3 Blades vs 5 Blades

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Comments

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

    The blades on mine take the dia from 4ft to 5ft and no matter what im told or what is written I just dont believe the 5ft blades go slower than the 4ft blades. The reason behind this thinking is simple.. if they went slower how does the generator then put out more power with the 5ft blades??? a generators output INCREASES with rotation speed. NOTHING ELSE.
    And mine went from a max of about 30a to over 40a in strong winds with the longer and more blades.
    Yes it would improve the safety of the generators blades and hub to lock the generator into one position at a small loss of power output..Im happy with it now with just the extra tail size and length
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades
    john p wrote: »
    The blades on mine take the dia from 4ft to 5ft and no matter what im told or what is written I just dont believe the 5ft blades go slower than the 4ft blades.

    I agree, I think the bigger the rotor, the faster it will rotate at a given wind speed and the more force will be leveraged against the hub and the more rotational inertia it will have which will make it harder to slow down. I had to swap a strut on my 4wd toyota last year and there was a big bolt with a lot of rust that wouldn't move and I got it loose by slipping an 8' iron pipe over the socket wrench which easily moved it. The same principle applies to the force the blade puts on the rotor. The longer the blade, the more force it exerts on the hub and the stronger the hub needs to be.

    In looking at ways to improve the output of a turbine by changing the rotor, there are two ways, increasing the diameter of the rotor and increasing the number of blades. Your installation does both which explains the fantastic output you're getting with your Air X as well as the problems you've had with too much mechanical force. Just thinking on intuition with no math to back me up, I would be inclined to think that more of the force is coming from the the increased rotor diameter and not the increased number of blades.
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    MISTER B you are right and wrong I did try using 3 blades 5ft dia only and YES did get increase in power and "BIG" increase in noise as compared to stock AIR X blades.. went to 6 blades noise dropped a huge amount below the std AIR X and more output
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: 3 Blades vs 5 Blades

    Some of these blade theories should be worth testing on the miniature scale.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    @John P
    Just to qualify things a bit about what I referred to in my previous post. By "force", I was referring to problematic excessive mechanical force that causes mechanical problems like bent rotor hubs even if it gives more power output.

    Reading about your installtion and your experiences with it has convinced me that the way to go for me is more blades but with the same rotor diameter. My experience from going to a turbine with a 2 blade prop to one with a 3 blade one is that the 3 blade turbine is a lot quieter which makes my neighbors a lot happier so I have no problem believing that adding more blades will make it even quieter.

    And just thinking about the mechanical issues, it seems a lot safer to add more blades to increase power output than to make the blades bigger and heavier. A 5 blade rotor with the same diameter of a 3 blade rotor and the same blades will be 2 blades heavier but the weight, if the rotor is balanced properly, will be evenly distributed over the diameter of the rotor and the force aplied to each individual blade by the wind will be the same as with the 3 blade rotor but if the blade size is increased, the mechanical force of the wind on each individual blade will be increased.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    Isn't 3 X nothing more or less equal to 5 X nothing? Plus expenses naturally.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades
    russ wrote: »
    Isn't 3 X nothing more or less equal to 5 X nothing? Plus expenses naturally.

    I wouldn't call the output of windturbines nothing in any way. It's true that the wind energy industry is filled with excessive salesmanship filled with inflated figures and there is a lack of any kind of standard in small wind but that's business, not the fundimentals of the technology which are pretty sound if done right.

    Wind energy is very good in an off the grid situation. I've gone through plenty of winter storms like the one that's just ending now without running a generator thanks to my turbine. I'm a bit more scetipcal of Skystream and using small wind for grid tied residential systems. Solar is much more neighbor friendly, simpler and cost effective.

    And back to the original subject of this thread. I have been getting a fairly good and constant output at 5-10mph wind speeds of 1-3 amps with 3 blades. This is happening pretty much daily while higher winds usually happen when weather is moving in or out which is when the higher output is most needed. Improving this low wind output to something like 3-5 amps at the same wind speeds and some output at even lower wind speeds with 5 blades would increase the overall harvest of the turbine a lot. The information put out by the various vendors about the 5 blade turbines is a bit contradictory and counter intuitive but the overall, I can see that more blades would increase output to a certain point but I'm really sceptical that going from 5 to 7 or 9 blades is going to make that much difference.

    I've decided against Missouri wind and solars blade kit due to their hub adapter which is held in by inset screws that would ruin the orginal threads on the Windmax's spindle and not let me go back to the original rotor. It would be so much simpler to have a hub designed for the Windmax. I'm also put off by the tone of the salesmanship in the Youtube videos about it. If they just stated the facts correctly instead of implying that the 3 blade HY400 is a lost cause without their blades, I'd be more inclined to deal with them. After the spring gives this turbine some good high wind tests, I'll think about buying a 5 blade HY400 and testing it and keeping the one that works best for me and selling the other one.
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: 3 Blades vs 5 Blades

    John's 5 blade turbine is 1.56x the area of his 3 blade prop.

    Sounds like the original 3 blade did not have enough torque in moderate wind speeds, so the turbine is turning too slowly for maximum current output.

    By the way, a 5' turbine's tips will exceed the speed of sound by 4,300 RPM. At that point you will hear the shock wave from the tips going supersonic (a crack like a whip).

    At that point, the output torque should start to be limited.

    What is the maximum rated RPM for an Air-X?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    i was hesitant to say anything before as i'm not sure if i'm remembering correctly or not what i'm about to say in the comparing of 3 blades to 5 blades, but here goes.

    more blades captures more power, but also creates a vortex (may be wrong word for this as eddy currents may be applicable) behind the blade for the following blade to hit. as such, these vortexes tend to slow down the tip speed and could lead to a need to regear to properly extract the power. there is also a diminishing amount of power gained with each successive additional blade added, but a marked increase in the vortex behind the blade as well as the distance between each blade is now shorter.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    I would suggest looking at Scirocco, Jacobs, Proven or Bergey - not SWWP unless you are a fisherman and will be needing a boat anchor in the near future.

    All more expensive than the small kind but if you have adequate wind along with the tower required they will provide good service - at least you have a chance.

    All are 3 blades - none of the commercially successful turbines that I have seen use 5 blades. Possibly helpful for lower wind speeds (say above 5 m/s) but when none of the people building 'real' wind turbines go for them I suspect there is a good reason.

    Russ
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: 3 Blades vs 5 Blades

    I spent a few years working around C-130 Hercules airplanes while in the USAF. These airframes originally had 3 blade propellors, but in time the AF upgraded the entire C-130 fleet to 4 blade turbo-props. I wonder what a 4 blade design would do for generating 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.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    I would expect that the 'real' wind turbine companies like Scirocco, Bergey, Jacobs and on have looked at this point of how many blades.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I got to see a really well done grid tied system this weekend with 1.4kw of solar and a 1 kw Bergey turbine. I really admire the Bergeys, they really pay attention to details that other manufacurers ignore in both the turbine and controller. SW Windpower is the curse of small wind, if anything. They have a huge market presence and dismal quality in comparison. This Bergey is one of 3 turbines in my area that isn't a SW Windpower turbine almost all of which are AirXs. One of the other 2 is mine.


    I just looked at the specs of the AirX. You get a glowing sales spiel on their website and have to download the real specs in PDF format. No mention of RPM, max or otherwise in the manufacturer's specs. The survival speed is rated at 110mph. The startup speed is 8mph. The rated speed is 400 watts at 28mph. The Air X, according to the specs, should hit 50 watts at around 15mph. If you look at the power output chart, it is an exponential curve and the useful power range is all between 20 and 30 mph at which point the overspeed control kicks in. Putting more and bigger blades should lower the rated speed(rpm/windspeed) but this is a narrow range to work with.

    Both the 3 and 5 blade HY400s have a rated speed of 400 watts at 26.8mph and the 3 blade model I have has a start up speed of 5.1 mph and the 5 blade version has a start up speed of <3.35mph. The power vs windspeed chart for the HY400 is much less exponential and the low windspeed output is much better--100 watts at 15 mph vs 50 for the AirX. I can verify this for the HY400. As with the AirX, no mention of actual RPMs at a given windspeed from the manufacturer in their specs.

    There is also no mention of current output in most wind turbines spec sheets, just watts at a given wind speed. This information would be useful both in confirming the ratings given by the manufacturer and just useful in designing a system. Solar panels come with ratings in Watts, Current and Volts. Why can't wind turbines come with the same information??

    And I wouln't make assumptions about what companies look at what design ideas. Innovation is more likely to come from a newer company than from an established one with a established market. SW Windpower doesn't do 5 or 6 blade rotors either but there are a lot of 3rd party ones available for the AirX. I like the basic idea and would like more output at lower wind speeds. I just would like more technical information from the manufacturers instead of sales spiels that amount to "trust us, we know what we're talking about."
  • VTP energyVTP energy Registered Users Posts: 7
    Re: 3 Blades vs 5 Blades

    we have built a 2400 watt VAWT. we do notice a what we call open door effect. our prototype is a 3 blade puch pull design. we have just began to skin a set of 5 blade for our larger 6kw turbine. depending on the power you are trying to make will aid you in the number of blades. right now we have 2 horizontail turbines 6 solar panels with 24 batteries and 4 XW6048 we also have added a back up propane generator of 12000 watts. we get approx 17.5 KW
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    I just dont understand some of the posts here about turbine speeds between 3 blade and 6 blade. If the turbine went slower with 6 blades than 3 it would put out LESS watts it cant be any other way. Output goes UP with RPM,,
    I have an AIRX it put out nothing in very low wind and reached about 30a in very strong winds Changed the blades to 6 and 5ft dia instead of the 4ft dia and found it was much less noise, it started to produce some power in winds that the 3 blades would still be stationary, top output went to 40a. there was so much power the tail that is part of it is then way to small to control it and it went out of control changing direction too fast it bent the 1/8 thick blade mounting plate. added much bigger tail and now all is good..
    I dont know why they dont make the AIR X like this to start with . then it would be a great wind genny straight out of the box
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I'm a little better read and informed on blade theory since the last post I put on this thread and what I've digested out of it is that more blades decreases tip speed ratio which actually slows down the turbine at higher wind speeds but gives it more torque which makes it start up at lower wind speeds. Increasing the blade length increases sweep area which is one of the fundimental factors in how much power a turbine can extract from the wind so you are definitely going to get more power out of a bigger rotor, provided the alternator can put out that much power, whether you put more blades on it or not. More blades also increases effeciency but the gain is very litttle beyond 3 blades. By putting on a bigger rotor with more blades you are making the turbine both start up a slower wind speeds and increasing the power it can extract from the wind at any speed. More blades alone should just improve low wind speed performance at the price of higher wind speed performance. That is exactly what the manufacturer of my HY400 states about the difference between the 3 and 5 blade models.
  • john pjohn p Solar Expert Posts: 814 ✭✭
    Re: 3 Blades vs 5 Blades

    6 blades 5ft dia put out more power than 3 blades 5ft dia.. Ive tried that and the start up speed is lower with 6 blades and a lot less noise
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I don't doubt your results John but not everyone who has tried this with an AirX has gotten the same results. This is an old thread where the blade upgrade totally bombed:

    http://forum.solar-electric.com/showthread.php?t=1454

    The AirX is a strange beast as wind turbines go and the internal electronics optimize it for a determined wind speed range. Your extended tail makes a big difference. My turbine is a simple 3 phase alternator up in the air with all the control electronics on the ground and spinning it faster will make more power. I am thinking about both the bigger rotor and just buying a 5 blade HY 400 next year after I've had this one up for a year and seeing the performance difference. It's not that big an expense moneywise but the time and labor factor is more a consideration. In the short term, extending the tail on mine would be the simplest and cheapest way to improve the performance.
  • VTP energyVTP energy Registered Users Posts: 7
    Re: 3 Blades vs 5 Blades
    john p wrote: »
    I just dont understand some of the posts here about turbine speeds between 3 blade and 6 blade. If the turbine went slower with 6 blades than 3 it would put out LESS watts it cant be any other way. Output goes UP with RPM,,
    I have an AIRX it put out nothing in very low wind and reached about 30a in very strong winds Changed the blades to 6 and 5ft dia instead of the 4ft dia and found it was much less noise, it started to produce some power in winds that the 3 blades would still be stationary, top output went to 40a. there was so much power the tail that is part of it is then way to small to control it and it went out of control changing direction too fast it bent the 1/8 thick blade mounting plate. added much bigger tail and now all is good..
    I dont know why they dont make the AIR X like this to start with . then it would be a great wind genny straight out of the box

    our 3 blade vertical turbine start up speed is 2 mph, the larger the diameter the better start up. smaller diameter more rpm less start up.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 3 Blades vs 5 Blades

    don't confuse the tip speed with power as more blades of equal length with the same wind speed will harvest more power. that does not mean that you are geared properly to reap this extra power. tip speed does increase with wind speed so many do equate it to more power in that sense.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    Larger diameter = larger swept area and therefore more power to be harvested - see Betzs Law.

    As there is very little power in breezes under 5 m/s (11 mph) it really makes no difference if the turbine starts or not - nothing * nothing still = nothing. 2 mph winds are useless.

    Higher tip speed will also cause the noise level to increase - whether the blades are moving fast enough under normal circumstances will depend on blade shape as well.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I've already pointed out that wind speed changes constantly and that a turbine that is already moving will be able to harvest energy when wind speed increases while a turbine that has a higher start up speed will use that energy just to start spinning. Winds that pulse between 3-4 mph and 10-12mph are common. The equations assume a constant wind speed which is not what happens in the real world. I just did a reading on my turbine spinning in a gentle breeze. When I put the clamp meter on, I got 100ma on the DC line. In a few seconds it rose to around 800ma, held that for a few seconds and then surged to 1.8 amps and held that for around 10 seconds and then current dropped to a few hundred ma. This is a typical early late night/early morning breeze at my site and this pattern usually holds to around 10am or so and has probably been happening through most of the night. I've also seen the same pattern at higher wind speeds and currents. I recently saw current surge from less than 10a to 30-40a in the same time frame.

    There are no turbines I know of that start at 2mph. The 5 bladed model of my turbine claims 3.35mph with a cut in speed of around 5 mph vs 5.1 start up and 6.7 cut in for the 3 blade model I have.

    I do agree that sweep area is the fundamental factor in power extracted from the wind. That doesn't mean that increasing blade count isn't a viable design option in some circumstances. A quieter more stable turbine that loses some power in really high winds speeds is not a bad design. I get the impression that increasing blade count to 5 or 6 makes the output more stable even if it doesn't increase total power.

    There is useful power in slow winds, not big power but useful. Having my batteries trickle charged at night by a 3-10mph wind is useful, not huge, but useful.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    If you get 'useful' power out of the 2 mph winds then you have just made a new scientific discovery!

    Patent it and make a fortune -

    The totally uninformed read these boards and take points seriously.

    I understand that you mean you are still getting a very, very small trickle of power to the batteries but others may assume 2 mph winds are really accomplishing something.
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    I said nothing about getting power at 2mph. Neither has any other turbine owner who has posted on this thread. Cut in for me is around 7mph. This mornings readings were at 7-10mph estimated by the current read. At 15mph I get around 100 watts. The difference between cut in and 15mph is sometimes not more than a few seconds. I am pointing out a factor--the constant variabilty of wind speed--that is often overlooked.
  • russruss Solar Expert Posts: 593
    Re: 3 Blades vs 5 Blades

    My mistake - I intended to type 2 m/s.
  • System2System2 Posts: 6,290 admin
    Re: 3 Blades vs 5 Blades

    Apples to Apples & Oranges to Oranges:

    If you have to mills with different sweep areas the ability to actually calculate what is making the difference is more technical than just saying "I notice more output."

    If you and I purchased identical 450 CFM 2 barrel carburetored, 1968 440 Dodge Chargers in the 60s, but I upgraded mine to a 800 CFM 4 barrel carburetor (sweep area) my engine would put out more power than your's at a given rpm based on the load. We both started with apples and I changed out to an orange, but we discuss the 440 engine instead. You could say you have a 3 barrel carb and now I have a 5 barrel carb and let's go racing and see who performs better or better yet; we both use an 800 CFM carbs, but mine is a 4 barrel and your's a 2; now we could see if the 4 barrel made a difference and what the large 2 barrel design is lacking.

    (For those car/motor head buff I will clarify using a 800 CFM 2 barrel carb would make off idle and low speed performance atrocious, waste fuel and metering inside the venturies less than ideal; with that said just focus on my point instead of cars)



    Though you start up earlier on the 5 blade; chances that start up is under an amp (.500mA). And at lower speed your 5 blade would definitely seem to turn fast; but then again match the blades sweeping areas and then do the visual amp check as much as you like, but stack KWH per month on both systems.

    The best way to actually substantiate the differences between a 5 blade versus a 3 based on amps alone during a given day is to normalize the factors and then see the gains or losses over real world time usages. Since during a given month the 3 blade will output more and then it will switch for the 5 blade; flip flopping back and forth day by day; hour by hour. 30 days later the results would be more realistic of what gains or losses have for your site location and by "your location" I stress someone else might not match up since they have 68% slow vs. 32% high wind all month and you might have 48% vs. 52% ratio. Wind ratios over a 30 day period are like apples and oranges again form month to month and location to location; even height to height. Now let someone quantify all those apples:confused:.


    ==============================

    http://www.windynation.com/articles/wind/tip-speed-ratio-how-calculate-and-apply-tsr-blade-selection

    Tip Speed Ratio: How to Calculate and Apply TSR to Blade Selection

    The Tip Speed Ratio (TSR) is used by wind turbine designers to properly match and optimize a blade set to a particular generator (i.e. the permanent magnet alternator). This is important to answer one of the most common questions we get: What size blades should I choose to match with my generator?

    We attempt to help you answer this question by focusing on explaining the simple physics behind calculating the Tip Speed Ratio!

    Understanding Tip Speed Ratio
    By definition, TSR is the speed of the blade at its tip divided by the speed of the wind. For example, if the tip of a blade is traveling at 100 mph (161 kph) and the wind speed is 20 mph (32 kph or 9 m/s), then the TSR is 5 (100 mph/20 mph). Simply put, the tip of the blade is traveling five times faster than the speed of the wind.

    Now, you must be wondering why this is important. For a particular generator, if the blade set spins too slowly then most of the wind will pass by the rotor without being captured by the blades. If the blades spin too fast, then the blades will always be traveling through used/turbulent wind. This is because the blades will always be traveling through a location that the blade in front of it just traveled through (and used up all the wind in that location). It is important that enough time lapses between two blades traveling through the same location so that new/unused wind can enter this location. Thus, the next blade that passes through this location will be able to harness fresh/unused wind. In short, if the blades are too slow they are not capturing all the wind they could and if they are too fast, then the blades are spinning through used/turbulent wind. For this reason, TSR’s are employed when designing wind turbines so that the maximum amount of energy can be extracted from the wind using a particular generator.

    Without going into details, physics and research have shown that the approximate optimal TSR’s for a given blade rotor are:

    TSR Number of Blades
    ~6-7 2
    ~5-6 3
    ~2-3 5
    There are many important conclusions one can draw from analyzing TSR’s. For the do-it-yourselfer that is putting together their own wind generator, let’s go over a few of the most basic and important points:

    Rotors with many blades (i.e. 11 blades) are generally not a good idea. An 11 bladed rotor would have an optimal TSR which is very low. This means an 11 bladed rotor would operate most efficiently at extremely low rpm’s. Because nearly all generators (permanent magnet alternators) are not optimized for extremely low rpm’s, there is no advantage or reason to use a rotor with many blades. Remember, rotors with lots of blades are capturing used/turbulent wind at high TSR’s and are thus extremely inefficient if used as a high-rpm blade set. This is a very important point because many people intuitively think that more blades equal a faster and more efficient blade set. But, the laws of physics say that this is not true.
    If you already have a generator or a motor and it requires high rpm’s to reach charging voltage, then your best bet is a two or three blade rotor. These rotors operate more efficiently at high rpm’s. Also, keep the blades as short as pragmatically possible because shorter blades obviously spin faster than longer blades.
    Last but not least, keep in mind the Tip to Speed Ratio! If your wind generator rotor is operating at a low TSR compared to the optimum value, then your wind turbine’s blades will tend stall before hitting maximum power/efficiency. If the wind turbine’s blades are spinning above the recommend TSR, then the blades will be traveling through turbulent wind. Not only is this inefficient, the turbulent wind puts your blades and entire wind turbine under unnecessary stress and fatigue.
    How to Measure TSR
    Measuring the TSR of a blade set is fairly easy. To accomplish this measurement you will need two things:

    A digital tachometer. These are available online for about 25 USD and can be used to measure the rpm’s of a blade set.
    A anemometer. A digital anemometer can be purchased online for fairly cheap (~20 USD) and is used to measure the wind speed.
    With these two items, you can obtain the necessary measurements to calculate TSR’s. But, one question does remain. How do we calculate the speed at the tip of a wind turbine blade, if we only know the rpm at the tip of the blade from our tachometer measurement? Well, we have to do a little math. Let’s break down this calculation step by step:

    Distance the tip of the blade travels to complete one revolution = circumference of a circle with radius r = (2)(Π)(r)
    where r = the length of the blade.

    Sample Calculation

    What distance does a one meter blade travel to complete one revolution?
    Answer: Distance = (2)(Π)(r) = (2)(Π)(1 meter) = 6.28 meters

    Now, let’s assume we measure an rpm of 450 at the tip of the blade using our digital tachometer. How far does the tip of the blade travel in one hour?

    Answer: 450 rpm = 450 (rotations)/(minute) = 450 r/min
    (450 r/min) x (60 min/hour) = 27000 rotations per hour = 27000 r/hour

    (27000 r/hour) x (1 hour) = 27000 rotations

    (27000 rotations) x (6.28 meters/rotation) = 169,560 meters
    Note: we know that the blade tip travels 6.28 meters in one rotation because this is the first calculation we did!
    So, now we know that the tip of the blade travels 169,560 meters in one hour. Now, let’s convert the meters to miles:
    169,560 meters x (1 mile)/(1609 meters) = 105 miles

    Alright, we are almost finished. Now we have to calculate the speed at the tip of the blade. This is easy because we know the tip of the blade traveled 105 miles in one hour. See calculation below:
    Distance = (rate) x (time) and rate = (distance)/(time)

    Rate = (105 miles)/(1 hour) = 105 miles/hour = 105 mph

    That’s it! The tip speed of this particular blade is 105 mph at 450 rpm. So what if the wind was blowing at 20 mph when we measured 450 rpm. What is the TSR? That’s easy:

    TSR = (Blade tip speed)/(wind speed) = (105 mph)/(20 mph) = 5.3
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭✭✭✭✭
    Re: 3 Blades vs 5 Blades

    Interesting read, Ciller.

    Thanks for posting,

    Edward
  • BilljustBillBilljustBill Solar Expert Posts: 212 ✭✭✭
    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.

    Maybe there's one element that's been overlooked.

    Ever tried to turn a generator that wired for charging? There is a lot of resistance on the shaft as the amp output rises. Picture the old Army crank generator you've seen soldiers cranking like an upside-down bicycle.

    It could be that with a 3-bladed rotor, you get most of your power on the upper end of the RPM. And because you have less rotor surface area, there's less surface for the wind to push against. Plus, the generator is harder to spin and causing more torque against the prop plate and blades. More "Slippage" as the wind goes by yields less power.

    A 5-blade rotor has more surface area to catch the lighter winds. Plus, because it has more area, there's more torque power to spin the direct drive generator shaft at all wind speeds, at least until the added number of blades produce turbulence enough to start a decline in the power curve.

    In my years in the R/C world, I read about the one-bladed props, but the two bladed prop was used most of all. When you added a third blade for a Tri-prop, it was usually because you needed a longer prop but due to ground clearance you couldn't or just because it was needed in flying scale judging events.. Before the 4-cycle R/C engines' lugging power came about, the 2-cycle engines got their power on the top end of high RPM's, and usually a third or fourth blade really pulled the RPM down mainly because of drag. Some of those fast or large scale models had to have their engines running on idle to produce a "Disk of drag" in order to slow them down enough to safely land. A "Dead Stick Landing", even into the wind was hairy when that prop wasn't spinning!

    In any event, more blades will provide more power at the lower wind speeds, but I'm sure there's a limit to the number
    Bill
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Missouri Wind and Sun emphasis

    I see that Missouri Wind and Sun sells the Solar Grid-Tied-Inverters which look very similar to products frowned upon by participants in NAWS forums. The state of Missouri must have a very different set of public utility guide lines for MW&S to sell that product without regard to permit, permission, or safety to their customers. I didn't see any disclaimers, warnings, or advisories referencing solar GTI products they sell, other than"The electrical meter will run slower, because power is being supplied on the homeowner's side. "
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: 3 Blades vs 5 Blades

    It is legal to sell, just not legal to connect to the grid (in many areas). Anyway MW&S is listing some of the downside of this GT inverter:
    • non ul listed
    30 day warranty
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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