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Date: Thu, 17 Aug 2006 20:25:38 -0600
From: Bob White <rlwhite@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Alternate Air
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On Thu, 17 Aug 2006 20:53:27 -0500
"Russell Duffy" <russell.duffy@gmail.com> wrote:

> So the question is, do most of you have an alternate air source in your
> intake system? Did the FAA inspector or DAR specifically look for it?
> 
>  
> Hi Bob,
>  
> This is a pretty timely question, since I'm working on this decision for the
> RV-8.  First, I've never had alt air on any of the planes I've built, and I
> don't think there's any chance my DAR would give me a hard time for not
> installing it now.  Van's didn't even make any provision for it until just a
> year or so ago, when they came out with an alt air mod, then a new mod
> because the first one didn't work so well. 
>  
> On one hand, I am thinking that I've never had it, and don't need it now.
> On the other hand,  I can easily see how it could be needed.  Van finally
> added it after at least a couple RV's went down due to freezing rain, or
> snow blocking up the air filter.  Even in the RV's with carb heat, there
> isn't enough heat generated by the crappy factory system to melt the
> blockage, particularly if you're late applying it. 
>  
> Bottom line is that I think it's a good idea if you have a filtered system
> fed by a ram air scoop.  
>  
> Cheers,
> Rusty 
> 
> 
Hi Rusty,

I found a method of supplying alternate air that is almost pain free.
In my case using it moves my air filter to about 1/2 inch from the
prop, but it's automatic, and doesn't present much of a restriction
when not using alternate air.  I might look for a shorter filter.  See
the AEM air bypass valve in the Summit catalog: http://tinyurl.com/luoea

I'm not sure how much air it flows in bypass mode but may find out one
of these days. If I put alternate air in, this is what I will use.

Bob W.