Review of Gesipa 4.8x10mm rivet grip range - non-reatined mandrel

It was noticed that while 4.8x10mm rivets are spec'd with a grip range up to 6.5mm, when used to rivet this thickness the mandrel was marginally retained. While it is understood that the mandrel does not play a significant role in the strength of the rivet it is believed undesirable that a mandel could loosen and pop out while in service. That this could conceivably occur follows from the observation that a centre punch set to the lightest impact setting could dislodge the mandrel.

Experimentation showed that the maximum grip range should be reduced to 5.5mm for the mandrel to be securely retained. For a larger grip range requirement the Gesipa 4.8x15mm rivets should be used, which have a grip range extending down to 4.5mm.

A review of the use of 4.8x10mm rivets was made. Of course the Sling kit was supplied with 4.8x15mm (non Gesipa) rivets. Seeing that many element of the ailerons and flaps, and some wing ribs had a grip requirement just under 6.5mm (typically 6.2mm) this builder went ahead and used the shorter 4.8x10mm rivets wherever allowed by the nominal spec.

Going though all such usages it was decided to rerivet with Gesipa 4.8x15mm rivets (since obtained) wherever the grip range requirement was in excess of 5.5mm. Affected items include: Flap ribs 2, 4 and 6, aileron ribs 2, and wing ribs 4. The good news is that most of the wing rib 4.8mm holes are unoccupied due to waiting on installation of the re-manufactured angles, and also some missing angles. Also, many of the wing rib hinge brackets are rivetted directly to the 0.65mm thick ribs, with no further layers. The grip reange requirement is therefore only about 5.7mm and the mandrel is well retained. The other good news is that the flaps and ailerons have not been closed up. Also, the horizontal stabiliser (which also upsized many 4mm holes to 4.8mm using 4.8x10mm rivets) had no grip range requirements large enough to cause this issue.