David Carter wrote:

Paul,

I just printed your essay on turbo-compounding that I found on the ACRE
website.

All I have ever considered as the purpose and mechanism of turbocharging
and supercharging is to increase manifold pressure, which can do either
or both of two things:   Increase maximum power and/or "normalize"
(maintain manifold pressure and normal cruise power at higher than
normal altitude).

The talk about turbo-compounding goes beyond that, to "lowering BFSC".
This is new to me, so I have a couple of questions, to begin the process
of expanding my understanding:

Turbo-compounding:  Is the key concept here that a turbocharger feeds
compressed air into a geared supercharger, giving higher boost than
either alone could provide?  B-36's pulled 72 inches of manifold
pressure on takeoff.  Were they turbo-compounds?  P-51s only pulled 60
or so, if I remember correctly - they definitely were not "compound".

If one focuses on lowering BFSC, as opposed to "increasing hp", and if
"turbo-compounding" is just putting the turbo in series with the
supercharger (assumes answer to previous question is "yes"), then what
is the basic relationship or mechanism that lowers BFSC at cruise power
settings?

About half way through your essay, you said, "My compound setup for the
rotary would use one Inconel blow down turbine feeding power into the
eccentric shaft and an optional centrifugal blower . . ."
        -  What is a "blow down turbine"?
        -  How would it "feed... power into the eccentric shaft"?

David Carter

In the rotary more than one third of the energy in a gallon of gas
goes out the exhaust pipe in the form of waste energy. What a blow down
turbine does is feed some of this energy back into the ecentric shaft
through
a gear box. In my web site drawings both a gear box and a belt are used.

Neither the P51 nor the B36 used turbo compounding. Only those airplanes
using the Wright R3350 TC (TC for Turbo Compound) used turbo
compounding.
Among these were certain models of the Constellation and the P2V Navy 
anti-sub patrol plane among others. There is a picture on the web site
of
a cut-away of a R3350 TC.

Paul Lamar
 
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