jimandmandy(at)yahoo.com
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 Posted: Sat Oct 25, 2008 6:32 am Post subject: Which Of Two STOL CH7XX Building Choices? |
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NVH (noise, vibration and harshness, from the auto industry) standpoint is another consideration that has nothing to do with performance.
My theory on this is that a three bladed prop on a four cylinder engine keeps the exhaust and propeller sounds out of phase, making it at least seem quieter. The same for vibrations. For a six, like the Jab 3300 or Corvair, three blades would be worse than two for the same reason.
Jim LoBue
601XL/Corvair
--- On Fri, 10/24/08, Dirk Zahtilla <ideaz1(at)sbcglobal.net> wrote:
[quote]From: Dirk Zahtilla <ideaz1(at)sbcglobal.net>
Subject: Re: Re: Which Of Two STOL CH7XX Building Choices?
To: zenith-list(at)matronics.com
Date: Friday, October 24, 2008, 8:00 PM
Bryan gives an excellent explanation of prop physics. In a prior plane I built I had an IVO 3 blade electric adjust prop. Because of the size and weight of the plane and engine many factors don't applly. I did however have real world experience as I could in a few minutes switch from 3 to 2 blades. I also could adjust the pitch in flight to get max efficiency at any time, i.e. climbing or cruise. The results were that 3 blades were a bit quieter and smoother (less vibration) and climb was improved. With 2 blades top level speed was about 3-4% higher, but of course climb suffered a bit. Remember I was able to adjust the pitch at will so as to get the most of the prop in any conditions, so theres no question of making a bad choice of pitch.
I preferred the 3 blades for my use as the climb and smoothness was more important to me than a slight speed improvement.
The differences were subtle but noticeable.
Dirk Z
[quote][b]
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