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wait in' on the wind
By phil b, Section Wind Posted on Mon Jul 19th, 2004 at 12:07:35 PM MST
First generator is in the air

The generator is a Leeson bought at a garage sale for 10 bux. On the test stand, it produces 300 watts. Not much power, but it's a good place to start for my first generator. The 4' prop was carved in about an hour from freewood and painted with $5.00 'oops' paint from home depot. It has black leading edge tape on the tips and alumnized tape on the outer 1/3 of the blade. I'll find out which one will last longer.
The tower is probably overkill. It's 30 feet tall, made from 3" electrical conduit. It will serve as a test stand for future generators, such as the new one I have almost completed in my barn. Everything except the guy wires are from the junk yard.
This is tooo much fun, it must be illegal!
Has anyone tried to use outriggers on their towers and put 2 generators on one tower?

wait in' on the wind | 6 comments (6 topical, 0 editorial)

Re: wait in' on the wind (3.00 / 0) (#1)
by TomW on Mon Jul 19th, 2004 at 12:24:50 PM MST
(User Info)

philb;

Has anyone tried to use outriggers on their towers and put 2 generators on one tower?

No, but when my water pumper tower gets finished I fully intend to hang at least 2 additional mills on it besides the big one on the apex.

I will more than likely just use pipe masts on standoffs from the main tower.

Oh, I forgot. I did actually do 2 TDM mills on one boom on one mast about a year ago but only temporarily and as an experiment. Info on that is in my diary area here:

http://www.fieldlines.com/story/2003/6/24/181634/764

The dual genny part seemed to work ok but pinwheels are not a very effective prop much like the PVC blades they spin like crazy but do not seem to drive a genny very well.

Cheers.

TomW

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

Re: wait in' on the wind (3.00 / 0) (#2)
by Norm (peppysue@suite224.net) on Mon Jul 19th, 2004 at 01:12:24 PM MST
(User Info)

Didn't you post about this Leeson a little while back? Would like to get a few more details ...what size prop TR...rpm etc.
( :>) Norm.
( :>) Norm

Re: wait in' on the wind (3.00 / 0) (#4)
by phil b (philb7369at-no-more spam-yahoo.com) on Mon Jul 19th, 2004 at 01:41:28 PM MST
(User Info)

Yes, I posted some info at http://www.fieldlines.com/story/2004/6/10/14292/5213. TSR is 5. 4' prop.
Phil

[ Parent ]

Re: wait in' on the wind (3.00 / 0) (#3)
by phil b (philb7369at-no-more spam-yahoo.com) on Mon Jul 19th, 2004 at 01:37:29 PM MST
(User Info)

"I think mostly because they use counter rotating shafts to keep things from getting harmonic vibration. Like in motorcycle engines and I believe props on opposite sides of a plane rotate opposite directions."

Woh! I didn't consider harmonic vibration that two gennys might produce on a single outrigger. Thanks alot Tom! Can anyone clarify?

Yes, props on planes do counter rotate. Otherwise, an enormous amount of rudder would be required to control the plane. Also, dual counter rotating aircraft engines tend to yaw when you loose power in one engine. In adverse circumstances especially on takeoffs, they are known to yaw, then roll right into the ground.

I'm not sure the yaw is going to be a problem on gennys unless one is directly behind the other in strong wind.

Phil

Re: wait in' on the wind (3.00 / 0) (#5)
by Ungrounded Lightning Rod on Tue Jul 20th, 2004 at 02:54:22 PM MST
(User Info)

Yes, props on planes do counter rotate. Otherwise, an enormous amount of rudder would be required to control the plane.

The air drag also produces roll. That cancels out when they counter-rotate, adds up when they rotate the same way.

Boats have a similar problem. In addition to roll from prop drag, the bottom of the prop produces more side-thrust than the top. (Think of it as 'walking along the bottom.") So dual-prop power boats counter-rotate to cancel it out. (Some have a gearbox, others have one engine with a modified camshaft so they spin backward.) It's especially noticable when just starting to back a sailboat (single-prop auxiliary engine and rudder) out of a slip: The effect is more pronounced in reverse (where the prop is less efficient and thus has more drag) and when just starting you have no "way", so the rudder does nothing.

Also, dual counter rotating aircraft engines tend to yaw when you loose power in one engine. In adverse circumstances especially on takeoffs, they are known to yaw, then roll right into the ground.

The yaw is from the one-sided loss of thrust. Rotation direction doesn't matter for that.

- - - -

Regardless: If you have two identical mills on a single tower, having them counter-rotate will cancel out a lot of small stuff - including maybe some of the sound and vibration if they sync themselves up. (And they're guaranteed to do that if you hook the alternators together upstream of the rectifier. B-) )

[ Parent ]

Re: wait in' on the wind (3.00 / 0) (#6)
by monte350c on Sat Jul 24th, 2004 at 12:59:24 PM MST
(User Info)

Actually, not all light twins have counter rotating props. Those that don't have a critical engine - the left one.

There's the matter of the location of the downgoing blade - and whether it's inboard (between the motor and the fuselage) or outboard. The downgoing blade creates more asymetric thrust and thus if it's the left engine that fails, the right engine's outboard downgoing blades create more problems because they have a greater lever to operate on. Leading to the above mentioned problems of roll etc.

For a good explanation of this and other twin engine phenomena:

http://www.avweb.com/news/airman/184438-1.html

From all this - I guess it's possible that direction of rotation may very well matter for 2 turbines on the same cross shaft. If the plane of rotation is angled at all (like a lot of mills for blade to tower clearance) it might pay to have the two units counter rotate, with their downgoing blades closest to the tower.

Fun!

Ted.

[ Parent ]

wait in' on the wind | 6 comments (6 topical, 0 editorial)

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