wind power

You should have learned the formula for drag in grade 7.

The only recent change has been to add the coefficient. It used to be 1 until they designed cars that had such good aerodynamics that it reduced the drag to make the object appear to have a smaller surface area then it really does.

See:

http://en.wikipedia.org/wiki/Drag_equation

The formula for lift can be found here:

http://en.wikipedia.org/wiki/Lift_(force)

I forgot to mention it: I am graduating as a designer, not engineering. But I surely appreciate your reply on the question posted.. In the drag formula, I understand that there is a drag coefficient regarding the surface, but when the surface area is facing the wind directly, like a perpendicular sail, what number should be used in the equation? The drag force should be multiplied by the distance from the centre of rotation, resulting into the torque, correct? and giving the torque together with the rotational speed I can find out the correct gearbox to be used for that input right? still trying to figure it out, as teachers in my collage were not able to explain completely what I needed to know.. Thank´s a´lot! and if you ever decide to visit Brazil, I can provide you all the tips you could need..

You are on the right path.

2 limits are to be respected:

- the transmission torque should be > the maximal torque which could under any circumstances occur

- the dynamo speed should not be > the limit of the device you choose.

There many much more detailed aspects to take care of but it goes too high and it will confuse you so that if you consider the above limitations you can make a good spec.

Consider also that the higher the speed of the dynamo is the smaller will be the device so that you are interested to work at highest possible speed.

Again good luck with your project.

Did you mean Generator or alternator or dynamo when you wrote "eletric engine"?

Also, please be so kind as to use the spelling checker, then at least you could have corrected "eletric engine" to "electric engine".

Remember, any words underlined in red are not recognized.

You´r right, I mean dynamo. After I am able to predict what my power input will be, with a given torque, I will be able to choose the gearbox suitable for it, and with the RPM output of the gearbox, the correct dynamo. this is a design graduation project, but it involves just as much of engineering skills..

If you use a car alternator with built in charge control electronics, they are designed to give a good output from an engine say from 1200 RPM to 6000 RPM (as a middle of the road range), this means that if you measure the difference in pulley sizes between the one on the end of the crankshaft and the one on the alternator, you can accurately work out the actual RPM range for that alternator.....

Whatever it is that is an extremely wide range of RPM that maybe you will NEVER need to think of a gearbox!!

Remember, a gearbox is an extra drag or loss on top of whatever you have already, if you can do without a gearbox, its better.

Instead of a gearbox, its better to have a pulley to pulley ratio to fix the speed range, with a "V" belt, its drag is usually much less.....its also far simpler to change things if you get it wrong!!Simple mechanics are always best, especially outside....

In general for the specification of a gear box you need to indicate:

- input & output torque or input torque and ratio between input and output speed

- input speed.

The power is for you electric device but not for the gear box.

Anyway a power is the product of a force or torque with a linear or rotational speed. Since you designed the wind generator you know all parameters for the computing of power and torque as functions of wind speed. If you cannot do it then some thing is wrong.

Forgot to mention it, I am a designer, that´s why my ability to solve this out on my own was a bit limited. Anyway, I appreciate you´r reply and it looks like I am approaching the resolution I need.

the input torque will have a rotational speed which should be maintained even if the wind velocity changes, but the torque power should variate progressively (possibly using a continuous variable transmission) so that as the wind speed increases, there is a larger RPM output from the conversion of a larger torque by the gearbox..

The wind is captured by a rectangular sail, so I will have to find out the expected power out from the drag produced by the sail attached to an rotational arm, multiplied by the distance of it from the centre of rotation (Multiplier effect). When the wind speed increases, the sail should keep rotation with the same velocity, but the torque ate the axis of rotation will increase and result in a larger RPM after the conversion..

Thank´s a´lot for your time, and if you ever come Rio let me know. always welcome.

Ok let us think together a bit.

The torque is proportional to the difference between the arm speed and the wind speed this difference gives the "drag" and the moment. If wind speed increases and (as you mention) the rotational speed stays the same then the torque will increase as well. The ways to maintain speed constant are either a change in the sail area or in the "resistance" of the electric machine (generator). If you keep the sail unchanged then the speed will go up and the power generated as well it will grow till a new equilibrium between input and output will be reached. To choose you transmission which ever type you want you should consider the situation where you get the maximal moment for transmission capability and the one where you get the highest speed for the bearings. The first is used to design/choose the transmission element as capacity and the second for estimation of life expectancy. Do not forget that a higher speed means also a higher power and thus a higher "resistance at the generator side.

Good luck for your work hope you will get a good mark.

great! so, for a 6metre squared sail, fixed at a 1 metre long arm, at 10km/h wind will give a certain torque, and with a 60km/h wind a much stronger torque, but with the sail turning with the same speed. I was planing on using a conical transmission, the continuously variable transmission, and a dynamo suitable for this wind range, but how should I complete this calculation in order to give the dynamo and gearbox supplier the correct specifications? the input RPM could be maintained, but the output need to be suitable for the dynamo range, which by it´s turn depends on the transmission input torque changing with the output RPM...which needs to be infinitely big compared to the sail slow but 'strong' turning speed. Thank you so much for your time and if you come to Brazil it will be of my greatest pleasure to show you around..

The only time you actually need a constant output speed is if you plan to make AC current for your own usage.....and you of course need a steady frequency.

Otherwise, if using DC with say one or more car alternators,(as i have already mentioned) it doesn't matter if the speed varies!! Therefore you need no gearbox!!

It would appear to be much simpler for you to use DC (at 12 volts or 24 volts with a truck alternator) )and not AC.

Learn to walk before starting to run.......there would appear to be more than enough problems for you to fix in that area, without adding to them....!

If you can keep a large bank of 12 volt batteries charged by the wind, you can use a converter(s) to make mains voltage from 12 or 24 volts!!

Surely, I agree. Sorry to bother you with this again, but the output speed will not be constant, my intention was only to have the input speed constant, as this is a sail system that can be compared to this vertical axis windmill http://en.wikipedia.org/wiki/Image:Windlahor.jpg. As I have no cost limitation at this stage I was thinking on using that modern transmission type that has two inverted cones changing angles and making the multiplication automatically (forgot to mention that too, the gear shift has to be fully automatic) and with this continuously variable transmission the gear change would be smooth and progressive. All I need now is to specify the space required for all that gear, and the dynamo, which I can only find out if I give the company who can supply this equipment the numbers for input torque range and the maximum possible output rpm range to select the best dc dynamo. If I have a 6squared metres sail, turning from a one metre long arm, what could be an interesting input speed for the gear system to start converting the strong drag from the wind into sufficient rpm to start charging the battery bank at a slow wind condition and what would be the maximum power obtained of a very strong wind condition of let´s say 80km/h.. thank you so much!

You are overdoing the engineering!

If you are producing DC for say battery charging, you probably only need to get to 1000 RPM with a modern Alternator to have 90% of the maximum output. A few hundred RPM more and you have 100%.....the Alternator will then produce 100% of its output up to probably 6500 or more RPM.

If you just want to throw money at the project, then do so, but please remember that a gearbox WILL REDUCE THE MAXIMUM POSSIBLE OUTPUT!!! Why, because it will impose an extra drag, in cool weather more as the oil inside gets thicker......

If you had read my last post more carefully, you would have seen a reason to have a constant speed, there is only one!!!

If you mean to get output when the winds are very light, THE LAST THING YOU NEED IS THE DRAG OF A GEARRBOX, taking maybe 90% of the energy at that time when little energy is available....!!!!!!

Please go an do whatever you want, all I am trying to do is make you aware of the pitfalls in what you propose.....then when it does not work as you would like it to, you will know the reasons why......

ok, so if I have a sail turning at 30 RPM, I would need to make a pulley ratio that would multiply it by 40 to get 1200 RPM. What wind speed would I need to get enough torque to reach this output RPM, and with what sail area..I need to add some kind of output power range prediction to this project, based on my scale size model, specifying it´s size based on the energy required to make a car alternator run to it´s maximum efficiency in a good wind condition, using this drag system. very difficult for a designer to find out this numbers..

In stead of getting affraid you should think logically:

- on one side you have your wind mill at the other side the generator and in between the transmission.

- the link of the transmission couples in a given way (rigid or variable) the 2 speeds so that you should first know the functions of the 2 end with respect to speed and torque

- when you know them you modify one or the other to the other end via the transmission which gives you the ratio of speeds and the ratio of torques considering as well the efficiency.

as a remark a ratio of 40 with pulleys is not so easy to obtain. you should think about ratios no more 2...3 per step with friction belts and for toothed belts you should look in the supplyer data sheets for a more detailed specification.

In your analysis do not forget that the drag is function of the "relative" wind speed with respect to the sail speed. This means that if the sail has speed null you obtain the maximal drag but no power output and if the sail has same speed as the wind you have no drag thus again output zero.

so from a dc motor specification I could know the speed and torque in which it operates(what could be a suitable specification to charge a large battery bank?), so that I can trace back and, with the same ratio find the torque needed from the sail. how to calculate the torque that could be obtained from a 3squared metres sail fixed at a one metre arm, and what should be it´s speed relative to the wind? that´s the biggest doubt, now that I understand you explanation..

Do not use motors as generators, they are notoriously inefficient, except for a few exceptions.

Use an Alternator that was designed to charge batteries, it will be about 4 x more efficient....

I would suggest that you start off in a small way and aim to learn a lot before investing any big money, your knowledge is just too little at this time.......

Have a look at Savonius windmills, they are easier to design and do not "look like" a windmill from a distance. Also connecting an alternator at the bottom is much simpler.

Checkout this link:-

Savonius_wind_turbine

For a given wind speed the wind mill will accelerate as long as the torque given by the wind will be equal to the resistance brought via the transmission to the mill shaft.

This concerns the speeds.

As I explained in a previous mail the torque decrease when the wind mill speed goes up because the relative speed decreases as well. On the other end the resistance grows up when the speed increases so that the 2 curves will cross at the equilibrium point. For every wind speed you will get another cross point if you work either with a fixed or variable speed.

The cross point depends on the wind mill design on one side and on the resistance offered by the generator on the other.

It is a pity that you are given such a project and you do not get in the school the necessary support. Usually a project should be so chosen that the staff of the school is in the position to bring the support students need.

Or is it a project you want to make on your own and the school has nothing to do with it. I start to have some doubts since i cannot believe that teachers in a school will give a project they cannot give the needed help for.

You pose some good questions, I hope that answers are forthcoming...

I have the feeling (rightly or wrongly!) that its his own idea and he has little knowledge and only us on CR4 for support!!!

I hope he starts in a small way and builds his knowledge gradually......

I am finishing my Product Design course, at PUC-Rio, one of the best collages around (compared to the rest), and the last subject we take before graduating is called "Final Project". In the beginning of last semester, mid august, I decided to change my final project from a 'breathing' lamp, to something more relevant compared to the world issues today, and as I was studying some environmental solutions for another business, working with venture capital (besides collage), I choose to create under the topic "Environmental Intelligence". From this point I started doing a mental map with all possible areas related with this topic, and it suddenly occurred to me, after having many ideas, the idea of a generator powered by the wind, having the strength of different sails turning the central axis, changing their angle depending on the position they were in the circuit. From this point on, I spend a lot of energy and time imagining how to make it work, and what systems to use. Initially I worked in a mock-up, made with wood, paper sails and skateboard bearings to see if the sails would behave as I planed, and then after a first presentation to have my teacher permission to keep on working with this idea, I started developing the shape and re-thinking the way it worked as a designer. I was advised by my teacher to look for help in the engineering department, but some of the teachers were not so available, and the ones that I managed to talk with did not anticipated all the knowledge you both made available for me. Regarding all this calculation, one of them gave me the lift formula to use and add a lost coefficient, but this is far away from any accuracy, and will not help me to calculate the minimal sail size required and what hardware should be specified. When I came back to my design teachers, in the final presentation (after staying awake for many nights I still was not able to finish my model and the power point presentation) they told me that it was a very complex project for a designer and that I should present it for research funds and possibly work further with it, besides giving me an extension to present it finished by 29 February. So now I am again working against the clock, and need to present it as a fully planed project. this means I do not have to spend any more money, as I have a mock-up scale model of the sails working and need only to predict where that hardware will stay, what it´s size will be and what king of electronic equipment should be added if it were to be produced. With all this I will be able to say in what scale my model is, and how much power could be expected from the real thing, with the necessary scale.

The resistance brought by the transmission to the mill shaft, need to be calculated based on the torque obtained from the sails, right? and the sail need to have a relative speed from the wind which will result in the larger possible drag. So how do I calculate all this?

The input torque range, which will depend on the force obtained by the sail, and the input RPM range, which depends on the best relative speed of the sail from the wind, will determine what transmission to be used. Using an alternator the transmission need to have an output RPM of 1000, to have it working with 90%efficiency, but with what torque? If I find this, and know what could be the best relative speed of the sail to the wind, I can predict the input torque necessary to have the alternator running at 1000 RPM, correct? Am I starting to learn all this?! What formulas should I use to predict these stages? I like it! I will find a way to thank you both.. specially if you come to Brazil...

This is late in the day and this information should have been presented on day 1.... some people here will not help with school projects, that is their take, it is not really incorrect either....I do not wory either way....

All the formula that you need you should bring or get from the school.....as you have the windmill design in your head.....its your idea

......it also needs a mast.....a pivoting generator head......and a way to get the electricity from a pivoting generator to the ground.....

.....which is why I like the Savonius design, it does not need to pivot and face the wind as the wind can come from any direction as it is vertical. This makes designing and building a lot easier.....the windmill can be covered also so that rain will never reach it, you can have doors to guide the wind or shut it off when desired.....

I have to say that from my personal point of view I would not have started in this direction of what would be termed a conventional windmill..........so are you forced to go on in this manner? Can we see any drawings that you have already made and presented.....and are you therefore forced to go in this direction? or can you "redesign" a little?

I do not think that you have any more time to sleep left before march!!

You are right! this is constantly on my mind, but it has been difficult to set aside all the rest and focus on this project only, specially when working with venture capital and with my father.

The wind power generator I´ve designed has a central mast connected with the 3 sails, all pivoting from their centre, and the electricity will be generated in the ground already, as the transmission will transfer the axis rotation to the alternator, multiplying it´s RPM.

My email is marcello_lb@hotmail.com

I have some diagrams scanned for the presentation so I could send them for us to discuss it better. Thanks for all!

I just sent you an email requesting copies.

Ok i accept your expanantion and i shall give you some support but i have not the time to do all the work needed to do it the right way.

I shall send you some input end of coming weekend. But for that i should have a sketch of your sail and how it stays with respect to the wind direction considered as horizontal. You can send it on a direct wat using if you prefer the private link.

I would like to have a look at this "modern" transmission with the cones could you mail the address wher i can see it? Thanking in advance.

http://en.wikipedia.org/wiki/Continuously_variable_transmission#Types

There are several which one is the one you thought about?

DEAR MARCELLO PLEASE CONTACT ME AT GMDEL@LIBERO.IT YOU CAN SEE MY WORK IN WWW.GMDEL.COM MY

Dear Sir,

I had a look at your products which give the impression to be very interesting. Which is the efficiency you obtain on your special propellers or turbines as you wish to call them?

I mean efficiency with respect to the wind power and of course the one on the electric side.

Thank you for more explanations.