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Tuesday, October 30, 2007



The build thread of the big DG500 continues, this post is about building the brute wing joiner out of carbon tows and epoxy. This method can be used for smaller wing joiners also.
The design differs from the joiner that I used on the Ventus which was round 19mm dia and about 75 x 60k carbon tows went into the mould. The advantage of a round joiner and tube is the ability to adjust the incedence of each wing and line them up accurately (I check the trailing edge).


On this joiner I decided to go for something much stronger and more blade shaped as the rigidety is required in the verticle plain. The joiner boxes will be made around the joiner and these continue well into the wing forming an integrated spar/shear webs as a box structure.
The airfoil is thick enough to accomodate a 40 mm high joiner and the outer joiner box.

This method will require carefull alignment of the wings to the fuselage.

The picture illustrates all the materials required for this important component.

From left to right.
RamRelease wax, acetone ,pocket scale,mixing sticks,box of latex gloves, bobbin of 60k carbon tows,lr20 epoxy and slc30 harderner , mixing cups and scissors. Finally some off cut 40x25mm pvc trunking as a mould.
Cut a suitable length of trunking and wax the inside, I have not buffed this off as finish is not important.
Now discard the gloves you may have worn when polishing, and with clean gloves cut a batch of tows , I cut 100 for the first layup wanting a joiner at least 10 mm thick by 40mm wide.

Now mixing a 50 gr resin and its harderner you need to wet out the tows as they get layed into the trunking mould(you can even fashion a mould out of balsa and line it with tape and wax)this may require a lot more finishing though.

I carefully stipple the resin, into the tows and every 3 tow layer I flatten the tows with a mixing stick, this also moves any excess resin into the tows (a flaw in this joiner could start a crack and ultimately a failure.)

When the required thickness was reached in this case 15mm and several more tows, I fitted the trunking lid back on working down the tows with a piece of mylar as it was closed. This allows for a more accurate square shape.

It popped out the mould perfectly and has a smooth accurate finish.

This whole process was repeated again so as to have two smooth accurate outer surfaces, the inner face(surface not in the mould) will be machined with a router and bonded together with black epoxy glue and clamped to the correct tolerance.
The final steps and some fuselage work will be in a future post.

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