I looked for a three blade prop. APC makes a 9x6 - too small, and 10x8 - too big.

I'd need something that has about the same load as an 11x5 two blade.

I've read that tip noise is not excessive until you get past about 0.7 mach. Round tip prop's such as APC's are supposedly better (less noise). I'm running an 11 inch prop around 14500. That is ~ 0.62 according to my chart. So I expect that it is a large contributor, but not extreme.

Talking about air brakes.... I ready in the "Bolly Book", on Bolly's web site, that a quiet pipe can aid in downline braking. That's the first and only reference I read to a pipe helping slow the engine..... yet another thing to understand