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Offset for Yaw
By coldspot, Section Mechanical Posted on Tue Mar 28, 2006 at 09:14:53 PM MST
Asking for some simple "Rules of Thumb" for amount of OFFSET from Tower center?

Hello,
Being that I have to replace my Ametek 30 VDC
Wind Mill with something else.
(See my Diary for Ametek Ceiling Fan Blade Failure)
Untill I get something different for the Ametek as
far as a hub/Blade set-up.
I'll be putting up some other mills for now for
testing mainly.(Ones I've gotten Blade/Hubs Finished for)
What I'm asking, (Post Title)
Is about how much Offset for Yaw
From Tower Center to Mill Rotor shaft center?
On my Ametek Mill, I had about 2 1/2"
But this Yaw set-up also has Three Bearings
So it would spin around easly, maybe to much.
I"ll be using the same Yaw mount for one,
It'll be the 0.07HP Induction Conversion.
So that one will have about the same Offset.
But, On my newest test tower, I'll be putting up
Maybe the CMI PM Motor, (28 Lbs).
So I'm building from scratch a yaw set-up for it
and would like it to be as good as I can do.

Offset for Yaw | 7 comments (7 topical)

Re: Offset for Yaw (3.00 / 0) (#1)
by electronbaby on Tue Mar 28, 2006 at 06:04:39 PM MST

if you want it to yaw slower, lengthen the tail.

what is the diameter of the prop? this (usually) determines the amount of offset, but there are a couple factors. If you lengthen the tail its usually heavier, so to lift the weight, the offset must be greater. also the tilt angle of the tail yaw pivot (compound angle).

a good place to start is the prop diameter.

RoyR
Have Fun!! RoyR KB2UHF

Re: Offset for Yaw (3.00 / 0) (#2)
by coldspot on Tue Mar 28, 2006 at 06:20:10 PM MST

I don't think all the normal rules of thumb
would apply to the "little Wind Mills"
like I'm building.
My prop diameter will be about 4'-6'
Thats right four feet to six feet.
And my yaw designs all use at least
one bearing, no slip over pipe in pipe!
On the ones that are pipe in pipe, I've got
roller bearing to fit on the top of the inner
pipe with the bearing riding on the pipe lip
and the washer on the outer pipe being the other
surface for the bearing to ride against.
From what I've researched on this forum, most of
the little mills don't get any furl. Just yaw.
Not my way of thinking, thats why mine do have
yaw with bearings and furl.
The Ametek ceiling fan blades worked great
But with 50 MPH steady and gusts over 70 MPH
I dought very many mills would have done any better.
Todays paper stated that a gust over 93 MPH was recorded
in a small town not very far from here with one town
about 35 miles away (Downwind) having a two mile tornado path
tearing up a lot of stuff heading this way.
Thanks anyway
:|

Re: Offset for Yaw (3.00 / 0) (#3)
by electronbaby on Tue Mar 28, 2006 at 06:33:08 PM MST

tornados, yikes... not much will survive a tornado.

but yes, even 4'-6' mills can be made to furl.

RoyR
Have Fun!! RoyR KB2UHF
[ Parent ]

Re: Offset for Yaw (3.00 / 0) (#4)
by electronbaby on Tue Mar 28, 2006 at 06:35:45 PM MST

Yaw only, requires NO offset. The offset IS needed for a gravity furling system.
Have Fun!! RoyR KB2UHF
[ Parent ]

Re: Offset for Yaw (3.00 / 0) (#5)
by coldspot on Tue Mar 28, 2006 at 06:56:30 PM MST

yes electronbaby
"Yaw only" wouldn't require any furling
But, I'll build with Furl, even a bearing furl
as did my Ametek have.
What Id like to know is how much Offset
should I build into a mill that weights 28 lbs?
I'd like to keep it at a minumum amount,
maybe 5"-7" MAX amount.
Would rather go with about 3"-4"
From center of tower pole to center of
shaft on mill.
Would like to keep the weight closer to
tower center.
Thanks

Re: Offset for Yaw (3.00 / 0) (#6)
by johnlm on Tue Mar 28, 2006 at 07:35:03 PM MST

On my 3 to 5 ft diameter props, Ive used around 3 to 3.5 inches of offset (pipe over pipe for the yaw bearing). You then need to adjust the weight of the tail to make it furl at the desired windspeed. I usually make the tail assembly light so I can add weight to get the desired result. I leave the end of the tail boom open ended pipe and insert a length of rebar (cut to a length to adjust the weight) inside the pipe to add weight. Then secure the rebar in place.

John

Re: Offset for Yaw (3.00 / 0) (#7)
by electronbaby on Wed Mar 29, 2006 at 06:16:32 AM MST

I would think 3.5" offset is a good place to start, maybe 3". i usually take the radius of the prop in feet, and thats the number of inches your offset is. Not very technical, but it seems to come close, considering you follow other basic rules of thumb. Maybe someone else has a better idea...

good luck,
RoyR
Have Fun!! RoyR KB2UHF

Offset for Yaw | 7 comments (7 topical)

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