Lynn,

  Another thought.............What do you think an "Extractor" system (In my "Delta's" case

one on each side of the bottom "V") consisting of large diameter tubes (5-6" ?) exiting

behind the cockpit with 2" tubes down the middle and open to forward motion and prop

blast would do to noise level ??............. 

 

 
Kelly Troyer

 

Just a guess. The sound is conducted out the front of the tube as well as the back.

 

Having such a tube around the exit of each pipe might have some good effect. At least worth a try. 

 

Or even end the pipes inside such a tube as a Swiss muffler. Sound control with a fabric skin will be tough.  

 

Lynn E. Hanover