snipss...

Doug,

I would suggest you start from scratch on the turbine. As Monty has

pointed

out, this will be far more likely to to bear fruit. There are at

least three

persons/firms making small production runs of vaccuum cast superalloy
turbine blisks for the model gas turbine world. The standard 66mm

turbine

for most model engines costs about $120. Join the gas turbine

builders

association or the yahoo group
http://groups.yahoo.com/group/homebuildturbines/

I suspect that automotive turbo's survive the high EGT's because they

are

only exposed to a relatively small mass flow and therefore low heat

flow.

They are able to reject this heat flow fast enough. As you up the

duty

cycle, although the EGT is not increasing,  you are flowing more heat

than

the turbine can reject. Thus the need for Inconel or superalloy

(MAR-M,

RENE... etc). The combination of Wankel EGT's, a high duty cycle, and

manned

aircraft expected TBO and reliablity may well exceed the material
capabilities of the super alloys and drive you to a cooled turbine

(thus

ending the project). Gas turbine engines only combust a fraction of

the

cycle air, and cool the cumbustion products significantly before they

are

passed across the first stage nozzle. We are not afforded that

luxury.

Replacing the shaft on an off the shelf turbo is not trivial. The

turbine

wheel is normally shrunk onto the shaft, and it's removal damages the

wheel.

Calculate the energy stored in a heavy radial inflow turbine at

100000 rpm,

and the velocity/ inertia of the parts if it lets go as two even

parts. Bad

idea using a damaged turbine.

For a given mass flow and fresh gas temperature (which you have) ,

you have

a single optimum nozzle throat area. Work out what that is and you

can play

around with the turbine diameter and blade length. Too large a

diameter and

the blades are too short and the tip losses dominate, too small and

RPM is

excessive.

If you design to a single point, you will still have to go through a

few

iterations to optimise it, and that will be at your test altitude.

For your design point I would see if Tracy could provide the

following:

At sea level, 65% RPM, the OAT, density, fuel mass flow, and air flow

ratio.

With this you can work out your mass airflow, and thus the HP the

turbine

delivers. You can then optimise the trade off between increasing

turbine

diameter simplifying it's design (and increasing it's cost) or higher

speed

gearbox (with higher cost).

Why not separate the tasks and use an aircraft turbo, and an axial

flow free

power turbine?

Regards,
Mark Wrathall

Thanks Mark

Yes you certainly have a good point.  At least on the bench test it

makes a

lot of sense to use two turbos.  It would speed up the testing a give us
some target data to shoot for. lt certainly makes turbo rpm balancing a
little easier because it is a simpler act of controlling the intake

throttle

valves. The response won't be very quick but for dialing in the economy
cruise rpms is doesn't have to be. In application it gives us an ability

to

send the kinetic exhaust energy to the boost turbine or power turbine or
combination thereof.

Eventually we will have to go to an aircraft turbo or turbos? and they

will

need some special order parts for the power turbine side. That phase of

the

program is down the road a bit.  Before designing any new equipment and
(thanks for the tip on the turbine club) I need to have a through
understanding of what is happening with some standard equipment. I am

still

a complete greenhorn when it comes to turbos.  Paul seemed to have
identified an old/new compressor Paxton that may be a good starting

point

for the  power turbine side of it.  I have to study it. Since we are

still

in the bench test mode I am interested in looking anywhere for ideas. I
appreciate yours. And also Daniel's . I did look into the Tesla turbine
concept early on.  Vance said it well about skin friction. My concern

was

more about accumulating particulate matter from the waste stream. I do

share

Vance's admiration for Tesla as well. The significance of this great
inventor's work have yet to be fully discovered.

For those of you already flying rotaries please wait until I can get

some

hard data on what is happening. This idea  is going to be a show stopper

for

my own plane and purposes unless I do one or all of the following;

1. Simplify the components
2. Make the components have multi-functions
3. Go with a smaller higher performing powerplant.
4. Find other ways to lighten the planes gross weight. ("Sorry honey, no
baggage and BTW we are going to have to fly in our underwear")

Two turbos are  heavy but then again so are the magnetic or mechanical
clutches, a toroid CVT, or planetary gear sets with one turbo.

For the two turbo bench test delivering power to the rear of the engine
gives us the advantage of replacing the heavy steel flywheel with an
aluminum toothed wheel thus giving us at least 10:1 reduction from the

power

turbine. In this configuration we need  a larger  exhaust manifold with

twin

valves (of undetermined design at the present)  on which two turbos will

be

directly connected. Exhaust can be separate or go to a common outlet.

I am now communicating with these people.

http://www.land-and-sea.com/dyno/dyno-price.html

"Dynamometer package contains components for testing many automotive

engines

up to 800 Hp.* Includes: shaft mount 13î toroid water brake absorber,

strain

gauge equipped torque arm, DYNOmite Pro data acquisition computer,

manual

load valve, full function data acquisition wiring harness, mobile engine
stand, bell-housing adapter plate, 1-3/8î x 10 splined clutch

input-shaft,

mounting hardware, stainless braided hoses with aircraft fittings, and
instruction manual."  Cost about $10,000.

All I really need is the water brake absorber, strain gauge equipped

torque

arm and their software.  Don't know if they will sell just those.  If

not I

would appreciate anyone's' advise on how to make or  purchase the first

two

items.  I already have the stand finished and am now upgrading an old
computer to run Windows XP.  And yes Paul it will  run Rhino as well:)

The cart when complete will have rain proofed sound deadening  panels
installed. With a forklift we can put the whole unit on a small truck

and

take it anywhere to demonstrate.

Doug in Japan

Doug, do you have access to a well equipped machine shop? At the very least,
you are planning to replace the shaft in a standard turbo-charger with a
longer shaft (which is not a good idea as detailed above). Can you machine
to a tenth or two? If you are equipped to make this shaft, then you are
probably equiped to make your own design from scratch.

Take a look at the Swedes write up of making his model turbo prop to get a
feel for the machining required of a free power turbine and high ratio
reduction drive.
http://www.5bears.com/tprop.htm

Ragrds,
Mark.

No shaft replacement required. The torque through a coupling is 2 foot pounds
or less. Why make a new shaft when all is needed is a coupling? I am all for 
making a new custom turbine but the optimum design is far from
my capabilities. Since the efficiency of radial inflow turbine (turbo charger turbine)
is currently 70% or better over a fair range  I think it would be hardly worth the 
cost and extra weight to build a axial flow turbine. You might at best achieve another 
10% turbine efficiency. Why reinvent the wheel when there are so many out there to 
choose from.

BTW  Scania apparently thought axial flow turbines were not worth the expense although they
did use a separate power turbine. They did not however use a CVT which is a large
difference in matching the power out of the turbo charger to a form the e-shaft
can accept. Even if the CVT is only used as a quick way to determine the best 
point design gearing for aircraft use. What Scania also had to deal with was the 
smoke limit. See the attached front page of a IMECH technical paper on the subject. 
They could not let the turbo charger section be bogged down by the power section. 
That would cause black smoke. I have addressed that by incorporating a disengagement 
clutch. The purposes of the clutch is to disengage the power out of the turbocharger 
during acceleration to allow the turbocharger to spool up unimpeded. In fact when 
combined with an electric assisted turbo and computer control of the clutch 
and CVT lots of flexibility is afforded to deal with any transient modes.
In the mean time we don't need computer control as we can control both the
clutch and the CVT ratio manually for test purposes.

Paul Lamar
 
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