Kontrarotationspropellrar

Kontrarotationspropellrar is a type of propeller design in which two or more blades rotate in opposite directions around a common axis. By counter-rotating the blades, aerodynamic forces that ordinarily generate torque on a typical single-direction propeller are largely neutralised, resulting in a reduction of shaft torque and an improvement in overall propulsion efficiency. The term is derived from German words for “counter‑rotation” (Kontraro‑) and “propeller” (Propellrar).

The principle was first experimented with in the early 20th century in naval engineering, where counter‑rotating shafts were used to increase thrust while mitigating the tendency of a ship’s propellers to bind the hull. In aircraft, the concept has been incorporated into turbofan engines and turboprop units, where a low‑speed fan and a high‑speed compressor or propeller rotate in opposite directions to enhance pressure rise and reduce the external torque that would otherwise be transmitted to the fan housing.

Key advantages include lower vibration, higher efficiency, and a smaller net rotational torque transmitted to the drive shaft. Disadvantages are increased mechanical complexity, higher manufacturing cost, and higher maintenance requirements due to the need for synchronised gearboxes or contra‑rotating shaft seals. Contemporary applications favour contra‑rotating main rotors on multi‑rotor drones, certain turbofans used on commercial aircraft, and research in high‑efficiency marine propulsion systems.