a lot more air.   I don't have a warm fuzzy about it though.   After this (if it doesn't work) I'll try a bluff body extractor vent as described by some CAFE Foundation reports.

Just as a point of reference, I have about 35 sq in of inlet area and 52 inches of outlet area with the stock cooling outlet.   Now I know that the inlet area is more than large enough (from the cowl off flight test) and the 52 sq In outlet should be enough but I think the pressure is too high under the fuselage where the outlet is.

Tracy

On Thu, Sep 17, 2009 at 6:13 PM, <SHIPCHIEF@aol.com> wrote:

Thanks for that.
I'm making my radiator chin scoop right now.
I made a 'buck' out of 2 part pour foam, then cut & sanded to shape. After laying up the part, and removing it, I began to remove the edges. Good thing I made it too deep. Now you guys have revisited the Exit/Inlet relationship issue.
A little time with a ruler, some quick math, and some trimming is leading me right to the reccomended 30% bigger exit area than inlet area for the radiator. I was going to use Van's original exit, but now I'm adding about 1/2" more depth.
My oil cooler exit area is really over sized. It is kept separate. The right cowl inlet is ducted to the oil cooler, then exhausted straight out the right side thru louvers.
The left cowl inlet has not been made yet. It will feed air to the turbocharger and provide surface cooling air for the exhaust system and fuel injectors. If that chokes the air exit at the bottom, I'll have to make a left side hot air exit as well.
Tracy, your comment about overheated coils and alternator has me thinking about blast tubes?
Scott

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