Ed Anderson wrote:

Well,
    In keeping with the muffler topic, I would like to add what happened
today to my two SS, holey fishtails tail pipes on my turbo 13B block.

  My pipes are each 15" long with 12" of 5/16" dia holes (40 holes in all
for each pipe).  Originally I had squeezed the end into a fishtail with a
1/2" open slot.

   Well the noise was still ear shattering at full throttle, so after
hearing from Finn that he lowered his noise level by squeezing the slot of
the fishtail smaller, I decided to do the same.  I squeezed the end of each
tube down to approx 1/8".  During ground runup, the harshness of the exhaust
bark did decrease and RPM stayed up.

 So today after flying for 45 minutes to check out whether my new oil vent
for the gearbox would stop the oil leaks (it apparently did - no oil on
canopy) , I landed.
Checking under the belly for oil, I was shocked to find that the fishtail
ends of the two 2" SS tail pipes had cracked on each side.  In one case the
crack was 2 3/4" long up the side and then turned 90 degrees across the tube
for another inch.  Both fishtails had these cracks and the slot had been
enlarged back to almost 1/2" by the power of the exhaust pulse.  I have
taken some photos and will post them when I get the roll developed.

 Even after Tracy's incident with his frayed muffler ends, I was confident
that the stronger structure of the 2" tube would withstand the turbo shock.
I probably weakened the tube to some extend along the side area where I
squeezed and pounded the fishtails into shape.  But, even then it was
surprising to find the ends cracked like that.

 Someone suggested (I think Bruce Turrentine) that something needs to be
inserted into the end of the header to function similar to the exhaust port
splitter.  I certainly agree that something is needed to break up the shock
wave.  Sure is a powerful critter.

Ed Anderson

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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