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-   -   Engine selection dilemma (https://vansairforce.net/community/showthread.php?t=32564)

Finley Atherton 08-06-2008 04:49 PM

Quote:

Originally Posted by Pirkka (Post 245466)

What comes to the fuel economy, does CS propeller really pay off here? If savings will overcome when initial price and overhaul price difference between FP and CS is considered for CS, wouldn't everyone get it?

I don't think anyone actually said that the fuel savings would overcome the extra cost of a C/S prop, although with fuel prices rising, who knows?
I think there would be too many variables to give accurate figures for any fuel savings. However here are some figures from the Lycoming 0-320 Operators manual that might help.
Engine IO-320 B & D series, mixture "Best Economy", producing 65% power at each of the following RPMs:
2000 rpm, 7.1 g/h
2200 rpm, 7.4 g/h
2400 rpm, 7.6 g/h
2600 rpm, 7.8 g/h
2700 rpm, 8 g/h
The figures are taken off a small scale graph so there could be a 0.1 inaccuracy.
I cruise at around 2,250 rpm & 61% power with my Hartzell. We work in litres in Australia and I suspect the C/S prop may be good for at least 1 ltr p/h (possibly more?) at cruise over a F/P prop. With fuel at around $2 AUD ltr this would be a fuel saving of at least $2,000 per 1000 hrs on current fuel prices.
This is all very speculative as I have no experience with a typical F/P prop in an RV and therefore do not know the RPMs and FF that would be needed to match my TAS. No doubt there will be others with a different point of view!

Fin
9A


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