X-Mozilla-Keys:                                                                                 
Jeff Spitzer wrote:

Here's an update for all those interested in the monolithic stainless
manifolds.

1) 13B design manifold:
I have a model I like and am quite sure is bullet proof.  Stresses are down
in the integer KSI throughout including thermal stresses while hanging and
shaking turbo .  The result of some calculations says the bolted joint at
the rotor housings *must* be allowed to move (due to differential thermal
growth) and that is also how the production ones work.  Don't worry, you
can't possibly tighten the bolts too tight and make it not move.  The
current weight is 4.8 lb and distance from housing to flange is 2.25 in.
So far I have 7 interested plus one for me.

2) A manifold for the 20B
While I was driving home last night it occurred to me that the same basic
design approach does work for the 20B as follows:  Two of the rotor
housings are spaced just like a 13B and that's where the turbo would mount,
just like the 13B manifold.  The 20B manifold simply needs another segment
with a wider opening on the turbo side.  This opening would be welded shut
with a simple piece of sheet stock.  This is easy enough to model (given
that I've already worked through the 13B issues) and I am pleased to
announce that signups for the 20B model start today.  As long as more than
a few people are interested the cost will not be horrible.  I really can't
say how much until I know how many.  It won't be over $1000.

3)  Running without a wastegate:
I did some modeling last night and found some good news and some bad news.
The T04 turbo with the H trim compressor looks just right for my stated
goals.  They are about 230 hp takeoff flat rated to 12,000 (13B).  Normal
cruise at about 140 hp at 10-12K.  More good news:  The turbine geometry
can remain constant (first order modeling) for those conditions (i.e. no
wastegate needed).  

Now for the bad news.  There is no T04 turbine housing
big enough to pass the required flow without some sort of bypass.  So,
options are: 

a) Add the wastegate simply to bypass the required amount, 
b) add a fixed area bypass and avoid the wastegate, 
c) add some sort of throttle plate somewhere in the system.  

The issues with option "a" are
well known.  I know why wastegates exist and know that they are good and
needed in auto applications and even in certain A/C applications. I just
don't want the weight, size, cost, maintenance, failure issues.  The
issues, if any, with option "b" need some more thought and modeling.  It
really doesn't sound like a bad way to go to me especially if the orifice
was replaceable and therefore (ground) adjustable.  

I really don't like
option "c" because it would negatively impact BSFC.  Again, more modeling
will give a better indication of how much but my first guess is that you
really have to throttle a bunch.  On the upside, it is in-flight adjustable
and is also a proven system.  For those who may be wondering the "throttle"
could be anywhere in the system from before compressor to after turbine.
More to come...with more and better modeling.

Jeff Spitzer

The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org