DaSH PA -- Dead Simple Human Powered Airplane: July 2013

Completed Test Wing Section (sans covering)

This week we completed the test wing section, except for the final covering with Mylar (we'll do that later, right before covering our first tail or wing sections in order to practice immediately before covering real parts).

We used this test section to try different construction techniques, and to learn the best techniques for assembling everything. We developed better tools for making the leading edge, and tried several different kinds of ribs and leading edge coverings.

Some other things we learned:

- the white EPS foam ribs are lighter (about 5 g per rib), but it is too easy to delaminate the rib cap, compared to the stronger pink Foamular 150 foam

- Kevlar tow is a bit of a pain to work with. We'll use the wire loop terminations instead of Kevlar for the X-bracing loops, and we are looking into alternatives for the cross bracing itselft (e.g. Vectran) that might be easier to work with and lighter/stronger

- we need a better way of clamping the Kevlar (or other cord) during tensioning than the spring clamps we used

- the bend angle for the Depron leading edge is critical to getting a good fit over the ribs. If the angle is too severe, things don't fit right. We'll modify the tool to give us a consistent angle for leading edges going forward

In general, though, the build went well and now that we know all the techniques involved, things will go a lot faster and smoother when we build the real wing sections with carbon fiber spars.

More photos from the build:

Marking the hole locations for the X-bracing

Cutting the holes for X-bracing with a hot wand

Checking X-bracing hole size & location with string

Ready for X-bracing

String's Eye View

Test Section repositioned and clamped on frame

Repairing Trailing Edge / Rib junction

When the wing was on the table, it was easy to accidentally place your palm on the trailing edge, and damage the connection between the trailing edge and the ribs. This happened in two places, but was easy to repair. We'll need to use care to make sure we don't damage the trailing edge on the real wing sections.

Junction where the X-bracing legs cross

Making adjustments to the width of a leading edge sheet

Bending the 90 degree bend on the end of a section in hot water bath

Video of bending of the leading edge nose radius in hot water bath

Most of the leading edge sheets cut and laid out, under the wing ready for gluing

Measuring Kevlar X-bracing before installing

Threading Kevlar X-bracing through the holes, prior to tensioning

Stringing the Kevlar X-bracing through the holes

Tying off the start of each Kevlar strand to the loop/sailing thimble

Kevlar strands ready for tensioning

Tensioning the X-bracing

Installing X-bracing

First pass of X-bracing clamped, before tensioning next pass

X-bracing tensioned and clamped (2 passes, back and forth of 5 X 1420 Denier cord)

Gluing the tensioned Kevlar X-bracing in place

Finished, tensioned X-bracing

Finished X-bracing

Tensioned X-bracing

Damaged rib foam that happened during tensioning

Repair doublers for ribs

Reparied ribs with doublers in place

Changing wing mounting for leading edge access

Clamping the wing section in place

Installing a leading edge sheet

Video of installation of one leading edge sheet (7 1/2 mins)

Installing a shim on the 90 degree bend to attach it to the rib

View of a shim

Gap between two leading edge sheets --

The gap between some of the leading edge sections is due to making them at different times, from different tools with different nose radius diameters. When we make everything with one tool, these mismatches should minimize or disappear.

Upper example has too tight of a bend, casing bad fit on the ribs -- we re-bent it back in hot water bath

Alex wearing new gloves for protection from hot water during rebending

The white EPS foam ribs had frequent delamination of the rib caps. We repaired with foam-safe CA

Finished wing section

Finished wing section from beneath

Finished wing section

Finished wing section

Finished leading edge

Pilot Seat Construction

We also worked some more on building the pilot seat. We're trying different techniques to bend the tubing to try to avoid crimped inner edges and work hardening. We've tried annealing with a torch (works well), and bending with an interior spring (doesn't work well, at least not with T6 material). We're going to try bending with a sand filled tube as well.

We continued work on the lashed version of the pilot seat that we started building the prior week. Wes machined the seat rail parts and we've cut out gussets to hold that part on the bottom of the seat, and brackets and gussets for the top cross brace that will be the attach points for the rear support.

Crimping the end of an aluminum tube for sand-filled bending experiments

Crimped tube end

Filling tube with sand for bending experiments

Tamping the sand

Sealing end of other end of sand-filled tube

Bending attempt with spring supporting inside of tube (didn't work)

We tried supporting the inside of the tube with a close-fitting spring, but each attempt to be the 6061-T6 tubing resulted in a break (when not supported inside, it work hardens and ripples, but doesn't break). We haven't tried this spring-supported technique with annealed (i.e. "T0") material yet.

We then tried annealing a section of tubing with a propane torch, using a Tempilstik temperature marker (which was very hard to use -- in the end, we melted the end of the tube, then just heated the rest of the tube for a time a few seconds shorter than the time required to melt the tube...)

The results were very promising -- a very smooth bend. (After bending this way, then welding the cross bracing, the resultant part will need to be re-heat treated back to the T6 condition)

We've filled a tube with sand for sand bending experiments, but haven't tried bending it yet.