Thank you everyone that has responded ...your input has spurred me on to a deeper understanding of what is happening here ...
I have now had another professional engineer review the WAF joint with the following conclusions drawn for 3/8 bolts .... Assuming that the coefficient of friction between the two WAF surfaces is 0.8, the WAF joint will resist about 2.5G by friction alone for 600 KG AUW aircraft (wing bolts tightened to 190 inch pounds of torque) and about 5.5G in total when the shear strength of the 3/8 bolt is included. This assumes a wing panel that has a centre of lift 1.0 meters outboard of the WAF bolt holes (my wing is a little longer and has a centre of area about 1.05 meters outboard, but then the wing twist reduces the lift towards the tip.) and the calculated maximum G force is likely to be conservative as it is based upon a bolt with a lower tensile strength than the AN bolts specified for our WAFs. This G force limit of 5.5 G relates to an aircraft flying at 600 KG AUW. So, provided that 1. The necessary assembly clearances are taken up by lifting the tip to the limit of its movement before tightening the bolts and 2. That -ve G manoeuvres of more than -2.5 G are avoided and 3. And that ground loads impose less than -2.5 G on the wing structure Then there will be no movement of the WAF fittings during normal operation. However, if any of these conditions are not met, or if the bolts are not properly tightened, then the WAF blades will move one to the other causing wear to the bolt holes and the bolts ..... I am thinking of applying Loctite "wick in" to the WAF blades after assembly to increase the friction and so improve my safety margins .... Cheers Martin Pearce - KR2 with Subaru EA81 + KR2 S with GMH Saturn - Both in my garage, neither registered or flying in Au ---yet! rocketdri...@optusnet.com.au
