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Tuesday, December 18, 2007

DG500 WINGS post 9

This is a long build thread because these are long wings, but here goes...

The feather cutter made a nice job of the cores which have all been bonded together and prepared for later vacumn bagging. Rainy weather over the past long weekend allowed me to accomplish a lot , but the coolish conditions slowed down the epoxy curing times(probably not a bad thing to put the brakes on a bit)

The leading edges have 5x 12k tows layed on just to add stiffness and a strong edge which stands up better to minor dings and bumps on landings.

The leading edge is painted with resin and this holds the tow on as it is wetted out , I dont use contact spray glue but some guys do. A layer strip of 104gr cloth is layed over the tows and wetted out.

The slot for the joiner box is cut out using a rib template for accuracy , note the grove I have routed out with a dremal tool , this is the channel for the wiring.

The joiners were glued in with Sika-dur epoxy and the wings aligned on a flat surface a little dihedral was also built in .The joiner was masked and held in position while things cured.

The groves were sanded into the foam along a straight edge and the 60k tows layed into the bottom surface. In this case two at the tip increasing in steps to 16x at the root (about a 1mtr long , out past the end of the joiner box)

Left overnight to cure.(Epolam 2022 epoxy system)

Some carefull measuring and , now cutting against a straight edge with a big stanley blade(the smaller blades tend to wander cutting through thick foam)I cut down to the carbon spar cap below. Using a large flat screw driver I broke out the foam. The exposed carbon is sanded clean so that the shear web can adhere well.

In this photo the shear web(premade earlier) was placed in the grove and needed a little shaping in the outer /thinner part of the panel .
I then bonded IT in with strong structural epoxy, in some places I had gaps, these I filled with Epoxy resin and flox, paste. This was placed on a flat surface weighted down and allowed to cure.

The initial wing design is a four part with removable tips for transport, so I have extruded 2 x carbon rods 12mm thick that fit into some aluminium tube(curtain rails ) a little overkill, but I plan some longer tips later so this is insurance. The tubes and the incedance tubes are epoxied in(the cut line is shown and measured) so I can cut exactly right once its bagged.

The top surface carbon tows are layed again into a sanded grove and after curing I have screeded on a paste of epoxy/ micro ballons.

The top surface is under compression when flying(normally this is were a failure occurs first) so it has more tows 3x at the tip stepped to 21x 60k tows at the root also about 1mtr out past the joiner box.

Here you can see the areas that have been filled on the under side , the hollows at the joiner box are filled with a strip of balsa and epoxy balloons.

The surfaces will be sanded smooth , blown free of dust and the skinned and bagged.

I weighed these super rigid wings and they weighed....

Left 2047 grams

Right 2054 grams

a differance of just 7 grams , this is good as a balanced aircraft is easier to trim and indicates consistant use of materials and epoxy.(and a little luck)

___Fiddly Bits____

While the big pieces cure , I multi-task and do little things such as

The top of the tailfin has been cut open and two pieces of ply , shaped to fit inside, these where drilled to accept the servo and then using a piece of balsa cynoed in place.

The cable tie prevents the piece from falling down inside, the servo tray is epoxied into position. Next I epoxied two captive nuts the kind with little points on them (as a precaution put some release wax on the bolt threads)using a tweaser these are held in place until the cap screw can be threaded in . I use a washer as shown and pull these up tight , the points penetrating into the ply, the cap screws are then removed .

Thats it for now , next the mylars need to be prepared and the wings bagged, I will post these later this week.
I hope this build thread is informative , but any questions are welcome other than those of the perceived angles, parallel or perpendicular type.
Cheers for now.

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