Received-SPF: softfail
 receiver=logan.com; client-ip=171.68.10.87; envelope-from=echristley@nc.rr.com
Message-ID: <43F372CD.3030108@nc.rr.com>
Date: Wed, 15 Feb 2006 13:28:29 -0500
From: Ernest Christley <echristley@nc.rr.com>
Reply-To: echristley@nc.rr.com
User-Agent: Mozilla Thunderbird 1.0.7-1.4.1 (X11/20050929)
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: Airfilters
References: <list-986034@logan.com>
In-Reply-To: <list-986034@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Tracy Crook wrote:

> If we were talking about an automotive application I agree that it 
> would be folly to run sans-airfilter.  And I qualify my non 
> filtered operation with the proviso that you must use care when 
> taxiing under certain conditions.   The air is a lot cleaner as soon 
> as you slip the surly bonds.   Flying or taxiing through a sand storm 
> would of course be disastrous without an air filter.
>  
> Only one sample but my first engine (a well used 88 2nd gen) showed 
> no measurable wear (compared to when first installed) to rotor 
> grooves, rotor housings, side housings, or side seals after 856 flight 
> hours.  The apex seals had a maximum of .012" of wear measured at 
> height of seal.  This is the least wear I have seen when disassembling 
> a used engine.  I've torn down about 12 so far, all used on cars 
> except for mine, not a big sample.
>  
> Tracy

That's good data, Tracy, and Bill presents a good argument for not 
needing a filter, but isn't it akin to unprotected promiscous sex.  You 
get away with it...most of the time.  I would balance the argument 
against the question, "How much speed will you lose on the top end from 
a 1" drop in MP?"  Possibly, some of the lost speed will be regained 
from less cooling drag from not producing as much power, but those 
numbers are most likely dropping off into the pitifully insignificant.

At the least, consider a centrifugal filter, which should be relatively 
easy to fit in most installations.  Bring in a 4" duct with a large 
sweeping curve.  Pick up the intake air on the inside of the curve with 
a 3" duct.  Let the rest blow across the coils or into the alternater.  
Heavier than air stuff (ie., sand particles) get thrown to the outside.  
These are just conceptual numbers.  An effective cleaner would need a 
little bit more analysis.  I don't think it cleans as well as a paper 
filter, but it doesn't produce nearly as much of a restriction and it 
will clean out the big junk that is likely to chip an apex seal.

-- 
         ,|"|"|,               Ernest Christley     |
----===<{{(oQo)}}>===----     Dyke Delta Builder    |
        o|  d  |o          www.ernest.isa-geek.org  |