> Easy question, lazy questioner.
>
> What is the minimum radius of exhaust bend that won't effect tuning?
>
> Decker, Michael
>
>
> Good question. I don't know the answer. Most people using tubing
> bends which are about 2.5 inch center line radius minimum as I recall.
>
> http://www.burnsstainless.com/321tubing/Ubends321/ubends321.html
>
> The stock manifolds are sharper bends. Particularly the turbo manifolds.
>
> -- > Paul Lamar ...No rotor no motor.
>
>
> STRAIGHT.  Anything resistance whatsoever in the exhaust flow will
> affect tuning. In fact, putting even a straight tube will affect tuning,
> compared to just letting it blast out unconfined.
>
> However, the Wankel gives a much smoother exhaust flow in the first
> place, so there's room to play.  You might make a water stack and try
> some flex tubing and see where you start getting some back pressure.
>
> I think the reason for the 2.5 bends is that the benders most people use
> were made for thicker steel pipe, and 2.5 is about as small as those are
> bent.  If they need a tighter bend, they just use an elbow.
>
> Keith W
>
>
>
>
> I agree that straight headers would be the ideal, but I don't know that
> I agree that, "blast out" is better.  My understanding is that for ideal
> tuning you are trying to set up a situation where the exhaust reaches
> ambient air just slightly before the valve opens to give another exhaust
> pulse.  This creates a pull that helps the exhaust stroke out.
>
> For 5400 RPM at 3 pulses/shaft rotation? 16200 pulses/min=270/sec
> Speed of sound @ 1080fps/270pps=4ft. Answer is ft./pulse.
>
> So if I have my pulses/RPM right then ideally one would need just short
> of 4 feet to set up the tune.
>
> Be gentle folks.
>
> Decker, Michael
>
> Michael,
> You have to change the pulses per rotor to 1 pulse per shaft rev
> (remember,
> the rotor turns at 1/3 shaft speed).
> Tuning rotary exhaust in an aircraft could be difficult. Years ago, we
> played with different lengths of primary tubes before the collector, and
> the
> best setup had the collector just in front of the rear axle on a RX3.
> Not
> going to fit in any cowl that I know of.
> Larry
>
>
>
> So the real answer to my hypothetical is 12ft.?  I agree, that wouldn't
> fit in a cowl.
>
> Decker, Michael
>
>
> These things tend to repeat at harmonics. Also the speed of sound varies
> with
> the temperature of the exhaust gases.
>
> Everett Hatch felt that 32 inches was a good compromise for 6000 RPM.
> I also think Racing Beat built a bunch at 32 inches as I recall.
> We used the RB header when we tested the p-port engine on the dyno.
>
> Here is a picture.
>
> -- > Paul Lamar ...No rotor no motor.

Paul--you use the magic word in your short note...."compromise."  In that
regard, here is a little background in that regard about our engine and

the

exhaust shown in your photos....this was the prototype Mazda conversion
engine installed in the RV-4 that I flew it toOshkosh in 1995.  We took it
out and it went in Alan's RV-3 for Sun'n Fun and we put it back in the

RV-4

for 1997.  The routing of the exhaust pipes shown in your photos here was
for the last installation back into the RV-4 in 1997.


This routing of the
pipes and length was driven by a combination of compromise installation
factors which included missing the engine mount tubes and running them
around various components such as the heat exhanger (it was at a 45 degree
angle between the engine and firewall), and then the pipes went down and

out

below the firewall to get the practically longest length.  We simply ended
the exhaust where it had to stop as result of the configuration and not

hang

out in the breeze.  This was the last configuration we tested on the RV-4.

Never did get it back on the dyno in this configuration but it

incorporated

the earlier lessons and configurations tested.  The pipes shown in your
photos terminated in a 7"augmenter mounted to a tunnel we fabricated
specifically for it in the floor of the RV-4 when we built the airplane.

The augmenter was used in early flight tests around 1989-90 but  removed
when we used a muffler. The augmenter worked well in flight tests during
climbs up to about 90 mph (good extraction) but started to simply get in

the

way increasingly at speeds above that.

The water heat exchanger was too
thick and we went to the thin exchangers on the RV-3 which worked much
better.  We put the augmenter back on the airframe for the exhaust
configuration shown in your photos because it was a handy way at the time

to

isolate the airframe from the exhaust pulses and basically for muffling

and

to alter the exhaust note.  The augmenter was light with a mesh metal

liner

with stainless and ceramic packing between it and the outer wall. Of

course

the exhaust blew out the packing over time.  But the augmenter did help
alter the exhaust volume and tone.

But it was a marginal at full song for
the long flight legs of 3.5 hrs.   This exhaust configuration shown in

your

photos included our first set of exhaust port/pipe swivels.  Dyno tests of
all our engines of this basic induction/exhaust configuration were very
sensitive to induction tuning but not so much so the exhaust tuning
regarding length.  As a general rule there it was the familiar old

chestnuts

of keeping the back pressure as low as practically possible and longest
pipes that fit around the engine and within the cowling and allowing for
muffer considerations.

Steve Beckham

Paul and Steve,
What do you recommend for material for an augmenter?  I plan on feeding it
with a muffler and use the length of the cowl for a somewhat rectangular
augmenter.  Is stainless required? Could I back it with fiberfrax?  This is
a pusher Long EZ type with the tube on top of the engine to take advanatage
of the length available.  Thanks for any help.

Joe Berki
Limo EZ

304 SS might work fine.