Compression dents on wood spars

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Jerry Jackson
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Joined: Tue Jun 24, 2008 07:59
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Compression dents on wood spars

Post by Jerry Jackson » Mon Dec 01, 2014 10:44

My IA doesn't have any guidelines for judging what compression dents are acceptable in a set of fir spars for a 65TC so I want to ask for recommendations and opinions here.

The dents are located where parts are bolted to the spar face--compression ribs, root fittings, ect. They are unremarkable in appearance, free of cracks, discoloration, or broken fibers. The dent depth ranges from about 0.015 inches to about 0.045 inches. They are shallow around holes fitted with bushings.

I need to replace the doublers at the root. Should the doubler material be installed flat, with the underlying dent filled with glue? Or should the doubler material be deformed to match the shape of the underlying dent?

What is the recommended tightening torque for bolts in wood spars?
Jerry Jackson
San Antonio
7ECA 65TC
8T8

Paul Agaliotis
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Location: San Martin, California
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Re: Compression dents on wood spars

Post by Paul Agaliotis » Mon Dec 01, 2014 17:13

Jerry,
Most of the time these defects are caused by overtightening of the attach hardware. I'm not sure if there is any specific inspection criteria for this condition, I've never looked. If you plan to replace the butt plates, I would try some distilled water on the area to try to restore the dishing. Add a little ammonia to the water if needed. This allows the grain to relax a little more.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

Jerry Jackson
Posts: 85
Joined: Tue Jun 24, 2008 07:59
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Re: Compression dents on wood spars

Post by Jerry Jackson » Wed Dec 03, 2014 05:51

Thanks for the response, Paul.

I will try using water and ammonia to reduce the dents. I plan to install the doublers flat, allowing glue to fill the dents. The only quantitative information I have found for bolt torque is from propeller manufacturers. They recommend 10-12 ft-lbs for 1/4" bolts and 11-13 ft-lbs for 5/16".
Jerry Jackson
San Antonio
7ECA 65TC
8T8

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