3 Blades vs 5 Blades

keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
Below I cut and paste some statements I found regarding wind turbine blades, comparing 3 blades and 5 blades. #2 is the most puzzling to me. How is it that a 5 blade wind turbine would turn slower than a 3 blade turbine? Seems to me that a 5 blade wind turbine would start spinning sooner and spin faster than a 3 blade unit at any given wind speed.

With all things equal (same PMA), wouldn't a 5 blade turbine spin faster than a 3 blade turbine??
________________________________________________________

Advantages of 5-blade wind turbines over 3-blade wind turbines
1) 5-blade wind turbines will greatly improve annual energy production in low wind conditions. For areas with average wind speeds of 11 MPH (5m/s). If you compare annual energy output to conventional 3-blade wind turbine, there is an increase of annual energy output of more than 60%.

2) 5-blade wind turbines will dramatically improve the reliability and safety of wind turbine. The blade rotation speed of a 5-blade turbine is 60% of the rotational speed for a 3-blade wind turbine. 5-blade wind turbines will greatly reduce chance of overspeed control malfunction. This will ensure operational reliability from a long term perspective.

3) The lower blade rotation speed of 5-blade wind turbine will lower wind turbine noise and make 5-blade wind turbines more community friendly than 3-blade wind turbines.
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Comments

  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    im running an Air x now with 5 blades. 5ft dia as against the 3 blade 4feet dia
    it definately is less noisy than when it had 3 blades. the manufacturer of the 5 blade set says its because the "holes " between the blades are smaller.. I have no idea except it makes a lot less noise
    The generator starts making power in much lower winds than when using 3 blades
    its production of power is much greater in high winds,
    it was producing so much power in high winds it bent the 2" dia last 3 ft of pipe. had to add guy wires.
    I cant see how 5 blades can be going slower than 3 blades or it would be producing less power ????
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    number of Blades.

    this was a big discussion topic among model plane bulders in the 40's

    My dad flew planes with single blade props, and a counterweight opposite it. Won many races.

    it involves a lot of aerodynamics. A single blade gets "clean" undisturbed air all the time, and does not "cavatiate" easily. More blades = dirty air, but that can be compensanted for by lower RPM's because you can handle more torque.

    So, more blades are better for low winds, you have more "sail" area up there (look at old Dutch windmills with cloth sails) and as you get higher winds, the dirty air from the previeous blade keeps your speed down.

    -- added--

    Single blade race props for model planes (+300 mph) http://www.bolly.com.au/models/glass.html

    single blade discussion:
    http://www.flyinggiants.com/forums/showthread.php?t=10595

    pics:
    http://www.rcgroups.com/forums/attachment.php?attachmentid=668516
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  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    John, That's interesting real world info from your Air X wind turbine. I agree that it seems that if a 5 blade wind turbine would spin slower then it seems it would make less power (assuming the same PMA).

    Mike, That is very cool that your Dad flew planes with single props. I never knew such a thing existed. Must have looked very interesting when the plane just sitting there!
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    mike touched on the key there as the blades now have a much larger area due to going from 4ft to 5ft.
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    Attached is photos of the 5 blade version... in one typhoon the top section of pipe actually bent . its now been better supported..

    But as I said the 5 blade version must go a lot faster or how can the generator put out a lot more power????
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    see post #5. it is tapping more wind and thus more power when the blades are longer.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 3 Blades vs 5 Blades
    john p wrote: »
    Attached is photos of the 5 blade version... in one typhoon the top section of pipe actually bent . its now been better supported..

    But as I said the 5 blade version must go a lot faster or how can the generator put out a lot more power????

    You're missing the tricky bit; converting the available wind power into turbine power. Since the 5 blade version can pick up the lower speed winds better and actually produce power when a 3 blade set-up will just sit there the over-all power is increased. In other words you are correct if both blade sets would spin the turbine at the same RPM for a given wind speed, but they don't. It's that losses bugabear again!

    Ever heard a two blade turbine? "Whomp ... whomp ... whomp ..." Very noisy! The 3 blade version "turn into the wind" (change direction) better too. Not sure if 5 would improve that any.

    Not sure if a 5 blade version would show any improvement over a 3 blade if the swept area was equal either. Probably would start better, due to the torque ratio differences (more wind acting on the same equivalent leverage). Kind of difficult to compare, given the numerous variables.
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    Do you guys agree that with all else being equal, that going from a 3 blade to a 5 blade wind turbine would not result in 40% lower RPM's?

    I just don't understand how they get the "5 blades turn at 60% of the rotational RPM of a 3 blade turbine".

    I can understand the concept of the 5 blade turbine producing more low wind power, but I don't see how it can produce the same power with 60% of the RPM's.

    My understanding (maybe it's flawed) is that with all else being equal, the higher RPM's will produce higher power output.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 3 Blades vs 5 Blades
    Do you guys agree that with all else being equal, that going from a 3 blade to a 5 blade wind turbine would not result in 40% lower RPM's?

    I just don't understand how they get the "5 blades turn at 60% of the rotational RPM of a 3 blade turbine".

    I can understand the concept of the 5 blade turbine producing more low wind power, but I don't see how it can produce the same power with 60% of the RPM's.

    My understanding (maybe it's flawed) is that with all else being equal, the higher RPM's will produce higher power output.

    I suspect that all else is not equal. The pitch of the blades, for instance, will change the speed at which they turn. The 5 blade unit is probably specifically design to capture and run in the more prevalent lower speed winds, resulting in better over-all "harvest".

    If anything, the 5 blade would turn faster if everything else were the same. I reason (possibly flawed) thus: the RPM of turbine is a function of the wind speed against the blade design overcoming the resistance of the magnetic field inter-action. With "zero" magnetic field (load) the speed is "X". As the resistance increases, the RPM will slow due to power loss. Add two more blades and you gain mechanical energy so the loss lessens.

    As a rule, you're right that higher turbine RPM equates to more power, up to a point. It's all about converting the mechnical energy in the wind at any given speed into as much electrical energy as possible. Unfortunately, that means the blade design would actually have to change with wind speed! So you compromise and make a design that works best under average expected conditions.

    Or I could be completely, utterly wrong. :roll:
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    one thing I didnt mention but you can see it yourself in one photo I had to add a extra big tail fin as in strong winds the builtin tail fin can not keep the blades facing into the wind. The torque of the bigger and more blades, just twists the generator to one side in high wind, so extra fin necessary,

    with 5 blades have seen over 40a output with 3 blades never over 30a
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    Marc, what you wrote seems sensible to me.

    John, 40amps is a lot to get out of an Air X! How many years have you been running that Air X turbine?
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    3 and one half years. has run perfect. But have read in many places people having many problems
    of course it doesnt put out 40a in general but it puts out 15 to 20 a a lot of the time on 3 blades its average was about 8 to 12a.
    but its now putting out 3 or 4 amps in very light winds when it was on 3 blades it put out nothing
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    Sounds like the new blades were a good change for the Air X. Wonder why they don't do something like this from the factory. From what others have stated (like TruthSquad), it seems that SWWP doesn't always make the best decisions.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I've been thinking about 5 vs 3 blades a lot with my Windmax H5. The newer models of this turbine come in what I've got, a 3 blade "high wind speed model" and a 5 blade "low wind speed model" The 5 blade rotor isn't offered for sale as an upgrade but there is a 3rd party 5 blade rotor for the Windmax H400 which I think is the same turbine as mine. I'm thinking that is the way to go if I really want to get the power out of it that I would like but I have to think about high wind conditions as well because the winds here are really freaky and even though I would harvest a lot more energy with a turbine optimised for low wind, the turbine has to be able to withstand some really exrtreme, turbulent and gusty winds at times. My general impression is that more blades means more power at low wind speeds but more risk at higher wind speeds. There is more angular momentum due to a heavier rotor and more surface area exposed to the wind which makes slowing the turbine down in high winds more problematic.

    40 amps out of an Air X is really impressive. It is such a small turbine that you have to get it spinning really fast to get that kind of amperage out of it.
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    MisterB, That's my thinking exactly... the 5 blade models are optimized for lower wind speeds, but would be more vulnerable in high wind events. The 3 blade models are optimized for higher winds and designed to withstand high winds better.

    BUT, the way that it is described, they seem to state that the 5 blade wind turbine is safer for high winds because it spins at 60% the rotational speed of a 3 blade turbine. ?????? Doesn't make sense to me. Seems the exact opposite in my mind. The 5 blade turbine would spin faster it seems to me - making it more vulnerable at high wind speeds.
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    At the 40a output the speed of the blades is very high . As I already said after it did that a few times it bent the top 2ft of the 2""pipe that pipe goes into a 21/2 " pipe about 8ft above the roof line..

    Something else I forgot to mention on the 3 blade set you get provided with a shorting switch to slow the blades in very high winds . And its very effective bringing them almost to a stop,, BUT with the 5 blades when you short the output wires it only slows down a little and the output wires #6 get very warm..

    I know just about everyone says wind generators should be mounted about 40ft in the air with nothing nearby..
    BUT according to the maker of the 5 blade set that is not always the best and if its mounted closer to your house roof you get better wind flow over the roof.. He has photos of his house showing the wind generators mounted just above it..

    Im not going to get into an arguement about it as im no expert on such things..
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    If anyone doubts the power of the wind when it gusts from diferent diirections here are photos of the 1/8 mounting plate from my AirX using the 6 blade kit(it came with the kit) At the time the generator was once again putting out over 40a.,.. The Air X is still in perfect condition,, it has an excellent shaft bearing
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    That's a lot of force. You must have some very strong winds around there!
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    I mainly showed these photos as I dont think many believed that I really was getting 40a from that generator.. People like Truth Squad try to make everyone believe the AirX is useless junk,, But I think a lot of the critic from them is because they are ex employees and have their own axe to grind about the company
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    @keyturbocars:
    Two things to consider: First is that even a 2 blade turbine, if spinning fast enough, presents itself to the oncoming wind, as basically an almost solid disk, causing the wind to pile up in front of the spinning disk and flow out around it, instead of through the blades. So additional blades only make that problem worse. The other thing to consider with high speed turbines, is the drag of the blades. The more blades, the more power robbing drag. And that's not considering the additional "dirty" air stirred up by multiple blades.
    Not so with slow turning turbines.
    For high wind, high speed turbines, 2 blades, or like the airplane prop mentioned earlier, one single blade with a counter weight would be best, EXCEPT that with less than 3 blades, changing direction into variable wing directions is VERY rough and choppy, very hard on both blades and bearings, that's one reason for 3 blades. With their mass more evenly spread, somewhat like a solid wheel when changing direction, they are far smoother. The lessor of two evils.
    Yes, I did many years ago build from scratch, my own 14 foot two blade prop and used it. Awesome power, awesome speed. On a windy day it could easily be heard almost half a mile away, OVER the sound of the wind, it was that fast, like copter blades. Problem was with changing wind direction, which eventually destroyed it. Most of the blade was never found. It happened during a severe wind storm and God only knows what speed it was going. The extreme vibration from changing direction broke the generator mount. The belt driven generator then swung down on it's electric cables, and into the high speed blades, shattering them. A learning experience.
    And of course "swept area" is extremely important regarding power output. All other things being equal, a 5 foot turbine will have it all over a 3 or 4 foot unit. Just no comparison.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: 3 Blades vs 5 Blades
    The 5 blade turbine would spin faster it seems to me - making it more vulnerable at high wind speeds.

    One way to find out, take a child's windmill and remove one of the plastic wraps. See if it spins faster or slower compared to a regular one.
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    Good information Wayne. That 2 bladed wind turbine you built sounds interesting. I think I'll be content with my 3 blade wind turbine. It makes plenty of power as is. I thought about trying to get the hub and blades from the 5 blade version. I found out that the generating head is supposed to be the same between my "2kW" 3 blade wind turbine and the "3kw" 5 blade wind turbine. That probably explains why I've been able to see 3kW+ out of my wind turbine during strong gusts.

    bmet, That might be a simple way to do an experiment.
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    What happens if you simply "Fix" or lock the yaw on the turbine, so that the wind is either favorable, or less favorable ? Is it the off-axis wind causing problems, or the yaw of the mill, as the blades swing around and complex things happen?
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  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    well i added this extra tail as in the photo that helped a lot.
    046.jpg 230.8K
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: 3 Blades vs 5 Blades
    mike90045 wrote: »
    What happens if you simply "Fix" or lock the yaw on the turbine, so that the wind is either favorable, or less favorable ? Is it the off-axis wind causing problems, or the yaw of the mill, as the blades swing around and complex things happen?
    It was definitely the yaw of the mill. Think of it this way - - -
    Hold an 8 foot board vertically, and see how easily you can move it to face different directions. Almost no inertia. Now hold it horizontal and do the same thing. You'll find a lot of inertia if you try to change it's direction quickly.
    What happens with changing yaw on a 2 blade prop, as the blade approaches the vertical, the tail suddenly, very easily swings everything to the new direction. Then as the blades start to swing down to the horizontal, they undergo extreme stress as they "want" to continue traveling in their former direction, but now the bearings are trying to force them in the new direction. The result is that the whole affair goes through a violent convulsion, that repeats every half turn of the blades.
    Locking it into one heading, or controlling it's yaw so it could only change very slowly, then there wouldn't be that problem.
    Interesting stuff. lol
    PS: for clarification, the pitch remained constant, except for possible some slight bending of the tower under heavy loading, bit that was never an issue. All problems were the result of being just two blades, and the vibration typical of such designs, when changing heading to face into changing wind direction.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades
    It was definitely the yaw of the mill. Think of it this way - - -
    Hold an 8 foot board vertically, and see how easily you can move it to face different directions. Almost no inertia. Now hold it horizontal and do the same thing. You'll find a lot of inertia if you try to change it's direction quickly.
    What happens with changing yaw on a 2 blade prop, as the blade approaches the vertical, the tail suddenly, very easily swings everything to the new direction. Then as the blades start to swing down to the horizontal, they undergo extreme stress as they "want" to continue traveling in their former direction, but now the bearings are trying to force them in the new direction. The result is that the whole affair goes through a violent convulsion, that repeats every half turn of the blades.
    Locking it into one heading, or controlling it's yaw so it could only change very slowly, then there wouldn't be that problem.
    Interesting stuff. lol

    The yaw, as I understand it refers to the horizontal rotation of the turbine in response to changing wind directions and that the turbines vertical angle facing the wind is called the pitch. It sounds like you're refering to a combinition of a furling mechanism that alters the pitch of the turbine from horizontal to vertical under high winds in combination with changing wind direction which would be the yaw. My first turbine was an old SW Windpower Windseeker 250 2 blade turbine which used a spring based pitch furling method as an over speed control and under high winds it went fully vertical which made it sound like a helicopter. The furling worked well and the turbine survived high winds for over 18 years but the neighbors hated the noise. One thing I've noticed is that my new Windmax turbine starts shifting direction a few degrees back and forth under high winds which immediately cuts the power output and then the direction will hold for a short while, the rpm and current will go up until the turbine shifts again. This isn't a very violent shifting and there don't seem to be any unusual vibrations happening but it is cutting power output. Lately when we've had winds, there has been a very gusty wind pattern and the gusts are around 10mph above the average wind speed and I'm waiting to see what happens in a strong steady wind. If this happens under this condition, extending the tail looks like something to try.

    I bought this turbine hoping that I would be seeing 20+ amps of charge current in wind speeds 18-25 mph and it is not doing it so I'm looking at the 5 blade rotor. Magnets4less sells longer blades but they don't sell the 5 blade rotor for the HY400 seperately. It looks like either way would increase output--John P's photo looks like his rotor has both 5 blades and longer blades. The 5 blade roter kit from Missouri Wind and Solar is only 2 inches longer than the original HY rotor which looks safer. The sales pitch for the 5 to 11 blade rotors actually claims they are safer in high winds than a 3 blade rotor. It is a bit counter intuitive so I am just going to quote it directly. If all of this is true, then using 5-7 blades instead of 3 would be the best of all posible worlds for this turbine.
    #
    WIND TURBINE BLADE FACTS:

    REMEMBER! Bigger does not always equal more electricity! While the bigger blade sets do have more torque and thus turn easier in slower wind areas they DO however turn SLOWER when compared to smaller diameter blade sets on the same PMA. Make sure this is what you really need or you could be sacrificing electricity in the higher wind areas since small blades turn faster. Of course we are again assuming you are using direct drive PMA's here.

    As a overall rule, larger diameter turbines will always make more power IF they are optimized for a particular generator's output with the proper gearing. Generally speaking 8 foot is the largest diameter you can go with an ECONOMIC direct drive system. After the 8 foot diameter range blades spin so much slower that gearing makes better economic sense for operating most PMA's or generator's. The other option would be to waste copious amounts of copper wire and expensive magnets making for a very wasteful, expensive and heavy direct drive generator or PMA design. It would seem that the 7 to 8 feet diameter range is the transition point between economic direct drive and larger geared systems.
    THE "MORE BLADES" THEORY and ARGUMENTS:
    #
    Having lots of blades really gives you the best of both worlds. In low winds speeds, systems with 6 to 12 blades are a real power house! No argument here! They also have an advantage in super high winds since they can't REV as fast so they end up actually protecting themselves by going slower than 3 blade systems would that either self-destruct or become very noisy!!! The more research we do with multiple blade systems the more we believe in the More Blades Theory. These systems always come out on top out performing systems with less blades especially in high amp loaded conditions! Wind turbines experience "PROGRESSIVE LOSS" or Cascade Failure when under heavy loads. This means that the slower the rotor spins under load the MORE likely it is to spin even slower and so on (Cascade Failure) until the blades are moving so slow they can't catch enough wind to be effective anymore because of excessive "Way-Holes". This is why two and three blade systems need a computer to keep the blades rev'd up to speed. The computer removes the load by making fast adjustments and this keeps the blades moving quickly eliminating cascade failure. However a computer is not necessary when you have lots of blades working for you since cascade failure is impossible with all of that surface area!
    "Cascade Failure"
    The slower a blade spins the more likely it is to spin even slower and so on until it can no longer adequately catch wind as "Way-Holes" form in the propellers diameter matrix area.

    "Way-Holes"
    A potential power producing area of a wind turbine propellers diameter that is allowing air to pass through in-between blade strikes.
    or - The absence of a wind turbine blade in the winds path at any given point in rotation time usually caused by over-amperage loads including connection to lower voltage batteries used in low wind speed areas or high amperage appliances or lack of blade area in the original turbine design.
    #
    IT ALL BOILS DOWN TO THIS ONE SIMPLE LITTLE QUESTION IN THE END
    The REAL question becomes, WHAT is cheaper. Extra BLADES or COMPUTER controls???
    Well, at least in the case of small wind turbines it's a no-brainer,, Extra blades are much cheaper than electronic controls and definitely more dependable too - no computer electronics to fail!!! In the final analysis more blades equals super low wind speed start up plus the added benefit's of simplicity and dependability.
    Final thought,the large commercial wind turbines use 3 large blades but they are also all GEAR DRIVEN,not direct drive and use a computer to control the speed of the blades,otherwise the blades if allowed to speed up in high winds would simply explode.These type of turbines DO NOT REQUIRE HIGH SPEED TO PRODUCE POWER LIKE THE SMALL TURBINES DO.

    Missouri Wind And Solar
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: 3 Blades vs 5 Blades

    The WIND TURBINE BLADE FACTS is from Missouri Wind and Solar "Falcon Blades" section.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades
    BB. wrote: »
    The WIND TURBINE BLADE FACTS is from Missouri Wind and Solar "Falcon Blades" section.

    -Bill

    I copied it from the "Raptor" blade section which is the blade set I've been looking at but no difference in the text which is also on their ebay listings.
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I wonder how much of what Missouri Wind and Solar states is proven scientific fact, and how much of it is just marketing to try to sell more of their products. What they state is interesting, but it's good to take things with a grain of salt when people have mixed motives (trying to make a sale).
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades
    What they state is interesting, but it's good to take things with a grain of salt when people have mixed motives (trying to make a sale).

    I agree which is why I'm posting this to see what others think. I'm not all that knowledgeable in aerodynamics but even at that, this sounds almost too good to be true. The only thing I'm clear about is that it would be better to keep the rotor diameter pretty much the same. Seeing the photo of John P's hub reinforces that idea. Magnets4less has a 3 blade hub with longer blades:

    http://www.magnet4less.com/product_info.php?products_id=475

    It looks like it would improve low wind speed output but I don't like having my turbine's rated wind speed reduced to 17.9 mph. I will definitely see if I can get the 5 blade rotor for the HY400 before I buy the Missouri Solar and Wind hub and rotor. I would much rather have the 5 blade rotor specifially designed and made for my turbine.
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