Wind energy - Wooden blades

Wood might be a pretty good substance to make some turbine blades from.

Unlike me, it's strong, light, flexible, and easy to work with.

It can also be shaped with a few tools that I already own. I also have a bit of experience with shaping wood from an earlier "thing" from my 120 things in 20 years.

Pictured here is a wooden lure body from a previous post on getting the most out of your printer by making hand made fishing lures with it. It even has the wing shape that I'll need as the profile for my turbine blade.

But enough self promotion...

By stacking a few different bits of wood together, it should be possible to give a turbine blade shape a bit of a head start.

We want an angled up, thicker wing shape in the centre, and a thinner, flatter wing shape at the tip.

Because the middle bit is moving slower that the tip, we need a bi-plane wing in the middle, and a jet wing at the tip, and everything else in between.

Then we should be able to cut away the bits that don't look like a turbine blade, giving us a nice curve that looks a bit like a propeller. 











And then shape the blade into that progressively thinner and flatter wing shape.

If we start by making cuts that join the dots so we cut from "A" to "B", we should get the angles roughly correct.

Then it should be a simple matter to round off the front edge (thick green smudge) in such a way as to make the front round, and the thickest point of the turbine 1/3 back from the front. So a line running the length of the blade running through point "C" would be the thickest bit.



With the guide points created by the corners made by the different heights of wood, there might even be a chance that I can make a second blade that looks a bit like the first. It needs to be very close to exact, so I might need a little luck, or some brand new skills.

That's the theory. I'll give it a go, and see what happens.

Wind energy - Aerodynamics

I just noticed a pattern.

Doing 120 Things in 20 years has taught me a few things about myself. One is that whenever I need to  discuss aerodynamics, my medium of choice gravitates toward crayons and my seemingly limitless ream of old dot matrix printer paper rather than animation or 3D design tools. Interestingly this was my preferred media for everything when I was a five year old.

I have no idea what that means.

A modern wind turbine blade has a few improvements over the old water pumping windmills. It's blades don't just get moved out of the way by the wind, the blades interact with the wind in a much more amazing way.

When the wind passes over a wing shape, it has to travel further over the top than the stuff that passes under the wing. The path of wind lump "B" is much longer than the path of wind lump "A". This means the air has to stretch out. And that means you get a lower pressure above the wing than you do below it. Put all that together, and you get lift. This means the wing wants to fly up to the sky.

Yep, that's right, to the sky.

An old bi-plane might have a thick, high lift wing on an angle to the wind like "A" . (I think that angle is called "angle of attack")

A fast modern jet might have a shape, and angle of attack more like "B"

*Do not use these crayon drawings to build a modern, high speed jet. It's possible they may have not been as rigorously tested as they should be.

If we put the bi-plane wing on the jet, it would slow the thing down too much, and would geneate hilarious flight antics, and many spilled coffees. If we put the jet wing on the bi-plane we would have a funny shaped, propeller powered car, with wing looking things sticking out the sides. It would never get off the ground, because at bi-plane speeds, it would never generate enough lift.

Another interesting thing has to do with the speed different points on a wind turbine travel at, relative to each other.

Point "A" travels only about a quarter of the distance point "B" travels.

If both point "A" and "B" do one revolution, but point "B" travels 4 times the distance, then point "B" must travel a stack faster.



What all this means is that as the turbine is spinning, Point "A" sees the windspeed of the day, PLUS the extra speed it sees because the turbine is spinning. Point "B" sees the windspeed of the day, PLUS AN ABSURD EXTRA SPEED, seen because the windmill is spinning.

Absurd!

This extra windspeed that different points on a blade see, is called "apparent wind". As far as point "B" is concerned the wind speed might feel like 6 times the windspeed someone not standing on the blade might feel. Now, interestingly, we need to take this apparent wind speed into account if we want to use "lift" to power our wind turbine. If we present a blade so that the bottom is flat and point it into the wind, it will lift. If one end of the blade is attached to the centre hub of a wind turbine, it will lift, and rotate. But now the thing is rotating, there is some apparent wind. This means that the wind is no longer hitting the blade from the right angle. It's now hitting more from the top down. We have to rotate the blade so that its interacting with the APPARENT windspeed not the windspeed of the day. Because the blades will be rotating quite fast, most of the wind will present itself almost on the plane of rotation, so we adjust the blades so they are flatter to the direction of spin. I need a model to show this better.

"Why are you telling us this?" I hear you ask.

It turns out very clever people in lab-coats use all this stuff to design really efficient blades.

An ideal blade would be like a bi-plane wing at the centre, where the apparent wind speed is slowest, a jet wing at the tip, where the apparent wind is fastest, and everything else in between.

The more accurately we set all these varying angles the better our wind turbine will work. But we can also get a turbine to work inefficiently. It's up to us. I'll find some nice comfortable spot in between once I've explored a few different ways to go about making a set of blades.

And a model. I'll make a model.

Handmade fishing lures - Hydrodynamics

I don't have the required funding for the wind tunnel I really need for this post, so at great personal expense, I'll be using crayon.

In air, a wing generates lift by creating a low pressure system above it by forcing the air to stretch out as it passes over the curve of the wing. The curve over the top of the wing means the air has to travel over a longer distance than the air going over the straighter bottom section. Stretched air equals less air per lump of space, equals low pressure. When you have less pressure above something, compared to that which is below it, that something gets sucked up.

A sail sucks a boat along in the same way, using the low pressure created by a wing shape to suck the boat forward. If you look down on a sail from above as in this realistic diagram, it has a cross section like that of a wing (thats the wing bit sticking out to the left). With a sail, the force generated is roughly at right angles to the bulging side of the sail. The wing shape is made by the bulging bit on one side, and on the other side by the tendency for the air to take a short cut straight across from one side of the sail to the other.


In a wing shape moving along level with the horizon, the force is roughly upwards.

I'm pretty sure the forces acting underwater are similar, or at least behave similarly, to those that work in air.

The force acting on a lure is also roughly upwards.

those diagonal purple wind lines are from a different diagram

A lure is often designed as a wing shape, but strangely, this helps the lure dive deeper. As far as I can tell, it does this by lifting the tail, and forcing the nose to pitch down.

It also has a bib. A bib doesn't act as a wing, but rather, acts more like a rudder. The bib adds length to the lure without adding lift at the front of the lure. The bib also encourages the lure to follow the direction to which the bib points, because it makes it too hard for the lure to swim directly towards the fishing rod. Point the bib down, and the lure will go down. The bib is set so that it presents as a flat plate resisting being pulled along. Picture pushing a flat dinner plate through the water. If you turn it edge on, its much easier to push. If you drop the plate flat into water, it wont just sink straight down, it will try its hardest to get some sideways to add to it's downwards. In much the same way, the bib wants to move in any direction other than flat up or flat down. Because the lure is being pulled along from roughly the front, the bib is limited in just how stubborn it can be. It negotiates a compromise and moves generally forwards, a bit down, and has a go at moving a bit to each side. The attached line gives it a bias to forwards.

A dropped dinner plate might also go to one side, spill a bit of pressure, then rock back to the other side. This may repeat so the path of a dropped plate may well be a zig zag all the way to the bottom. I generally encourage experimentation, but if you must drop plates into the bath, I suggest waiting until you find yourself bathing at someone else's place, and use their plates. Interestingly, and not without an incredible amount of forward planing on my part, this dinner plate zig zag might also go some way to explaining how a bibbed lure gets it's swimming action.

A sail boat achieves a similar compromise. If the wind is coming from one side, it wants to blow sideways with the wind, but the shape of the boat, and the sail set so that it sucks the boat forward, make the boat track roughly forwards.

That means a sailboat can sail into the wind, but not directly. In fact there is around 45 degrees each side of dead into the wind where you can't point your sail boat (pictured here scribbled in red). Whilst that last point is perhaps the most interesting, it isn't really relevant.

So, to reuse a previous crayon graphic. A long bib set at an angle pointing just slightly lower than flat, can force the lure to pivot at the tow point, and point down. This will force it to rotate about the tow point.

Some kind of vague approximation of that effect is depicted here by green arrows pivoting around a drawing of a bow, tied in imaginary string.





A long flat bib encourages the lure to swim to the bottom, a short, sharply downwards angled bib makes for a shallow diving lure.

Exactly why a short, steeply angled bib makes for a shallow diving lure remains a mystery to me, so for the time being, will remain unexplored.