dany93 wrote in Thu Sep 16, 2021 6:38 pm:The disagreement may be due to improper propeller curves (other blade section? efficiency?) or to aircraft drag at cruise velocity.
I think I've found an a explanation: the Aeromatic propeller efficiency is almost equal to 1 (97%) in cruise conditions. Differently, the efficiency curves I've seen (NACA 640 measurements) are at max about 86%. The curves are close to each other for C_Thrust, but C_Power is about 15% lower for Aeromatic at useful advance ratio (J=1). Thus, the needed torque is lower for the Aeromatic one in the same conditions. Which gives that, for the same torque, either the propeller can spin at a given blade angle and higher RPM, or for a given RPM (here, 2500), it can spin with a greater blade angle. Hence, a higher airspeed. (not easy to explain, I hope not writing mistakes)
To summarize, the Aeromatic curves are slightly optimistic, above realistic usual ones IMO.
More recent propeller might have a better efficiency than those from NACA 640, but not 97%. Unfortunately (on purpose?), these values are not given by manufacturers.