співісні утримувальні гвинти
dual rotors / twin rotors
twin rotors / dual rotors
upper and lower coaxial rotors
tandem-rotor helicopter (twin rotors mounted longitudinally)
coaxial
coaxial machine gun
coaxial mounting
coaxial-rotor helicopter
hollow shaft (of lower coaxial shaft)
through shaft (of upper coaxial rotor)