Belleville Washers Revisited
Photo by Patrick Panzera
In the December 2011 issue of EAA's Experimenter e-newsletter, we listed a little blurb about Marc Zeitlin's successful use of the Belleville washer to maintain propeller bolt tension during the expanding and contracting cycles of wooden propellers. Marc recently made some minor changes to the spreadsheet he has on his website, and we felt that they are important enough to bring to your attention.
From Marc Zeitlin:
I've updated the instructions and spreadsheet for Belleville washer usage with some fixes and new features. I've added a "Safety Margin Graph" tab to the spreadsheet which graphically shows you how much better two Belleville washers are over no Belleville washers, and how much better four washers are over two washers. You can change your prop hub shrinkage/growth to see what happens to your installation with humidity changes.
I've also added a 5/16-inch washer solution and tried to make the spreadsheet a bit easier to use and more readable. In addition, I've rewritten parts of the instructions to reflect this new spreadsheet info and the 5/16-inch washers, removed out-of-date information, and changed the language a bit.
If you're already using Bellevilles, you'll likely see very little difference in the recommended solution from what you're already using. (The spreadsheet might recommend slightly more compression than before.) But you might be interested in going through it and ensuring that you have the latest recommendation so during your next condition inspection, when you check your prop bolts, your aircraft reflects the latest information.
You can download the instructions and spreadsheet files at http://CozyBuilders.org/Prop_Bolt_Bellville_Washer
As always, any comments, flames, feedback, or corrections are welcome.