Everything Old is new again - Flettner Rotor Ship is launched

Having read the article above by Stephen Thorpe and read the content of his web page that details his experiments at dinghy scale (here: http://www.rotorboat.com) I'd say that it should be possible to use renewable energy (wind or solar) to provide the power needed to turn the rotor(s). The critical issue would be how the rotor rotational power vs size scales.

For the small scale experiment on the rotorboat website, and using a guess at the total hull resistance for the 3.5m dinghy, it looks like the ratio of power in to useful power out is between 1:4 and 1:6. I've no real idea as to whether or not the drive power scales linearly with increasing size, I suspect it scales with rotor weight, as from my own work on efficient electric propulsion I've learned just how much power bearings can absorb.

In many ways rotor sails can be considered to be a little like a heat pump. A small amount of energy is put in to the system to move a much larger amount of energy.

I'll admit to being intrigued by the whole rotor propulsion idea, but it does have serious limitations that make it only really useful for a limited range of uses. It's still a sailing boat, so has all the same limitations as a conventional sailing vessel plus a few more (not being able to sail dead downwind, for example). This limits its commercial application, as one major reason for the success of steam over sail was the freedom from being bound by the vagaries of the wind.

I would quite like to try the idea out on a small riverboat though. Replacing sails with rotors seems to offer some advantages where speed is of little importance, but ease of handling, plus the potential to point higher into the wind, would be a distinct advantage. Getting the small amount of electrical power needed from a solar panel would be quite easy and not take up a great deal of space. If a non-rotating end plate was used on the rotor it could probably carry a big enough panel to do the job, when coupled with a small storage battery. The panel would only need to be sized for the power needed to top the battery up during daylight hours, which will be a lower power requirement than that needed to run the motor for only part of a day (which would be a likely pattern for recreational use).

Jeremy

 

Check out the performance graph in post #45 to put and end to the myth that rotors dont sail downwind.

 

Curious. My background is aerodynamics, I was a flight test scientist for 20 odd years, and have designed and flown light aircraft. Whilst not a specialist in complex aerodynamics, I do understand the basic principles, including the various analyses of the Magnus effect that have been undertaken.

Simple circulation theory (from Kutta-Joukowski) suggests that the drag and lift vectors are always orthogonal and that drag is always aligned to the direction of the apparent airflow vector, with only the relative magnitude of these vectors being affected by the rotor spin rate. So, when the wind is from dead aft the only effective forward thrust is drag, rather than the forward thrust from lift that will be obtained when the apparent wind is perpendicular to the longitudinal axis. In the case of an apparent wind from dead aft, the lift vector will be acting to heel the vessel (assuming a single rotor, or two rotors spinning in the same direction) rather than provide propulsion. Given that the lift vector cannot be translated forward by the vessels keel if it's at 90 degrees to the vessels longitudinal axis, I can't see how it can contribute to thrust.

I strongly suspect that, just like a conventional sailing vessel, it is only rotor drag that is going to act to propel the vessel with the wind dead aft, as I can't immediately see another source for a force vector in this direction. The drag vector will be significantly lower in magnitude than the lift vector, so the vessel would seem to have only have a very modest forward thrust under this condition. Given that a conventional sailing vessel can set a greater area of sail when running before the wind, theory seems to suggest that the rotor should perform far less well than conventional sails for an aft wind, something not apparent from Flettner's data.

Having read a fair bit over the past couple of days, there does seem to be a lot of conflicting "evidence" regarding the veracity of some of Flettner's data. Some is just errors that have been repeated by people who haven't bothered to check the veracity of their source, some may be just an original error or misunderstanding, or even a little optimism from an individual who was clearly trying to sell the idea to investors. At least the experiments performed by Stephen Thorpe seem to be valid and immediately give some clues as to one or two of the errors, like the oft-reported story that the Buckau would have performed better had the rotor power plant been used to drive a propeller. As has already been mentioned elsewhere in this thread, as far as I can see the only power needed to turn the rotors is that required to overcome viscous drag (proportional to rotor surface area and speed) and bearing drag, both of which should be quite low.

If there is something I've missed with regard to understanding the relationship between the force vectors that act upon a Magnus rotor then I'd be grateful for any pointers to sources. I've spent a few hours searching the web for definitive data to no real avail (other than the sources already referenced here).

Jeremy

 

Cousteau was reporting decent speeds. I think that is because he had sails behind his masts (by the look of some pictures I am looking at). Just a rotating mast is quite inefficient set-up.

Also, his was a mast with holes just behind the leading edge but it did not rotate. It was designed to only open and close the holes along the mast to let the air flow faster over the sail, and a fan to pump the airflow out of the mast. I think that someone said that he also had a rotor mast, which is not correct.

I think that his turbosail would be a winner if coupled with an airfoil-shaped rigid sail.

 

The attachment is from the original study done by Flettner, and supported by actual sailing results of the Buckau, and though subject to his optimism, should be quite reliable.

If the figures are fairly accurate, I would suspect the performance downwind is created by providing forward momentum via the 'right angle' vector acting on the a fore aft hull shape, giving a fair degree of forward momentum.

Given that the big windjammers with their very boxy hulls could get decent speeds with the wind right on the beam, and even slightly ahead of the beam, this seems to make sense, as the effect is similar to what the rotor ships would be subject to.

I guess a small model would quickly sort out the facts.

 

You would probably enjoy becoming more familiar with the operation of the turbosail. There were no sails behind his 'turbo sails'. The holes werent always stern orientiated, you could actually rotate the 'sail' by nearly 45 degrees, to port and starboard.

The fan did not pump the air out of the mast, it sucked it in - thereby increasing the speed of the airflow over the lift surface.

The turbosail WAS an airfoil shaped rigid sail, but optimised and designed for relatively low speeds of wind as compared to an aeroplane.

The reason he did not use Rotors, was that he sought to avoid the vibration of the rotating cylinders that plagued Flettners Rotor ships, and the relatively larger diameter of a rotor system - which just looks ugly.

 

Good point. A fat hull might actually work better than a slim hull when going directly downwind, and definitely better than a high aspect ratio keel. This prompts the thought that the ability to angle a keel around the centre of lateral resistance might achieve an even greater benefit when running down wind, which seems a pretty counter-intuitive thing to do at first sight.

My thoughts are to replicate the work that Stephen Thorpe has done, at about the same scale, but using a parallel rotor with an end plate. Working through some basic numbers I don't think that the real aspect ratio advantage of the tapered rotor vs the apparent aspect ratio of a shorter rotor with an end plate is worth the additional complication of building a tapered rotor. In many ways, the cylindrical rotor with end plate has a distinct advantage when used on a boat, as it can be shorter and give a lower overall C of G and lower heeling moment when not in use than a taller rotor.

I'm also not convinced that the idea of fitting multiple fences (the Thom design) is a good one at these low speeds. Fences come into their own where relative flow velocities are high, by reducing spanwise flow and retaining flow attachment, conditions that don't seem to be relevant for low speed sailing craft with modest rotor peripheral velocities. I believe that the additional viscous drag losses from the fences will exceed any small benefit they may give in terms of slightly higher lift.

I think it would be neat to build a self-contained system, that could, perhaps, be tested fairly easily on a number of different small hulls. Using a 300mm diameter rotor around 3m long, with a 700mm diameter non-rotating end plate covered with solar cells, and arranging for the motor, controller and battery to be fitted internally into the base of the rotor, would give a module that could be removed fairly easily and fitted to other boats. This thick mast could then be fitted into a mast step as a self-contained unit, replacing all the standing and running rigging on the boat.

Although the solar panel might struggle to provide the required motor power all the time, it should be able to provide enough power to meet the average daily power requirement, so the battery wouldn't need to be very large or heavy. There is a slight power saving by not rotating the end plate, as it otherwise creates a small amount of viscous drag. I am sure it will work just as well aerodynamically if fixed, in fact I think it might well work slightly more effectively at reducing tip vortex magnitude like this.

Jeremy

 

Old is new. From another website, I was directed to Popular Science 1933. Apart from the steam powered biplane, there was an article plus plans for a catboat designed by E. B. Schock, N.A., what looks like a prototype VW campervan made from scrap and the front cover carries an illustration of a rotor ship with an article about this vessel, scrolling about half way down. A five bladed safety razor is also illustrated. Gillette Fusion is not the first it would seem.

http://books.google.com/books?id=Ay...r Science 1933 plane "Popular Science"&f=true

Lesh boat.

http://blog.modernmechanix.com/2007/11/07/new-rotor-ship-sails-in-lightest-wind/

 

Personally I think it behoves us to revisit ideas from the past from time to time, and investigate whether or not they might have merit in this day and age. Often ideas are ahead of their time, so forgotten as being impractical or not having the technology to implement them when they are first thought up, or circumstances change, so that the priorities that determine which solutions dominate are no longer the same. Flettner failed to get his ideas adopted because of the rise in dominance of motor vessels over sail, together with the ready availability of cheap fuel to power them, be it coal or oil. Harnessing the wind to power a vessel back in 1925 would have been seen as a retrograde step, against the march of mechanised power in every walk of life.

One particular bugbear of mine are the plethora of grossly inefficient hull shapes that abound on our inland waterways, with their ugly, boxy hulls, dragging transoms and excessive wake and noise. They can only function because power became cheap with the advent of the infernal combustion engine and hull efficiency became a minor consideration. Now we're looking at fuel efficiency more closely, and are more concerned with matters like bank erosion and pollution, it seems worth looking back at some of the lovely hull shapes that evolved when we only had the power of oar, pole, sail or perhaps a low power steam or even electric motor for propulsion.

It's one reason I'm interested in looking more closely at Magnus rotors, as I think there is a place for a zero emissions propulsion system like this on small inland waterway craft.

Jeremy

 

Jeremy,

A strict definition of zero emissions propulsion as defined by Obama's EPA would not even permit you nor me to row a boat, as those ***kin' clowns have decided in their infinite wisdom that natural CO2 is a pollutant. Such crass stupidity should be rewarded with a swift debagging and the brutal insertion of of a high colonic lavage tube up their equine orifices.

It's extremely difficult for such people to maintain their dignity and composure, when the world wants to drop out of the rsole. That's my personal opinion after partaking of three bottles of the world's finest cyder (yes, with a why), known as Aspalls 7% Premier Cru. I shall now have a fourth, if I can make it to the (hic) refrigerator.

http://dev.aspall.co.uk/products/cyder-3-6.html

So, I ses to this 'ere EPA Lisa Jackson.

http://www.google.co.uk/images?q=li...PN8mXhQeGkczmAw&ved=0CFAQsAQ&biw=1024&bih=593

I ses, "Hell's teef, yore ugly! You look like you've chewed a nest of wasps". She replies, "You disgustin' filthy creature. You are drunk!". I ses, "Yes luv, but inna mornin', I'll be sober.".

 

Jeremy,

Another collection of Popular Mechanics possibilities.

http://books.google.com/books?id=fv...t&resnum=1&ved=0CCMQ6AEwAA#v=onepage&q&f=true

A link to Besler via WHR.

http://www.archive.org/details/BeslerCo1932

http://www.isengard.co.uk/

River cruisers.

http://www.craftacraft.com/river_cruisers

 

Much as I admire some aspects of the culture of some of our ex-Colonial cousins, I do draw the line at accepting that any of their political policies are anything but farce, worthy only of being made into comedy. Personally, I've always been amazed at the way that Western countries in general are so willing and able to elect buffoons as their leaders. It speaks volumes for our average intelligence, or perhaps is just a reflection on our state of general apathy.

BTW, both my parents hail from your neck of the woods, mater's family lived at the top of Marlow Hill, pater's halfway up Amersham Hill. It's a small world.

Jeremt

 

Thats not a silly assumption in itself as intuitively, that would seem to be the case. However, many, many years ago I got into some correspondance with an engineer who sent me over 150 pages of designs and calcs, and his 'ultimate' design for a smallish boat actually had up to 5 Thom fences.

His contention ( unproved in practical application, but demonstrated with small model tests using a power drill ) was that conservation of the airflow was even more critical at relatively low wind speeds, as the low velocity flow tended to head 'off the line' quicker.

So, if you got a test cylinder up and running, it might be interesting to add some additional Thom fences and check out the result.

 

Who else but egocentric, approval starved ,low mind powered individuals would work in a such thankless, high pressure, super exposed and tradition encumbered positions. As long as we keep the same job description, we will only get what Sting aptly described them as - "Gameshow Hosts"

 

What a great site - I note that one of the articles in that link was
"Automatic Steerer for boat relieves helmsman"

Imagine thinking that a boat could ever steer itself - how crazy is that