Thought a few of you might get a surprise from this. I know I did. [X(]

Bench ran my C/L O.S. MAX 20 again yesterday. Different weather, so initially same fuel, same prop to establish any variation from the previous datum.

Datum result was the same as Sunday, Bolly Clubman 8.5 x 4 turned 13,300 RPM peak.

Swapped props fitting an new condition but old square tipped black Master Airscrew 9 x 4 I had to hand. Mk I Eyeball of the respective pitches revealed they looked pretty similar, but of course, the blade shapes are radically different with the Master Airscrew also much wider at the tip. Fired her up. Same fuel, but several clicks richer needle setting was required to tune a peak with the Master 9 x 4 of 11,200 RPM, a loss of a whopping 2100 RPM! Even I was incredulous at the difference ½" diameter, but probably more importantly, the radically different blade shape made!

I'll have an APC 9 x 4 and a Bolly Clubman 9.5 x 4 (assuming they make the size) soon, so the further comparison will be interesting. I'm willing to hedge a bet the larger 9.5" diameter Bolly will actually turn faster than the 9" Master. I confess I was expecting anything up to 1000 RPM drop, but over 2000 RPM for ½" of diameter and larger surface area?!!!! I had heard all the disparaging Master Aiscrew "paint stirrer" remarks and previously put them down to just colourful hyperbole. Admittedly I haven't used anything Master Airscrew myself in an age in R/C, but this empirical evidence which can't logically be denied really did shock me. [sm=spinnyeyes.gif]

Wish I had a thrust gauge now out of sheer curiosity. [:@]