Instructions - Rev. G Revise for addition of 5/16" bolts Spreadsheet - Rev. J Add Safety Margin Graph 01/07/2012:
Spreadsheet - Rev. K Add Pictures of configurations
Rearrange for usability
Add individual wood stiffnesses
Add better error checking
Instructions - Rev. H Revise section 1.2 - Propeller Bolt Length Determination
Instructions - Rev. J
Add 8 mm bolts
Fix spreadsheet references; minor typo fixes
Spreadsheet - Rev. L2
Add 8 mm bolts
Add bolt length error checking
Add Prop Drive Flange Lug picture
Instructions - Rev. K
Updated for changes in spreadsheet - emphasize WASHER COMPRESSION - NOT bolt turns
Moved Spreadsheet instructions earlier in document
Added Graphic to depict washer compression
Spreadsheet - Rev. M
Updated to emphasize WASHER COMPRESSION - NOT bolt turns
Revised Drive Lug depth graphic
Expanded Washer Compression Range from 45% - 65% to 35% - 75% to allow for more solutions
After losing a wood core propeller on an O-360 Lycoming engine due to improper torquing of prop bolts, I re-discovered an old system for ensuring hub compression on wooden props involving Belleville Washers. You can see a presentation on my prop loss here, and a presentation on the belleville washer system here.
If you are interested in using a relatively lightweight system on your prop bolts that will make your wood prop installation far more robust and less likely to depart your aircraft, as well as reducing the amount of maintenance and care that is normally required for torquing prop bolts, you can download the instructions (which also include belleville washer part numbers) and washer selection/installation specification spreadsheet below. Solutions are provided for 1/2", 7/16", 3/8", 5/16" and 8 mm prop bolts - I do NOT have a solution for 1/4" or any other prop bolt size (yet).
If you have a prop bolt size that doesn't currently have a solution, get in touch and we might be able to work something out.
DO NOT USE BELLEVILLE WASHERS THAT ARE NOT SPECIFIED IN THE INSTRUCTIONS / SPREADSHEET - the force deflection curves for specific washers are very important to the safety of the installation. Using the wrong washers can result in loss of the propeller or damage to the propeller.
If anyone has any comments, corrections, flames, suggestions, or questions, or anything else related to using this system, please contact me at the email address listed below and I'll be happy to respond.
Also, please keep me up to date with your usage of this system and how it's working for you.
As with any and all things related to experimental aviation, no warranties, express or implied are given with respect to using Belleville washers on your aircraft. You, as the manufacturer, owner, builder and/or pilot are 100% responsible for the safety of your aircraft. These instructions and the accompanying spreadsheet are merely advisory and if you're not willing to be responsible for your own actions and installation, please do not use this system.
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