"coaxial-rotor" . "coaxial main rotor" . "coaxial rotor" . "co-axial" . . "coaxial counter-rotating main rotors" . "coaxial, counter-rotating" . "dual counter-rotating rotors" . "contra-rotating coaxial rotors" . "coaxial main rotors" . . . "coaxial rotorcraft" . "coaxial helicopter" . "Coaxial" . . "contra-rotating, coaxial rotors" . "coaxial rotors" . . . "Coaxial rotors" . "coaxial helicopters" . . "co-axial rotor" . . "coaxial rotor helicopter" . . "co-axial rotors" . "coaxial design" . "Coaxial rotors" . "coaxial rotor system" . . . "coaxial double rotor" . . "rotors" . "coaxial proprotor" . "coaxial" . "coaxial, contra-rotating" .