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Tail boom mount question
By johnlm, Section Homebrewed Electricity Posted on Sat May 1st, 2004 at 12:05:11 AM MST
?

I have not built a windpressure activated / gravity controlled furling assembly that is used by many of you so I have a question. I think I understand that the mounting post for the tail boom attachment is tilted from the yaw axis by 20-30 degrees but it appears that the position rotated about the yaw axis relative to the rotor plane is about 120 degrees. Is this correct and if so why? Why not at 90 degrees directly behind the yaw bearing?

Why is the position as in drawing A and not as in B ?
Johnlm

Tail boom mount question | 7 comments (7 topical, 0 editorial)

Re: Tail boom mount question (none / 0) (#1)
by Norm (peppysue@suite224.net) on Sat May 1st, 2004 at 02:35:24 AM MST
(User Info)

I'm just guessing...but it has to do with how
much the rotor bearing is offset from the yaw
bearing, at 90 degrees the tail would have
hardly any leverage at all and the tail would
have to be quite heavy or at the first lightest
wind the mill would furl. Like I said I'm just
guessing and thanks for asking the question.

( had heartburn and trying to answer your
question distracted me from it and now it's
all gone....)
( :>) Norm.
( :>) Norm

Re: Tail boom mount question (none / 0) (#2)
by lecoursc (lecoursc@sympatico.ca) on Sat May 1st, 2004 at 02:30:08 PM MST
(User Info) http://www3.sympatico.ca/lecoursc/genny.htm

Another wild guess, it also balance the weight each side of the pivot, in the full furling position weight would be on one side only, the best of all it works, can't wait to finish my genny and see this furling system in action.

Have fun.

Re: Tail boom mount question (none / 0) (#3)
by PaulJ on Sat May 1st, 2004 at 09:14:43 PM MST
(User Info)

In diagram B, the tail is at the lowest point on its mount. If the tail was made without "stops" to limit its travel, this is where gravity would bring it to rest. It takes very little force to start moving it from this position.

In diagram A, the tail is resting on one of its "stops" about 40 degrees up from the lowest point on its mount. Gravity is pulling it quite strongly against this stop; consequently, it takes a fair bit of force to get it to start moving.

This initial force is what is overcome to start the furling process, I guess it's similar to preloading a spring in some respects. Without the preload, furling will start as soon as there's any wind at all. With the preload, you can set the furling windspeed by varying the weight of the tail assembly.

Note that in diagram A, the tail needs to be offset about 15 degrees or so to counteract the yaw force of the offset rotor, or it won't quite face the wind.

I hope this helps, I learnt the hard way on my first attempt by building what you drew in diagram B!

Re: Tail boom mount question (none / 0) (#4)
by TomW on Sun May 2nd, 2004 at 05:43:52 AM MST
(User Info)

johnlm;

Near as I can tell it works essentially the same way an automotive front steering works. Caster and camber working together. Of course I am no mechanic and never built one of these furling systems.

With no force on the prop it is balanced such that the generator axle is straight into the wind. As force increases on the prop it forces the prop to misalign from the wind based on size of tail combined with weight of tail and boom length.

If the generator [and prop] were not offset to the side the force would not misalign the prop from the wind near as I can tell.

Cheers.

TomW

"Education consists mainly of what we have unlearned."--Mark Twain

Re: Tail boom mount question (none / 0) (#5)
by scoraigwind (magnet@scoraigwind.co.uk) on Sun May 2nd, 2004 at 06:41:20 AM MST
(User Info) http://www.scoraigwind.co.uk

"Why not at 90 degrees directly behind the yaw bearing? "

The wind is always blowing against the rotor blades (propeller) and pressing it backwards. This works for us later when the wind is strong, but when it is not so strong we need to hold the blades straight into the wind against this force. This is why I would offeset the tail in the opposite direction a little bit.

It is a good idea to have the hinge axis as shown in A for reasons already given about preloading and resting on a stop. it is also a good idea to have the tail swung out a litle to the right opposing the blades when sitting on its stop.
Hugh Piggott http://www.scoraigwind.co.uk

Re: Tail boom mount question (none / 0) (#6)
by johnlm on Sun May 2nd, 2004 at 04:07:39 PM MST
(User Info)

Thanks for the input. I was thinking that the reason was to put some preloading force back to the rotor arm to give more initial force offsetting the pressure of the wind on the rotor. And you have confirmed that notion. Until you have built a model or an actual one of these furling systems it gets a bit abstract trying to imagine all the forces with the various angles involved. I suppose drawing one out and doing the vector math would be an alternative or precursor to building and experimenting. Am I correct to assume that as the tail furls it begins to roll its fin face from a vertical plane to a more horizontal plane? Does the lift force of the wind against the tail fin as it rolls toward horizontal actually begin taking some of the weight off the tail boom (sort of like it is acting like a kite attached to an arm) counteracting its forces to push the rotor back facing the wind? Once again thanks for the info.
John

Re: Tail boom mount question (none / 0) (#7)
by Norm (peppysue@suite224.net) on Tue May 4th, 2004 at 06:00:49 AM MST
(User Info)

Does the lift force of the wind against the tail fin as it rolls toward horizontal actually begin taking some of the weight off the tail boom (sort of like it is acting like a kite attached to an arm) counteracting its forces to push the rotor back facing the wind?
To be honest about it I've yet to make a large mill....but I find just the geometry of a furling system quite intriguing and of high interest...I haven't thought about this last item you mentioned, but I can see now that you asked that it might be a contributing factor, and I too wonder if the original designer had that in mind ....some of the design intentional or accidental and who gets the credit for designing it in the first place? All kind of thoughts and ideas ....Right?

Well back to the Rolacolasolar hot air engine or wherever the day takes me!
( :>) Norm

( :>) Norm
[ Parent ]

Tail boom mount question | 7 comments (7 topical, 0 editorial)

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