Back to school

Not much visible changes have taken place since we joined the shell: We made a couple of reinforcements, which is not really worth mentioning in detail… No visible progress does not imply that nothing happend. Many things around Schneewittchen took place. We’ve been preparing and planing the pattern of the cabin. As for the center section, we will use the pattern to make a mold. The material should be delivered soon and we are finding out how and where to produce the necessary templates for hot wire cutting. Three days ago I got a special high temperature infusionable epoxy resin: EPIKOTE RIMR 935 (Hexion). We will need it to make a tool for production of the clear canopy.

Anyway, the last week felt like beeing back in engineering school: I had to revise my calculation of the structure. Sweep back makes everything much more complicated… This book on aeroelasticity by Bisplinghoff et al. has been my best friend—and my worst enemy at the same time—the last couple of days:

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The good news is that my calculations on bending and torsional moments turned out to be alright!

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Worth the effort

Finally! The shell of the center section is joined. It was a long and tedious way, but worth it:

We had to solve many problems to get there! It is astonishing how well it worked out considering that a couple of years ago we had not much more besides an idea.

Joining the shell was more or less straightforward. We mixed an adhesive based on expoy-resin (130 g), cotton flakes (15 g) and thixotropic agent (3 g). The adhesive was spread on the contact surfaces and the shells were pressed against each other with the mold. While the aft joint is wide, and hence, strong enough, the contact surface in the front is small. Notice also, that the aerodynamic pressure is highest here, as the stagnation point moves around this region. A bursting shell would we simply catastophal. Reinforcement was a must. We laminated and vacuum bagged a layer of biaxial non-crimp carbon fabrics (200 g) from the inside and outside. This should be enough to keep it together in all circumstances.

Here’s a video of how we joined the shells:

 

The next steps? Well, we  have enough to do in the center section: reinforcements of the ribs, canopy, fitting of spars, seat, controls, etc. We hope to start soon with the pattern of the cockpit and canopy. If everything works out as expectect, we should have at the end of the year a cockpit and a clear canopy (produced by Plexiweiss GmbH).