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Date: Tue, 19 Apr 2005 11:17:47 -0400
From: echristley@nc.rr.com
Subject: Re: Air filters
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Jerry,

I've been thinking about your intake.  I think it is actually and excellent design, and there is only one thing I would do differently. Angle the back forward just a couple of degrees and provide a narrow exit slot on the bottom rear.  As the air enters, heavy stuff will get slammed against the back wall by centrifugal force.  A cutout on the bottom will let the dirt pass right through, and the filter will rarely need servicing.  

It will decrease the pressure in the plenum slightly, but even a 1/16" slot will let all but the largest grit through. (Can it still be called grit if it is larger than 1/16"?)  What's more, the bypass air doesn't have to be wasted.  Use it for blast air across your fuel line or down across the exhaust header to remove that heat from under the cowl. 

I think the way you have the conical filter in the housing will provide a lot of benefits.  As the air comes in and has to circulate around the bottom of the box, the bottom of the filter will get dirty first and slowly fill upward.  The higher the dirt gets, the harder it will be to fight gravity to get to the next level.  I'm thinking a little attention to a manifold pressure gauge would show a very gradual but front loaded drop in pressure as the filter fills up.  That is, the biggest drop will happen early on and then the drop off will moderate.

Overall, I think you have laid out a very effective setup.