Foam-less molds

Discussion in 'Composites' started by rtfm, Mar 10, 2008.

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  1. Jun 8, 2008 #41

    Rom

    Rom

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    I made a sample layup of the method previously described.
    [​IMG]
    The basic setup before applying syntactic foam.

    [​IMG]
    1/8" deep roller for applying the foam.

    [​IMG]
    The wing skin with foam. I have not yet glassed the inside.

    The foam was rolled on under a layer of polyethelene plastic on a flat surface. The mix was 1 part epoxie resin, 2 parts microspheres and 4 parts expanded polystyrene micro-beads.
     
  2. Jun 8, 2008 #42

    Rom

    Rom

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    Regular PVC foam is probably a better material for the gentle curves. The best place to use the syntactic foam would be the places were the PVC would be difficult to bend, such as at the leading edge radius.

    As far as the fuelage goes the method described in:

    I have done this with wood and fiberglass as in a canoe and the results were good.
    [​IMG]

    Does anyone have an example of an successful aircraft that was actually built, using the strip method?


    ______________________________________________________________________________________
     
    Last edited: Jun 9, 2008
  3. Jun 9, 2008 #43

    wsimpso1

    wsimpso1

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    There are threads on this forum (the search function will find it) on whole topics of buildling fiberglass structure over cores of wood, end grain balsa, and foam.

    If'n I remember correctly, someone was talking two plies of 7 oz cloth on each side of end grain balsa and it weighed about 0.88 lb/ft^2. Stripper canoes go quite a bit higher because they need the crush resistence for beaching that a wooden core gives.

    Just for reference my primary sandwich (wing and fuselage skin) is 22 oz Triax on one side, 18 oz Biax on the other, 3/8" 3lb/ft^3 PVC foam, and my layups run 0.55 lb/ft^2. As I said before, I vacuum bag. Without vacuum, making the core comply with the mold looks to be impossible. I also seem to remember a thread on this.

    Strip canoes are sturdy wooden boats with a little fiberglass reinforcement. In a wing skin, we don't really need the support of the skin that a canoe or kayak needs...

    Billski
     
  4. Jun 14, 2008 #44

    AVI

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    Duncan:
    More research for you. This is a Kiwi company so you may already be familiar with the website. Kelsall's work preceded the American Vision aircraft.

    http://www.kelsall.com/articles.html
     
  5. Jun 14, 2008 #45

    rtfm

    rtfm

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    Hi,
    Fiendishly clever, these Kiwi's...

    No, I hadn't come across this site before. Thanks for the link. Yes, it is very much along the lines of the Vision method. But just like we Kiwi's were the first to ACTUALLY fly a powered aircraft but let the Americans take the credit later :gig: - we seem to have done it again with this construction method.

    We're a humble lot... :)

    Duncan
     
  6. Jul 2, 2008 #46

    AVI

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  7. Jul 11, 2008 #47

    Scott

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    Here is an example of the strip method used on a composite airplane.

    http://krsuper2.com/themanualfuse3.html#radius

    The tail section is also interesting because it is built flat then "bent" into shape. An easy, formless technique....

    Scott
     
  8. Jul 11, 2008 #48

    AVI

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    Scott
    Thanks, we've already posted that link. It's a good take-off of the Vision construction. Great website.
    There was also an article in the EAA Sport Aviation a few years ago about a guy who'd built his fuselage tub with veneer faced balsa core strips. If anybody has a copy of that article, or a link to the EAA backissues, how about posting?
    Alex
     
  9. Jul 11, 2008 #49

    Tom Nalevanko

    Tom Nalevanko

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    Sport Aviation back issues are available online to EAA members fyi.
     
  10. Jul 11, 2008 #50

    AVI

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    Re: EAA Back Issues

    Tom
    Thanks.
    However a search for "veneer balsa core" was unsuccessful.
    Alex
     
  11. Aug 10, 2008 #51

    F82man

    F82man

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    Hi composite enthusiasts, The info you shared is great, as I will be starting on my plug soon, but will be making the mold out of foam between wood bulkheads similar to Tony's Corsair 82. Is there a max length that is best to work with?, or should I limit it to about ten foot sections?? My fuselage will be over 30 feet long. I would like to make the plug all in one piece if I can. Then I will make the molds in sections. Let me know what you think. Thanks, Don Lowe.
     
  12. Aug 10, 2008 #52

    orion

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    The size of the tool is really limited by the amount of space you have and by the weight that you can handle. The ideal construct would be a full length tool for a composite structure as that will allow for a continuous laminate. Any joint is a stress concentration so proper care has to be taken in those areas where different sections come together - the reinforcement that is needed then becomes a slight weight penalty and of course, additional work, especially in finishing.

    The other part of the equation is of course cost. Part of that comes from the support equipment you might need for the removal and handling of the tools and the other comes from the fabrication technology you'll need to use in making that part. For instance, doing a wet layup in a large tool is very difficult since the amount of time you'll have to do all the associated tasks with multiple layers will be strongly driven by the gel times of the resin of choice. As such, methods such as vacuum infusion might be preferable over wet layup simply due to the fact that you can get most, if not all, material in place before bagging and plumbing in the various lines.

    The other aspect of tooling is the structural type you'll be using since that has to be addressed in the structural design phase, before you ever get to your first part. One of the key decisions to make is whether you're going to use a sandwich type structure or whether you prefer a solid laminate. The former is more difficult to fabricate using most methods, even vacuum infusion, since in order to get a good core bond, you'll most likely need to do the laminate in three steps (laminating the outer skin, bonding in the core, and then laminating in the inner skin), vacuum bagging between each. So then the amount of work becomes part of your decision process also.

    The other item to consider when looking at tool size and lamination process is the amount of time you're willing to be bent over that tool and how deep that tool is going to be. Between laminating and bagging, your back might get a pretty good workout, something that could get rather annoying as you get deeper and deeper into your project.

    Regarding the plug, for that it would be ideal if you could build it in one piece since that will allow you to get the fairest lines. For proper surface quality, the final layer of finishing material (I use Duratec Surface Primer - a Vinylester based high density primer that polishes up nicely) should be able to be sanded to about 400 grit, then polished to a fairly shiny surface. Under florescent lights, that will show surface quality and fairness quite well.

    I've posted this picture before but here is a plug I did a few years ago (today virtually all of my tools are CNC machined as molds) - it's a bit over 20 feet long from firewall to vertical tail post.
     

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    Last edited: Aug 10, 2008
  13. Oct 31, 2008 #53

    rotorexec

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    Hello,
    I'm Chuck but known as Rotorexec in this forum. Let me give you another alternative mold forming method. All these fellas have a great wealth of knowledge as to how's and to dos, and please understand I'm old school when it comes to molds and plugs. You might want to consider the plaster method of airframe and wing construction, let me explain.
    Wood and plaster can be used to shape any type of form that you will need to accomplish your goal. Most construction sites have available excess wood scraps that are still sufficient for reuse and are free to be picked up by you. These scraps can be 2 bys, plywood, and other treasures that most enthusiasts overlook. Consider this, a wheel pants can be formed from a concrete block with a 4 inch grinder and the proper masonry wheel. A wing skin can be formed with a simple piece of 1/4 in of plywood over a 2 bys frame. This form can be used for the topside and bottom with a slight adjustment for the leading edge. Most creativity is done by your own imagination. See it in your mind and make a cardboard form of your design. Then, create it from wood, concrete block. or something as simple as a hole dug and shaped in the the ground of your backyard. Where do you think ponds started from.
    Okay enough history, let's get down to it. Take your plywood and cut it out to be the shape of your fuselage. In other words, start from the front (the cowling), then cut the firewall to shape. Next, figure out how wide your cockpit needs to be and cut out your next ribs. Continue on to the taper of the fuselage all the way back to the tail. Be sure to have furring strips (3/16 inch thick or reused plywood from construction site), to align these ribs you are forming. Once you have the design you want, refine it. Cut the furring strips in short lengths at first to shape this fuselage to your design. Remember to include the root hub for the wings after you have attained the full fuselage. Also because you are working for the finished product,allow your cuts to be smaller than the finished product. In other words,your form (plug) will be slightly smaller than the finished product. Next, after you have made a completed plug (mold) of your fuselage, cover it with burlap or as we call them in the south croaker sacks. Again, you can use a heavy fabric, roofing felt, or other materials to build this craft. Now, if you followed along, your fuselage should have cost you next to nothing so far. You could have made this same wood form in the ground of your backyard with that shovel your wife got you years ago.
    From here you use the plaster to shape and mold your fuselage to final stages. A 5 gallon bucket of drywall mud can be had for less that the price of a 12 pack on sale. While shaping this fuselage, wings and other parts you can always cut out the canopy frame with a jig saw or a piano wire saw. Draw the lines where needed and go. And the most expensive item during this construction is your labor. If you build this fuselage in two halves, you can join them with the final seams. The only disadvantage to plaster molds and plugs is weight, but you can build more than one aircraft with this design. In other words, you can market this design.
    Finally, prep the surface to be fiberglassed (carbon fibered, aramid, kevlar, etc), and you're ready to go. Black electrical tape overlapped across the surface will provide a good working surface. And don't forget the hairspray as the release agent. Suave extra hold I found works best. I learned this at a EAA workshop. Oh, don't raid the wife's hairspray or the honey-dos will get worse.
    I worked in boat building during my younger years, and still have my chopper gun. This is where an old salty dog like myself showed me this technique of building. Remember , don't get discouraged and persevere. Work slow and take your time, Don't get in a hurry. Let me know if you need a little help. I travel this country 280 days a year and I could stop by sometime.
    You'll need someone to help you handle the larger molds and plugs. Or build you a swivel stand (similar to an engine stand), so you can turn your work to different positions and if it has wheels will be mobile.
    Another tip I'll tell you is a way to get the epoxy into the foam of your fiberglass sandwich. Take two 4x8 sheets of 1/4 inch sheet rock and place your foam in between( no more than 2 sheets at a time). Be sure to secure the rock to your working surface. I use c-clamps for this feat Next, measure how far apart the holes need to be in the foam. make your marks at each end of the rock, and snap your chalk lines. I make mine every 3/8 of an inch. I take my pneumatic finishing nail gun using 2 inch nails at 45 lbs air pressure and drive the nail into the rock at the chalk line junctions. The lower air pressure allows the nail to not go all the way into the rock and is removed after I'm done. The rock can be reused numerous times if you align both sheets of the rock to do the next foam pieces. Also, next time all you need is an ice pick to punch the holes.
    I hope this long winded explanation will be helpful. I'm presently working on my Wizard P-38, but have another design I'll be starting on next year. It's a monocoupe knockoff of a Polliwagen design and will meet LSA standards. Thanks for the chat...............Chuck
     
  14. Oct 31, 2008 #54

    rtfm

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    Chuck,
    Hi, and thanks for the description of the "Rotorexec" method. Makes for fascinating reading. Especially the parts about saving money :) I will need to read it a few more times to get full value, so thanks.

    Regards,
    Duncan
     
  15. Nov 3, 2008 #55

    rotorexec

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    If you need more info, give me a holler. Remember also that this method of wood and plaster is mostly wood form.The plaster content is only 1/4 to 1/2 inch thickness. You're looking at less than $50 to attain your dream and some construction debris treasures. I can give you specific books and articles to clarify your questions. Letmeno..............Chuck
     
  16. Nov 3, 2008 #56

    mckes

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    Orion - what Fuselage is that???
     
  17. Nov 3, 2008 #57

    orion

    orion

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    It was to be the first of two near term product lines of a company where my company formed a partnership with two other individuals for that development. The primary product line was to be a large six place utility aircraft (both were my designs). But the partnership went sour and we broke the project up so that each of the three of us took one of of the three prototype airframes (there were three prototypes under construction). Neither of the other two had time to do anything with the concepts so after about two years I ended up with all three.

    Unfortunately though I didn't have the time either so I ended up donating the whole thing to Cornerstone Ministry, who in turn sold it to a gentleman in the South East somewhere. He had ti for three years but due to his own business concerns he too didn't get too far so he again donated it back to Cornerstone. They sold it again (about three years ago) and although I did talk to the new owners twice, the communication stopped quite a while ago. I don't know where ti might be now.

    The airplane was to be a fairly large two place tandem powered by either an IO-540 or a Walter 601. The prototype was actually slated to be powered by the Walter-Mikron six cyl. in-line. The idea was that it was a very large airframe so that the aft pilot did not need to straddle the front one. Sufficient room was allowed for two full instrument panels and two occupants my size.

    The project was going well - too bad the partnership went bust.
     
  18. Nov 6, 2008 #58

    gschuld

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    I believe that it was AVI that was asking about the vaneer/balsa/vaneer strips. I am not certain that Baltek still sells the strips, but below is the book about the use of their product. I have a copy myself (I am from the boatbuilding world). The description below is from a builder that used it on a project. The stuff does have a very favorable total laminate strength to weight ratio, especially if glass(carbon?)/resin ratio is kept reasonable(vacuum bagging). Overall, it will be slightly heavier as a core material than most foams, but the durakore will contribute a bit more to the overall stiffness of the laminate. Durakore also would be much more puncture/dent resistant than the average core material.

    [​IMG]


    DuraKore, Pros & Cons

    DuraKore is sealed end-grain balsa bonded to 1/16" hardwood veneer skins. The material is available in 8' strips, 1" x 8" planks and 4' x 8' sheets. The DuraKore strips range from 1/2" to 1-3/4" in thickness and incorporate matching finger joints at both ends for creating longer lengths without the need for traditional scarfing. The strips are installed strip-plank fashion over male or female station molds. Once planking is completed, bi-axial E-glass is typically applied to both sides to complete the laminate.
    Compared to cedar strip-planking, DuraKore strip composite construction is stiffer and lighter. As with solid wood planking, the strips conform easily to compound curves. In using this material much time is saved because milling, scarfing and most of the careful fitting has been eliminated. The strips lay very well, so time spent fairing up after planking is minimal. As with any cored hull, damage below the waterline must be attended to quickly. Because of the maximum 8 foot plank length and epoxy glue lines between the planks, the area of water intrusion tends to be limited.
    The main drawback in using this material seems to be the cost. 1/2" DuraKore strips run about $7.86 per square foot. This is about twice the cost of strip-planked cedar and approximately 50% more than cold-molded cedar veneer. The other problem with DuraKore is the fact that it is only available in boxed quantities. One box of 1/2" DuraKore strips contains 146 square feet of material. If the designer is not careful, you could run out of strips when your project is 95% complete, forcing you to shell out for a whole new box when only a few strips are needed. Obviously, waste needs to be minimized. Some builders deal with these drawbacks by using only 1" x 8" DuraKore planks. Strips are ripped to width as needed and finger joints cut using a router fitted with a special jig. 1/2" planks are running about $4.20 per square foot, making the material less expensive than cold-molded veneer and competitive with cedar strip. This cost savings comes at the expense of greater labor, but no more so than other materials.
    Is it worth it? The only way to answer this is for the prospective builder to sit down and honestly add up the cost of everything going into the boat. Be careful here and try to include everything. Final cost will vary widely. If you make your own sails (Sailrite), weld-up your own trailer and have access to good used hardware, then you can make a large impact on overall cost. The inescapable fact is, quality materials and hardware are expensive. Most amateurs tend to focus on the cost involved in building the hull shell and don't realize that it only represents a small fraction of the total man-hours and cost of the completed yacht.
    The last step in this exercise is to compare the cost of your project with the price of the nearest commercial designs. If you do this I think you will find that your costs are very reasonable and the price of DuraKore may not be that much of a factor.

    George
     
  19. Nov 8, 2008 #59

    rotorexec

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    Orion,
    The fuselage of reference is the finished product that you as a builder have started, formed, and completed after your labor. Remember that as I stated above, your imagination creates and dictates what you complete. Whether you're building from plans or trial and error, a model of scale or actual size is needed. I'm just presenting a different and extremely cheaper alternative to mold and plug building. Thanks for the response.........Chuck.
     
  20. Nov 8, 2008 #60

    orion

    orion

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    I'm not sure what your answer refers to Chuck or what you're trying to say - it almost seems like you thought I was criticizing something you said, which I wasn't. Please clarify?
     

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