The thing that makes the difference is the amount of mass flow through the prop. More mass flow, more thrust, less delta-v, more efficiency. I designed Jim Smith's three-blade for best cruise. It had less static thrust beacause of the planform of my design, but higher ROC and cruise than his 68-72 Aymar DeMuth. At 8000' dalt the three-blade gave 190.5 mph GPS-determined TAS vs 186 mph for the A-D, even though the A-D was turning an average 100 rpm more. The speed increase was worth 7.5% and when you throw in the 2800 rpm/2700 rpm that gives an efficiency increase of 11.4%. Keep in mind that I said that multi-blade propellers with the same diameter, pitch distribution, and planform shape, that is, chord distribution but with reduced chords, will have more static thrust and ROC, whether FP or CS. BTW, with his new wingtips, Jim is doing 193.5 mph at 8000'dalt! You really need to read the articles I have written in Contact! magazine that go discuss planform, pitch, and multi-blades. I think you will learn a lot from them.
Last edited by elippse : 04-02-2011 at 11:12 AM.
Reason: Added ending
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