Fiberglass Fairings

Discussion in 'Composites' started by Wayne, Aug 13, 2018.

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  1. Aug 13, 2018 #1

    Wayne

    Wayne

    Wayne

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    Folks,
    There are a number of places on the Cruzer that will benefit from a fairing, and I'm thinking fiberglass is the easiest, quickest, and least expensive way to go. I plan on making a fairing for the lower edge of the windshield that will double as an attachment instead of the rubber that Zenith provides. On the club plane we had to use small bolts to hold the windshield to the sides of the plane drilled through the acrylic - I'd rather keep it in place with the fiberglass fairing. Another spot is where the vertical fin meets the horizontal stabilizer. Truth be told there are loads of places, but these are the biggies.

    I'm hoping I can make these look nice once painted but could use a few pointers, such as:

    1) Which fiberglass should I use? I know there are many different types, thicknesses and ways to align them
    2) Which epoxy is best?
    3) I'm assuming I can put duct tape on the surfaces, glass over, then pull the whole thing off - is that too much of a hill billy approach?

    Thanks for any tips!
     
  2. Aug 13, 2018 #2

    billyvray

    billyvray

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    masking tape
    duck tape or packing tape over
    layup glass/epoxy
    trim

    Here's a good link: http://www.curedcomposites.com/fiberglass.html

    I like West systems and 206 slow hardener, or Total Boat epoxy.
    If you have a vac pump you can get a better finish but for a fairing it might be odd.

    Bill
     
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  3. Aug 13, 2018 #3

    Norman

    Norman

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    If you're making a part with compound curves a twill weave (the article Bill pointed to called it crowfoot, sometimes it's also called herring bone) will make your life a lot easier. It snakes around a lot and the edges can unravel during handling so we outline the laminates with blue painter's tape before cutting them out of the roll. Buy cutting down the middle of the tape it holds your pieces together during handling and keeps the working end of the roll neat. There are lots of good tips in Mike Arnold's moldless wheel pants video.

     
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  4. Aug 13, 2018 #4

    dcstrng

    dcstrng

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    I find Mike Arnold's instruction/guidance invaluable and bought the DVDs before they were YouTube available... You might also peruse Mark Langford's site where there are several sections on reducing drag via composites (and other interesting stuff). Please see: http://www.n56ml.com/
     
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  5. Aug 15, 2018 #5

    wsimpso1

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    Rutan BID is almost universally used for this sort of thing, it is an 8.8 oz/yard^2 fabric. Two plies makes a laminate about 0.020" thick that feels substantial and makes reasonably sturdy pieces. Any twill (crowfoot) glass fabric will drape nicely and fit many shapes. If you go lighter, you may find that you end up going to similar laminate thicknesses;

    Which resin is best? is a better question. Epoxies are great, but has Tg in the area 160-180 F, so it can get hot enough to distort just by painting it red or darker and putting it in the sun. Vinylester is rumored to be pretty darned good too, has a much higher Tg, which allows dark paints, but it has handling foibles and shelf life that is kind of short. Polyester should be avoided in airplanes.

    Which Epoxy? Epoxies are all pretty darned good, but some are a little better than others. For fairings, it probably matters little if any. Folks love West System, it is widely available in reasonably small quantities, has slow and fast hardeners, has its pump systems for getting correct proportions, and is wonderful for wood, and works great in fiberglass. Good stuff. I use Gougeon ProSet (West is also a Gougeon product) - it makes parts stronger than "book" values for glass-epoxy and it post cures for higher Tg than many room temp cure epoxies. If you are really after higher Tg with epoxies, they exist, but they usually require higher cure temps (in ovens or autoclaves). There are many others.

    Epoxy does not stick to duct tape, packing tape, and others. Remember that texture and wrinkles in the tape will telegraph through to the outside of your laminate, which will mostly require more fairing and finishing. You will want to keep resin out of the rest of the airplane, so masking everything is important. For making fairings, I would cover things with packing tape quite tightly to keep stuff out, then smoothly fair the surfaces with modeling clay, then tape and/or wax that. Remember that any defects in the underlying mold will show up in the finished part, and require more fairing work afterwards.

    Think your way through how you are going to remove the part form the form you now have, where any cut lines will be, how you will avoid damaging the underlying airplane, and how you will attach the resulting fairing when it is done. Some folks put in some small screws. Many composites guys stick them on with dots of silicone sealer that they renew at each Condition Inspection. Anyway, once you have the form perfect and the way to pull it and service it figured out, you can apply 2 BID to the whole thing, let it cure, and pull the part. Resist pulling the molding stuff off until you know that you have a good, workable scheme and good part. You may have to build several to get it all right.

    Once you have a good parts with workable schemes, you will trim it to shape and fair it. That is you will scuff sand or sand blast (low pressure) or soda blast to scuff the surface, then overfill the surface with 1/8-1/4"of dry micro and then profile sand, seal, and paint.

    http://curedcomposites.com/ and http://www.ez.org/pages/waynehicks/ are two websites positively LOADED with good info on doing this stuff, and are the two sites I refer folks to for fairing, finishing, and painting.

    Have fun!

    Bill
     
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  6. Aug 15, 2018 #6

    Marc W

    Marc W

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    I have been using Alpha Poxy from Aircraft Spruce for fairings. It is not intended for structural parts. It's advantage is it can be shipped without paying a Hazmat fee, which saves a little money.
     
  7. Aug 17, 2018 #7

    billyvray

    billyvray

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    So this is not expressly aviation related so feel free to delete, but it does apply to general new guys with composites so maybe the shared experience will benefit someone.

    One of my projects is changing a 1994 Harley Softail Heritge motorcycle to something different. My chosen style is a more upright scrambler/standard style motorcycle.

    The composite application is the formation of the seat pan base I made from fiberglass/epoxy/foam.

    I wanted a thin seat pan base to affix the seat to so I wanted to use fiberglass. But, I needed some stiffness between the frame rails so I added a foam insert.

    For a smooth surface on the top I elected to use a plexiglass panel to lay the glass up over. I had a thin piece of it from a discarded projection tv....from another wayward project...

    Long story short, the epoxy and glass laid up directly on the plexiglass just as smooth as butter. I trimmed it to final shape using a cheap Harbor Freight oscillating tool.

    image.jpg image.jpg image.jpg


    Bill
     
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  8. Aug 17, 2018 #8

    dcstrng

    dcstrng

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    An Evo Big-Twin Softail Scrambler – Wow, ya don’t see those every day… :)
     
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  9. Aug 17, 2018 #9

    BJC

    BJC

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    Sounds like the makings for a roll-your-own HUD project.


    BJC
     
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