Hi Motorman,
EParrot (attached) uses APC 11x5.5 MRP propeller, weighting 18 grams (0.63 oz.).
This propeller is lighter than APC 11x5.5 E that weights 25 grams (0.88 oz.).
APC 11x5.5 MRP has smaller hub and slightly wider and thinner blades. The bending stiffness of this prop. blades is about 75% of the bending stiffness of the APC 11x5.5 E blades. I know that the gyroscopic moment in corners can bend less stiff propeller blades out of the plane of the prop. rotation and that this creates a momentary dynamic imbalance with the buzzing sound.
I have tried flying eParrot with APC 11x5.5 E propeller and it flies a bit slower at 9,800 RPM. The difference in speed is especially visible in the second corner of the hourglass that becomes lazy with the tendency to stall the model.
If this abysmal weather that we have in Toronto ever improves, I will try flying eParrot again with APC 11x5.5 E, boosting the RPM to, say, 10,000.
Anticipating the question: EParrot is well trimmed now. It grooves well, maintains the level normal and inverted flight with no hunting and almost "by itself", and reacts predictably to the input. It flies on 60' long (eye-to-eye), 0.015" stranded lines and, in general, it is a competition quality airplane now.
Howard, Crist,
Like I wrote, I will be soon flying another, larger model using Cobra 3515/18 with Igor's 11x5 carbon composite 3 blade prop. and/or with 11.5x6 carbon composite 3 blade prop. "Pol-Prop". For your information: "Pol-Prop" is slightly heavier than Igor's 11x5 but also much stiffer. Cobra 3515/18 will be front mounted.
Happy Flying,
M