Postings about the DaSH Human Powered Airplane project. Our goal is to have fun and learn while building an HPA on a budget of no more than the price of a new car by keeping the design simple and the build time to a minimum.
Test wing section with trailing edge and end rib support tubes installed
We glued the trailing edge and the end rib support tubes to the test wing section, and also finished developing the tooling for bending the nose bend into the leading edge sheeting.
Applying glue to the rib skins for attaching the trailing edge
Pultruded carbon rods used as pins to hold the trailing edge sections in place while the glue dries
Gluing one third of the trailing edge to the wing
Trailing edge installed
Installing an end rib support tube -- tacking in place with CA while the epoxy dries
The completed tubing on the right side glued in place
Close-up of joint -- Kevlar lashing for strengthening to come
The bending jig for the leading edge nose bend drying after gluing
We had lots of activity at the work session today. The ribs were fully glued to the spars, the support tubes were cut and fitted, and a lot of work was done perfecting the Depron bending of the leading edge.
A test bender with a 1" diameter was made to see if bending in the same hot water bath that we are using for the 90 degree bends on the trailing edges of the leading edge foam would work on the nose radius -- it did, and seemed to make a very smooth and consistent bend. So we started building a full-sized tool using 7/8" diameter aluminum tubing to give the (we hope) proper nose diameter, and we'll try it early next week.
Next work session is planned for Monday evening.
A short cleanup session starts every day
Lots of people at work today on different areas
Gluing the wing ribs to the front spar
Hashing out support tubes and Depron bending
All the ribs glued in place, trailing edge ready to go next
Frame for bending the leading edge in the water bath
All the Ribs assembled onto the aluminum dummy spars
Yesterday we assembled the ribs onto the wing, and prepared the trailing edge pieces in preparation for gluing at the next work session.
Ron designed and built, with Tammy's help, a frame that we'll be able to use to pick up and clamp the wing section in various positions between horizontal and vertical while we are working on assembling it (particularly for use when we are gluing on the leading edge, to provide access to the glue joint). He also built a rib pusher that allow us to safely push the delicate ribs onto the wing.
Craig and Francois worked on the tools for bending the Depron foam leading edge, and produced the first example. Over the previous weekend, Francois built a special jig and a hot water bath that are used in concert to bend the 90 degree bend on each end of the leading edge. This method works much better than the previous one using heat guns. Craig built a new curved pusher that is used to help curl the leading edge nose bend around a heated tube, with additional heat coming from heat guns.
Videos
Photos
Test section clamping jig
Fastening the end pieces to the wing jig
The rib pusher
Pushing the ribs onto the spars
Markings for rib placement on spars
Pushing ribs onto the spars
Ribs, waiting to be pushed into position
Inserting the rib pusher
Distributing the ribs to their final positions
The ribs all in position
Squaring up the ribs
Curved bender for the leading edge nose bend
Bending jig for Depron leading edge
Cutting the Depron sheets to size (700 mm wide, 1028 mm long for root chord)
A short sample piece loaded in the jig for a bending test
Hot water bath for bending Depron foam
Loading a full-sized sheet into the bending jig
Dipping the sheet into the hot water bath to bend it
Test fitting a bent and formed Depron sheet to the leading edge
Last week we continued work on the ribs and end ribs for the test wing section, worked more on the Depron bending jigs, and Bob Parks gave a demo on lashing tubes with Kevlar, which will be the method we use to join the tubes in the DaSH fuselage.
We also repaired some damage to the small, portable 3-rib test section we built the prior week (it was damaged when removing it from a car trunk, and picking it up only by the rear spar, which caused the rib caps to delaminate at their weakest, unsupported point).
At the start of this week, we worked on marking the aluminum spars for the test wing, in preparation for gluing the ribs, and building a frame for each end of the aluminum spars to let us move the wing spars up to make room for sliding the ribs into place, and then to rotate the whole wing once the ribs are glued in place, to allow easier access for gluing the leading edge.
Details below:
Kevlar Lashing
Below are some videos showing preparing and tacking the tubes together in preparation for Kevlar lashing of the tubing, then the Kevlar lashing itself:
Tack Gluing Tubes
Lashing of tubes with Kevlar
Applying epoxy to Kevlar Lashed Joint
Cutting excess Kevlar from Cured Joint
The same process in photos:
Cutting a balsa plug with the tube itself
The result, after cutting the base with the band saw
Epoxying balsa plug in place in end of tube
Mitering the tubing (cutting out a "fishmouth" shape)
Fine tuning the shape by taking small bites out edge-on with the saw. Final sanding will be done with a dremel with drum attachment and/or a round file.
Sanding the tubing where the glue joint/Kevlar lashing will be.
Fitting the tubes together before tack gluing
Tack gluing the tubes with 5 minute epoxy
Hose clamp with hooks, used to hold the Kevlar loops
Working on Kevlar lashing
Kevlar lashing of two tubes complete, awaiting epoxy
Applying epoxy w/ heat to reduce viscosity and fully wet fibers
Removing excess Kevlar from completed joint
Small Test Section Repair
When removing the small test section from a car trunk and lifting it from the rear spar only, too much torque was applied to the weakest part aft of the leading edge, and the white foam broke in front of the doubler and at the top rib cap, and the pink foam ribs had the caps delaminate. Fixing it was pretty straightforward with a combination of foam-safe CA and re-application of polyurethane glue.
The delaminated rib caps (not shown, broken white foam rib and severed cap)
Broken white EPS foam rib and rib cap at rib doubler
Parts were repaired with a combination of foam-safe CA and polyurethane glue
Wing Work
2 balsa end ribs, one with cap applied before balsa facing, one with cap to be applied
Vacuum bagging rib cap on EPS/balsa end rib
Building a 'rib pusher" to allow the fragile ribs to be pushed smoothly onto the main spar and rear spar simultaneously
Sanding the spar holes in the ribs in preparation for gluing
Cutting lightening holes in an experimental plywood-faced end rib (next time: laser cutting! :-)
The lightened rib, 50 grams lighter (but twice the bending displacement)
Measuring a displacement test for the end rib
Marking the spar for rib location
Marking the spar
End Rib Location
Building a frame to hold the test wing section at different angles during assembly
Laminating scrap balsa to make balsa blocks for potential use as plugs
Ruined Ribs
The plywood faced ribs had light fiberglass cloth added to the edges of the ribs to tie the plywood face sheets and rib caps together (we tried 1.4 oz/sq yd cloth on the solid rib, 0.6 oz/sq yd cloth on the lightened rib). These were put under vacuum at 15 in Hg (roughly 7.5 psi), which we had successfully vacuum bagged pink Foamular 150 parts at before with no problems. However, somehow in the 2 days they were under vacuum, the vacuum crept up to 20 in Hg, ruining the lightened part by crushing the foam. Either the valve jiggled open more due to the vibration of the vacuum pump on the same table, or when it was set and left, the vacuum hadn't stabilized yet and crept up further over several minutes. Either way, the parts were trashed. So that is a lesson for the future -- check the pressure again about 15 minutes after setting it, tape the valve position once set, and don't have the vacuum pump on the same table as the pressure valve.
The lightened end rib part, as discovered, crushed under high vacuum
Ending Vacuum too high - 20+ in Hg (should have been 15 in Hg or less)
The wobbly, crushed part after vacuum bagging at too high a vacuum
