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Another T45 Swallow - Slingsby --

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  • #16
    Covering with PolyFiber Fabric -- Modified process.

    The main modification is to paint all the surfaces you want the fabric glued to ( twice with thinned Poly-Tak ) Of course, letting it dry in-between coats. Thinning it makes a smoother surface.

    For the Elevators, I'm gluing the fabric to everything to try and prevent air bubbles on the rib cap strips of the exposed fabric.

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    Next step is to determine where the fabric overlap is going to be. Luckily I can do a full wrap around with one piece of fabric so the overlap is on the bottom of the leading edge ( wrapping bottom first around to the top ) I used a ruler to cut a clean edge before application.

    Use an Coverite Pocket thermometer to get the Iron at 200 degrees F to smooth the wrinkles out of the fabric ( doesn't have to be perfectly flat, just no major bumps )

    Lay the fabric down on the surface and just wipe MEK or Painter's Solvent ( replacement for MEK in California ) across the surface. I used a folded half sheet paper towel dipped in the Painter's Solvent . The Solvent dry's pretty quick.

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    The end of the elevators is a little thin to glue the fabric to so I elected to form the fabric over the end.

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    I let the excess fabric hang over the work bench and the use the 200 F iron to form the fabric around the trailing edge.

    Then flip it over and continue the fabric forming process so it lays relatively flat. Then continue the process of Solvent application
    If you see bubbles, just apply a little Solvent and rub it in with your finger to smooth it out.

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    On the Leading edge overlap, I applied a little more Poly-Tac on the fabric overlap area.

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    • #17
      Next step in the process is to Heat Smooth all the surfaces with the 200 F iron and a little pressure. It also helps remove some of the excess Poly-Tak too.

      After that its time to dial the Iron up to 225 F for the first shrinking - going over all of the open areas that aren't glued. Next is the same process a 250 F
      I don't recommend going any higher as there's a good chance that the structure will start to deform
      I held the elevator up to the morning sun ( contrast ) to check for any areas I might have missed.

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      Then on to the first coat of Un-Tinted Poly-Brush to seal the fabric. It looks a lot better in this photo than the Contrast one........

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      Fuselage is looking a little Shinny after the weave fill coat of Epoxy, too bad I have to sand it all off.

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      • #18
        Had a dickens' of a time finding my other 10 yd. order of PolyFiber Lite fabric ........but I was successful, so , ...On to the Fuselage
        Since the fabric is 60" wide and .....10 yds. long, it really give you a lot of options when covering..........

        Covering the bottom first , I'm really liking the modified application process as it leaves really smooth fabric attachment.


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        Then came the top / sides......., trying to do it in one piece and of course .............I cut the wrong direction.....oops.
        Not to worry, as the PolyTak softens with the Painter's Solvent (MEK) and just lifts up.

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        Once I got the fabric off, just applied another coat of thinned Poly-Tak and off to the Races again.

        Cut the right direction this time......

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        • #19
          Scot, so what is the modified application process you did and like? and where did you get the roll of covering?

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          • #20
            Hi Gunny,

            Fabric is 60" wide and as long as you want ( price is $8 per linear yard ) ...clickable .link at the bottom. ( I think its 1.87oz )

            From Stits , the fabric comes folded up in a sealed plastic bag
            http://www.stits.com/store/poly-lite...near-yard.html

            From Aircraft-Spruce its the Uncertified Light fabric and comes rolled up on a tube.
            http://www.aircraftspruce.com/catalo...clickkey=49019


            Stits / PolyFiber is normally applied by brushing the "glue" on to the air frame ( which is slighty viscous ) in 12 to 24 inch sections ( dries fast ) and then laying the fabric down and squishing the glue thru the fabric. Then moving on to the next t section until the fabric is applied. This tends to leave a bumpy surface and a lot of excess glue ----not a big deal on a Full size aircraft but on a Model it's a bit more apparent.

            Here's a link to the Full Scale Aircraft Covering Manual PDF - page 18 for "cementing process"
            http://www.conaircraft.com/polyfiber-manual.pdf


            Modified process is to thin the PolyTak ( 4 to 1 ) and then brush it on the surface you want the fabric glued to ( two separate coats - this leaves a smoother surface ).
            Lay the fabric down on the surface and then wick MEK / Painter's solvent / PolyFiber Reducer with a folded paper towel soften the PolyTak force it up thru the fabric fibers.
            I don't use a lot of pressure with my folded up paper towel, just enough to smooth the fabric and work the air bubbles out.

            This is similar to the wing skin / white glue / hot iron technique used on the wing sheeting sections.
            Last edited by MarnochS; 05-12-2018, 02:40 AM.

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            • #21
              Excellent information and good source for the fabric. Thank you for sharing this because a guy asked me about where to get fabric for the 2-33 and PT-19 kits I sell since solarTex is no more.

              Gunny

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              • #22
                Thanks Gunny,

                That was my thinking behind this " tutorial "......

                After Fabric is attached, Second step is to brush on the Poly-Brush coating. Normally the Poly-Brush is tinted pink so you can see where you already applied the coating but the Swallow's case, a natural fabric look is desired over a lot of the airframe so Un-Tinted Poly-Brush is "brushed" on. Only thing here is to watch not to brush on too much and cause pooling and drips on the inner surface.

                After the Poly-Brush dries the fabric edges need some attention as they usually fray and stick up a bit. I found a quick pass with my trusty Top-Flight Trim Seal Tool set to high does a great job.
                Also use of a 600 grit sand paper / sanding stick helps clean off the iron surface as the Poly-Brush builds up and burns.

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                Starting to look like a Sailplane

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                • #23
                  I received a great tip from Keith Shaw about applying liquid coatings. We were discussing doping structures. He suggested making a tool from a scrap balsa stick and attaching fabric to it. Put this tool against your structure with fabric in place. The stick is what you hold while slathering dope onto the tool's fabric. As the dope soaks into the tool's fabric capillary forces hold the tool against the model's fabric and you drag the tool across so that the dope is transmitted through the tool and onto your model without pushing excess dope into your model where it will pool and cause other problems! Apply dope (or, in your case, thinned Polytac as needed) while dragging the tool across the model.

                  I modified the tool by making the fabric in the shape of the curved portion of a letter 'D'. The 'handle' is the straight portion of the 'D'. The reason was the fabric tried to fold in the middle. Put the fabric onto the handle 'on the bias' to reduce shedding of loose fabric fibers. Keep a tweezers handy to pull off any loose bits! Once the loose bits have worked off the tool you won't be bothered with them any more. Make the tool at least as wide as one rib bay of your wings. With dope I was able to get the weave filled in just two coats! I use 50% thinned nitrate to fill the weave and it dries really fast. The process is a whole lot faster than trying to load brush to paint fabric without pushing dope inside the structure.

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                  • #24
                    Keith Shaw? The electric guru God?

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                    • ARUP
                      ARUP commented
                      Editing a comment
                      Yep! The same fella!

                  • #25
                    Thanks Mike for the hot tip, I will have to try that out........currently I'm using the "cheap" 1" chip brushes from Harbor Freight as they don't hold a lot of material in the bristles so it doesn't flood the fabric.........

                    Fun with Aerothane Clear this morning for the Rudder and Elevators - two mist coats and then a wet coat........Its really easy to spray when you follow the directions.......( thinned 20% )...
                    I use a spot lite and angel the piece to highlight where I'm spraying / sprayed.
                    Clear Aero-Thane has UV blockers already added so the "natural" section will be protected from that harmful Orb in the sky......

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                    The really nice thing about the Stits /PolyFiber fabric size is that you can cover the wing in one piece.....Yea..........overlap is on the bottom of the trailing edge.
                    Starting from the top trailing edge, wrapping around and then securing at the bottom D-box.
                    .

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                    Since the wing is under-cambered, fabric is attached to cap strips with the PolyTak ( well its attached glued to the top cap strips too....but not till after shrinking )
                    The under-cambered area was only shrunk to 250 F temperature , all the rest was to 275 F to get the fabric wrinkles out.

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                    Last edited by MarnochS; 05-06-2018, 02:04 AM.

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                    • #26
                      Productive weekend covering Wings and Aileron up thru Poly-Brush stage........Then Inspection time.......

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                      Time to start painting the big stuff........and work on the dreaded canopy

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                      • ARUP
                        ARUP commented
                        Editing a comment
                        What did your inspector think of the covering job so far?

                      • MarnochS
                        MarnochS commented
                        Editing a comment
                        Non-committal (..typical Cat.....) - She was interested but I was hoping she wouldn't perform a fabric "punch test".

                    • #27
                      Awesome work Scott, makes me want to build another one and cover and paint it. Look forward to seeing it in Monticello

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                      • #28
                        Thanks Pete, this stage is rewarding........visually and ......aromatically ( well-ventilated area required ) ..... Click image for larger version  Name:	PolyTak.JPG Views:	2 Size:	45.5 KB ID:	25977


                        Some early morning Clear Aero-Thane 100 on one wing. Always a bit of trepidation when painting outdoors with bugs and wind but got lucky today as both were still asleep.
                        Wing and painting jig, used 5/8" oak dowels ( with a little bit of sanding ) in the wing tube so I could spin the wing and hold it in place. ( I'm still working on how to do the same with the fuselage )
                        The Photos are at the 2nd mist coat stage....with my spot lite painting "aid"

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                        Waiting for paint to dry......the bottom is the sacrificial surface.....

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                        If anyone was wondering what happened to my Payload Master 100 or SGS 2-33 ......well ......still ...."in Progress".....
                        Last edited by MarnochS; 05-12-2018, 02:35 AM.

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                        • #29
                          There's the 2-33 fuselage...

                          Nice work Scott.

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                          • #30
                            Knuckled down and started sanding away on the canopy frame pieces.....alot of sand, check....sand, check....sand,check....sand, check.

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                            Fuselage getting it's Clear AeroThane, now I just have to wait the proscribed 7 days for the paint to cross-link. I think I'll give the Clear a couple of days before I start masking and priming the solid sections.

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                            Last edited by MarnochS; 05-14-2018, 12:05 PM.

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