"Bass, Jerry" wrote:

I have run my Fishmouth extensions on high speed taxi and like them.

Each

extension is 4.5 inches long from a 2" dia pipe.  I wired the mouth

shut,

down to 1/4 inch.  and ran the engine at 5000 rpm on three runs, with

and

without the extensions.         The extensions quiet the roar some,

but do

not have a sound meter.
J.Bass

P.S., I have a Bose Series II headset to sell or buy. $700  I

eventually

will

need two for this noisy craft.

Ed Anderson wrote:

Jerry, I had the same experience with my fishtails.  My pipes were 15" long
with 30 5/16" dia holes in each pipe and the ends squeezed to first 1/2"
slots and then 1/8" slots.  With the 1/2" fishtail slots the fishtails lived
through 10 hours of flight.  I then squeeze them down to 1/8" slots and ran
it up on the ground and it did reduce the noise level.  However, I came back
after a 45 minute flight and both were shredded.

 I have made dual  48" long 2" dia pipes with 260 1/8" holes and have added
on a section of pipe to each end that I made into 1/8" fishtails.  At least
that way if the fishtails shred again I can just replace them rather than
cutting the ends off the pipe.  I hung them on the aircraft today and they
do make a considerable difference in the noise (still not likely to fall
asleep, but certainly quieter) and they did not appear to affect static rpm
which was 5600 rpm.

 I plan on flying again later this week and will see if they survive.

Best Regards

Ed Anderson

What wall thickness on those fish tails Ed & Jerry? They are small so you can 
afford to go up on the wall thickness for the flat parts. I have no doubt they
catch holy heck from the supersonic exhaust pulses vibration wise.
Note the doublers in this picture.

Don't let me forget to bring my DB meter to S&F :-)

Paul Lamar

 
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