At last, a thoughtful video maker that gives you a concise answer right up front with an option to stay tuned to find out more. Thanks Rosie

Major props for putting the "tldr" up front and expanding afterwards. This is a very viewer-friendly video structure and makes me watch on even more

Just brought to your channel by the algorithm. Excellent video. You have a new subscriber. I love how concise you were at the beginning, but still went into depth afterward. You are great at explaining complex subjects in an easy to understand way. I'm looking forward to watching more of your videos, and seeing your future uploads!

I really thought the single blade was just a joke until i saw the real ones.

Hello Rosie, nice vídeo! When I studied this at uni, I was taught by my professor that wind turbines with up to 20 blades where usual in the past... We have all seen them in cowboy movies, usually used to pump water from underground deposits. The main advantage of these windmills was that they could self-start easily with really low air velocities so you had a water supply always guaranteed. On the other hand, the efficiency of those windmills was really bad, so even with higher wind velocities, the power outcome would always be low. SO I guess that you could also say that the optimal number of blades for your wind turbine also depends on the use you want to give to it :)

Answers question in a minute and then lets viewer choose to watch for longer answer? Instant sub!

Fascinating! I hadn't thought about the difference of 2 vs 3 when yawing

I really appreciate how you started your answer with a summary before going into detail.

It is amazing how with only one smile can be stable and balanced through the all video!

This is the first actually good explanation of this I've managed to find after working adjacent to wind power for years now. Thank you!

You are not only a great engineer but a great communicator too.

Trade-offs mentioned early and you know you're listening to a fellow engineer! Turning dreams and hard science into practice is at the end of a day an art. And so is making concise but still factual and _pleasing_ videos. Keep it up and thank you!

I have started my certification program in the Wind Energy. You are doing great job, thanks a lot, you definitely have at least 1 long-term subscriber! ;)

Thank you for that clear and concise explanation. I’d noticed the spring mechanism on small two blade turbines but I didn’t know what it was for. Now I do.

The moment you mentioned the figure skater I completely understood the issue. Great analogy.

I really appreciate the short answer in the beginning!!

My first job as an engineer was working on the blades and hub retention design of the Hamilton Standard and KKRV designed 3 and 4 MW wind turbines, with construction starting around 1981. These were the world's most powerful wind turbines at the time at 78 m diameter and proved to be successful. Simplicity and low cost were drivers so as you explained, two filament-wound fiberglass blades saved on material cost (the resin) and this allowed the steel hub casting to be smaller as well. These were downwind, free yaw turbines that used a similar rotor design as found on two bladed helicopters, namely, a teetering rotor with a teeter pin offset by 30 degrees so that teetering causes pitch change to make the rotor self stabilizing. The teetering rotor was especially good at reducing the fatigue load on the blades as they passed through the 'wind shadow' behind the tower. One problem found in service was that an excitation caused the tower to go into a bending mode of vibration which was at times disconcerting to workers at the hub/nacelle level during operation. To make an analogy, this system was similar to a two-bladed helicopter in auto-rotation, where the rotor in-flow comes up around and past the fuselage. As this is an emergency life-saving maneuver, no one complains if there is a little extra jouncing in the cockpit on the way down. However, for a two bladed wind turbine, perhaps a better solution would be an upwind machine with the added cost of an active yaw drive system to avoid the wind shadow excitation. The problem of yawing a two-bladed rotor is similar to tilting the rotor of a two-bladed helicopter. This has been solved by various means and most lower cost helicopter designs use two-bladed teetering rotors. I dont have a preference either way. The machines I worked on were ahead of their time, US Govt funded, and defunded in the Reagan administration in favor of battleships.

Always wondered why 2 blades were not used as they work fine for aeroplanes. All makes sense now, thanks

I totally like your visual animations!

4:25 I subscribed when I saw the tower wobbling excitedly

really liked your video. You got a new subscriber. I didnt anticipate having a different answer than you when you said "if you ask 5 engineers from the wind industry, you will get 5 different answers" but here i am. Another problem with two bladed wind turbines is the aerodynamic force distribution over the rotor plane which will excite the turbine further. There are different effects that play together on this. First of all the natural wind speed distribution. The higher you go, the stronger the wind blows. Because of that the top blade will get pushed harder than the bottom blade. In combination with the rotation of the rotor you get a "nod moment". This is the probably the biggest aerodynamic problem of two bladed rotors. Another important aerodynamic effect is the tower dam. Right in front of the tower, the wind slows down. during the rotation of the rotor, the blades travel through that area. There the blades dont get pushed back as hard as right before or right behind the tower, which also induces a nod moment on the turbine. Those two effects combine on even bladed turbines. On odd numbers they act phase shifted to each other and dont put such a stress on the nacelle. Plus these effects are stronger on lower numbers of blades. This really shows the different aspects you need to consider when designing a wind turbine. Its not as simple as "just a tower with 3 rotor blades". I like the idea of having more blades in the future to make the blades thinner. It could also reduce the rotation speed which would make the turbines less stressfull to look at and maybe more bird friendly.

Absolutely fascinating and fantastic. I had never even imagined an issue with 2 blades being to do with uneven rotation.

The best video I have ever come across related to wind turbine

Good explanation, but you could also add. The wind speed is slower close to the ground and is also affected by the tower. For 2 blade designs the force on the upper blade will be much higher than for the lower blade, and when passing the tower you get extra low force and vibrations. Over water the wind speed will change less with height and 2-blades are therefore common off shore. Another reason is esthetical. Early on in Denmark the general public preferred the sight of slower moving 3-blade design. This is less of an issue off shore where 2-blade designs are more common.

Very, very helpful explanation. Please make more videos on this topic deeper into the details.

Veritasium brought me here and I love this channel!

I loved figure skating as a kid. I'm excited that you used a figure skater analogy.

How engineers choose number of blades: Ask queen!! Once I have talked with Henk Lagerwey, one of pioneers in wind turbine business, great guy. He (his company) produced 75kW/15m, 80kW/18m and later 250kW wind turbines with two blades. I think this was first turbine with pitch control (passive) and first turbine with invertor regulation. Those turbines were popular in Japan because of ease switch to 50 or 60Hz (invertor). On one dinner with royal family (technology open different doors) queen asked him: "Why your turbine has two blades? For me it is nicer with three blades." He answered: "Your Majesty, you are right, three is better" And his next turbine was three blade turbine. :-)

Thank-You for these wonderful programs! At the end of a recent one you asked for comments on production, amount other things. I think your shows are all-round great picture-wise and editing, and sound is pretty good. MY ADVICE WOULD BE TO IMPROVE THE SOUND FURTHER. GET A MIC CLOSER TO THE MOUTH OF THE PERSON SPEAKING, monitor the sound with headphones, check the sound carefully in the edit. Particularly with this technical stuff it’s important that people hear clearly. You know this material so it’s easier for you to figure out what is being said, so maybe have another set of ears check it out. The picture is important, but the SOUND is even MORE IMPORTANT. People will put up with an imperfect picture, but bad sound will cause them to switch off and they won’t even know why! Anyway, thanks so much for the totally supersonic shows you are making. I’m seeing this in the US and sharing it as much as I can!

Absolutely brilliant thank you!! I honestly thought it was just because 2 blades were an older design and they found it more efficient to have 3 and make it move with the wing. Wonderful explanation, you did so in such a comprehendable way, thank you!

What a fantastic video! Great explanation, no annoying music and the whole tl;dr at the start then the nice in depth talk afterwards is such a great format. You explain things so nice and clearly too. Thanks!

Thanks, Rosie for the informative video. I read that turbines with 2-blades have unequal forces when at the 12 and 6 o'clock positions because the upper blade has full wind force while the lower blade has wind that is blocked by the tower. I guess this isn't much of a problem with lattice type towers that allow the wind through. What mystified me was why the blades had to be so long and skinny. Now I see that it saves money. Thanks for giving me a firmer picture in my mind why wind turbine blades are the way the are.

What an awesome explanation. You have a great way of explaining things.

A minute in and I knew I had to sub, great work!

awesome. Rich content provided in quite simple way with nice graphics. Like good lecture but packed in few minutes.

Those turbine animations are the coolest!! Too cute! 😂

hey..after being confused and bored and confused again i stumbled on a diamond..good video

Much better explanation than the one from Real Engineering

Really really cool video! Well explained, thank you! Please keep them coming :) Loved the graphics in it too!

Why I haven't found this channel before? Superb! I loved the rotoscoped clips. :)

Thanks. Nice explanations of some of the trade-offs involved. However (you knew this was coming!), my understanding from some work I did in an M.Eng a few years back m(oh joy, the Betz Limit!), is that the 3 rather than 2 decision was because of visual effects ("visual disruption", perhaps? - can't remember). It seems when an observer looks at a big turbine with 2 blades each, say 50 metres long, the width of the turbine when the blades are horizontal registers as about 100metres, but when the blades are vertical the width is almost nothing, just the width of the tower. So as it rotates there is the effect on the observer's eye, or brain, of something in their vision expanding and contracting, and the effect is even worse if there is an array of turbines. Apparently the same effects are not experienced, to anything like the same extent, with 3 bladed turbines - there's always something about 100 metres wide in view. Manufacturers are very sensitive to minimising visual effects as they are often claimed by objectors to windfarms to induce migraines, depression etc.

Great concise answer, and then elaborated. If everybody could do that...

Simple, effective and clear explanations + pleasant speech + nice animations. Thanks for your work.

There are quite a lot of older two-blade wind turbines in Northamptonshire and into Warwickshire. Many of these were British-made, but production ceased through a lack of subsidy. When German and Danish three-balded turbines entered the UK market, the UK government belatedly turned up the subsidies and the three-bladed design proliferated. Almost certainly, a two-bladed design of relatively modest size was the most sensible choice for Northamptonshire, where suddenly-shifting sea gales are rare. They proved that wind turbines were worth a try, at least.

Really thought provoking video. I didn't thought about 2 blade wind turbines as mostly my professors in university taught that 3 blades increases structural stability of tower & decreases oscillatory vibrations.

That academic background of summarising the following content as part of the introduction is so appreciated in this form factor. Thanks for the explanation 🎉

Well done Rosemary! Loved it.

I wasn't really interested in the question but had some vague intuition of what the answer would be. I have no idea why Google proposed this video to me, but clicked on it on a whim. I am so glad that I did: This is the best technical explanation video I have ever seen. Structure, pacing, technical level of explanations, illustrations, balance between information and humour (2:34!), ... -- everything is just perfect. Congratulations for this little masterpiece. Now I am going to watch a few more of your videos on topics I am not intrinsically interested in.

Yes - love that you explicitly include a stopping point at 1:10. I realise that doing this might make your channels watchtime analytics look bad, but thanks for the humane design. I appreciate it.

That was a very interesting video! This weekend in Cornwall I passed a wind farm of two bladed turbines (the Cold Northcott site I believe) and it was definitely out of the ordinary, but now I know why! All the turbines where stopped at the time with their blades horizontal which I can't think of a reason for. It did make me wonder more about the process of starting and stopping the turbines, and how quickly they can be "switched on" as such. Keep the good content coming!!!

Excellent teaching and learning Observations.

KZfaq just recommended your channel to me. Thank you for your professional explanations. I really enjoy these videos!

Thanks Rosie - a nice easy explanation for us intrigued layfolk. You have a breezy and easily relatable style. Subbed :)

Great structure of video, say the shorter quicker answer to main question at the beginning then elaborate.

Liked the presentation and also loved your animations !👍

Used to make small "turbines" from wood - started with small (~0,5 m each) 2 blade design - at low altitude proved to be not pleasant to eye. Next was 3-blade design (~0,8 m each) that was pretty nice and stable. With some insights went forward and next/final was 5-blade design (~1,1 m each blade) - smooth and beautiful, trying to get rid of as much wood as possible to make blades thin (yet still strong enough) - got each blade weight down to 105-110 g (small difference for balancing as it all was hand work with knife and sand paper). That was like ~15 yrs ago but now remember details after this video - thanks!

Some 25 years ago I constructed a model wind turbine with 4 blades just as a school project to illustrate a principle. But it had two rows of blades in tandem ie. two at the front and two at the back. The front blades and the rear blades rotate fully independently and in opposite direction to each other but still connected to the same shaft. It was only made to illustrate a point that you get a lot of untapped air containing K.E. going between the blades of a wind turbine . Quite knowing that only about 47% of the K.E. can be used it would be useful to tap that part that goes through the front blades by putting another set two blades behind.. Also the air that goes through must be affected by the front, by being slowed and maybe given a bit of spin in the direction opposite to the rotation of the front blades and therefore containing some rotational K.E. too. This air leaving the front blades will find it has to go through the rear blades turning them in opposite direction to the front even if at decreased K.E. Notwithstanding the contra rotating blades the magnitude of the rotation of each set will be added at the shaft end producing more rpm and power.

Teknologi yang bermanfaat untuk mereka yang mengembangkan teknologi turbinnya. Salam hangat dari Indonesia 🙏

If they didn't have blades they would be just a stick poking up out off the ground.

I had not heard of the stability issues of a two bladed turbine when changing it's orientation to face the wind direction. Of course it does make sense. Very interesting to think about. Thanks for this explaination!

This question was in the back of my mind for a long time. Thank you for the best explanation I could imagine.

Very good video and very good explanation. Big fan of your videos and channel.

Same as aircraft, fly in plane with two bladed props vs three. You will enjoy the three far more.

_Just Have a Think_ sent me over here. I don't know why I hadn't heard of this channel before. Sub earned.

4:25, that one is an excited turbine. :D

Excellent explanation for those of us who are none the wiser but still fascinated. I always thought the number of blades was determined by how many birds and bats needed to be killed.

amazingly well explained! loved the simplicity of the production

a video which start with a TLDR? instant sub :)

Fascinating video, presented in a very straightforward and easy to understand style. New subscriber here. Regarding rotational speed, I remember hearing in a documentary that somewhere around 300kmh is the maximum tip speed that can be attained without the blades producing high-amplitude low-frequency noise that carries for kilometers across the landscape. Is noise abatement the only limitation for tip speed? (Beyond the obvious limiting factor of forces trying to rip the blades out of the hub or shake the whole assembly apart) Do prevailing wind conditions in a given location also affect this limit? I never thought about preservation of angular momentum or structural resonance as they pertain to a yawing wind turbine! Great video!

Hey Rosie! Your videos are fantastic, very helpful, informative and easy to understand! Amazing! :)

I live in Gjølga Norway and I am neighbur with one of the largest windmill Parks in europe (storheia) The wilderness and wildlife was ruined and the area is now dangerous for people and wildlife because they hurl iceblocks up to 200meters. They needed to build 20 meter Wide roads in the Mountain and the untuched wilderness is gone.

As usual with this site......Very Logical.

Great video! I can't believe you've only got 13.4k subs! This was wonderfully concise and a good explanation. :)

Hi Rosie I've just found your channel and have definitely subscribed, the "not an accurate physical representation" text made me laugh way more than it should've ........love your videos ..........keep up the good work

Yay! What a gem! Summary in 1 minute, satisfying explanation in the other 5. I almost forgot they used to make them like that. Now they're all 20 minutes of circling around the subject and calls to action. Thanks for this!

One of the major reasons I have come across for why 3 blades is more common is due to the ground layer of wind being slower than wind higher up. So a 2 blade design when it is in the vertical orientation, the top blade has clean air, which will provide more torque than the lower blade which has dirty air from all the turbulence of the ground boundary layer, resulting in a mismatch of torque. Where as three blades, when you have one blade in the clean air at the top, you have two blade in the dirty air, resulting in a more even loading of the system

Great explanation! This was question I hadn't realized that I needed answering.

Thank you Rosie.

This was informative, I enjoyed the discussion of tradeoffs. Keep up the great work!

Very instructive video! Thanks. Some ideas for next content: why is the drivetrain tilted a few degrees wrt horizontal? Why are blades pre-bended? Why does a rotor has an umbrella-shape? How are blades recycled when end of life?

KZfaq algorithm brought me here. However, I'll love to witness in real life, a dancing wind turbine like this. Will be fun 4:24 Great explanation. Subbed!

Short answer was totally ok :D thankyou no need for more

Some years ago i was commissioning some 3 and 6 MW prototype turbines with 2 blades. Very interesting. The main reason they decided for 2 blade was, like you said, the easy offshore installation. The tower vibration was suprisingly low, even during yawing. Later they wanted a dynamic pitch system thet would pitch a little bit during one ration to eliminate the vibration. Another thing was, during storm, the blades should be parked horizontal to keep the force to the power low, even when the yawing did not work. Btw: It looks nice if you have a windfarm with serveral of this 2 bladed and the rotors where synchronised, so they are during all in the same angle and speed :-)

Hi Rosie, the algorithm brought this today, and wow, what a really cool and informative video! Thank you for taking the time to explain this from the wind-power perspective. I'm not sure if you are aware but there a 2- vs. 3-blade argument in some aviation circles as well. Two-blade designs are said to have better cruise speed while three-blades offer superior climb performance. Not sure if this translates into the wind turbine story, but either way, I'm a fan, and have subscribed .. looking forward to more!

Excellent information, thanks. For *fan* blades, there is another reason to have an odd number of blades - this distributes the noise harmonics, so they can be quieter / less noisy. I have wondered if this is also a factor with wind turbines, but because the rotational speeds are so much lower, maybe it is, but not as critical?

I learned something today. Thank you.

Your explanation doodles are wonderful.

Excellent. I’ve never heard a digestible explanation of the 2-blade turbines’ problems - as the turbine hub is rotated in azimuth. Thanks!

When I used to drive along the E80 route through the mountains in central Italy, it always came as a surprise to see so many single-blade turbines rotating high on the steep hillsides. With their large single arms and squat counterweights, from a distance they looked like they were off-balance and about to shake themselves apart! (Keep your eyes on the road though, as the average speeds seem to be good enough to qualify for Formula 1 racing).

Beautiful explanation

The topic is really interesting, but as an information channel your first priority should be to record clear audio and have clear diction. You need a good condenser mic, EQ, compression, not to mention the audio is really low too.

Great answer to questions I had!

2:35 That explains so much about my life.

Im glad I clicked on this video! This came up in my recommended and was a great watch. Clear, concise, quality information and the animations were fantastic. You’ve got a new subscriber. Rarely do I click subscribe after watching a single video, but your other video looks excellent too. Thanks Rosie 🙂

Well done giving the answer right at the start!

Fascinating. A gliders wings are very much like the blades on a turbine, and they are pretty noisy, when you get close enough. Especially when landing, where the speed i high.

Great video, thank you for explaining it in such a good and concise manner

I've always been surprised that turbines with more blades, like 5-10 for example haven't proven to be more efficient. It seems that the majority of wind passing a 3 blade turbine goes right past it, never coming close to a blade to impart energy onto it.

Mesmerizing topic.

Thank you for a most informative video. Greetings from Tanzania.