Barry,


The AOA of the blades is one factor in efficiency.

The CL does become greater, so the smaller blades of the 12x6 prop do produce more thrust (compared to a flatter AOA). But their CD, or coefficient of drag increases to a greater extent, causing their L/D (lift/drag) ratio to decline, as AOA is increased.

This is a major factor of prop efficiency and one reason a larger diameter, identical pitch prop, will produce a higher speed at identical RPM.

...But this is really not an issue. The same engine will not be spinning a 12x6 and a 14x6 at the same RPM...

If the model you are flying isn't the sleekest around, using a relatively low pitch prop will provide your model with better performance.


Using a 10x6 prop on your .40-.50 trainer is nearly the worst choice you can make (better only than using a 9x8, or an 8x10 on the same trainer...).
An 11x5, an 11.5x5, or a 12x4 even, if ground clearance permits, will load the engine down a bit, but will provide better take-off performance (shorter run, much better climb-out, never a ground-loop) and better off-throttle breaking, which makes landing easier and shorter.

The cost; a lower top speed, which you have no need for anyway.


So, if the LHS guy tries to sell you 10x6 props with a new trainer, you can tell him that he's a complete idiot...