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Subject: [FlyRotary] Re: Area calcuation for Cone air filters was [FlyRotary] Re: Air filters

I’m just going to make my educated guess that for a minimal/neglible loss of pressure head you would want a filter element area of 10 to 15 times the required inlet area of the scoop. So the surface area that you have, Jerry, is getting into the ballpark. What is K&N’s criteria?

Ed, the surface area of the filter is much greater than its circumference x height due to the folding of the element. I just checked mine and each inch equals 4 inches if stretched out. Thus the surface area on my 5.5 in. round x 5 inch high filter would be over 300 sq. in. Jerry

On Monday, April 18, 2005, at 07:00 PM, Ed Anderson wrote:

Bill,

I did some research on the K&N site - they have a formula for determining filter area needed - the trouble is there is no correlation (I could find) between the area you calculate and the surface area of their filters. So I just did a rough calculation of their filters surface area based on small end - large end and length. On their double cone types I assume the inner cone is only 10% the area of their outer cone (which is probably very conservative). I used the 160 CID 4 stroke equivalent displacement area for the 13B and the below formula. Which gave me at 7000 rpm a minimum of 53 sq inches required.

Then I did the calculation using the attached spreadsheet to compare their different size filters for area - since they don't give it. Attached is the spreadsheet for using the below formula and the calculations for a truncated cone surface area.

Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting .75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area.

<image.tiff>

Ed A

----- Original Message -----
From: William
To: Rotary motors in aircraft
Sent: Monday, April 18, 2005 5:54 PM
Subject: [FlyRotary] Re: Air filters

If one looks at the K&N cone filters, how big a one is required?
Bill Schertz (really tight under my cowl)
KIS Cruiser # 4045

<affform1.gif><affform2.gif><Filter Size Cone.xls> Homepage: http://www.flyrotary.com/

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