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Old Dec 28, 2012, 03:38 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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Build Log
F3B NYX replacement wing section build

This is the build of a replacement center wing section for an F3B NYX composite sailplane. Although the original is hollow molded, this will be a hybrid-composite/wood over foam structure. CNC router and CNC foam cutters will be used for creation of the primary components.

I will use some methods that others might find odd or simply different than what might be considered 'normal'.

This is being done for another RCG member. He sent the remaining airframe and the salvaged spar and flaps from the original section of wing. The spar had been broken in the center, and I intend to re-use it in the new panel. The bagged wing method will be strong enough without the spar, but because it also has the tip joiner boxes, I have decided to re-use it, and after repair, it will simply add to the overall strength of the new section.

Feel free to follow along. Comments welcome. I do realize that there might be 'better' ways to do some things, but I do have my reasons for the way I am doing this project. I am also working on several other projects at the same time, and keeping a log slows everything down a lot.

Please forgive the low quality images. I have intentionally set the quality low so I don't have to process any images, and can post them directly to RCG without excessive image file size.

Here we go.

Edit: If anyone needs CNC foam cores cut, I will supply root and tip CNC cut matching ribs with every set as standard. No extra charge, and no more tracing the foam cores and cutting and sanding to get a good match. Multi-panel wing sets (like a 3 piece wing) would get a set of 6 ribs total. 2 for the center section, and a root and tip rib to cap the outer panels as well.

I can also do Composite Bagged wings or Obechee, balsa, ply or nearly any other combo you might want or need. Let me know if I can help you with your project. justin@edgerc.com
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Last edited by birdofprey; Dec 30, 2012 at 09:46 PM. Reason: Added info.
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Old Dec 28, 2012, 04:47 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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So, after that work, and cutting the rib, I got a surprise. This was believed to be the F3F Slope Racer version, but the rib I created using the HN354SR foil was far to thin for the section. So I had to start over, this time using the F3B foil HN785. I figured I would try cutting one without any compensation for skin thickness, just to see where we would come out. I figured that this would be exactly the same size as the root of the outer panel that I am trying to match, and I would have to cut a new one again, this time including compensation of about 0.02 inches so after bagging the panels would match in thickness.

Well, I find it interesting that the full rib with no compensation for the skin is already perfect, and I don't need to cut a new rib. What does that mean? I don't want to say...But, lets just say that,ummm... Hmmmmmmm.... That, maybe, many or our super CNC aircraft with super accurate foils, may not be so accurate??? I'm just sayin'...

But that is OK! The project goes on. I now have the 2 ribs I need to get started.
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Old Dec 29, 2012, 01:25 PM
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Offset

Is there a possibility that your tool offset isn't correct, thereby causing the small difference between your cut ribs and the molded parts?
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Old Dec 29, 2012, 01:45 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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We are now into the creation of the foam cores for this wing. The cores should match the CNC wood ribs if done properly. They do, perfectly.

The 55 inch panel is cut in 4 sections, keeping any wire lag to an absolute minimum. I also program spar locations by cutting a 5x10mm notch in the upper and lower core surfaces. Later, I will slice the cores apart and attach them to the spar.

I also have the machine cut a wire channel behind the spar for the flap and aileron servo wires.

Justin
justin@edgerc.com
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Old Dec 29, 2012, 01:49 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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Cores out of the beds and checked for alignment. I have slipped a plastic tube in the wire channel to insure proper alignment.

Justin
justin@edgerc.com
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Old Dec 29, 2012, 01:54 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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Quote:
Originally Posted by gavoss View Post
Is there a possibility that your tool offset isn't correct, thereby causing the small difference between your cut ribs and the molded parts?
No, because the final part, when measured with digital calipers, matches the thickness profile of the .cor file to less than 0.001 inches. My ribs also match the foam cores perfectly. So both machines would have to be off exactly the same way, and the ribs are dimensionally correct.

Justin
justin@edgerc.com
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Old Dec 29, 2012, 06:59 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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'Bench Flying' the wing. The existing outer panels fit the new (un-bagged) center section as expected. Joiners are in and the tips are being fully supported by the spar. A little bit of prep work tonight, and the wing goes in the bag tomorrow. I love it when a plan comes together.

Justin
justin@edgerc.com
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Old Dec 29, 2012, 08:53 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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Well, did not get pictures of the filling of the wire channel on the bottom of the wing, but not much to see anyway. After installing the tubing in the cores, I mixed epoxy and micro balloons and used a plastic spreader to smooth it into the remaining void where the CNC hot wire had cut to make the wire channel. I put the wing panel in the hot-box to cure over night.

Then, I located the Obechee that I plan to use for the wood portion of the skins. It has been rolled for a long time, so I laid it out to relax over night. This is some very nice stuff. It is plenty wide enough for the wing, but I will have only 1-inch of extra length after cutting it to 55 inches. Must get it right on the first cut.

Justin
justin@edgerc.com
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Old Dec 30, 2012, 09:43 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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OK, the wing section is in the bag and curring for the night in the Hot Box. It should see about 110 degree F for about 12 hours.

In my typical fashion, I managed to get pictures of the prep for bagging the wing, but once I mix resin, I get serious tunnel vision, and did not pick up the camera until it was sitting happily under vacuum in the box cooking.

I would have to believe this is some kind of survival or preservation instinct. Once epoxy is mixed, and you start to apply it, it is do or die. You are instantly under a time limit, or everything you have worked on goes in the trash. Can't afford that.

Anyway, as you will see in the pictures below, we got everything prepped. The Obechee got a layer of glass under the skins, and after some debate on the use of carbon, it was decided to go with a Tactical approach to the use of carbon rather than Strategic. Did not feel like dropping the proverbial Carbon Bomb on this thing since it already has a carbon spar, and the skins will be plenty strong all by themselves. So the tactical use of the carbon was limited to the center of the wing to reduce the stress at the fuselage area of the wing. Since all of the load is transfered to the fuselage via two wing bolts, and the wing will also have a substantial notch at the trailing edge, I figured it good to use the carbon to spread the stress a bit. Plenty of carbon was supplied, but not enough to do full carbon skins (not that it would have needed it anyway) so I felt this was the best way to go.

I also wrapped the leading edge of the cores with Kevlar to provide protection to the leading edge when I sand it. One of the things I do a bit different than many others that do wood skinned wings is allow the Obechee skins to meet at the leading edge. I feel that it makes for a more accurate wing than the use of hardwood that is sanded to shape. My method only requires the very leading edge to be sanded to remove what amounts to nearly nothing but about 1/32-inch of material. The Kevlar prevents me from going too far.

Now some pictures.

If anyone needs CNC foam cores cut, I will supply root and tip CNC cut matching ribs with every set as standard. No extra charge, and no more tracing the foam cores and cutting and sanding to get a good match. Multi-panel wing sets (like a 3 piece wing) would get a set of 6 ribs total. 2 for the center section, and a root and tip rib to cap the outer panels as well.

I can also do Composite Bagged wings or Obechee, balsa, ply or nearly any other combo you might want or need. Let me know if I can help you with your project. justin@edgerc.com
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Old Dec 31, 2012, 10:48 PM
The Magician.
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Lucas, Kansas
Joined Nov 2002
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The wing is out of the bag, and looking good. After removing it from the bag, I went directly to work on the rib caps, cutting the excess material away, and then sanding with a small DA sander, and then finishing up with a sanding block/bar. Once cleaned up the wing tips are plugged back in to insure a flush joint between the center and the tip. A small amount of sanding was required on the ribs to get this fit nice and tight.

With no sanding of the skins yet, the match of the foils root and tip are as good as could be asked for. I am very pleased.

I then used the DA again, and sanded the skins with 80 grit to remove the excess resin and the raised grain of the Obechee. Once again, it came out great. I also used the sander to knock down the small amount of excess material at the leading edge and the followed up with the bar sander to round off the ~1/16 inch thick seam along the leading edge where the upper and lower skins meet.

Next I measured and marked the exact center of the wing section. This gave me a reference point to begin marking where I needed to trim the trailing edge. The root needs to be about 9-5/8 inches based on a measurement of the fuselage wing saddle. I also re-attached the wing tips, and marked the trailing edge there as well at 9 inches. A long steel straight edge makes connecting the dots easy and quick. Since I planned well, I only had about 1/4 inch of material to remove, and a razor blade, followed by the sanding bar made this job easy.

Now I need to make sure the wing fits the fuselage. There is a fairing that the wing needs to match up to when it is mounted, so I made a tracing of it with masking tape and and a sharpie to highlight it. I then used a razor blade to trim the tape to a perfect match. Don't forget to mark the center. Now the center line of the wing becomes useful again, and gives me an alignment mark to make sure I get the template for the fairing notch in the right place. A good sharp pencil makes a good cut line around the template. A Dermal with a cutoff wheel gives me a good cut into the skin, and a sanding drum removes the material in the curved section. I took my time and the result was very good.

Justin
justin@edgerc.com
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