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Composite Aircraft material selection? I have started the long process of building a mold for a large aircraft & I am in need of some advice/direction concerning composite material selection.
The Fuselage is aprox 80” in length & is 12-13” in height at the girth of the fuselage.
I have no idea what material to use & I would greatly appreciate any advice from some of you who have the experience to guide
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For the mold, use a good quality automotive paint on the plug, and as a ''gel-coat" on the mold. Make the first layup of the mold with 1/2 oz fabric, and let it set to tacky before laying up the second 1/2 oz layer of cloth. This will help you get the smoothest posible mold surface. It is a real PIA to babysit those first couple of layers, but the epoxy will outgas, and you will get bubbles, so you have to sit there with an epoxy brush and keep working it till set.
I also do not try to get these first two layers around sharp corners, like where the plug meets the parting board. I lay the fabric right up to the the corner, then start another piece on the other side of the bend. I put a fillet of thickend epoxy over this. It helps make the corners less prone to chipping and bubbles.
After this lay up the next few layers with 6 oz fabric. Heavier will build up faster, but will not go around curves and filleted corners as well.
I used to follow this with several layers of 10oz, but am planning to try using a material like coromat from CST to build up the thickness faster. I have also seen threads here where people have built up thickness by mixing epoxy and sand. On a project that size, I could see that getting real heavy.
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dreadnaut, I do not know what I ask but I must ask, would it be best to vacuum bag the first layer? I like the fillet tip, I can see that being an issue
< Message edited by HO-229 -- 11/9/2007 6:23:07 PM >
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Vacuum bagging the first layer will not hurt, but it is a lot of trouble. Use a perforated release film to keep the resin from pooling. Pooling resin can cause the fabric to bunch up and wrinkle.
I DO fillet the corners, but after I run a layer or two of fabric all the way up to the corner. This makes it stronger, otherwise the sharp corner of the mold at the parting line is prone to becoming chipped.
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FYI: You guys are talking about two different things; mold laminating vs part (fuselage) laminating.
For mold making (wet lay up), you generally don't deal with vacuum bagging. For laying up a part in the mold, vacuum baging can give you an advantage in producing a lighter part with stronger physical properties. BUT, it is not necessary and adds a whole 'nother level of complexity.
If you are doing an 80" fuselage as your first project, you may want to try a couple smaller molded pieces before jumping in.
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Moldmaking and pulling parts takes a lot ot time, money, and experience. It is not an easy to learn technique from reading posts, experience and live help make a huge difference.
I highly recommend starting with a cowl, wheel pants, or other smaller type project before embarking on such a huge undertaking.
Composite parts can be great, but they can also be pretty frustrating until you figure out what you are doing.
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quote:
ORIGINAL: daven
Moldmaking and pulling parts takes a lot ot time, money, and experience. It is not an easy to learn technique from reading posts, experience and live help make a huge difference.
I highly recommend starting with a cowl, wheel pants, or other smaller type project before embarking on such a huge undertaking.
Composite parts can be great, but they can also be pretty frustrating until you figure out what you are doing.
I agree. My first molds were for cowl and wheel pants for a Goldberg Ultimate. Then 30% Extra Wheel pants. I got better at it with each one.
quote:
FYI: You guys are talking about two different things; mold laminating vs part (fuselage) laminating.
For mold making (wet lay up), you generally don't deal with vacuum bagging. For laying up a part in the mold, vacuum baging can give you an advantage in producing a lighter part with stronger physical properties. BUT, it is not necessary and adds a whole 'nother level of complexity.
If you are doing an 80" fuselage as your first project, you may want to try a couple smaller molded pieces before jumping in.
I have vacuum bagged mold layups (those Extra wheel pants). I had issues with voids and bubbles, especialy at the parting line, and vacuum bagging helped hold the layup against the plug.
After that I did a fuselage for a 60" span Sukhoy 26. That step up in size was a lot more work. I am currently working on a smaller project (42" span Yak 54 for e-power) I plan to use some of the things I learned the hard way on the Sukhoy. Once I have tested those ideas on the yak, I am planning a 72" span Su 31. (I am a sucker for those round engine planes, and will probably finish the next one in a Gee Bee Tribute scheme)
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I am very sorry, but I am not sure were you got the idea that I was going to mold the fuselage on my first attempt, I have never thought to mold that big of a project first. I am merely on a fact finding mission so as to have the lessons learned & material selections correct.
People such as yourselves can often guide the newbie in the proper direction so I do not go down a dirt road & have to relearn all your lessons learned. I would like to believe I understand the basic concept of vacuum bagging/mold making & that the only areas of the mold making process I lack is the details & material selection (lessons learned)
I believe the separation between failure & success is research & interaction with the people who have done this before “you” Your willingness to share your experience & thought is a reflection of who you are (your character) & your willingness to pass on the craft.
My plan as of today (subject to change) is to cast the spinner mold first (simple parts) I think I have read this someplace before.
My end goal of this thread “originally” was to select the proper fabric & fabric weight for the “fuselage” not the plug (cost & weight estimate). The information dreadnaught passed on is great & very helpful, as I do not see any posts in this forum that contain shopping lists of material for the process of mold making.
Thank you.
I scanned through the links posted & they also were very helpful. Thank you I would like to believe that I am on a path for success & with the proper guidance in the gray areas my project will succeed without to many lessons learned.
I think I could write a book on this subject for the layman & it would do well.
Thanks everyone, Dave
< Message edited by HO-229 -- 11/10/2007 3:05:47 PM >
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No need to vacuum bag the mold...I would recommend using tooling gelcoat (it is what it is designed for). This is a tricky process full of tiny tricks and know-how that takes a while to learn. It's not as organized as it could be, but I've documented a lot of mistakes on my website (www.teamseacats.com) - search for "mold" and start going back through the posts. I'm certainly not an expert but I'm learning.
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quote:
ORIGINAL: HO-229
My end goal of this thread “originally” was to select the proper fabric & fabric weight for the “fuselage” not the plug (cost & weight estimate). The information dreadnaught passed on is great & very helpful, as I do not see any posts in this forum that contain shopping lists of material for the process of mold making.
quote:
ORIGINAL: HO-229
My end goal of this thread “originally” was to select the proper fabric & fabric weight for the “fuselage” not the plug (cost & weight estimate). The information dreadnaught passed on is great & very helpful, as I do not see any posts in this forum that contain shopping lists of material for the process of mold making.
I hope you weren't offended at the info given. Sometimes it's necessary to know what experience someone has before they start giving advice. I had seen your questions in another thread and knew you were on a fact finding mission to get into composites.
Posting in here you can hope that someone who has done an 80" fuselage can chime in with their lay up schedule. Some guys build heavy, others build light. I can say that if I were going to be building a large fuselage with a lot of surface area (girth) I would look at doing a combination of glass with some core material to build thickness and rigidity and adding some carbon reinforcement in high stress areas. You should keep a supply of 3oz and 6oz glass handy as well as some carbon cloth in the 6oz range. Some guys use nomex honeycomb for fuselage construction or thin, high density foam like Rohacell. You can also use balsa as an inner skin but care has to be taken so it doesn't absorb too much epoxy and add dead weight. Basically you do a couple of outer layers of glass, then a layer of core (1/8" honey comb), and then cap off the core material with another layer of glass. This is usually done in a couple of stages so you can get the first layers down well, lay the core, and then come in last with a top layer of glass (like 3oz). You don't need the core to cover the entire fuselage but certainly in the tail boom and around the wing saddle are the most common. To do this you need a vacuum bag set up and peel ply to aid in the layers process. It goes down on the glass and peels off when cured to provide a matte finish and good mechanical bonding surface.
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About a year (okay, 2 or 3!) ago, I finished my polyester molds and did a layup for an approx 94" length jet model (epoxy) fuselage. I found my layup map, and I used a layer of 4 oz, and a layer of 6 oz for the entire fuselage. Then, in various areas, for example, landing gear areas, hatch edges, and other load carrying areas, I'd add an extra layer of anywhere from 4 oz to as much as 5 oz carbon ( the carbon for an area that would get warm, and I'd need additional torsion strength ).
It is always hard to get the layup right the first time. If I were to do it again (and I probably will this winter), I might consider 1 layer of 3/4 oz, then 2 layers of 4 oz, with extra 4 oz pieces once again in load carrying areas. If you don't add enough in the load carrying areas, you can always add more. Once you add it in, you won't want to remove it! Having said that, the layups will always differ from airplane type to airplane type...
Going with the first 4/6 oz layup was an experiment for me - I wanted to see if I could get away without the 3/4 oz stuff. In the end it worked, but the amount of airbubbles in the layer closest to the mold was unbelievable. 3/4 oz cloth will help most of that - it saves alot of surface prep (primer) time.
My opinion is that 4 oz cloth is a good all-around cloth to work with. 6 oz sometimes won't get to the corners as you need. If someone were to give me a free roll of cloth, I'd prefer it be 4 oz. I'd also ask for 60 minute epoxy laminating resin, or thereabouts. For bagging, you might want even slower cure, which will allow more resin to be evacuated from the layup.
To get a feel for what layup you might want to use, I'd recommend laying up "test panels" of roughly 6" square on a glass sheet. For example, a layer of 4/4, and 4/6, 4/6/4, etc. This will give you a better feel for the stiffnesses of various layups. Also, you'll see the panels will get stiffer over time. Its a quick indicator - it will also give you an accurate build thickness.
I should also say I did not bag the fuselage, but I did bag the H-tail and V-tail surfaces, since they are simpler curvatures. I probably would have made a mess trying to bag the fuse...
I got all my stuff from Fibreglast, although there are many other good suppliers too. The epoxy I used was Fibreglast 2000 - not sure if it is available - I know they update their material from time to time. I agree with your point about research and interaction with others, but just as important is Experimentation. That's where the resin hits the cloth!
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RonS is correct. Test peices are a good idea I used my wheel pant molds for this. I made about six sets before I was really happy. Of course, I was testing more than just the material weight. I was trying d
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Composite Aircraft material selection? - 
RE: Composite Aircraft material selection? - 
Having said that, the layups will always differ from airplane type to airplane type... 