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Thursday, December 20, 2007

DG500 post 10

Wing bagging

The techniques I use work for me but there are many little tips and tricks that other builders use that are good , so experiment and find a method that works for you.
The photos here are not great ,but its difficult to use a cell phone with a hand full of epoxy.
Hereunder the lay-up of the DG500 wing , which will be done in four steps bottom of each wing then top of each wing one at a time.

This photo shows, 1. prepared ,sanded and cleaned wing core.
2. vacumn bag material (tube, blueish colour)
3. mylar thick (white under the wing)350micron
4.breathers I use batting from a sewing shop, which is rolled around some dowel sticks(left)
5. Roll tacky tape for bag sealing(prestik also works)
6.strips of peel-ply (on the right).

The mylars are cut to shape and waxed with release wax. Then the bag is prepared with the breathers down both sides and across the ends.Note the breather cloth wrapped around the vacumn pipe on the near left hand corner.

Ghetto blaster on the left provides music and is of vital importance.(yellow.)

The mylars are polished off with a soft clean cloth and then sprayed with 2k as many coats as is needed to get good colour coverage, in this case about 4x I also do not thin this paint to much, about 10 percent thinners for a low presure spray gun about 2bars , the gloss will come from polishing later.

Once the 2k paint has dried ,the 1st layer of glass cloth is cut out to shape, as is common practise a fine weave against the outer paint gives the best finish , here I have used 106gr not at 45degrees, but straight.

Next I have cut at 45 degrees the 196gr carbon
cloth, this is were the torsional stiffness will come from. This layer is cut to size on the mylar with the 106gr underneath(dry).

I now pre-weigh several cups with 50gr of resin in each(epolam 2022), the harderner is added as I go along, it takes some time to wet out and work the resin in ,on these long wings.

I carefully fold back halfway the carbon cloth and then wet out the glass cloth, speading the resin in evenly with a plastic telephone card.

The carbon is then folded back and wetted out
and then the dry half folded back and the wetting out repeated . This way the cloth is not removed from the mylars which sometimes distorts its shape.(you can clearly see the wet out area).

This step is to lay on the UD carbon which is layed on and then had the pink plastic backing removed, I add resin which I work in lengthways with the fibre grain.

After a few minutes the backing strands seemed to soften and with a little work can be scraped off with the card.

A second layer of UD goes on the first meter of wing and the srands also removed, I check for any dry spots and add a little resin if required.
At this point I transfer the mylar onto a strip of
paper towel this aids in sliding it into the bag, and soaks up excess resin.
The wing core is placed onto the wet skin , and carefully aligned, then because I am only doing one side I tape some strips of peel-ply over the leading and trailing edges.

The whole thing is slid into the bag and rechecked for position and then sealed and the vacumn applied, the wing core is now placed on a
flat surface and the core shells placed under the core and weighted down, this prevents any warpping that the bag may impart onto the wing.
The vacumn will be held for at least 10 hours.
With a bit of luck this side when opened will reveal a smooth strong shiny surface(I am holding thumbs).All the above work was done yesterday between 11-00 and 17-00 hours including coffee and lunch breaks .

The wing took 300grams of resin to wet out .
The above process will now be repeated for the other surfaces, after which the edges will be cleaned up and touched up with 2k and my airbrush, then comes polishing and finally the cutting of the control surfaces and servo fitment and wiring.
The next post may well be the first flights .

Have a great festive season
cheers for now.

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