Why do windmills typically have 4 blades, yet all modern wind turbines have 3?
In: 9124
The are many reasons and the most important are:
4 blades from the past ==> Easier construction to make it rigid. Both blads on opposite sides are actually 1 piece that crosses the rotational axis.
More blades were used as well, such as for water pumping windmills.
Why? In general you an say: More blades means more torque, Less blades means more rotational speed.
For modern wind turbines, we have a lot of better construction techniques, and as such the 4 blades for easier construction is no longer required.
3 is used because it simply is the most effective number.
These blades are very heavy and expensive.
2 blades means faster rotation and more vibration, meaning more wear and tear.
4 blades means more expensive, while not adding any real benefit. Or at least not enough benefit to justify the costs. (While knowing these blades are not easy to recycle or reuse.)
Mice can have OCD and they didn’t like having an uneven number of blades on their windmills in old Amsterdam
Windmills with wooden spars need to have even numbers of sails – one on each end of each spar. Wood construction technology demands this because of the huge forces involved. Modern turbine blade technology allows the three blades to be mounted on a central boss because the strength and resistance to lateral forces of the materials are much greater than wood. There were, of course mills with six and eight ‘jib sails’ each one being much smaller and only suitable for sites with nearly constant strong winds.
Why use many blade when few blade do trick?
Old windmills were made before you could consistently make things the exact same size and weight. In order to balance a three-bladed windmill, you have to make each blade weigh the same, otherwise the heavy one will fall to the bottom. To balance a four-bladed windmill, you just have to make two spars, find where the balance point is at the middle, and attach each one to the axle at that point.
Modern wind turbines go for a couple things.
1. Amount of wind captured.
2. Manufacturing and construction cost.
3. Stability
So for 1 more blades is better. But 3 blades capture almost as much of what 5 or 7 blades do. This doesn’t affect capacity as much as say the height of the turbine.
For 2. Less blades is better. Less connections. Less failures. Less shipping cost. Less Manufacturing cost.
There’s prototypes with more blades but don’t usually get Mass produced.
For 3. Odd number of blades gives lateral stability so it doesn’t swing back and forth and fall over.
So 3 blades is what gives the best economic payout for your wind energy buck.
I see a lot of answers talking about the efficiency, but 4 blades are actually more efficient aerodynamically. 3 blades are used due to econimical reasons as well, as the blades are the most expensive part of a wind turbine. When you compare the efficiency, it won’t make sense to add a fourth blade for a bit of efficiency.
It’s true that 3 blades are more stable, but the tower of a turbine could be improved to keep the same stability with an extra blade. Due to econimical reasons this is also not worth it.
Source: I’m a wind turbine engineer
And ceiling fans have 5 blades, wtf!?
Vibrational balance (prevention of self destruction in high winds) is easier to build with 4 blades exactly 90 degrees apart. However, with modern design and construction methods, it costs far less to build, transport, and maintain with only 3 blades. Each of the 3 can also be larger in surface area to compensate for the “loss” of that 4th blade.
Ok I used to work at Vestas, I worked both in attaching and testing the ring gear motors that rotated the unit, as well as I worked in finishing for blades. The blades are heavy, very heavy, some models have blades that weigh 35 tons. Most of the weight is in the mounting rig however. To finish the blades it takes about 7 employees 10 hours of sanding with hand held power sanders. The finish material is epoxy and fiberglass composite sandwiching a foam center with a more dense microballoon and epoxy spar in the center bringing the load bearing aspect to the blade. however some of the new new models proposed for future will use carbon fiber blades once a manufacturing process that doesn’t cost above $10 million or so is reached.
Each blade in itself is a costly process not just to build but to also install. The highest paid in the company outside of the execs, so specifically blue collar employees at Vestas, are the field installers. These fellas are driving a specialized truck that has both a driver in the front and the back, they have an insane crane that costs hundreds of dollars an hour just to pay the operator, not including any logistical costs (which could probably be in the hundreds of thousands of dollars per blade, installation logistics only). Each blade is already a massive undertaking requiring finish sanding by 7 decently paid employees for 4-6 hours, that’s not including the cure time beforehand for the materials as they get out the specialized vacuum chamber oven.
This is a massive undertaking and taking away 1 blade from a 4 blade design gives you 10 completed wind turbines if you have 30 blades, which is actually can at times be the main production bottleneck as well. It’s arguably easy compared to just assembling a bunch of gearboxes and plugging in some generators, testing process is simple too with designed software that can completely test the unit from 1 IO socket.
So imagine you own a wind turbine company, your not going to keep a lead engineer that tries to talk you into building less wind turbines for more money. Maybe you could build 4 blade turbines with 16 blades and end up with 4, but is it really worth it? Why not just build 5 and have another blade left over to use as a replacement in the event one of the units off lines due to blade related fault?
And 2 blades just isn’t enough, you get more power from 4x of 3 blade units than you do from 6x of 2 blade units per dollar spent. Wind turbines are actually sold to customers by power generation, in megawatts, so power generation per dollar is the name of the game. Get as much as you can out of each nacelle, but don’t spend too much money on blades when you reach the point of not gaining enough to rationalize doing so
Why do windmills typically have 4 blades, yet all modern wind turbines have 3?
In: 9124
The are many reasons and the most important are:
4 blades from the past ==> Easier construction to make it rigid. Both blads on opposite sides are actually 1 piece that crosses the rotational axis.
More blades were used as well, such as for water pumping windmills.
Why? In general you an say: More blades means more torque, Less blades means more rotational speed.
For modern wind turbines, we have a lot of better construction techniques, and as such the 4 blades for easier construction is no longer required.
3 is used because it simply is the most effective number.
These blades are very heavy and expensive.
2 blades means faster rotation and more vibration, meaning more wear and tear.
4 blades means more expensive, while not adding any real benefit. Or at least not enough benefit to justify the costs. (While knowing these blades are not easy to recycle or reuse.)
Mice can have OCD and they didn’t like having an uneven number of blades on their windmills in old Amsterdam
Windmills with wooden spars need to have even numbers of sails – one on each end of each spar. Wood construction technology demands this because of the huge forces involved. Modern turbine blade technology allows the three blades to be mounted on a central boss because the strength and resistance to lateral forces of the materials are much greater than wood. There were, of course mills with six and eight ‘jib sails’ each one being much smaller and only suitable for sites with nearly constant strong winds.
Why use many blade when few blade do trick?
Old windmills were made before you could consistently make things the exact same size and weight. In order to balance a three-bladed windmill, you have to make each blade weigh the same, otherwise the heavy one will fall to the bottom. To balance a four-bladed windmill, you just have to make two spars, find where the balance point is at the middle, and attach each one to the axle at that point.
Modern wind turbines go for a couple things.
1. Amount of wind captured.
2. Manufacturing and construction cost.
3. Stability
So for 1 more blades is better. But 3 blades capture almost as much of what 5 or 7 blades do. This doesn’t affect capacity as much as say the height of the turbine.
For 2. Less blades is better. Less connections. Less failures. Less shipping cost. Less Manufacturing cost.
There’s prototypes with more blades but don’t usually get Mass produced.
For 3. Odd number of blades gives lateral stability so it doesn’t swing back and forth and fall over.
So 3 blades is what gives the best economic payout for your wind energy buck.
I see a lot of answers talking about the efficiency, but 4 blades are actually more efficient aerodynamically. 3 blades are used due to econimical reasons as well, as the blades are the most expensive part of a wind turbine. When you compare the efficiency, it won’t make sense to add a fourth blade for a bit of efficiency.
It’s true that 3 blades are more stable, but the tower of a turbine could be improved to keep the same stability with an extra blade. Due to econimical reasons this is also not worth it.
Source: I’m a wind turbine engineer
And ceiling fans have 5 blades, wtf!?
Vibrational balance (prevention of self destruction in high winds) is easier to build with 4 blades exactly 90 degrees apart. However, with modern design and construction methods, it costs far less to build, transport, and maintain with only 3 blades. Each of the 3 can also be larger in surface area to compensate for the “loss” of that 4th blade.
Ok I used to work at Vestas, I worked both in attaching and testing the ring gear motors that rotated the unit, as well as I worked in finishing for blades. The blades are heavy, very heavy, some models have blades that weigh 35 tons. Most of the weight is in the mounting rig however. To finish the blades it takes about 7 employees 10 hours of sanding with hand held power sanders. The finish material is epoxy and fiberglass composite sandwiching a foam center with a more dense microballoon and epoxy spar in the center bringing the load bearing aspect to the blade. however some of the new new models proposed for future will use carbon fiber blades once a manufacturing process that doesn’t cost above $10 million or so is reached.
Each blade in itself is a costly process not just to build but to also install. The highest paid in the company outside of the execs, so specifically blue collar employees at Vestas, are the field installers. These fellas are driving a specialized truck that has both a driver in the front and the back, they have an insane crane that costs hundreds of dollars an hour just to pay the operator, not including any logistical costs (which could probably be in the hundreds of thousands of dollars per blade, installation logistics only). Each blade is already a massive undertaking requiring finish sanding by 7 decently paid employees for 4-6 hours, that’s not including the cure time beforehand for the materials as they get out the specialized vacuum chamber oven.
This is a massive undertaking and taking away 1 blade from a 4 blade design gives you 10 completed wind turbines if you have 30 blades, which is actually can at times be the main production bottleneck as well. It’s arguably easy compared to just assembling a bunch of gearboxes and plugging in some generators, testing process is simple too with designed software that can completely test the unit from 1 IO socket.
So imagine you own a wind turbine company, your not going to keep a lead engineer that tries to talk you into building less wind turbines for more money. Maybe you could build 4 blade turbines with 16 blades and end up with 4, but is it really worth it? Why not just build 5 and have another blade left over to use as a replacement in the event one of the units off lines due to blade related fault?
And 2 blades just isn’t enough, you get more power from 4x of 3 blade units than you do from 6x of 2 blade units per dollar spent. Wind turbines are actually sold to customers by power generation, in megawatts, so power generation per dollar is the name of the game. Get as much as you can out of each nacelle, but don’t spend too much money on blades when you reach the point of not gaining enough to rationalize doing so
Latest Answers