We were looking for a bottle of champagne the other night. We didn’t have one and we didn’t need one because no synthetic mind-riser can lift the spirit like a real success. I am talking about the proof loading.

The LN-3 stress analysis report contains several hundreds of pages with formulas, diagrams and FEM results and we feel confident that the whole design is sufficiently backed from the theoretical side. We have also made numeral NDT’s (Non Destructional Tests) on various components like struts, hinges and the like.

Still, the thought of sandbagging the whole wing with almost 1.6 tons was making us nervous. In agreement with our Technical Counselor, we had decided to go for a 4 g loading as preparation for the first flight. We knew by previous tests that the wings and wing struts should make it easily. We had even made a destruction test on the center carbon tube in the wing to fuselage attachment. That tube is subject to 1.4 ton compression load at 6 g’s and broke with a bang at 2.8 tons. Despite that, I was personally most concerned by the wing to fuselage attachment since this is stress wise complex.

Anyway, we started the sandbag loading interrupted by laser measuring of the deflections on various stations. Sooner than we thought all the 78 sandbags were on the wings with no complaints from the Seagull. Not a sound, not a squeak and no deformation what so ever. The wing tips ended up 24 mm (one inch) lower than unloaded! (the Seagull is on its back). The cantilever sponsoon stub wing was bending 8 mm at the tips! And this is reality, no play with figures.

This corresponds 4 g’s with the Experimental weight of 600 kg (1,322 lbs) that roughly equals 4.8 g’s at the max UL weight of 500 kg. All with an empty weight of 300 kg. We do expect problems in getting this believed.

The proof loading was a success and a major milestone is passed on the way to the first flight around the corner.

Thanks for your interest

Lage

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