Trailing Edges and Foam Bending

laying out the trailing edges before epoxy and vacuum bagging

This week we made a lot of progress with making the full trailing edge of the test wing section, cutting out the rest of the ribs, and building some tools for holding the test wing, and for bending the leading edge foam.

Above:  Cutting the trailing edge core (out of Rohacell material)

cutting the shallow angle on the trailing edge

Closeup of pinning 4ft TE sections with pultruded CF rod to make 8 ft sections

ready for vacuum

Under vacuum

The rest of the ribs, ready for doublers

Test wing section spar cradles

All the rest of the ribs for the test section

Experimenting with stiffening the trailing edge of the leading edge foam

Another view, slight bowing

Practicing the leading edge bend

DaSH Wing Planform sketch

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Here is a quick wing planform sketch of the DaSH v5 plane, with the v6 version (longer wingtips) overlaid in red.

Ribs Complete! + Trailing Edge tests and more...

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We continued building the ribs over the last several days, which included slicing the 6 mm thick ribs from the 2 or 4 inch section blocks, laser cutting balsa doublers and gluing them to the ribs, and cutting away the foam.  We now have the first completed ribs.  Next step, build more of them (20 total), and then build a complete 6.6 meter wing test section with an aluminum dummy spar, to get practice building wings before we tackle the real one with the carbon fiber spars.

Example of crushed foam -- need to use light vacuum on white foam!

vacuum bagging the rib sections

We also made the first prototype trailing edges out of Rohacell and Kevlar.  These trailing edges will connect the back of the ribs, and fit between the last ~50 mm of plywood cap strips on the ribs.

Laying up the Kevlar trailing edges

Grant and Ron also redesigned the idler pulley.  The previous version was two aluminum sheets clamped to the side of the chain tube.  Everytime there was back pressure on the system (i.e. stopping pedaling abruptly), the metal tended to bend and get things out of alignment.  Now there is a solid block attached to the chain tube, and the metal is attached firmly to that and provides the spacing and bearing surface for the two pulleys.  It now seems much more robust.  We'll make the real setup from foam and carbon fiber, with the pulley holder still aluminum, having an adjustment slot that will let us pivot it forward and back to adjust the tension.

New idler pulley prototype

Rib Test Section build

We have started making test rib sections, using various different glues and processes to join the wing rib skin to the foam rib section.  Once we've sliced off the 6mm wide rib sections, weighed everything and done some pull tests, we'll decide which glue and which manufacturing technique to use for the production ribs.

So far, polyurethane glue is looking promising (and lightest), and vacuum bagging is a lot easier and gives a better result than clamping with clamps, or clamping with tape.

We'll also be trying different kinds of foam.  The first 4 test rib sections used Foamular 150 pink foam, which is available in a maximum 2" wide material.  We'll also try Foamular 250, which is about 7% denser (and thus heavier for same rib size), but is available in 4" wide material, and "one pound" EPS (Expanded Polystyrene) foam that is about 60% of the weight of Foamular 150.

Below are some photos of the process of building the ribs, from cutting out the rib skins (aka 'caps'), forming the jog in the skins with a custom clamp, gluing the strips and then clamping or vacuum bagging them.

Clamping with Clamps

wetting the surface to activate the polyurethane glue

Adding peel-ply

Clamping with tape

Fully 'clamped'

Taped for vacuum bagging (a lot less tape!)

Attaching Vacuum

Peel Ply & Bleeder material

Under Vacuum