Normally propeller efficiency of piston engine fighters I have looked at seems to range from 80% to 90% in a plane’s ideal speed range, depending on engine settings and flight conditions. The Ki-84 on the other hand ranges from the low 70% to not higher than 78%. This is really abnormally terrible, even compared to other Japanese fighters. On the IJN side, the N1K2 is a contemporary aircraft using the same engine, and it’s propeller gets up to 83%, which is poor but a lot better. The J2M gets up to 87%.
This awful propeller efficiency squanders so much power from the engine, and thus the aircraft’s potential. it’s insane to think of how many hundreds of horsepower from that 2000hp engine are not being converted into useful thrust that could go towards a higher speed, rate of climb, and maneuverability on such a lightweight, low-drag plane. How and why is it’s propeller so bad? Japan clearly struggled with propeller design during the war, but this stands out from the rest to me.