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Blade Balance
By JW1111, Section Wind Posted on Sun May 11th, 2008 at 09:27:30 PM MST
Blade Balance

Sorry to flood this board with questions but maybe my novice questions will help other people too. My current turbine with plastic blades spins very quiet. I only notice a slight wobble in the back end. Maybe 1/2 inch. All the blades weigh 7oz and balance on my finger half way down the blade. How do you know when the blades are out of balance and how do you check this on the bench? Is 1/2" wobble at full spin too much? Thanks

Blade Balance | 4 comments (4 topical, 0 editorial)

Re: Blade Balance (3.00 / 0) (#1)
by wolfie on Sun May 11th, 2008 at 03:45:15 PM MST
(User Info)

i believe what needs balanced is the assembled rotor assembly, based on the hub hole...
similar to balanceing a lawnmower blade when sharpening it.

Re: Blade Balance (3.00 / 0) (#2)
by zeusmorg on Sun May 11th, 2008 at 04:25:33 PM MST
(User Info)

Good discussion on blade balancing: http://www.fieldlines.com/story/2007/11/7/95318/7995

Re: Blade Balance (3.00 / 0) (#3)
by neilho (neilho at innevi dot com) on Mon May 12th, 2008 at 06:04:07 AM MST
(User Info)

Your balancing methods need to be accurate to about 2% to result in a smooth running rotor. I use the moment method- similar to what you've done. Weigh the blades, find the balance point (preferably on a near knife edge) on the blades, multiply weight by distance for each blade, and weight accordingly so that the results for each are within 2% of each other.

Tail wobble is often caused by the blades not tracking properly, that is, by the blade parts not rotating in exactly the same plane. Check tracking by measuring the distance between the tip of one of the blades (at the leading or trailing edge) and some stationary object. Rotate the rotor and check the next blade, etc. Adjustment can be done by shaving or shimming the root of the blade where it contacts the rotor/hub.

neil

[ Parent ]

Re: Blade Balance (3.00 / 0) (#4)
by neilho (neilho at innevi dot com) on Mon May 12th, 2008 at 06:13:30 AM MST
(User Info)

Oops- in the third sentence in the first paragraph; "multiply weight by distance for each blade" should read "multiply weight by distance from the center of rotor rotation for each blade"

neil

[ Parent ]

Blade Balance | 4 comments (4 topical, 0 editorial)

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