I am comming to the conclusion that it is the half moon sadles that come with the U clamps that are the problem.
To start with they are soft pressed metal and the edge that butts up to the wing stay is not flat to start with. As Robin pointed out the wing stay bars are nearly horizontal so any wing movement from side to side causes the flat mounting plate to rock against the saddle which deforms and the bolts come loose. Once it starts to loosen it only gets worse as the amplitude of the wing vibration increases.
I think Stuart's suggestion above or the 'double clamp' technique is the way to go?
..........peter
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