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  1. #1

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    3D Printing of a C-130

    I am beginning the process of designing a C-130 in a 3D CAD program to print with a 3D printer. I know there have been at least 3 planes that have been printed and one has flown.

    Has anyone printed a scale model plane and flown it?

  2. #2
    Moderator BMatthews's Avatar
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    I can see printing the shapes needed for the framing and such. But the plastics used for the printing are simply too weak to be directly used as structural members without becoming too heavy. On the other hand if the printed items are combined with various wood, metal or other composites glued to the printed items I could see the model being quite successful.

    The trick is to know the limits of the materials and when weight control and strength is enhanced by using added options.
    Witty saying to be plagarized shortly.....

  3. #3
    Moderator BMatthews's Avatar
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    Um..... just wondering. I have zero clue about how 3D printers work so this is strictly typing out of the blue. Would the printer allow for the items to be printed in two stages? For example a wing is "printed" up to the point where some carbon rods can be inserted into channels to receive them in what would be considered as the wing spars. Once the rods are inserted the printing is continued until more reinforcing elements are needed. And so on until the structure is completed.

    As I say, I don't know enough about the process. Also it may be more a case of the printing isn't one item that is interrupted but rather two, three or more "items" that are printed in succession without removing the first. If this was possible then it allows for producing a final "single" item with the optimal strengthening elements molded into the structures.
    Witty saying to be plagarized shortly.....

  4. #4

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    Hobby size printers are not big enough to print an entire RC plane. Will have to divide the plane into sections, print and then glue them together. I am considering printing each section with holes in the ribs and bulkheads for carbon fiber shafts.

    I will also have to test the 2 most common materials, ABS and PLA, vs balsa and ply samples of the same size. I know the plastics are heavier but they should be stronger as well. Search Youtube for "First flight of 3D printed plane." In that video the plane's interior is empty compared to built-up balsa planes. No stringers or bulkheads. The neat part is that once you have the file you can just reprint badly damaged sections.

  5. #5
    Moderator BMatthews's Avatar
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    I'd suggest that the "stronger" is one of those "it depends" sort of things. Balsa is weak in one direction but it's actually darn strong along the grain. Meanwhile plastic sections of the same weight will tend to be brittle.

    Mind you much could be done by using capped I and T sections for the printing. And since you appreciate that the whole model can't be done I like the idea of sections that go together and then have carbon rods, tubes or strip stock slipped into place and bonded to take the actual loads. That sounds like a rather workable option.

    The neat thing is that with the right option the sections could be make already "covered" and with slick panel lines and other details molded in place. Joints between sections could fall at the joint lines for the full size surface panels and lip and tongue joints would ensure a good fit and maximum gluing area.

    The sub structure that these sections are assembled over could be a mixture of carbon rod, tube or strip for longer structural members and plywood plates or built up box sections for connectors and specific load fixings.

    All in all it's a slick sounding option. But I feel that until they can produce fiber filled layups to enhance strength that the optimum use will be as "covers" with carbon and plywood internals that join and carry the loads. That would allow the printed portions to be as light as possible consistent with the need to be strong enough for normal ground handling and basic flight loads.

    The slick thing is that pushrod guide tubes and hinges can all be printed right in place. Flaps and ailerons would come off the printer platen already hinges with just the need to connect pushrods to the molded in place control horns. Complex Fowler flap tracking on smaller and lighter loaded models could similarly be printed right in place since they would not require the sort of reinforcement that metal pins and the like would provide.

    Of course what time we save at the building board would be more than taken up by the poor guy doing all this CAD work....
    Witty saying to be plagarized shortly.....

  6. #6

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    My plan is to print the exterior skins starting at 1mm and then go thinner until the skin starts to feel flimsy. I will have to experiment to see just what it takes to make the plane strong enough. Will most likely need to make the areas where the wing, elevator and rudder attaches thicker. I'm hoping that by eliminating the balsa ribs, plywood bulkheads and hardwood stringers the whole plane might even be lighter.

    The more I look into it, no one claims to have printed a scale model for flight. If nothing else I'll have a neat C-130 to hang in the garage. I found a free 3D C-130 file that I'm using. Free is good. It's only the exterior surface like what you would use in a video game. I'll have to build the interior myself. I'm not an aerospace engineer, but the cross section of the wing looks right. It is a semi-symmetrical wing.

    I like the idea of making sections that attach at the real plane's panel lines.

  7. #7
    Moderator BMatthews's Avatar
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    Your best bet is to kick out any idea of the "usual" style of construction. To get the best out of the plastic while keeping the weight low you can't think like a balsa modeller. You have to think like a plastics modeller.

    For example off the top of my head I'm thinking that the "skin" should have support from some ribs but between the ribs there should be a lot of "T" like stringers printed in to support the skin between the ribs. Full size aircraft use "L" shaped stringers along the wing for this same function. But the surface leg of the "L" in their case is there to allow riveting to the skins. In your case you only need the lower leg of the "T shape as the stringer since it'll all be "grown" as one piece during the printing stage.

    With this sort of support stringer every couple of cm's along the chord I suspect you will be able to go with a skin which is 0.7 to 0.8mm. And possibly even as thin as 0.5 to 0.6.

    When you're comparing the weight to a wood structure or skinned foam be sure you include the weight of any surface prep that would typically be used on balsa skins to prep for the final paint finish. After all the plastic is paint ready where the wood skins need quite a bit of prep and product to get ready for final colour painting. If you don't include that I doubt if the plastic method will compare well for weight. But with this wood prep included I'm pretty sure you can get very close to equal weights and likely equal strength.
    Witty saying to be plagarized shortly.....


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