I was watching the shadow of a wind turbine in Cornwall (great hobby 🤪) and noticed than 2 blades created light grey, almost non existent shadows whilst the third blade produced a darker,  much more defined shadow. I guess the blade was at a different angle, but why? Anyone know about these things?

ps how do I find my old posts/threads? I started one on waterfalls that I want to look at, but even an advanced google search does not find it:-(

Don’t go searching waterfalls.

Turbines pitch their blades as one, so unlikely it would have been running with one a mile out.

Must have been some kind of visual or atmospheric effect? Or you were on drugs….

Don’t go searching waterfalls.

Oh that’s very good 😀

🤪 no drugs involved!

it was a clear sunny day on top of a hill so I can’t think what kind of atmospheric conditions could have taken effect…

Google search site: singletrackworld.com/forum bentandbroken waterfall

Reveals this Ta-da!

You’re welcome. It’s a bit out of order from the last ‘improvements’.

Thanks for the link, I thought there was one listed in the thread that was in Cornwall, that may now be a goal for the weekend 🙂

As above they should pitch together, manufacturing defect or damage are the only explanations I can think of, unless they are painted different colours for some reason.

My wife thinks there was a van parked in the field so maybe it was faulty or under maintenance…

They’d probably not let out of balanced blades turn. It would shake itself apart in jig time.

In wouldn’t be “Unbalanced” in terms of fundamental frequency (ie once per rev cyclic balance) just because one blade had a different AOA to the others!  It would have a un-usual moment applied to the hub around the shaft axial direction but that would not likely be a problem because the hub / bearing is stressed for worst case conditions, and the “upper blade” always sees the highest wind gust loading, so that’s allowed for.

Don’t go searching waterfalls.

In wouldn’t be “Unbalanced” in terms of fundamental frequency (ie once per rev cyclic balance) just because one blade had a different AOA to the others!  It would have a un-usual moment applied to the hub around the shaft axial direction but that would not likely be a problem because the hub / bearing is stressed for worst case conditions, and the “upper blade” always sees the highest wind gust loading, so that’s allowed for.

singletrack at its best 😀

Will it not cause an issue with speeds though  three matching pitcges will put a constant speed  through the hub the one at the top providing the most power but as the next one comes around it creates an equal amount so it all balances.

If you you have one pitched differently will there not but a deceleration acceleration for one third of the rotation? So the massis the same but as the accelration will be different the force will be different.

Thats what i was meaning.

Perhaps it is painted differently to reduce bird strikes or something.  Whilst we are the subject…

If one blade presents a different AOA (angle of attack) and hence provides a different L/D then sure, it will present a different force profile to the hub, resulting in torsional vibrations.  The thing, as i previously mentioned, is that these TVs are expressly designed-in and allowed for under normal operation because the upper blade always sees the highest wind speed. (because the closer the ground you get, the slower the wind blows due to friction and eddy currents from that ground (boundary layer interactions)  In the ideal world, the centre of the blade hub would be at least 3 blade diameters above the ground, but practicalities and costs drive most turbines to have towers that puts the hub height at about 70% of the diameter.

Yay! Wind gradient! Welcome to sail design.

i initially assumed that all 3 blades would drive pitch from a common ring but a bit of research showed individual pitch control on some turbines. That gives an interesting opportunity to increase efficiency as you could set the blades to alter pitch as they rotate. The twist will be fixed, but heck, we live in a turbulent world.

I work with wind turbine techs but these are the bad boys we are installing

Yep my mate works on them, all individually pitch controlled 👍🏻