AIC's 46th Annual Meeting

Doped fabric is ubiquitous on historic aircraft found in the collection at the National Air and Space Museum (NASM). Doping is the practice of applying a waterproof coating to fabric, which also serves to shrink the material over a rigid structure. A doped surface is traditionally made of multiple coats of clear cellulose nitrate, acetate, and/or acetate butyrate applied over a cotton or linen fabric. These cellulosic resins, known as aircraft dope, have a limited usable lifespan once applied to flight surfaces as dictated by their material properties. As these resins age, they become brittle and shrink, sometimes cracking or splitting in the process. Because of the requirement for scheduled inspections of the structures beneath, doped fabric materials have long been considered dispensable and are expected to be replaced or patched during routine operational maintenance or restoration. Restoration practices for patching localized damage entails the application of patches with new dope according to strictly defined methods illustrated in the FAA Advisory, AC43.13. This irreversible application of new dope can lead to further damage to the surrounding areas as the fresh dope shrinks. Traditional restoration practices can compromise the authenticity of the aircraft through the re-fabrication, removal, or covering of battle damage, historic finishes, and original art. Alternative options to preserve original doped aircraft fabric in situ through lining and surface patching techniques require further research as these topics are not well published in the field of conservation. NASM conservation is currently deviating from long-established restoration protocols to develop new methods to preserve original fabrics. New processes being explored include full lining of fabric components and employing localized patches using conservation fabrics and adhesives. Visible surface patching from the exterior is necessary in many instances due to constraints of the aircraft structure. In cases where lining is required, it provides much needed support to damaged and structurally weakened doped fabric. Over the last two years, NASM conservation treatments of aircraft fabric included the application of surface patches with nylon gossamer and Lascaux 498 HV and full lining of doped fabrics with BEVA 371b onto Ceconite 102 (a polyester fabric). This poster assesses these past treatments and explores two additional adhesives (methylcellulose and a wheat starch paste/sturgeon glue blend) as potential surface patching materials. The patching and lining materials were tested using t-peel and lap/shear tests as evaluation tools to determine adhesive/bond strength. The goal of this research is to identify reversible and stable materials and techniques to replace traditional methods of restoration.