NeilsenRM(at)comcast.net
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 Posted: Fri Nov 23, 2007 9:47 am Post subject: Prop Sizing for Redrive VW powered MKIII |
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I have been thinking about prop sizing lately. I have a 72 inch Powerfin F model prop. It performs very well but doesn't give me the best engine RPMs. I have it set for best cruise at 3200 RPMs but this doesn't work for the best RPMs on climb. When climbing I only see 3500 at full throttle but the best climb RPMs should be 3800 to maybe 4000. I talked to Powerfin and they now recommend a 70 inch prop with the figures I have given them. As a interim I'm sending them the prop to have it cut to 71 inches because you really get the best thrust with longer props and they are willing to cut it more than once for free. Powerfin recommends longer props for the best climb performance but also recommends shorter props for compromise of better climb and cruise.
I'm also going to try a Culver prop next spring. They recommend a 74 inch two blade for my set up and it will be very interesting to get the results with that prop. They are saying they will send me one for free just to try.
Based on the Magic that the Jabiru folks are getting with their props I looked at Prince Props. Wow a prop for a Rotax on a Kitfox which is as close to a redrive VW as they stock normally is $1,300 with out leading edge protection and $1,400 with. In a Kolb it would likely be longer and more expensive yet. I wouldn't even consider one till after trying the Culver prop to get a sizing starting point. The idea of some automatic pitch changes is attractive. Also when I hear about the performance differences between what John W. saw and what the UK guys are getting with the Prince props the results for us VW owners and Rotax guys could also be as dramatic?????
Does any one know how resistant the Prince props are to damage? They make wood core carbon fiber props.
Rick Neilsen
Redrive VW powered MKIIIC
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