Glenn Scherer wrote:

Paul, I don't know if you'll want to forward this to the list. It may
be a little too far out for useful debate. :)

Your comment the other day about a turbo compound rotary started the
rocks grinding together in my head, and I have a few thoughts and
questions on the subject that I'd like your opinion on.

As I understand it, the three common whines about the rotary engine
(high SFC, high exhaust temps and high exhaust noise) are all
byproducts of the rotary's lower thermal efficiency compared to modern
piston engines, it just doesn't do as good a job of extracting work
from it's combustion process. A good turbo compound rig should (in
theory, at least) kill all three of these birds with one well-aimed
stone.

Realizing that actually making something like this work in the real
world would be a huge engineering effort, I have some basic questions
that arise from a wild idea that occurred to me last night. The idea
is this: Could the impeller section be integrated with either the
driving or driven sections of a planetary gear PSRU? That is, could an
impeller be mounted either to the shaft driving the sun gear, or to
the driven gear?

The thing that I don't have a clear grasp of is how fast the impeller
needs to turn in order to efficiently capture work from the exhaust
flow. Turbochargers normally run at speeds up to 20K RPM. Is this
necessary in order to utilize the exhaust flow, or could meaningful
work be captured at the 2-6K RPM speeds of either the input or output
shafts of a PSRU?

If this kind of setup were possible, one could envision a "flywheel
back" package that would both provide useful prop RPM and pay for it's
weight by capturing wasted power.

I know this is *way* out in left field, but I'd really like to hear
your thoughts on it.

TIA, Glenn

I have been thinking about a turbo compound rotary for many
years. I spoke to David Cole about it at least 15 years ago.
NASA thought it was a good idea and recommended it. Nothing
ever came of the NASA recommendation.

Here is a concept I came up with a couple of years ago. I have many
drawings like this. Basically the way it works is there is a free 
turbine driven at it's rim by exhaust energy impinging on Inconel
blades. The exiting exhaust from the blow down turbine adds it's
remaining heat energy to the duct. 

The center of the turbine is an aux ducted fan that adds its energy to
that provided by the main ducted fan at the front of the engine. 

A two rotor is shown but it would work better with a three rotor
providing more HP. I recently figured out how to retract 
the nose  gear as well. There is much more to this if you are
interested.

The turbo compound  drawing on the web site is a more conventional 
approch where the blow down turbine energy  is fed through a gear
box back into the e-shaft. There is also a geared cent. supercharger
shown on that drawing.

Paul Lamar
 
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