Blades...

[hvirtane]

The idea for the blades

is coming from this machine.

We made with Taisto Suihonen something similar

with 3 m long 100 mm x 10 mm wooden boards.

We made it with four blades.

For each blade there are seven boards

on the top of each others.

On the tips the boards are 25 mm on the top of

each others.  

We cut every second of each of

the crossing boards to get

the blades on the same plane.

Taisto used a power plane to smooth

the blades.

We used normal white glue and some screws to

to fix the boards.

Finally we used a lot of linseed oil

and oil paint on the top.

On the tips we used

some fiberglass resin

to protect them.

In the center there are

two plywood disks

of 8 mm thick on the both sides

of the wind rotor.

The wind rotor is fixed through the center

by five bolts to the nacelle of a

permanent magnet generator.

The generator is quite similar

as the original 'OP Volvo'  alternator.

The wind rotor stood all the bad weather

and storms of the Finnish winter

2003-2004 without any problems.

The advantages seems to be

that it never goes very fast

and it starts really easily

with low wind speeds.

On slow wind speeds it works better

than a perfect airfoil three blade wind

rotor with a little bit bigger dimensions,

which was used before this rotor.

The general method how we made it is

something like this:

You can make using this system quite good airfoils by cutting the wooden blades something like this.

I think that it is good to make blades

wide on the tips to get them working

well on really slow wind speeds.

Anybody else made the blades

wider on the tips than on the roots?

- Hannu

[witapple]

I find that blades that are slim at the tips turn faster and produce more power that blades with wide tips. Sure the wide tips will give you great start up torque but it will also have huge amounts of drag once they get moving. I am no expert but I guess it depends on what you want.

Dan

[johnlm]

Looks like a slight variation of the great old American farm windmill that is used to pump water.

[hvirtane]

With this method the blades can easily be made

to use good airfoil sections as shown on

my picture. With American style wind pumps

the blades are normally made of curved flat

metal sheets.

In any case, I think that a kind of self-regulation

is good for wind turbines working

on slow wind speed conditions.

It can be achieved if the blades

are built so that they don't

go too fast even if the

wind is fast.

On the other hand I think that with most wind

turbines the air hitting the blades will move

toward the tips of the blades. If the tips are

wide, that creates lots of power?

- Hannu

[windstuffnow]

  Theoretically, a given size blade in a given wind will extract the same amount of power.  The main factor will be the efficiency of the blade itself in extracting this power.  

  The difference between the two is simply the speed and torque at which they operate.  1hp is 1hp no matter how you look at it... whether it comes in the form of 100 rpm at 52 ft lbs or 500 rpm at 10.5 ft lbs.

   Its much easier to design an alternator to run at higher speeds than at lower speeds.   Also, the skinny airfoils are a bit more efficient.

A rose by any other name....

Have Fun

Windstuff Ed

[hvirtane]

Its much easier to design an alternator to run at higher speeds than at lower speeds.

Also, the skinny airfoils are a bit more efficient.

I agree that slow speed alternators

are difficult to design.

The problem I'm trying to solve is to extract

power from slow speed winds. For that we have

realized that blades, which are wide on the tips

might outperform skinny blades.

So we just decided to make the alts

even slower speeding...

On the other hand we have realized

that these blades, which are wide on the tips

need very little if any furling methods,

because on high winds they will

not spin much faster.

The best possible efficiency is not the

problem, which I'm trying to solve, but

in any case I think that the air, which hits

the blades will travel to the tips of

of the blades and then the tips can extract

power from the air...

as the new GGS model is suggesting.

Please see:

http://mystic.math.neu.edu/gorban/Gorlov2001.pdf

One more reason to make blades this way is

that it is quite easy.

You can of course make blades of piles

of wooden boards so that they are not at all

wider on tips, too...

- Hannu

[brett]

Hi would you mind taking the time to specify/sketch the cut on every second blade that you were mentioning, please? I like that blade design for low wind apps. It is smart.

Thanks

brett

[hvirtane]

Hi,

basically you just cut off from

every second board the width of the

board in the middle.

The only difficult part is

how to start it so that it

goes neatly to spread

on the tips. After started

it is very very easy.

You can first try with pieces of

cardboard how it goes.

I think that it might be not

difficult to mark with paint

on the boards, how much to cut them,

after whole pile is ready, to get

good airfoils out.

I will try making more

sketches tomorrow. Now

it is a bit late...

Had to do something else

the whole day and it

is in the night a quarter to 2

o'clock after midnight now.

- Hannu

[windrules]

Hi Hannu,

           I also like the way you are thinking on this. Can you give us more info. on the alternator you are using and at what watts output does the normal blade catch up (or wind speed).I guess you are using axial flux but can you give info on diameter and mags and windings.

Regards,

Mos

[johnlm]

You are right about the self limiting on speed on this style of blade .  I suspect it is due to large drag losses as the rpms get higher.  Also this type has good low wind speed starting torque due to the wide tips -just like the farm windmill has to pull the pump from the low point it usually comes to rest at it needs a good starting torque but would not increase speed much after the wind got above 25-30 mph. I carved a 2 bladed prop (with more or less a std ClarkY airfoil) with the tips slightly wider than the root one time and it seemed to work ok except I have never left it mounted up in a high wind to see what the self limiting effect would be.

[hvirtane]

Here are two pictures with

texts on how we started

piling boards on the

tops of each others.

- Hannu

[hvirtane]

The turbine is not with me,

I haven't got any place for such one.

We built it with Taisto Suihkonen

and it is at his place.

The problem Taisto has been facing

is regular slow wind speeds.

So finally we made the wind rotor

with the specifications as above.

(3 m dia, four blades each made of seven

10 mm x 100 mm wooden boards and

rough airfoils cut after.)

The alternator is quite similar

as the original 'Volvo OP' alternator.

Single phase axial alternator,

single magnet rotor with laminates.

It is made of a Mercedes front wheel,

with the disk dia 28 cm.

24 neo magnets, round 12 mm x 30 mm

each. We have tried with different

coils and at present there are

40 turns in each coil. The stator

is made of a 2 cm thick 'Industrial Formica'

plate and for the laminates we have

tried several methods, plastic coated

iron wire seems to be working OK.

The exact figures about

watts available at different

wind speeds are not available,

because Taisto never measured them.

At present the setup is done so that

it almost at once when started moving,

starts charging 12 V batteries.

A secret by Taisto to achieve that,

was to use a transformer before

the rectifier (1) so that

the voltage rises high at slow speeds.

The current can bypass the transformer when

the speed increases, because there is another

rectifier (2) parallel to the transformer,

which leads the current to the batteries

directly.

There is as well a side furling system,

similar as used by Hugh Piggott

and many others with the gravity

balanced tail system.

I will try posting pictures of

the machine later.

- Hannu