Historical Development of the Coaxial Contra-Rotating Propeller

Antonino Filippone PhD, FRAeS, FIMechE, CEng, Professor of Computational Aerodynamics, School of Engineering, The University of Manchester explains how the contra rotating propeller was initially proposed to increase speed, then to increase propulsive efficiency, but ultimately they were limited by too much noise. Engine layouts & propulsion configurations are analysed. It is concluded that propulsive efficiency can only be achieved at the cost of multiple engineering problems, some of which still remain unsolved.
Antonino also looks at the historical context and comments that the same conclusions were reached in several different time periods, and much effort could have been saved had reference been made to previously published research; a lesson which might apply to many fields even outside aerospace and engineering.
For anybody wishing to deep dive a bit further, here is a paper on the subject. tinyurl.com/57...