Flettner rotor hydrofoil

I’m guessing they don’t exist for the same reason aircraft have fixed wings, not Flettner rotors. But wondering if anyone has done it for research or fun?

But I do wonder if spinning Rotors underneath a hull would be a way of making angle of attack look after itself?

Short of spinning the rotor the wrong way, a Flettner rotor hydrofoil would always have the correct angle of attack for its foil. Surely that has to be a positive?

Also, wouldn’t it also be easy to change its lift, so when the boat is going slower you can speed up the lift rotor to keep it foiling longer and when the boat is going faster you can slow down the lift rotor to create less lift so it saves on power and doesn’t surface.

Wouldn’t be hard to do. Two vertical masts. Outrunner motor glued into a tube between the masts for the rotor. Wiring down the masts. Masts continue below and fore and aft of the rotor to operate as endplates. Has it been done?

 

And. And. You could have two sides to the rotors, port and starboard that you could spin at different speeds so when you steer the boat you can speed up the outside rotor and slow down the inside one so it leans in corners like a planing boat, doesn’t lean the ‘wrong’ way like most hydrofoils…

 

Always been aqainst vertical masts .
Voith Schneider Flettner hydrofoil ?

 

Yacht Stabilizers | 100% Electric | RotorSwing Holland B.V. https://rotorswing.com/ does it for stabilizers

 

Using the Magnus Effect in design.
https://www.autodesk.com/products/fusion-360/blog/what-is-the-magnus-effect/

-Will

 

A surprise for me: I always thought that Flettner rotors under water are a bad idea. First, we rarely need big Cl in the water; next, big Cl causes cavitation. These people seem fo find a reasonable use of the underwater rotor. I wonder, how it works in practice.

regards

krzys

 

Its done on a aircraft.

 

Not sure model above really is Flettner rotor . This one is for sure :

This does not change the fact that there are huge differences in the viscosity of water and air and, consequently, the ratio of the fluid drag force to the force generated by the rotor can be reason of impossiblity of practical implementation .

 

As nice as the variability of lift (and, to some extend, drag) would be in a marine setting, i fear the approach won't make it past POC stage for efficiency reasons.

- Modern inshore foils with some laminar flow can reach L/D above 20
- Modern rough water foils are still reported at 12 to 15
- Planing is rarely past 4-6 but single-speed semiplaning optimisations can bring that quite high up
- Super-slim hulls can reach 30 at useful speeds (Infinite even ... at less useful speeds. They just float)

I've rarely even seen full figures for Magnus effect / Flettner but what i saw was more on thd order of 4 to 8, which might explain why the L/D ratio didn't quite make it into the headlines of the papers. (If someone here has hands-on experience, i'd be curious)

So probably the point is just that they would perform equal or worse than a planing hull, and with 2-3 times the energy consumption of a modern foiler.

(The stabilizers aren't optimised for efficiency, but for practicality, retrofittability (small size due to high lift!) and the safety of the instant-off lift when power goes away. Their drag will be smallish compared to a whole large motor vessel in waves, and even if it mattered, puking less would be quite the rationale.)

 

Tom Swift had a Flettner rotor aircraft in one of the books of the series in about 1965.

One problem with Fletner rotors is a relatively low lift to drag ratio compared to fixed foils. They do have potentially a very high lift coefficient, but it comes at a cost of high drag.

 

Wind tunnel campaign for Flettner up to Re=800 000 underway at Politecnico Milano : #windtunneltesting #flettnerrotor #kriso #windassistedpropulsion #sustainableshipping | Politecnico di Milano Wind Tunnel https://www.linkedin.com/posts/windtunneltesting-flettnerrotor-kriso-ugcPost-7463143108361289728-VdiU/?utm_source=share&utm_medium=member_desktop&rcm=ACoAAAFGLhgB3W4U8exX4Oy0h0d6AsL6Joo5UFw
Perhaps there will be a paper ?

 

Has anyone investigated the use of a Magnus rotor placed horizontally in the water? When heading into a current, if a Magnus rotor is affixed to the stern, it will create a lift at the stern which will end up giving forward propulsion. The Magnus effect is 830 times stronger in water than air. The cylinder can be much smaller. If the cylinder has stiff bristles like a paint roller, it will entrain more water around the cylinder increasing the lift and forward propulsion.

 

Any lift device produces lift force perpendicular to the flow. A horizontal rotor would produce force up or down.

Any lift device also produces drag force in the same direction as flow so a horizontal rotor in a head current would produce drag aft aft as well.

 

Think of a flat plate of steel on a slippery surface. If you lift an edge of the plate, the plate slides forward. Just as the development of a bow wave impedes forward motion, and a stern wave boosts forward motion, the lift ends up as propulsion.

 

It would not be that difficult to build a model and test your ideas Loq.