Tail spread of 4x10mm and 4.8x10mm Gesipa rivets

Tests for tail expansion were conducted with Gesipa 4x10mm and 4.8x10mm rivets, with 3.15mm sheet equivalent to the main spar flange with an additional 0.63mm sheet representing the fuel tank skin.

For the 4.8x10mm rivets the tail expanded to 6.8mm somewhat in excess of the 6.35mm = 1/4" diameter of a recentered clearance hole in the inner flange. The use of a 5/16" counterbore is indicated.

For the 4x10mm rivets the tail expanded to 5.8mm well under the 6.35mm = 1/4" diameter of a recentered clearance hole in the inner flange. The use of a 1/4" counterbore is indicated. If the inner flange hole is significantly offset, as is common, then presumably this ois ok as this is a common scenario. However I plan to recentre the 1/4" clearance holes wherever possible.