Originally Posted by
Agile
That is interesting insight, In aerodynamics, induced drag is the overwhelming factor that drive efficiency, Induced drag is generated by the blade tip vortices. As the result a long aspect ratio blade will always be more efficient (akin a high performance glider). Robinson blades are one of the highest aspect ratio blades around, and I contend that it is one the design choice that has driven the success of the R44 especially. Think about it, 4 passenger with 225hp (Astro and Raven I) could only be the result of a higher efficiency rotor. roughly computed:
R44 1089Kg 225hp 4.8Kg/hp
EC120 1715Kg 504hp 3.4Kg/hp
H500 1610Kg 425hp 3.8kg/hp
So even with the benefit of the lightweight turbine engine and a heavier airframe nobody come close to the weight carrying capability of the R44 per hp.
You bring a good subject, the drivers have changed, look at Archer aviation and Joby, their creative design make you think about blades differently, aiming for different drivers (noise)
You might want to check your numbers -
EC120 1715Kg 402hp 4.26 Kg/hp
H500 1610Kg 375hp 4.29 Kg/hp
Power figures with MGB TOP input.
For sure it is "a" metric but not really a practical one.