Variable Rotor to Constant Voltage

[sailwing]

A fixed blade design must assume an operational windspeed, above and below that efficiency drops off.  If blade could conform with high efficiency and low complication to all wind conditions would it pay?  Mechanical output varies with RPM and blade shape, even at very low wind speed a high pitched, full cambered blade will produce torque.  Can the variable output be used to generate electricity and fill all those idle hours.  I'm working on a relatively simple variable blade system, but have yet to warm up to the electron.  Any answers to this problem?  Or should I just keep lifting weights?

[drdongle]

A variable out can be compensated for with some clever electronics such as "buck/boost" regulators and MPPT's (maximum power point trackers). While less than perfect they can provide a reliable and effective alternative to variable pitch control systems.

[DanB]

"A fixed blade design must assume an operational windspeed, above and below that efficiency drops off."

I dont think so... it assumes an 'operations tip speed ratio' meaning the blades want to turn a certain amount faster than the wind. So - in a 10 mph wind the tips are cruizing along at 70mph, in a 20 mph wind they're going 140 mph etc. From my understanding most 'variable pitch' machines are really 'fixed pitch' under normal conditions when they're running most efficiently and they pitch the blades (usualy to stall) in order to keep from overspeeding in higher winds.  Fixed blades can be very efficient across the range of windspeed and there are several ways to furl in order to protect them (and teh alternator /tower etc)...  changing the pitch of the blades is definitely one good way - probably the most complicated though.

[Nando]

The mills with pitch control will rotate at their TSR design following the wind velocity BUT once the RPM reaches certain level the TSR is reduced by changing the pitch of the blade.

Many blades have a twist angle that is a bit more critical to assist in the RPM regulation by presenting from the tip of the blade towards the hub a negative angle, this looks for some like reducing the length of the blade, in reality the upper section starts to present a braking effect to reduce the TSR more accurately than with pitch angle and with the addition of a pitch angle the wind mill behaves in a constant flat power output with increasing wind velocity.

For general work the blade twist could be reduced since the pitch control does a good job as many can see it in the wind mills advertisements.

I was told that this type of wind mills have been used in Artic and the Antartica sometimes at 150+ MPH, with a reduced TSR to less than 1 .

[SamoaPower]

Can't agree Dan. I think you'll find that the typical fixed pitch air rotor's TSR varies quite a bit over the speed range with the attendant drop in efficiency on either side of optimum. Usually higher at the low speed end and lower at the high end due to the applied load mismatch. It's a pity that anemometers and tachometers aren't included as standard equipment on DIY machines - we'd have a lot more data. Variable pitch offers more than just high-end speed limiting and shut-down. I would take your last statement one step further and say that controlled variable pitch is the BEST way to go in spite of it's added complexity and, if you add Dr. D.'s suggestion for electronic alternator load control, you've got it nailed.

Systems matching - all important!

[sailwing]

Not using pitch to control RPM but to improve airfoil efficiency.  System changes pitch, camber and twist, could be used inefficiently for constant RPM but seems a waste of available energy.  See drawings.  In sailing, the origin of my interest in this, reefing was used in high wind, now through better sail shape control you would never win a race if you reefed.  In the energy race why furl in the face of rising power potential?  My inspiration was the 5 year Princeton sailwing project, unfortuneately run by aeronautical engineers not sailors, the nature of their double skin foil is to distort, their fixed wing approach had problems, this tendancy to distort controlled by centrifugal force can be positive if trimmed to conditions.  Drawing shows system as built and even with round leading edge unloaded TS of 8 was easy, Princeton got 4?  I realize load tests need a leading D section, would like to test potential of this rotor, any suggestions?

[sailwing]

Over speeding is not in my sailing experience but other than RPM which has to increase for more power extraction, is most stress due to turbulance of foil not conforming to higher apparent wind?  An extreme example is TS ratio of 8 at 100MPH wind, and you're past the sound barrier, other problems aside if the foil could morph into the right shape, you could just cruise along.  But low winds are the real problem most of the time and most fixed foils can't go there.  The wind bag, it starts as a bag but can morph into a board, might just clean up at this lower end.  But I need usable output at variable RMP for testing.  Any ideas?

[sailwing]

Seems to reduce effective length of blade to me, as length of tip's negative angle of attack will never be part of the effective area swept, but at 150+RPM my golf club shafts and bicycle derailer cables may not be enough.  I don't know how much range on the upside this system could improve output but over the long time period of the downside small gain might pay off.  Any ideas for testing program?

[sailwing]

Encouraging to read "higher at low speed end" where this might be most useful, but "applied load mismatch"?  As a sailor, the wind is my medium, when the apparent wind kicked in and the rotor roared to life I felt its power but the electron is waiting at the other end, "systems matching - all important"?  Need help here.

[ffoegw]

"The wind bag, it starts as a bag but can morph into a board, might just clean up at this lower end.  But I need usable output at variable RMP for testing.  Any ideas?"

Putting a board further away from center should give a lower wind speed start.

Having a board closer to center should give higher RPM's.

Somewhere in between the best of both worlds might be obtained?

Having the board move towards center as the wind speed reaches optimum and further away as the turbine starts to overspeed?

Not exactly morphing but I think it might be closer to a realizable solution.

I you can figure out how to do it, please let me know.

Geoff

[hvirtane]

Really nice drawings.

But I think that

the control system as

described is quite complex.

Some time ago we discussed

pitch control systems.

I made a draft drawing

how it could work in

my opinion:

- Hannu

[sailwing]

Drawing 2 was for experments of 1 blade rotor.Drawing 1 disreguard tip pitch device and lower left hub drawing,complex again only for experiments.Drawing 1 right with tip and root fixed at 0 angle 2 sliding blade spars driven centrifugally control pitch camber and twist,think of wing of landing aircraft,it takes more than pitch to maximize power from the wind. From a bag to a board better seen in a model

[sailwing]

Look at left side drawing 1,high torque start[bag with max twist outfrom hub]to high speed flat[board for angle  of increasing apparent wind ]think aircraft,high speed cruising :flat wing,low speed landing:flaps down-bag or go sailing!that is how I got here.

[ffoegw]

Interesting description of how a torq-a-verter works using a snowmobile as an example.

http://www.gates.com/brochure.cfm?brochure=1033&location_id=542

"If the drive is properly calibrated, it will seek the best ratio for maximum speed under the existing conditions."

Translated to renewable energy windpower"

It helps start and then reach the maximunm RPM for the wind speed available.

This should work well for a high torque, low rpm VAWT.

Regards

Geoff

[sailwing]

Years ago I had simular system on 11o generator to run at constant RPM off a vehicle engine.I assume high power loss but no data,feel electrical rather than mechanical conversion would be more effecient,anyone know?