 |
 |
|
|
|
SAS is in the process of recreating a Commonwealth Skyranger 185 using airframes, wings, etc. salvaged from various different individual aircraft of the correct model. This aircraft is in the process of being recovered and the project is being used here to tell the reader about the Poly-Fiber© system that SAS uses.
Here is the Commonwealth fuselage ready for fabric. The airframe tubing has been striped, restored, cleaned, and primed in preparation for fabric. Loose Poly-Fiber fabric is being clipped to the airframe in the second picture. The fuselage can either be covered with long panels of fabric (70" wide) which have been sewn together or a fuselage envelope can be purchased or made. An envelope is more or less like a giant slip cover. It is open in the front so that it can be slipped over the entire fuselage from the rear. An envelope is being used here. The front of this fuselage is held by a special support jig which allows the fuselage to be rotated 360 degrees around the longitudinal axis. The tail section is setting on saw horses which allow for good support of the airframe in the upright position or when laid on either side. This envelope was first attached to the vertical stabilizer trailing edge. Fabric is roll around the airframe and attached using Poly-Tak. Since there is an opening in the envelope at the tail, one piece is rolled about 3/4 of the way around the tubing and then the second piece is placed on top of the first about 1/2 way around the tubing. The overlapping fabric is then covered with reinforcing finishing tape. The tape is attached using Poly-Brush. The opening of the envelope at the cabin is then attached to the airframe. You can see the fabric rolled around the tubing of the cabin in the photos above. The fabric is attached using Poly-Tak. To be more specific, the tubing is pre-coated with Poly-Tak and allowed to dry. The fabric is heat formed around the tubing and then trimmed and cemented with Poly-Tak. The pre-coating provides better adhesion and as much fabric as possible is wrapped around the tubing to maximize the strength of the attachment. After attachment the fabric is heat tightened over the entire fuselage. This is done with care to insure that seam alignments are not moved during the tightening process. After tightening, the envelope has to be cut in places to allow for protrusions, fittings, etc. These areas are also attached to the airframe. The entire envelope gets a hand brushed liberal first coat of thinned Poly-Brush. Reinforcing tape is applied with Poly-Brush around all of the fittings, protrusions, and other necessary areas. Rib lacing is done to wing ribs to increase the mechanical attachment of the fabric to the ribs. There are false ribs in the top of the Commonwealth cabin which, therefore, get rib laced. You can see (above, right) John and his wife working together to do just that. Rib lacing is done because aircraft fabric cement is made for shear loads and not for peel. However, in flight, an aircraft is subjected to constant peel loads from the lift on the top of the wing. Inspection hole reinforcements and drain grommets are installed followed by finishing tape and gussets. This is followed by two sprayed on coats of thinned Poly-Brush. Before painting, the fabric receives three cross coats of thinned Poly-Spray with sanding after the first and second coats. Poly-Spray is an aluminum pigmented finish. This serves two purposes. It provides UV protection for the fabric thus prolonging its life and it provides a sandable fill coat for the top coat that will follow. For even more information on the Poly-Fabric system of products and how to use them see their very informative web site at www.polyfiber.com. Last updated on August 13, 2004 |
