prop size, number of blades and rpms etc.

Some people think this several prop thing is not good..a single blade is best etc. We went all this in RCUniverse aerodynamics section just a month ago.

If you compare props and their thrust you have to remember larger dia means faster tip speed at same rpms.

Here we are after the optimal thrust at low rpms ( 10-15 % throttle ) but with great velocity of the craft ( world smallest drag allows this to happen ). Therefore we need a lot of prop blade area in a small prop.

Above there are 3 Fournier known prop sizes. If my craft's prop goes at mach 0.45 and Fournier at mach .75 tip speeds how much more power do you actually need for the Fournier prop ? The circumference of the largest prop is 5026 mm and some 2580 mm for the smallest.
Anyone have good tips how to make your own prop...fixed pitch I mean. It is like a small wing..is that all I need to know..that it works like a small wing ?
here is once more the Ellipse's new 90 % efficiency running quiet prop; http://www.eaa.org/experimenter/articles/2009-02_elippse.asp

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