Ken Powell wrote:

Tracy,
This is our chance to find out if a 31" to 32" long exhaust
really will increase power.  The only downside that I see is
that the muffler might still be in the cowl (almost right under
your feet) so you might loose some of the benefits of cooler
under-cowl temps.

How loud was the tempoary system?

Ken Powell

Finn Lassen wrote:

Ken, please refresh my memory on tuned exhaust systems. Optimum length
from port to Y-joint and then length thereafter (if it matters).

Finn

Ken Powell wrote:

Finn,
I do not know how to make these calcs and readily admit that the
theory of all this is beyond my abilities, but optimal lengths
for 5000 - 6000 RPM are said to be ~31" or ~72".  Other lengths
(longer) have been given (108"??) but I didn't make a note of
them due to the limitations of aircraft use.  If I have this
wrong, would someone please correct the data.  I would interprete
these lengths as from the face of the rotor.  Note that Paul's
chart is for a 500cc rotor, not for a 13B of ~625cc.  What I
found revealing in Tracy's latest findings is that there did not
appear to be appreciable drag in the hanging the muffler out in
the breeze.  Anyway, what I picture for an exhaust are two (2)
31" pipes of 1.75" ID being 'y'ed' together into a 4" collector,
then a muffler on the end of the collector.  Read Paul Yaw's
excellent explanation on exhausts on his Web Page.  Note that the
tuning of the pipe ends when the pipe opens into a larger area,
for this is when the reverse pressure wave is generated.

Ken Powell 

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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