Ignoring clamping friction in a bolted shear joint calculation seems to be a worst case analysis in that the assumption is: the bolts are torqued just enough to keep from rattling around. The total load then would be applied in shear to the bolt. That assumption does not seem realistic for practical applications. No one in their right mind would deliberately put a shear joint assembly together without proper torqueing on the bolts. The folks at Imperial put a lot of emphasis on getting the proper torque values on bolts. http://www.imperialsupplies.com/pdf/A_FastenerTorqueCharts.pdf The FAA provides some guidance on bolt torque values in Figure 5-34, page 5-55 of https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/amt_airframe_vol1.pdf I use the Imperial torque chart for lubricated SAE Grade 5 bolts. These bolts are equivalent to the AN aircraft bolts (120,000 psi tensile strength). I use AN6C ss bolts with washers under both the head and nut, and lube the threads very lightly with SAE-30 motor oil before assembly. The torque value that I set in my torque wrench is 25 ft lb. The stainless steel bolt threads must be lubed prior to assembly to prevent galling. This business of bolting outer wing to stub wing is indeed critical to get done properly. However, standard guidance in the plans does seem to be lacking. As Mark, Larry and others point out, your mileage may vary.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA -------------------------------------------------------------------------- Sid Wood wrote: > I had understood that the WAF bolts in shear were a backup for the > real attachment: The clamping action due to the bolts squeezing the > two outer and inner WAF plates together. The stress guys I've worked with over the years don't even consider friction as a useful force in a bolted shear joint calculation, and don't include it in the analysis as a result. This includes NASA, ASME, and military work. Your mileage has obviously varied... Mark Langford ML at N56ML.com http://www.n56ml.com
