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3d printed fuselage plug for a new moulded F5J

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CTR

Finished the small gel coat repair and polished & waxed the mould.

Decided to use PVA too. Sprayed this with my air brush to get the smoothest surface possible.

First 2 light coats with undiluted PVA. These were ‘dust coats’ This ensured the heavy wet coat didn’t fisheye on the waxed surface. A sort of key coat.

After 30 minutes (when dry) I then sprayed the heavy coat, well relatively, with the airbrush. This gave a good surface on one half of the mould, but there were some rough patches on the other half after it had dried. No idea why!

My thought process and trial on the poor half was to thin the PVA by 10% water to give a longer flow time. Sprayed this on top of the previous poor finish and the result was good. I’ll probably do this as the standard process next time.

My next step; my job for tomorrow is to layup the new pod at last 🤗 (With some trepidation).

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Brett82

Hope it goes well on the next layup.

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CTR

Encouraging success 😁

The latest mould and resulting moulding has come out reasonably well. No burst bladder, much better edges along the wing seat and released easily from the mould without damage.

I used 20psi for this result. Looking carefully, there are some areas along the small radius edges that didn’t get the carbon fully pushed in at this pressure. I was focusing particularly on the sharp wing seat edges which came out well (photo 2) and not enough on the radius edges in front of the LE. (Photo 3) .

Next trial will be with the same layup but increased pressure in an attempt to improve the consolidation along the radius edges.

The layup was 50gsm glass cloth; 300gsm carbon twill; five carbon tows full length along each sharp edge; 100gsm glass plain weave cloth as the final inner surface.

The pod is very stiff and has a weight of 87g which I am quite pleased with. The Final weight will be about 90g  after the cutouts are made and the hatch and ballast tube added.

C7D3F73E-623A-4177-85BB-05792F60D896.jpeg

48339B34-0739-49FC-A248-9BB06130C2EB.jpeg

8A7A72AE-EFCE-4834-BA3E-BA16F5CCF6FC.jpeg

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Brett82

Do you put epoxy thickened with milled carbon fibre or fumed silica powder into the wing root edges along with Carbon tow before laying up the carbon fibre? 

From what Iv'e seen in videos (so I personally am no expert) most of the manufacturers of planes put that into the tights edges and spaces because its almost impossible to get the layered up carbon into those tight spacers. Just a word of caution, DO NOT use microballons... 

They may save weight but they reduce the strength of the structure and its one of the things highlighted by owners of some Aeroic models after the manufacturer fell out with the designer, James Hammond. I think those effected were found, Im not trying to raise debates on the quality of a particular manufacturers products, just that it was one of the issues that was highlighted so dont use microballons if you give the epoxy and filler option a try.

Brett

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CTR

Hi Brett

I didn’t use milled carbon this time (did on the first one).  1% fumed silica in normal epoxy or ester resins produces a consistency like gel coat. I wanted to get the carbon fabric right into the corner rather than a filleted radius.

The best way I found to do this was to cut the carbon into two pieces so each cut edge goes right into the sharp edges. I then backed it up with five carbon tows to form a fillet on the inside, then the fibreglass cloth as a final layer. Good strong result.

You’re right regarding your warning about micro balloons and the lack of strength. Great for filling and sanding hanger rash dents etc but not for structural applications.

Neil P

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JBF

This is a very interesting thread.  I wonder whether non-planar 3D printing could be useful here in terms of significantly reducing the surface finishing/prep?

 

 

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CTR

Very interesting. Need to watch out for further developments on this process; particularly when there is a true 5 axis printer.

As for the 3D printed plug, the layer stair casing was the reason I printed the fuselage vertically.; that is, the length of the fus’ printed in the vertical axis of the machine.

 That way, with a 0.1mm layer height, it gave me a very small step dimension on the finished surface. Typically this was less than 5 deg. and amounted to approximately 0.02mm surface deviation in real terms.

When it comes to any print which has a small rate of change in one axis, it will be better to have that axis printed in the Z direction of most, if not all  current designs of 3D printer.

Things have slowed recently with the moulding because of comp’s and necessary repairs. I am also building a new printer which will allow me to print 400mm in the Z axis. This will reduce the number of sections to print for the length of the fuselage.

I hope to have the boom section of the Rad1 fuselage completed in the next 2 weeks. Soon after that we should be able to report on the maiden flight of the complete prototype (wings have already been tested with promising results at the nat’s).

Neil P

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