[elippse]

There was an article a while back showing how to make a device to get very accurate static balance of a propeller. When properly adjusted, it will show an unbalance of a #4 thinny washer at 30" radius. One ingenious fellow even adapted this device to use to balance his airplane's wheels! Check the Contact! magazine web site www.contactmagazine.com for the magazine issue that contains the article. You can even have the prop on this device while you spray black paint on the back side to achieve final balance.

 

[Walt]

Balancing

Just as an FYI;

One small thin washer weights about .5 gram so at 30" that's 15 inch/grams.

When we do dynnamic balancing we use that same thin washer at a 7" radius (3.5 inch/grams) for final adjustments.

15 inch/grams at a 7" radius is equal approx 2 grams which is 2 thick 1/4" washers (quite a bit of weight).

Bottom line: Dynamic balancing can be more accurate than the average static balancing by an order of magnitude of 2.

 

[az_gila]

Numbers

Just as an FYI;

One small thin washer weights about 1 gram so at 30" that's 30 inch/grams.

When we do dynnamic balancing we use that same thin washer at a 7" radius (7 inch/grams) for final adjustments.

30 inch/grams at a 7" radius is equal to 4.3 grams which is 2 thick 1/4" washers (quite a bit of weight).

Bottom line: Dynamic balancing can be more accurate than the average static balancing by a magnitude of 4.

Actually, since the initial reference was for a #4 washer, the balancing is about equal.

A standard #4 SAE washer is about 1/4 gram (1650 per pound), not 1 gram, and that is a standard, not thin washer.

I think it ends up about equal....

 

[Walt]

I just weighed a thick AN 1/4" washer, exactly 1 gram.
I corrected the above numbers to reflect 1 thin washer is .5 gram.

 

[az_gila]

Washers

I just weighed a thick AN 1/4" washer, exactly 1 gram.
I corrected the above numbers to reflect 1 thin washer is .5 gram.

No - the original post talked about a #4 washer, not a 1/4 inch washer.

Are you saying the original poster was wrong?

The link is to a paysite, so I can't check the original article.

 

[Walt]

No - the original post talked about a #4 washer, not a 1/4 inch washer.

The link is to a paysite, so I can't check the original article.

Oops my bad, I'm thinking -4 which I automatically equate to 1/4"

A -4 thin washer is really small.