The most important finish of a fabric covered airplane is the sprayed on silver finish. These multiple coats of silver are basically aluminum particles suspended in the vinyl chemistry to protect the fabric from the harmful effects of the Sun. There is usually a minimum of three coats of the Poly Spray material needed to bury the fabric in metal. A work light is placed behind the fabric to inspect if enough silver has been applied to totally eliminate any light penetration through the fabric. The silver/fabric material is carefully sanded with 320 / 400 grit sandpaper between coats.
The next spray coats will be a White Poly Tone Color that is used as a base finish prior to spraying the final classic 146 J3 Yellow. The White is needed to cancel the gray tone of the silver otherwise the Yellow color would be a greenish and hideous color.
Attaching large sheets of sticky medium weight Polyester fabric to the sticky Poly Tak edges of the fuselage frame became a two person job. The objective is to attach the fabric before the Poly Tak glue starts to set up and dry while also leaving enough time to get the right amount of slack in the fabric for shrinking allowance. Too little slack could deform the metal frame during shrinking and too much slack could result in a saggy skin.
Side walls of the fuse were covered first, then shrunk and trimmed. The Belly panel was attached next and overlapped the side walls. The roof panel was attached last. Fabric tapes were attached on the edges and over the stringers using Poly Brush as the glue. Poly brush coats were then brushed on next over the entire fabric surface. Poly Brush coats were then sprayed on as seen in the photos above.
The Turtle deck had its own spray booth and is shown with tapes attached. There is no “Red Tint” on the fabric finish since the “Untinted Poly Brush was used.
The next step will be the Silver Coats using Poly Spray for UV Protection.
The Poly Fiber Instruction manual warns about over tensioning the fabric during the three stage Ironing process as it can deform metal parts. I was deeply concerned that this may occur on the Turtle Deck since it is an open ended frame so a Test Fit was in order to check for proper fit on the Fuselage. Luckily there was no deformity and as I gained expierence I found that it was next to impossible to deform parts, even light weight aluminum parts. The only caveat is, if you glue the fabric too tightly around the part to begin with then it is entirely possible to deform it as the fabric pulls itself together. The best practice is to leave a little slack in the fabric when it is first glued to the frame, then as it shrinks it will not deform the part it is covering.
The sides of the Turtle Deck were fabric covered first and heat shrunk and then the top fabric was attached and shrunk down. The above photo shows the fabric before tapes were attached. Because the inside of the Turtle Deck can be seen when it is raised, I used the “Untinted” Poly Brush which is basically a clear finish product. The regular Poly Brush has a red tint and as you brush it on before, during and after the taping stage the brush marks and runs all begin to show. The red tint is there so you can see where you have brushed and where you haven’t. Theses brush marks will all be coated over with the sprayed on silver and color finishes but they will always be seen from the back side of the fabric. That’s not a problem when it’s inside the fuselage and can’t be seen but any fabric that can be seen from the back side such as fabric that faces the cockpit or in my case is seen when the turtle Deck is raised is an area where you would want to use the “Untinted” Poly Brush product
With the Fuse painted, it was now ready to fabric cover. However before I tackled the largest fabric covered component I decided to first test my skills on some smaller parts. The Turtle Deck was my first experiment in learning the fabric cover process. I researched various covering methods and products and decided on The Poly Fiber System. I liked the Instruction Manual and I also attended a two day class which helped me gain some confidence. But the most important aspect was the product itself. The Poly Fiber System is durable, easy to install and easy to repair.
In the photo above the fabric has been glued to one side of the Turtle Deck and is in the process of being heat shrunk. The next ironing at the highest temp setting will smooth the wrinkles away.