<large Snip>

Monty

Thanks again for the info. I think I'll pass on creating an axial

turbine

from scratch. It looks like you are describing part of a jet engine
compressor:) I don't plan to spend that type of money. Cost/performance

wise

radial turbines are fine for the research phase and perhaps for the
application phase as well. If not I will spend my effort on finding
something or modifying an existing product and accept the

consquences.BTW

and this is not directed at you only, but everyone is stating the fact

that

I have to pick a narrow range to operate the Power turbine in.  Please
define 'narrow range'.  Is a 40K-50K turbine speed narrow enough or do I
have to narrow it down to plus minus a few thousand?   I know on each

side

of the narrow range the operational efficiencies of the turbine will

drop

off but they don't go suddenly to zero.  Of course when an airfoil

stalls it

stops performing. By monitoring the turbo rpms and controlling load

torque

we prevent that from happening. I personally wouldn't mind nailing a
particular efficient sweet spot on the fuel burn /performance curve and
accepting the consequences of wandering away from it.  Like Paul says,

with

an efficient transfer device (a low friction CVT), we can let the

turbine

run in its sweetest range and broaden the engine rpms usable range. The

CVT

should transfer power at more than 90% effecientcy.  If the turbo itself

can

transfer 70% of the kinetic energy that passes through it in the range

we

want that is great news. Better 70% of something then 100% of nothing.

I work more like a Japanese researcher now I guess. 90% study and

planning

and 10% making it. Actually I'm a hybrid:)  I like personal contact. So

the

usual  spurts of wild ass ideas are tempered by long boring data

searches or

very inspiring  discussions with people like you. I have  found that

every

project I have worked on for the past 23 years, has been assisted in

some

way by someone  in the world who was working on a similar idea or part

of

the same idea. Before the Internet communication it took awhile to make
contact and I had to travel to a lot of conferences.  When possible I
networked with this people and together we create the item for mutual
benefit.

That is the main attraction of the this rotary mailing list. People are
sharing ideas.  I look forward to sharing some more of mine with you at
Tracy's. I am still going if my wings are still available.  So far my

plane

has survived one hurricane. I sure hope it gets through the next one.

Doug in Japan

There are at least two factors that determine the optimum range. The

amount

of exhaust pressure you have to work with and the RPM of the engine. As

the

power of the engine is increased at a given engine RPM the turbine RPM

will

increase. From the looks of the radial flow turbine charts I see in the

"book"

you get the highest efficiency out of the turbine when the flow velocity

is about

twice the blade velocity I think. You get more engine power at a given

engine RPM by

increasing the boost. A third factor is cruise altitude. Right at the

moment I don't

have a handle on the optimum situation so that is why we need a CVT in the

drive

but you know that. If you used a fixed gear ratio between turbine and the

engine

shaft it would be optimized for only one engine power level say 75% power

and one

turbine and engine RPM. That is what is meant by a point design or narrow

range.

R3350 TC was probably set up for one cruise power level and that was it.

You know all this. I am just rewording it.

Here are a few charts for the R3350 TC and an early 18 cylinder radial TC.
You can download Report No. 822 technical paper from the NACA technical

report server

web site.

Paul Lamar

Listers;
Check my thinking here.
Given that at any HP approxiamtly the same HP POTENTIAL is in the exhaust.
Assuming we can harness at most 50% net of the exhaust potential.
Then at the point we choose the net hp with the device active will be, again
approximately, the power % * 1.5
So if we pick, as Paul mentioned, 75% that becomes 112.5% power with the
device.

A device that gives 112.5% power at 75% fuel consumption would be
impressive.  Indeed the problem would be being laughed at for making the
claim.

My point is we do not need a perfect point.  Any point roughly between
50-100% power, if actually built and FLOWN, would be very big.
Actually building and flying it would teach us more than all the gedanken we
will ever do.

So why not just have a point design?
Typical point design is simple light and cheap compared to the wide band
(CVT).
What is the downside of a point design?

An aside to Paul et. al. regarding Paul's last restatement of what we know.

A third factor is cruise altitude.

If we assume a turbo charged installation, then the turbo should keep the
"exhaust pressure" or exhaust mass flow the same as altitude increases
within typical flight.
But even if it works at 2000 feet it will be an unheard of breakthrough.
So I ask do we really need to worry about altitude?  Should we not instead
plan for a second version to include the refinements we will learn from the
first version.  We will not get this right on the first try.
Eric Ruttan

BTW The big expense is not the CVT but the first stage gear reduction.
These tiny precision gears alone are somewhere btween $500 and $1000.

Paul Lamar
 
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