flyrotary@lancaironline.net Mailing List Archive

John, I agree,

the way your cowl looks, it does not make sense (to me....) to reduce the intake size the way you indicate.

If you were to reduce the intake from the outside in, including narrowing the cowl, then discuss the size.

As is, might as well use it, the frontal area is the same, whether it is open or closed off.

Thomas

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

From: Ed Anderson

To: Rotary motors in aircraft

Sent: Thursday, March 01, 2007 9:53 AM

Subject: [FlyRotary] Re: diffusers

John, I would go with the 22 1/4 sq inches. For these reasons:

1. Your engine may produce more power than the one I run with - requiring more heat rejection.

2. It is easier to neck down the opening (than widen it) if it turns out you have more than what is necessary - or do nothing

3. My cowl exit area is probably a bit larger than most which may produce less back pressure enabling smaller opening to flow more air.

Ball up your fist and see if you can stick it through the narrowest opening - it should just almost go (that is if you have the same size hands I do {:>)) How's that for a standard of measure?

Ed

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

From: John Downing

To: Rotary motors in aircraft

Sent: Thursday, March 01, 2007 9:39 AM

Subject: [FlyRotary] diffusers

Ed, If I add the extension, indicated with cardboard w/lines, I have the original 22 1/4 sq. in's. If I block off the cowl openings to match the diffuser, I will have 18 7/8 sq. inches. The neck at the smallest point is approximately 15 sq. inches as close as I can determine by my barn door math. Which is the better way to go, opening wise, the larger or the smaller opening. If these numbers are in the ball park, I'll lay up the glass. Thankyou JohnD

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