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Date: Wed, 07 Mar 2012 21:26:25 -0500
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Turbo charger setup
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On 03/07/2012 06:51 PM, Patrick wrote:
> I'm planning to use a turbo on a 20B, primarily as a muffler, but 
> would like to set it for 3-5 psi boost.
> A lot of current techniques are based on street car experience, which 
> are not always directly applicable to airplanes, ie. no need for rapid 
> throttle response (usually) and run at high % power continuously.
>
> I'm thinking of a setup modeling refrigeration techniques:
>
>  * Run all exhaust through turbo, no waste-gate, larger A/R
>  * Compress higher than needed, which makes air very hot
>  * Run through intercooler, which is more efficient with higher temp 
> delta
>  * Allow to expand using larger pipe and blow-off valve to regulate
>    pressure before intake
>
> The result "should be" cooler intake air at a slight boost.
>
> What am I missing?
>
The energy cost of compressing all that air and then throwing it away?  
Though,  like Tracy has said, pressurized air is hard to get on an 
airplane.  It wouldn't be so bad if you could use it for something.  The 
two things that spring to my mind are:
1) engine cooling: blow it through a radiator.  The drawback is that 
you'll want more boost on climbout, and that is when you'd want the 
extra air through the radiator.
2) exhaust cooling/thrust: push the extra cool air into/around the 
exhaust.  As I understand it, rotary mufflers die quickly because of a 
combination of heat and sonic pounding.  Cooling it will reduce both, 
and if there might be a slight amount of thrust available if everything 
is set up just right.