Flettner rotor

Lore & Background

The Flettner rotor is named after German aviation engineer and inventor Anton Flettner, who started developing the rotor sail in the 1920s. The Magnus effect, named after German physicist Gustav Magnus, describes the force generated by fluid flow over a rotating body at right angles to both the direction of flow and the axis of rotation. This force on a rotating cylinder is known as Kutta–Joukowski lift, after Martin Kutta and Nikolai Zhukovsky (or Joukowski), who first analyzed the effect. The Flettner rotor is just one form of the Magnus rotor, which in general need not be cylindrical.

In a rotor ship, the rotors stand vertically and lift is generated at right angles to the wind to drive the ship forwards. An early prototype, the Baden Baden (formerly the Buckau), crossed the Atlantic in 1925, but interest was not revived until energy saving became a major concern in the new millennium. The E-Ship 1 was launched in 2008, and new vessels continue to appear. Multiple rotor installations have been completed, including tilting rotors to allow passage beneath bridges. Under favorable conditions, rotor sails have been reported to generate 5–20% fuel savings.

In a rotor airplane, the rotor extends sideways in place of a wing and upward lift is generated. Some flying machines have been built which use the Magnus effect to create lift with a rotating cylinder at the front of a wing, enabling flight at lower horizontal speeds. An early attempt was made in 1908 by US member of Congress Butler Ames of Massachusetts. A later example was the Plymouth A-A-2004 in the early 1930s, built by three inventors in New York state. French designer Jean de Chappedelaine developed his Aérogyre at much the same time; a prototype based on a modified Caudron C.270 Luciole was flown in 1934 with the wing rotor stationary, and crashed on its next flight, though whether the wing was rotating during that flight is unknown.

Reader's Guide

The Flettner rotor is notable for its application of the Magnus effect to generate lift in both marine and aviation contexts. In marine applications, rotor ships use one or more Flettner rotors mounted upright, rotated by the ship's engines to act like sails and propel the vessel under wind power. A conventionally-powered underwater propeller may be provided for additional operational flexibility. The concept saw early demonstration with the Baden Baden crossing the Atlantic in 1925, but widespread adoption only resumed when energy saving became a major concern in the new millennium, with the E-Ship 1 launched in 2008 and subsequent vessels incorporating tilting rotors for bridge clearance. Under favorable conditions, rotor sails have been reported to generate 5–20% fuel savings. Additionally, a Flettner rotor mounted beneath the waterline of a ship's hull and emerging laterally can act as a stabilizer in heavy seas by controlling rotation direction and speed to generate strong lift or downforce; the largest deployment to date is on the motor yacht Eclipse. In aviation, the rotor has been used experimentally to create lift with a rotating cylinder at the front of a wing, enabling flight at lower horizontal speeds, though early attempts such as those by Butler Ames in 1908 and the Plymouth A-A-2004 in the early 1930s did not lead to widespread adoption.

Did You Know?

• The Flettner rotor is named after German aviation engineer Anton Flettner, who started developing it in the 1920s.
• An early prototype rotor ship, the Baden Baden, crossed the Atlantic in 1925.