Twister what prop are you using? I ask because I just purchases two new Falcon props. A carbon 20x9 and a beech 20x10. I have only flew the 20x9 which seems to be fine but on the ground the 20x10 beech turned 600 less rpms and was very quiet because of it. It has been very windy lately for my flying so I don't really want to experiment is tough wind.
I am not sure what prop you are using, but I switched to a 21x8 mej this spring and told the noise police that I made a bunch of changes. It as quiet as any of the other gassers. Or at least it appears to be. It definitely keeps the prop from ripping and keeps it slow, probably perfect for the bigfoot. If you like low and slow it definitely is quiter than either the Vess or the wood XOAR I had before.
U shape or Y shouldn't make much difference. The length from the exhaust to the "tee" outlet pipe and the change in volume at that point (and resulting sound wave reflections - either positive or negative) will have most to do with it. My understanding is that the tubing is 1" od so the velocity of the exhaust gas would be much lower than a typical sized exhaust for a 20cc cylinder - shouldn't be a flow problem. Talking with Tim on the second prototype, he was getting an increase of about 400 rpm with a medium smooth pipe and no loss of power with a medium can. I am intrigued.
It was planebenders.
Heck, didn't realize the ES composites were so light. Wonder if they make a small version (less than 2" diameter). Though that would be an expensive venture to shoe horn two of those into the tunnel in my 78" Extra!
