Flettner rotors as turbines

[Andy Hamilton]

Just watched a thing on BBC that mentioned Flettner rotors, could these be used as more efficient turbines? Or am I missing some basic physics?

[Martin]

they're not generators of power as such, they use the power of the wind to drive the boat (just like hi tech sails), and the propellor is dragged along by the boat, which revolves and generates the power!

[Andy Hamilton]

Just thought that if it can turn a propellor then it could turn an engine.

That aside it seems daft that more yachts and boats are not fitted with a 'sail' like this.

[Muddypause]

I seem to remember seeing pictures of a big ship that was powered by some of these things - probably early 20th century.

I don't really know much about them, but from what I understand, you have a big vertical cylinder that rotates; this means that as the wind blows around the cylinder, it is divided into an unequal flow - the air that goes around one side of the cylinder is 'helped' round by its rotation, but the air that goes around the other side is opposed by the rotation. This gives rise to a pressure difference that pulled the ship along.

From an uneducated observation, I am prompted to ask if this is not basically what an aerofoil section does - dividing the airflow unequally, creating a pressure difference. There have certainly been sailing boats built with aerofoils (think of a long, narrow aircraft wing standing upright) instead of conventional fabric sails, and I think they are fairly efficient.

Aerofoil shapes also play a part in wind turbine design, giving a shape to the sails that makes them more efficient. Some types of vertical axis windmills depend entirely upon this aerodynamic shaping to make them rotate (see the Darrius design). So, I suppose it would be possible to mount a couple of rotating Flettner cylinders in place of the sails on a Darrius type turbine.

I don't know nearly enough about aerodynamics to comment upon whether the Flettner rotors could be made to be more efficient than any other sort of sail, but I imagine the extra weight and the mechanics involved in making them rotate would be extra hurdles to overcome.

[Andy Hamilton]

I don't know nearly enough about aerodynamics to comment upon whether the Flettner rotors could be made to be more efficient than any other sort of sail, but I imagine the extra weight and the mechanics involved in making them rotate would be extra hurdles to overcome.

This is perhaps why they are not more common place. The reason that I saw them was for one of the ways to combat climate change. 50 yachts will be powered by these and will shoot sea water into clouds to enhance them and make the world cooler.

[CG]

I'm a bit of a nerd when it comes to Flettner rotors, so I hope this will not be too boring for anyone who reads it.

Anton Flettner used his idea of the rotor to build a wind turbine. It was for the time is was built (about 1926) a very large turbine. It was a hawt with four rotors instead of blades. There was a control cabin above the blades with a gantry running around this cabin. Flettner's idea was to put small turbines on the tips of the rotors where the higher windspeed would mean higher energy input. But this was not implemented on the only turbine he built and Flettner went on to other things such as helecopters.

The most interesting use of the Flettner rotor in wind energy was the Madaras plant that was planned for a site in New Jersey. This would have had forty giant rotors travalling around a circular railtrack. These rotors were 90 foot high and the generators were in the axles of the trollies that they ran on. Only one rotor was built and tested statically pulling against a steal bar, which it bent. The theory was most or less proven that the system would work, but the plant was never built.

If you can get hold of Flettner's book, The Story of the Rotor, you should find it a good read, it's a book on engineering that the layman or worman could understand. But it's a rare book, I had to borrow it from the London Library; that costs about £3 and there's a hefty charge if you don't return it.

Every time there is a fuel crisis Flettner's rotor ship comes up, but there hasn't been one built since the Barbara, his second and last ship. Jaques Cousteau built something similar, but it was not a true rotor ship, in fact Cousteau hated Flettner rotors. The Americans built a tiny rotor ship soon after Flettner's but nothing else. It is hard to understand the huge amount of interest there was for a short time in Flettner's idea, but the world relied so much on shipping at the time his idea came out.