17 Foot Offset & Forward Offset

[freejuice]

Hi Folks,
 I have been using the search function lately and it seems the jury is still out on offset and forward offset on the 17 footer.
It appears left or right offset does not matter...well to make a longs story short I have welded up a right hand offset of about 12 inches, after some people were saying the orginal offset of the 17 footer might not have been quite enough.
 To this offset I also added about 7 inches of forward offset....which my fuzzy trig tells me its just over a 30 degree angle for forward offset.
 
 Mr. Piggot's manual shows some forward offset ( about 45 degrees) in his larger generators and I thought I could also incorporate his concept it in my 17 footer, but with a right hand offset and with the tail furling to the right, and clockwise blade direction, I'm wondering if I'm building in to some problems which I might not be seeing at the moment

Is ths configuration possible: right hand offset, right hand furl and clockwise blade direction?

One last question: should I modify my tail offset angle? It appears 45 degress from the face of the alternator is common fare.
 All comments welcome...even harsh ones!
 Gavin

[nekit]

Just curious.  How are you measuring your 7" of forward offset?

[freejuice]

Nekit,
 Hummmm interesting question! Now you've got me thinking!
I based it on from the center line of the yaw bearing to the face of the trailer hub before  the rotors are mounted if I went to the centerline of the blades it would probably end up with about 12  inches of forward offset, thus with 12 inches of offset and 12 inches of forward offset, it stacks up to a 45 degree angle.
 All the best,
 Gavin

[jlt]

The bigger the offset is the harder it is to face directly into the wind . make your tail large and lite with adjustable offset. to help . don't worry about rotation it will work ether way.Better to have too much than too little.   

[freejuice]

Thanks Jlt,
 I hoping to hear that....Its good I can tweak the tail in case it pushes out of the wind too soon....the rotation is also good news...it will keep it just the way it is!
 All the best,
 Gavin

[dsmith1427]

... don't worry about rotation it will work ether way.Better to have too much than too little.   

I have a hard time with furling.  Maybe somebody can help me clarify a point.  Given the above statement, if all other design aspects are held constant, doesn't the rotational direction of the blades factor into furling?  If the blades are rotating clockwise the resulting force due to the angular momentum will be down wind.  If the blades are spinning counterclockwise the resulting force will be into the wind. (Is this what people refer to as "wind seeking")  Based on the direction of the spin won't the force associated with angular momentum contribute to the turbine's ability to furl?

n my mind, the contributing factors to furling are as follows: Tail area, tail weight, area of the blades, aerodynamic forces (lift), and the angular velocity of the the blades. 

For example, Consider a turbine offset to the right (tail offset to the left) and spinning counter clockwise.   As the blades spin faster, the angular momentum, which is a force that opposes the wind, increases the; therefore, the spinning blades keep "seeking" the wind resisting the systems ability to furl.  I some posts people have observed a wind turbine operating without a tail.  If this happens in our example, could it be said the force of the wind is equal to the angular momentum of the rotating blades?  If the same system (turbine offset right/tail offset left) is spinning clockwise, the force resulting from angular momentum is in the same direction of the wind helping to furl the system out of the wind.  Therefore, for furling purposes, blades should spin clockwise. 

The following is a short Youtube video illustrating Angular momentum:

http://www.youtube.com/watch?v=r__nGqGpTD8

Are my thoughts on the right track?  Any feedback/help is appreciated.  Thanks

Don

[fabricator]

A lot of folks here, including me, believe you are on the right track, the theory says when looking at the alternator from the front a right offset should have clockwise rotation, left offset CCW rotation.

[TomW]

A lot of folks here, including me, believe you are on the right track, the theory says when looking at the alternator from the front a right offset should have clockwise rotation, left offset CCW rotation.

fab;

No argument there!

In the early and experimental days there were some issues with minimal tilt back on props where tower strikes occurred. the force one way or the other might encourage the tips to move inward to the tower at the 6 o'clock position?

Newer designs seem to have plenty of tilt back that makes this a non issue.

Not sure on the detail but remember it being discussed.

Tom

[Dave B]

... don't worry about rotation it will work ether way.Better to have too much than too little.   

I have a hard time with furling.  Maybe somebody can help me clarify a point.  Given the above statement, if all other design aspects are held constant, doesn't the rotational direction of the blades factor into furling?  If the blades are rotating clockwise the resulting force due to the angular momentum will be down wind.  If the blades are spinning counterclockwise the resulting force will be into the wind. (Is this what people refer to as "wind seeking")  Based on the direction of the spin won't the force associated with angular momentum contribute to the turbine's ability to furl?

n my mind, the contributing factors to furling are as follows: Tail area, tail weight, area of the blades, aerodynamic forces (lift), and the angular velocity of the the blades. 

For example, Consider a turbine offset to the right (tail offset to the left) and spinning counter clockwise.   As the blades spin faster, the angular momentum, which is a force that opposes the wind, increases the; therefore, the spinning blades keep "seeking" the wind resisting the systems ability to furl.  I some posts people have observed a wind turbine operating without a tail.  If this happens in our example, could it be said the force of the wind is equal to the angular momentum of the rotating blades?  If the same system (turbine offset right/tail offset left) is spinning clockwise, the force resulting from angular momentum is in the same direction of the wind helping to furl the system out of the wind.  Therefore, for furling purposes, blades should spin clockwise. 

The following is a short Youtube video illustrating Angular momentum:

http://www.youtube.com/watch?v=r__nGqGpTD8

Are my thoughts on the right track?  Any feedback/help is appreciated.  Thanks

Don

Take a good look at your u-tube example with respect to the string support (rotor shaft behind rotor, the wheel) and wheel rotation. If the wheel is the rotor and you are looking at it from the front (upwind) then you will see that the wheel rotation is counter clockwise and the assisted yaw is to the right or counter clockwise looking down from the top. This would assist furling the opposite of what you state. I corrected my anti furling machine by having counter clockwise rotating blades with a right offset (this looking from upwind straight on the front of the blades.) I think if you check with Hugh and the Dans they have changed over to this combination or the opposite. (clockwise rotation offset to the left). I think they're reasoning is that it helps avoid a tower strike from the blades when yawing quickly and fast RPM. This could very well be true also, for me it has always been to assist the furling for the very reason you indicate and the many u-tube examples show. Check your u-tube example again, I think you may want to change your offset side or rotation direction to prove out your observation. Bravo !! Be persistant with putting the whammy on the mystical blade seeking curse, no garlic required.  Dave B.