Bad News & Good:
* APC is not willing to make an electric 3-blade. This unchanged from what they told me in the past, only they were a little more adamant about it this time!
* APC suggested what could be a very good alternative. They apparently developed a special prop for R/C Pattern Flyer Chip Hyde. Chip was interested in good static thrust and good braking. In his case they DID try 3-blades but they did not work well. What did work was a new wide blade wide blade design. Chip's using a 24" diameter, however APC proposed to applying the same design philosophy scaled to a 13" dia prop.
* This sounded like a viable alternative and I gave them the go-ahead for prototypes of a new 13x5.5E Pusher Wide Blade. The new prop will be based on the 13x4.5 EP, with the blade profile widened - it is not a linear scale-up. The pitch will be increased to 5.5". That should make it a low 9000's RPM prop.
While this is not the 3-blade people were asking for it should have design elements that work in our favor:
* The 2-blade design will be more efficient than 3 blades.
* The wider blade fills up the disk area - mimicking what we achieve with a 3-blade design.
* 2-blade will be lighter than the 3-blade would have been.
* The new design taps into APC's design experience on the wide blade design for pattern props. From checking their web site, APC makes a wide blade electric prop in 17" - 22"; the 24" prop they mentioned to me must be a new one. I am hoping our RC Pattern & IMAC voices can check in on this point and affirm (or counter) whether the wide blade props have been a success for those folks.
* Finally, from a purely pragmatic point of view, APC is willing to make the 2-blade; they are not willing to make the 3-blade!
* The lead time on the prop will likely be in the fall, the prove-out samples later than that. NOT what we wanted to hear but we are waiting in line behind several other APC projects.
Back in the IC engine days (!!!) lots of empirical data - and opinions - were generated on wide blade versus narrow blade props. I suspect a lot of those rules will apply EXCEPT with a governed electric the braking effect for wide blades should be even more powerful.