Modeling the Jacobs VP system

[wdyasq]

I have been looking at the Jacobs Variable Pitch Prop system.  Today I decided to cobble together a quick model so I could study with my hands and eyes. It starts with the blades fully retracted and as "flat" as they get. The blades slide out and twist on the hub. A collar with ball joints controlls the tail of the blade on the later model Jacobs. Springs hold the blades in retracted mode - "Flat"





As the speed goes up, the centrifigal force pulls the blades out. This pitches the blades more coarse.





If the mill speeds more the blades pitch even more.

Well - that's about all for "Just looking".

The thing was pretty mysterious the first few times I looked at it.

Ron

[oztules]

I don't wish to deride your explanation, but for me it still is mysterious.

Does the blade retreat from the hub radially...and ... at the same time do something else.

The black cylinder appears to move out of the white pipe whilst the blade moves up and rotates around ... is that it?

Are two systems working in tandem, or is one system(blade outwards movement) controlling the twist, as well as the black cylinder with the "ball joints" (which appear slightly adumberate at this stage.)

Before I was just ignorant, now I am confounded as well.

Can the black cylinder moving out of the white pipe do away with the radial movement, and so get rid of one more variable (dynamic blade length and tip to tip balance) - radius change of the blade.

Please keep up the good work as it will help me design a variable system for over here one day.

You'll never get it to work ya know....your bench is too tidy....a messy bench yeilds the best results.... ask Joe's brother.

..............oztules

[wdyasq]

Here is the best image I have found

I'll try the explaination again. The blades moves out radially.  As they do, the (reference new drawing) spider twists and causes the blades to rotate to a more coarse setting.  The balance of blade radial position and "Spider twist" controls speed and pitch.

Easy - RIGHT?

Ron

[Dave B]

Here it is for real. I can't remember the name of this unit ( I believe 3kw and 14') but the auto pitch sure looks the same as the drawing.  Dave B.

[SamoaPower]

A neat, simple design. One disadvantage I see is that it starts out in flat pitch which wouldn't be the best for low wind start up.

[Flux]

Not normally a problem , just the same as a fixed pitch rotor at low speeds.

The Jacobs was a dc machine with no field at starting.

If you have a pma with very poor starting characteristics such as the F & P  then it might be an issue.

It would never be worth the effort to make a pitch control that worked backwards to help start up, better to use a sensible alternator and keep the benefit of pitch control as over speed control.

Flux

[oztules]

Now that makes sense, thanks Dave B

[hvirtane]

One disadvantage I see is that it starts out in flat pitch which wouldn't be the best for low wind start up.

It is a really nice and simple design.

I see no reason, the same design couldn't be done such a way that it would start in a course pitch to help low wind start up and finally would go too flat to prevent too high speeds.

- Hannu

[SamoaPower]

Flux,

Judging by the photo and although we can see only a small portion of the blade roots, it sure looks like zero pitch which wouldn't be the same as a fixed pitch rotor. It also suggests that the blades have no twist. I'm the first to admit that this is only conjecture based on insufficient data since I've never even seen a Jacobs.

I also haven't seen a power curve for a Jacobs. Did they have any output below 10 mph? I would still expect the start-up to be slow in coming.

I agree that a reverse function would not make good sense. It just needs to park with some positive pitch which should be easy.

I've been doing a little work on the pitch controller design for my 16' machine. The current control algorithm calls for zero wind parking with rather coarse pitch for faster start-up. Upon reaching 10-20 RPM, the pitch would flatten out to maximize RPM. Sort of like MPPT except RPM as the control input. When the wind reaches about 6 mph, control would shift to a ratio of RPM to wind speed to maintain a constant TSR of 4.5. This would maintain until a wind speed of 20 mph when control would shift to maintain constant RPM to act as a power limiter. At 25 mph the pitch would be directed to full feather to protect the hardware. Any comments on this algorithm would be appreciated.

[jmk]

 The Jacobs down the road from me starts spinning in the slightest breeze. Its spinning when the Wind charger, and AWP are sitting still. They are an excellent wind turbine. They are heavey machines though. The blades up close apeared to be straight with no twist.

[dalibor]

one basicly simple way to control blade angle i have seen on web site of french producer Eoltec

http://www.eoltec.com/English/Main_en.htm

if i get it properly, on every blade there is spring and small metal plate with weight at the end of it.

when turbine is turning on desired speeds, all is in balance. but, when stronger wind cause faster and faster turning, weight on the blade becomes stronger than spring and starts to "pull" out blade from basic attack angle to reduce rotation speed.

this picture is from their site, showing two blades and weights on them.

[Flux]

The Jacobs blades were virtually parallel and with no significant twist as far as I know. They are not zero pitch as you can set the minimum pitch in the design of the mechanism..

As I said previously they used a wound field machine ( dynamo in the early units) this always reduces low wind output compared with a pma. Even so they are a highly regarded machine and if you manage to equal the performance you will do better than most commercial manufacturers.

I assume you are using an active pitch mechanism with a servo. In which case you could use coarse pitch to help starting, but if you need it there is something wrong with the alternator that will rob you of low speed power. If the thing will not start at normal pitch in winds below cut in you have excessive friction or iron losses.

Over the working range you should not need to alter blade pitch, your alternator power tracking should take care of this.  If you use clever aerofoils with lots of twist and taper then you may need to play with pitch but you are on your own with that. Better aerofoils can help to some extent but I don't think the extreme chord at the centre and excessive twist that the calculators predict will help at all. Beyond the point where you can handle the power produced you can use your pitch control to maintain constant speed and output.

If you are using a servo you will need some fail safe way to protect things when something goes wrong.

[Flux]

Perhaps I should have that what you are looking at in the picture is the plank the blade is cut from. That has no pitch just as in the normal fixed blade designs, the pitch is carved into the blade a few inches beyond the spring fixing brackets.

Flux

[Nando]

Models of mechanical parts operation is the best arrangement to learn how the design may work and as well to find improvements or problem solutions.

You have had an excellent idea that has opened your mind to understand such principles.

In the Pitch control environment, there are two common RPM controllers that do not require electrical setting means -- this for the small wind mills

One is the Centrifugal Pitch control

Another is the Torque Pitch control

And an improvement, for some, is the marriage of both

Torque Pitch control is the most logical with present available technologies and one that is quite appealing when set with negative feedback.

This negative pitch control sets the blades to an angle that requires certain air velocity to start the rotation to produce a minimum energy for the load to start acting to set the blades angle for the RPM defined by the generator load and torque that may be higher than normal.

Centrifugal pitch control sets the blades to "flat" angle to allow the turbine to start at low wind velocities and the Centrifugal elements sets the Maximum RPM that the mill may operate even when fully loaded.

The Torque controlled blades are set by the load, so if the load goes away the negative feedback forces the RPM to lower is number that may be just enough to rotate and initiate power generation if the load requires power to reset the turbine to the LOAD RPM needed to fulfill the load requirements ( this is assumed that the wind has enough energy to supply such power).

The Marriage of Centrifugal and Torque control is the ideal case, specially in low wind regimes areas.

The centrifugal part sets the blade for the best angle to start at low wind velocities and once rotating (set to an RPM just enough for the load to set the LOAD RPM) for the Torque pitch to enter in action, and centrifugal elements are not longer active.

Nando

[Warrior]

I must be missing something here, but the Eoltec VP mechanism does not seem right. Won't the weights move outward when the speed increases?

That actually makes the pitch less coarse as it speeds up. At one point they will be flat and then it looks like it going to pitch the other way around to a negative angle.

Please correct me if I'm wrong.

Warrior