I am planning on using the turbine of a turbo to spin a generator. I want the 
muffler action. I don't want the added weight/drag of the "Turbo setup" which 
can be quite large when factoring in all the components. 

I plan to do most of my flying below 10k so it doesn't make sense to have the 
boosted air. On the other hand - having electronic engine control and electronic 
flying instruments electricity is becoming increasing important to me at all 
flight regimes.

What I fly for a living has a similar electrical demand - so there are two 
primary generators and a third powered off an APU, just in case. But those only 
provide electricity to the instruments and mission equipment. The engines have 
small alternators on them for providing primary power to the engine control 
units. Redundancy is the name of the game.

So my plan right now is to have an alternator providing power to the EC3 and 
EM3. and then a generator providing power to the glass cockpit and avionics. of 
course the two will be redundant to each other. 

Then for full redundancy - the glass cockpit has their own backup battery and 
the airframe battery provides backup for the engine control and monitoring. 

I am still very early in the process though - but I believe there is a lot of 
energy to harness out of the exhaust of the rotary. But as you mentioned there 
is something to be said for the muffler action being harnessed for something 
useful.

 Your plan though seems to work in theory - I would probably use that as a Turbo 
Normalized setup though.

Mark


On Mar 7, 2012, at 6:26 PM, Ernest Christley wrote:

> 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.
> 
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