Malfunction and Defect Report
REF: All light weight dacron tapes.
AIRCRAFT TYPE: All fabric covered aircraft.
PROBLEM: Shrinking tapes due high skin temperatures caused from
dark color paint and direct sunlight.
There has been several instances that the light weight dacron tapes have shrunk due to extreme skin temperatures caused by the sun shinning on the dark paint that the aircraft has been final painted with. The skin temperatures of a black aircraft can go up as high as 250 degrees while setting in the sun, which in turn cause all brand of light weight dacron tapes to shrink more easily than the medium weight tapes. Fabric covering processes, (Ceconite Process, Stits Process, Air-Tech Process, Super Flite Process, etc…), has nothing to do with this not happening. It takes less time heat to shrink a 1.7 ounce dacron light weight tape than the 2.7 ounce dacron medium weight tape or say the 3.2 ounce dacron tapes. The transfer of the skin temperature will affect the thinner light weight tapes easier because there is less thickness to absorb the temperature. All fabric covering process adhesives will thermal soften when heat is applied and in this case the sun is the heat source. As the skin temperatures begin to rise the tape adhesives becomes soft and the tapes begin to shrink therefore sliding on the adhesive base. This will allow the paint to separate and leave a primer filler line showing along the tape edges. The use of the medium weight tapes, (2.7 oz.), has not been a problem in the past but it could happen. The light weight tapes are a pleasure to work with, but one must understand how to use the light weight tapes in order to keep this shrinking problem from happening.
The planning of a fabric covering job should include addressing this issue if you are going to topcoat your covering job with a dark color.
Pre shrinking the 1.7 ounce tapes is a must before installation. Consider using 3 inch pinked edge light weight tapes and preshrinking with an iron to at least 250 degrees --- do this in on a soft cloth with the same iron you would use to shrink the fabric. This technique is very easy and quick to do. Once the 3 inch tapes have been shrunk you will find the tape to measure aproximately 2.75 inches. Test iron a few pieces of tape and develop your own technique that will give you uniformity in the width of the tapes. The tapes are now ready to glue into place using the same procedures called for in the Fabric Covering Installation Manual. The ironing of the tape edges to make the pinked edges smooth will not be affected by the preshrunk tapes. When one irons the tape edges what he or she is actually doing is thermal softening the adhesives causing the tapes to lay down into the softened adhesive and end up smooth to the touch.
Technology has come a long way in giving us products that will work better. We have to understand these products, know their limitations and adjust accordingly by developing a different application technique that will not cause a problem later on.
If you need more information about this problem, give me a call.
M. K. Blalock
Special Products Aviation, inc.
FAA Repair Station SPDR118K
E-Mail firstname.lastname@example.org Phone (501) 327-4339