In article <1992Aug20.131653.3656@linus.mitre.org>, mmcevill@mitre.org (Michael A. McEvilley) writes:
|> In article <Bt8q1t.EpJ@world.std.com> jlw@world.std.com (James L Walker)
|> writes:
|> > I run my Enya .45 CX with a 10x7. As I understand it this slows the
|> engine
|> > down and reduces prop noise. At my field we are pretty paranoid about
|> > sound, so I would always raise the pitch before the length of the prop.
|>
|> Either increasing prop diameter while keeping prop pitch constant, or, increasing prop pitch while keeping prop diameter constant increases the loading on the engine and will result in less peak RPM, which translates into slower propellar tip speed which |> is where a lot of the noise comes from. So it is not necessary to 'always'increase the pitch before the length to get
|> lower peak RPM.
|>
|> BTW, if you are really interested in minimum noise, try soft-mounting your
|> engine as well. It works!
|>
|> BTW-FYI, once an optimum peak RPM/pipe length has been established, as peak RPM increases, pipe length must decrease and vice versa. When measuring pipe length, measure along the header center-line, not a Point A - Point B straight line type measurement|> .
|>
|> Michael
But...
In increasing the prop length, you also increase the prop tip speed.
So in increasing the length only to slow the engine down could result
in maintaining the prop tip speed. I usually increase the pitch while
