Expert: Mark Janus - 3/25/2007

Question
Hallo!

Could you please explain to me the aerodynamic advantages of coaxial contra rotating propeller?

Thank you!

Answer
I'm so sorry this question got by me....my e-mail notice must have gotten lost with other messages

Coaxial contra rotating propellers raise the overall propulsive efficiency by removing the residual swirl (actually called whirl) in the flow dowstream of the prop. A single propeller causes the air to spin along with it (in addition to pushing it axially).  All of the energy associated with the swirling air is lost, representing a reduction in overall efficiency.  The disadvantage to contra rotating props is the sophisticated gearing (and weight) necessary to implement the design.

Thanks for your question and again so sorry for the delay in getting you an answer...
mj