What might cause fabric to sag after application?

Insufficient tautening or shrinkage of the fabric after it has been applied is a primary reason for sagging. When covering an aircraft structure, the fabric needs to be applied tightly to prevent movement and ensure stability. If the fabric is not taut enough during the application process, it may not achieve the necessary tightness during subsequent shrinkage once the heat is applied, or upon drying the finishing chemicals. As a result, the fabric can lose its initial tension, leading to unwanted sagging, which can affect both the appearance and performance of the aircraft.

In contrast, over-stretching during application could lead to excessive tension and potential tearing rather than simply sagging. Excessive use of dope can create a rigid surface but would not directly cause sagging post-application. Improper color application generally pertains to aesthetic aspects rather than affecting the structural integrity or tautness of the fabric itself. Thus, insufficient tautening and shrinkage is the most logical cause of fabric sagging after the application.