Question about mechanical arrangements for furling

[zinguvok]

Pretty well covered it in the intro copy, I guess. Does the alternator/spindle have to be offset vs. the yaw axis of the windmill for it to furl properly, or is it just the tail hinge that needs to be offset? Reason I'm asking is that I'd like to use bevel gears to bring some mechanical watts down to ground level for various purposes -- probably running vacuum pumps, air compressors, and refrigeration pumps, although I'm not dead set on anything in particular. Thanks for reading!

[electronbaby]

Yes, there are a number of offsets used in the common design. The alternator assembly is offset from the yaw pivot point. This is to allow the alternator to want to twist around the yaw axis when the wind blows (harder). The tail keeps the machine from furling out of the wind until the force on the offset alternator is enough to overcome the weight of the tail (which is also offset, in the opposite direction from the alternator, to achieve some sort of tower balance). The alternator offset and the tail offset are compound angles. The tail offset, is a loaded hinge, it can never open greater than 90 degrees.

The point of furling has to do with a bunch of variables. Not limited to, but including, alternator offset, weight, tail offset, weight, tail ft^2, blade ft^2, blade solidity, and blade weight. It is a complex system that should balance out when working properly.

[electronbaby]

correction, the alternator offset does not need to be a compound angle. This is just how its usually done to allow more tower clearance at the bottom of the blade sweep. The tail offset MUST be a compound angle for the furling to work right.

[Flux]

You need some sort of component trying to rotate the thing around the yaw axis and this is balanced by the tail restoring component up to furling point.

If you can't offset the shaft you can use a second vane like the tail mounted at right angles. The pressure on this will do exactly the same thing as offsetting the prop axis, the original design by Wheeler was on these lines, but somewhere along the line someone had the bright idea of eliminating one component. It looks better without the side vane.

If you go that route it only needs to be reasonably small vane.

Flux

[zinguvok]

Hmm, and I could change the size of the vane to change the point at which it furls...

[TomW]

zing;

Might I suggest that you build one to spec first. Then experiment on that working unit.

Unless you are either very good mechanically or just like to play. First attempts often fail when new folks decide to "improve" the design before they truly understand it.

If it is simply for the experience have fun but if a working turbine is the goal build to plan and go from there. A LOT of thought and hands on experience has led to this design and it would seem silly to just start tossing changes at it until you understand why it is the way it is.

Just thoughts that might save you [and others] some resources.

Tom

[zinguvok]

I wholeheartedly agree. I fully intend to build an Otherpower 10' pretty much exactly to spec before I do this. I don't even have to change the design for what I'd like to do with the bevel gears and shafting -- it would just simplify it significantly. Now that I've read the responses, I understand the way the furling system works better -- I was having trouble visualizing the forces involved and the replies to my post were enlightening. I think it may end up being simpler for me to build a machine with the same physical arrangement of rotor, tail, and yaw axis than to reinvent the wheel in trying to eliminate one pair of bevel gears. Thanks, everyone!

[Flux]

Yes. It may work like the offset alternator, there may be a minimum vane size below which it will work so I wouldn't go for a vane that is too small. Better to do most of the adjustment on the main tail weight and pivot angle.

Flux

[fungus]

Just a thought .. you may not need the offset because of the torque produced by the vertical running shaft? .. Just throwing a thought out ..

[zinguvok]

Oh lordy, just like a helicopter. I hadn't thought about that... I'm going to have to talk to some of my ME buddies. I hope the RPM is low enough that it isn't critical.