'Sailing'?? Directly to Windward

High Tacker www.damsl.com

backyardbil

If there is a politician here, it's you, trying to claim that inefficiency is good. Here is what dictionary.com says about the word "inefficient":

inefficient
—adj
1. unable to perform a task or function to the best advantage; wasteful or incompetent
2. unable to produce the desired result

Now, I will try to make a point again in different words: a reefed but still efficient sail is better than a reefed but still inefficient sail. Some efficient sails become inefficient when reefed.

Re your questions, which I think I had already answered, here goes again: Compared to a 3-bladed turbine with blade twist, a multi-bladed turbine will have more drag on the entire turbine assembly, tending to prevent the boat going forward (and indeed stopping the boat altogether at higher wind speeds), and, if it does not have blade twist, then it also will have more drag of the kind that tends to prevent its blades going around as fast as they could if they had twist.

I repeat, in somewhat different words, another point: When you need to slow down the speed of rotation of the most efficient, all-around-best kind of turbine, a 3-bladed one with optimum twist on the blades, and variable pitch, you simply vary the pitch, that is, you reduce the angle of attack of the blades to the wind. In doing so, you not only reduce the speed of rotation, you also reduce the overall drag.

In contrast, with a multi-bladed turbine with no blade twist, the inefficiency of the blades, causing drag that slows down the speed of rotation, as well as more overall drag on the assembly, remains high, whether or not you are able to vary the pitch of the blades. That is because, even when you vary the pitch, the pitch is ideal only at one point along the length of the blade. The rest of the blade is at an inefficient angle of attack, because points at different lengths out from the center of the turbine experience different wind speeds and directions. In order to optimize overall pitch, and minimize overall drag, it is necessary to have twist.

The fact that bad pitch over much of the blade tends to slow down the speed of rotation is not a good thing. You do not need inefficiency in order to slow down, to control, the speed of rotation. I repeat, you would not choose an inefficient motor for your car in order to prevent going too fast. And if somebody warns, "Walk! Don't run!", the person who has weak legs does not have an advantage over a person with stronger legs.

Have you ever done any actual experiments with turbines, or are you just trying to visualize what might happen? Are we just arguing about what you think might happen? What does any rocket scientist worth his salt do, after all the theorizing? He builds a model to see what really happens. I built a few models with different numbers of blades, but Jim Bates was way ahead of me. He built scads and scads of models, and then scaled up and tried the best ones on life-sized boats, before finally arriving at the optimum design, 3 blades with optimum twist.

 

He has made a couple of reasonable attempts that I understood without any problems. However, you seem to be on a tangent with your thinking.

A low efficiency rotor for the turbine will fail to produce as much power (torque times speed) and will produce drag that pushes the shaft harder against the thrust bearing.

For overall craft performance upwind, efficient wing operation is always good, poor efficiency is always bad. The force of the rotor pushing against the thrust bearing is directly opposite of what you want. Even though apparent wind speed (available energy) is higher than actual wind speed, the drag forces (all of them: wing pushing against thrust bearing, boat through water, prop turning in water, etc.) go up a lot the faster you go.

On a downwind run, there is less of a penalty to the rotor drag, but for the same "lift" better efficiency will still perform better. For a downwind run, a rotor can sacrifice some efficiency but only if there is a payoff with substantially more power.

This is the same trade-off with fixed wing boats. The slots in the C Cat wings allow a transition to a high camber configuration with very high lift for downwind runs even though the lift vs drag ratio is not as good.

High-tacker et. al. may have made more use of this than they realize. The actual wing section of the rotor has maximum efficiency range for angle of attack. This is the ideal choice for trimming when for driving upwind. Typical rotor wings will produce much more lift at a higher angle of attack even though drag goes up. On downwind runs, the craft reduces apparent wind as it speeds up (less available energy). On the flip side, these runs allow for rotor trimming for maximum power output regardless of drag. This is why downwind performance was on par with other angles.

Hopefully, I have put the answer in a way that will make more sense to you. Physics is what it is and and a rotor driven boat is still trying to extract wind energy to produce motion.

 

I too have built "scads" of models and tested them and this is well documented. Backyardbill knows of my work and seems to understand it. I've tried many times to get 2 and 3 blade rotors to work as well as the multibladers, but they just don't, and as you know I've published plans for people to test this themselves, but no-one has done it. Hightacker criticises me who has done many tests, he also criticises Backyard for not doing tests. How can anyone win?

 

I wonder if this could be related to gearing. Wouldn't a turbine with more blades have greater torque at low wind speeds? If so, then it implies that to use more efficient turbines with lower torque, you have to use different gear ratios.

 

Multiple blade rotors can probably produce more power for a given diameter. Fat blades vs. skinny blades would also have more potential for extracting power.

However, blade to blade interaction becomes a concern for increasing drag.

If you can get a good combination of power and efficiency, the smaller diameter would have advantages.

For most of us, the resources to do fancy computer modeling or really well controlled testing is just not in the cards. Therefore we look to others to see if someone with lots of resources has figured out what really works. Although the stationary power producing windmills are not quite the same as rotors for wind power craft, they are probably the closest thing out there. Since that industry has the money to get serious with optimization, the configuration they seem to have settled on would appear to be a good choice.

On the other hand, for the craft being considered, there could alternate configurations that work well. Adjustable pitch and proper blade twist are probably no-brainer required features for good performance. There are probably techniques that allow for good efficiency and power in more than three blades. Just realize that you may be trying to re-invent the wheel when going with a more conventional approach may allow you to get a free ride on a lot of research by competing companies with a lot of real money on the line.

 

If you want to learn from organizations that have spent enormous sums of money on R&R, look at power companies. The result of their studies is that a three bladed turbine is the ideal compromise. It offers good power production with good balance. Also, the blades are long and narrow, with variable pitch.

 

Hello again, Windmaster,

You can win by scaling up to a life-sized, practical boat that will go to windward, and in all other directions, at better than 55% of the wind speed, beginning at, say, 2 knots of wind, and then in more than a mild breeze, which you have not done yet, even with little models, so, say, 20 knots of wind, and in something with more of a fetch for wave action than a millpond, say, at least in a sizable lake or river, if not the sea.

But before I get further into that, please note that I did not get into this forum to criticize anybody. I started off by trying to tell the history of my experience with wind turbine boats, especially my personal experience with Jim Bates's very successful boats. I have no axe to grind with respect to such boats, no patent, no claims, no vested interest in development of such boats by Bates or anybody else, but would dearly love to see somebody take up the torch and continue development of the concept.

I took the turbine propulsion system off my boat because it was unsatisfactory, largely due to mistakes that were made in changing Bates's design. See photos below, one of her original incarnation and then three photos of the boat as she is rigged now, more photos and details at

www.damsl.com

Note that she now has conventional sails...uh, well, an A-frame mast and 4 furling and boomless sails deployed in unusual configurations is not quite a conventional sail plan, yet.

I wish that I could continue work on the wind turbine project myself, but am too old and have long since shot my wad on it. In fact, my time and money spent on the project, between 1965 and 1992 when the boat depicted below was launched, figured heavily in my divorces from two wives. My number two wife, soon to be 2nd ex-wife, said to me, "Why are you doing this? This is something the government should be doing. YOU don't have enough money." And she was right.

Nothing would please me more, Windmaster, than to live to see you scale up your little toy boats to life-sized, sea-going boats, say, of the size that Jim Bates did, a 30-ft. monohull and then a 40-ft. cat. And I would be delighted if you proved me and Jim Bates wrong with respect to 3-bladed versus multi-bladed turbines, and go on to a commercially successful design.

But I don't think that's gonna happen. And so far, you have presented no evidence that your little boats prove anything more than that MAYBE they are indeed going slowly to windward in a very mild breeze. You have admitted in previous posts that Youtube videos do not constitute documented proof.

I'm sorry, but I don't see any incentive for anybody to build models according to your plans, just to see if it will work. Essentially the same models you have exhibited, so far, were done by Bates in the 1950s and also by me in 1965, and similar models were done by others before us ages ago.

Rick Willoughby, whose posts on this forum are very informative, recently updated me on the DDWFTTW guys at

www.fasterthanthewind.org

and they are supposedly getting ready to try to go upwind faster than the wind. I have my doubts about that, but learned long ago to be very careful with use of the word impossible.

But a look at their two blades at the beginning of that website indicates to me that they are on the right track with respect to the shape of the blades. They also have good streamlined shapes on the hub of the prop and the mast on their DDWFTTW vehicle. They will have a better chance of accomplishing the same thing upwind with a land vehicle than they would have with a boat, I think.

As I've said in previous posts, a 2-bladed turbine is more efficient than a 3-bladed one, and is probably the best choice for trying to set a record in a specialized craft built for upwind only. But, in real life, for practical applications and for survivability, I think the vibration and noise levels of a 2-bladed turbine will indicate that 3-bladed is the best compromise.

 

High Tacker

Thanks for your reply.
I'm very pleased to hear you wish my endeavours well.
But you did seem to be pouring cold water on anything that departed from your fixed opinion - remember - no-one knows everything.

I know what I know, and I have learned it through testing, not theory. The work goes on - regrettably at a slow pace.

Although, as you admit, your wind-turbine rig did not come up to expectations, the concept is proven elsewhere, and I can see you are still fascinated with the subject and I hope others will be to.

 

Wind powered vehicles

Hello everybody.
I am the project leader of the SpiritOfAmsterdam.com wind powered vehicle during the 2011 race and i have been a member of the team since the beginning of 2010 (Participated in 2 races).

The wind powered vehicle race (WPV) is a race between multiple WPV that can travel directly into the wind by. De race itself is only into the wind. We basically drive a track (like a runway) of about 200 to 400 meters long and we measure the achieved wind efficiency. This means that if there is a 10 meter per second wind and the vehicle drives an average of 6.6 meter per second than that vehicle will have a score of 66%. The current record is 74.5% set in 2011 by the DTU breaking the previous record (66%) set by my team the Spirit of Amsterdam 2.

The vehicles itself are most efficient while driving strait into the wind. If the vehicle goes downwind then the rotor will not function like it is designed and will not provide power to the system. It will instead function like a sail and push the vehicle downwind. however with this concept this is not efficient and is therefor not part of the race.

It is true that driving into the wind creates more drag, but because of the aerodynamic shape around the rotor the achieved power input can almost double witch it enough to offset the additional drag element to a certain point. And that point is a point that every WPV at the race will try to prolog. Because this point determines the efficiency of the vehicle. Theoretically a efficiency over 100% should be achievable. Infact this has already been proven to be possible if you don't confirm to the rules and regulations set by the race committee. So every year we try to get to the 100% threshold and try to overcome this within the limitations set by the committee.

One of the limitations is that any kind of propulsion other than wind energy generated by a rotor is not allowed. Creating a hybrid that also has sails and a rotor or has solar panels or any other kind of generator is not allowed in the event.

The aerodynamic shape around the rotor can determine the characteristics of the vehicle by utilizing the Venturi effect. (See http://en.wikipedia.org/wiki/Venturi_effect) We basically compress the wind so it flows faster thru the rotorblades and therefor achieve more power input. But this also increases drag. For example the spirit of amsterdam vehicles are very good at low windspeeds because of a big venturi ring. With this aerodynamic venturi ring we are able to overcome the betz limit (up to a certain point).

Every teams has its own kind of wind propulsion system. Some use pitch fixed blades and control the input with the rotor speed and others control the power input by keeping the rotor speed at a constant level and adjust the pitch of the blades. This adjusting can be very complicated for the driver to do while driving so some vehicles have computers inside the vehicle to do this for the driver. Most vehicles are mechanical however some are completely electrical. So far the mechanical vehicles are performing better then there electrical sisters. However more and more teams are taking the step to go electrical because with a mechanical vehicle it is almost impossible to adjust to fast changing wind speeds while electrical vehicles can! Sadly building an electrical vehicle is much more complicated than a mechanical vehicle.

I think that the concept of this race could also be applied to a boat race like the Dong Energy Solar Challange for boats(http://youtu.be/xLnEcUAHupc). However would there be enough support for this by universities or individuals with to much money? I don't know! It has taken a long and painfull time to get the Wind powered vehicle race event to the point it is today.

For more information about the event and/or the Spirit of Amsterdam vehicles then please visit www.SpiritOfAmsterdam.com or reply to this post!

With kind regards,

Ingmar Hendriks
Member 2010 Spirit of Amsterdam team
Project leader 2011 Spirit of Amsterdam team

 

A 2-bladed turbine is not always more efficient (At least depending on its purpose). It completely depends on the aerodynamic shape of the blade (how big is the wake behind the blade?), the wind speed condition and the purpose of the turbine (low drag or high power). During the Wind powered vehicle race in 2010 and 2011 we always measured the current wind conditions in order to determine how many blades we should use. We could could chose between a vehicle with 3, 4 or 5 blades depending on the wind speed. At low wind speeds we used the 5 blade setup. However in general you are mostly right, 2 Bladed turbines are in most conditions more efficient.

 

Hi Ingmar,

Congratulation on your many successes in the WPV races. Do you think that you will ever reach more than 100% wind-speed given the limits imposed on the turbine size by the rules? The team that went directly downwind 2.8 times faster than the wind last year plans to achieve it in the upwind direction too:
http://www.fasterthanthewind.org

But if you would build appropriate rotors (propellers instead of turbines), do you think you could achieve directly downwind faster than wind, or is that too difficult with such small rotors. In strong enough winds it should work.

How do you make sure the electric ones don't store energy somewhere in hidden batteries?

 

Thank you.

We actually had some contact with the DDWFTTW Blackbird earlier this year. I am very excited by there ambitions to try it upwind as well. Luckily for them they don't have the ambition to join the race and don't have to conform to the rules and regulations that apply for us. I believe that will allow them to be just as successful upwind as they went downwind.

We believe that it is only a matter of time before a WPV in the race breaks the 100% limit. But it depend on so many thing. Every year we try to reduce aerodynamic drag and optimize the rotor, but we also try to reduce the weight and roll resistance.

In the last 3 years we have managed to achieve very good results will this. For example the Spirit of Amsterdam 1 had a weight of 220Kg. And the year after we build a WPV with a weight of 110Kg. And earlier this year we build the Spirit of Amsterdam 3 with a weight of 60Kg (All measurements were taken without a driver onboard). The reduced weight result in less roll resistance.

When you look at our vehicles you can also clearly see the evolution of the aerodynamics in the vehicles. The Spirit 1 for example has a very big body. This was the first time we entered the race and aerodynamics weren't that important that year. That year we just wanted to build a vehicle that was able to drive. The aerodynamic body was only added 2 weeks before the race.

With the Spirit of Amsterdam 2 this was a completely different story. Instead of building the WPV and then placing a aerodynamic body on it we first made the body and then build the vehicle into the body.

We did the same with the Spirit of Amsterdam 3. It has the most optimal body yet. Only downside is that you have to be very small if you want to drive the vehicle.

Because we already build 2 mechanical vehicles we decided that the third vehicle was to be an electrical vehicle.

At the moment the current official record is 74.5% efficiency however during a test run in 2010 the Spirit of Amsterdam 2 achieved a 78% efficiency. Sadly this was not during the event and therefor is not official.

The theory about DDWFTTW vehicles is almost the same. So yes with some modifications is should be possible to make our mechanical vehicles downwind vehicles. However with the Spirit of Amsterdam 2 this would require us to redesign our entire drive train.

In the Spirit 2 we actually have 2 drivetrains and 2 gear boxes. By having 2 drivetrains we are able to shift gears in a fraction of a second without a clutch. We do this with 2 electromagnets that can switch the drive train.

The current design doesn't allow the wheels to drive the rotor. In fact, the vehicle is not even capable to drive in reverse because of its low resistant freewheel bearing.

The Spirit 1 however is easier to modify. With the spirit1 this would only require different blade. And the Spirit3 can drive any way the driver wants as long as it is generating power with the turbine. But it can't use the turbine to propel the vehicle forward.

See http://youtu.be/T1wJuUGGJV8 for the construction process of the Spirit of Amsterdam 2. And for other videos visit http://www.spiritofamsterdam.nl/media/video-s/2010/

It is not allowed to use batteries that are charges before the race. In the rules and regulations of the event it states that the use of precharged batteries is not allowed. The battery has to be empty before the race.

Before a race the race officials inspect all the vehicles. They check wether the vehicle is compliant with the rules and regulations. For example they check if the driver has 2 mirrors and if the horn works and if the batteries are not connected to the drive system. The use of batteries is only allowed for systems that don't contribute to the power output of the vehicle to the wheels (Like a screen or for the communication system).

With the spirit3 however we don't use batteries to temporarily store energy during the race. We use very large capacitors that can buffer the energy for a few seconds.

The spirit of amsterdam 3 is basically a very big buck converter. The "generator control system" outputs a maximum of 400Volts. This voltage needs to be converted to a maximum of 60 Volt DC. This is achieved by the buck converter that has the capacitors. Then the energy is used by the engines. So there are no batteries. We can't even charge the vehicle and go for a ride that is more than a few seconds. The buffer is mainly used to capture energy spikes in the output.

In 2009 and 2010 we were able to win the race. Sadly the electronic system in the Spirit of Amsterdam 2 and 3 didn't perform as expected during the 2011 race because of an electrical failure and we were not able to participate in most of the races on the qualification day.

But in 2012 we will be again participating and we will be there to win.



Ingmar Hendriks

 

Spirit Amsterdam: Are you claiming in post 132 that you can produce over 100% efficiency? In engineering or physics terms that means you claim to have designed a turbine that creates energy. I can't believe that and it puts all your other claims in a bad light. That is, it makes them suspect and not readily credible.

 

When i talk about more than 100% efficiency i mean the windspeed compared to the vehicle speed. This however is possible! (So i am not talking about the power coefficient ( power output from wind machine) vs (power available in wind ) but between the ratio of wind speed vs vehicle speed.) So i am talking about the efficiency of the vehicle and not its turbine.

When there is a 10 meter per second wind and the vehicle drives 10 meters per second into the wind that is 100% efficiency. When you drive the vehicle you create your own wind. So in fact the wind that goes through the turbine will travel at a speed of 20 meter per second. So the faster you go the faster the wind will blow into the rotor. This is an acceleration that is only limited by drag and roll resistance. At the moment this limit (world record) is set at 74.5% but just like traveling downwind faster than the wind (Like the Blackbird) it is theoretically possible and proven in a wind tunnel.

By utilizing the venturi effect (explained in post #129) with the aerodynamic ring around the rotor we are able to push back the theoretical betz law of the turbine. The Betz law means that wind turbines can never be better than 59.3% efficient.

I will attempt to explain this:
The aerodynamic venturi ring around the vehicle actually forces more wind into the rotor than the actual size of the rotor normally has without a ring. This compression of the wind also accelerates the wind into the rotor. The turbine we have can, under optimal conditions, speed up the wind by a factor of 1.41. Thus the power coefficient for our vehicle is higher than an rotor with a similar size but it is the same for a rotor that is 1.4 times larger.
http://en.wikipedia.org/wiki/Betz'_law

Ingmar Hendriks

 

using term efficiency in that context is very faulty. It also makes reaching exact wind speed seem some kind of barrier what it in fact is not (except in our heads).