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Mark,
Since you have not gotten to the muffler part of your
design, here are some thoughts (Yes, I did do 6 muffler experiments - don't ask
me why)
The one design that was "almost" totally successful
in achieving my goals is attached. Hard to make out the details, but
enough to give you the general ideal.
My objective was trying to decided how to muffler the
shock wave (which creates most of the ear problems) but let the exhaust gas flow
freely. My conclusion was that reactive design muffler was the only
acceptable choice given our constraints.
What I came up with was the idea of stuffing (I put
five but I think three would make a considerable difference) disc with outer
parts cut into blades and bent at a 45 deg angle into a tube. Looked a bit
like an old farm windmill.
The idea behind this approach was if you looked
head on at the fan-disc - you see basically a solid metal front. That is
what the shock wave would see and most (a lot?) of the energy would be reflected
back toward the engine (actually to the next disc in the tube). The bent
blades on the other hand would permit exhaust gas to flow with minimum
restriction.
It really did deaden the sound where folks could stand by
the wing tip with no problem hearing someone else talk. I was
thrilled. It also met my minimum restriction as I could still get my
6000 rpm static.
Ok, what went wrong - well, not being a welder I resorted
to other methods - which ultimately failed.
Two things occurred -
one if the disc broke loose of the small 5/8" thread SS
shaft from the Jam nuts on each side holding the disc, well, the disc could (and
did) begin to spin inside the tube like the turbine wheel of a jet
engine. This windmilling effect acted just like a windmilling prop on the
exhaust gas and definitely impeded gas flow. So can not permit the disc to
spin (the tips polished the inside of the tube where the spun)
Second because I donot weld, I did not secure the
tips of the blades of the disc to the sides of the tube. Well the shock
wave naturally causes those blades to flex and eventually break
off.
The SS disc were 2" in diam 1/8 thick and fit really
nice inside the 2 1/4" tubes. I cut slots in the outer part of the
SS disc and then used pliers to bend the tabs to an approx 45 deg angle
(see attached Jep).
So none of this was difficult to fabricate (tedious
perhaps but not difficult).
I gave up on it because without welding skills I could not
figure out away to secure the tips of the blades to the tube to give them better
support. Perhaps better than disc would have been cones but couldn't find
any {:>).
So since I couldn't see any way around my lack of welding
(and too cheap to hire someone), I went the hushpower II
route.
Just thought I would throw some fuel on your fire
{:>)
FWIW
Ed
Sent: Wednesday, December 01, 2010 2:09 PM
Subject: [FlyRotary] Re: Modified header
Calculations
"That PPort sounds angry!"
...and it is! ;-)
Mark
On Wed, Dec 1, 2010 at 1:02 PM, Bill Bradburry <bbradburry@bellsouth.net>
wrote:
Mark,
I watched the video
as you started up in front of Chris’ hangar and taxied away. I then went
back and watched the video where you made the flight 2 years ago. The
difference in the sound is way more than just volume! That PPort sounds
angry!
Bill
B
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mark Steitle
Sent: Wednesday, December 01, 2010 12:44
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Re: Modified header Calculations
Not sure what you're asking. My p-port will idle
down to below 1000 rpm, although not as smoothly as my side port 20B did, or
like my LS1 Chevy V-8. This thread was addressing WOT issues caused
by an overly restrictive exhaust system. Changing to my previous
"tangential" exhaust made a HUGH improvement in WOT power (exactly
as the chart that Ed posted earlier showed). I am now in the
process of building an equal-length header/exhaust to maximize power at
around 6500 rpm. The runners on my current exhasut are not
all the same length and are made from 2.0 DIA .140"
304SS. The new exhasut will be made of 625
inconel.
I hope to get it right this
time.
On Wed, Dec 1, 2010 at 11:23 AM, <wrjjrs@aol.com>
wrote:
Mark, and group,
If p-ports are so difficult why
was the first car with a rotary equiped with them? P ports can be fairly tame
if you put the throttle plate, (butterfly or slide), close to the port, or in
the port. The original powersport guys put together an in-port butterfly that
idled very well. In fact Steve Beckham told me that when using their
pendrolous damper they could idle their p-port engine at 1000 RPM! Their
p-ports were 1-5/8 diameter.
Bill Jepson
Finally, I liked
their comment regarding the peripheral ported engines. It
reads, "Traditionally relegated to speciality race cars, occasionally a
peripherally ported engine finds its way onto the street in some
high-performance vehicle. These engines are not, however, for the faint of
heart." LOL Not to worry, my heart is
strong!
Mark
-----Original Message-----
From: Mark Steitle
<msteitle@gmail.com>
To: Rotary motors in aircraft
<flyrotary@lancaironline.net>
Sent: Wed, Dec 1, 2010
8:37 am
Subject: [FlyRotary] Re: Modified header
Calculations
Ed,
It took a while, but my copy
of Street Rotary - How to Build Maximum Horsepower & Reliability
into Mazda's 12A, 13B & Renesis Engines finally arrived
yesterday. Thanks for the recommendation. Lots of good info,
everyone on the list ought to order a copy and read it from cover to cover,
except for Lynn H. - he ought to write his own book on rotary
engines. (I'd buy the first copy.)
As you suggested,
I've been reading the chapter on exhaust systems. I found a paragraph
that is right on target relating to what we've been discussing (exhaust system
restriction). They compare a 2-rotor wankel to a 2 cylinder
4-stroke where both cylinders share the same exhaust
port.
Quote, "...the exhaust system on a 12A or 13B rotary
engine is roughly analogous to a two-cylinder piston engine in which both
cylinders are served by a single exhaust port. If cylinder #1 was in
overlap period, and the exhaust valve of the #2 cylinder then opened, high
pressure gas would flow from the #2 to #1 cylinders. A highly
restrictive exhaust system would aggravate the situation. This, the
authors point out, is the major reason why a free-flowing exhaust system is so
important in a rotary engine." This explains why I saw such an
improvement when switching exhaust systems.
There is also
much discussion on primary header length. Disregarding the "long" header
system as we don't have the room, the "short" header length shown for a p-port
engine is between 10 and 18 inches. So, your calculations for header
length seem to be right in the ballpark. Now I have to figure how to get
the three very short primary tubes of 11 3/4" to meet on the same tangent
at the collector.
Finally, I liked their
comment regarding the peripheral ported engines. It
reads, "Traditionally relegated to speciality race cars, occasionally a
peripherally ported engine finds its way onto the street in some
high-performance vehicle. These engines are not, however, for the faint of
heart." LOL Not to worry, my heart is
strong!
Mark
On Sun, Nov 21, 2010 at 7:53
AM, Ed Anderson <eanderson@carolina.rr.com>
wrote:
Mark,
I did some additional reading in the
rotary book I recommended to you and a bit more head scratching on exhaust
systems.
I modified the tube length formula I used
earlier to compensate for the fact the rotary puts out two exhaust pulses per
port per 720 deg cycle compared to 1 for the piston engine. This in
effect halved the length of tube needed to get the same scavenging
effect.
Also using the recommended rotary book values for
area of a rotary exhaust tube , I calculated the tube diameter which came
out to 1.8".
In any case, I have attached the spreadsheet
with those modifications
Ed
Edward L.
Anderson
Anderson Electronic Enterprises LLC
305 Reefton
Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com
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