Inexperienced technicians are encouraged to construct a  test panel upon which they can practice with the fabric and  various substances and techniques to be used on the aircraft.  It is often suggested to cover smaller surfaces first, such as  the empennage and control surfaces. Mistakes on these can  be corrected and are less costly if they occur. The techniques  employed for all surfaces, including the wings and fuselage,  are basically the same. Once dexterity has been established,  the order in which one proceeds is often a personal choice. Most covering procedures for polyester fabric rely on doped  or glued seams as opposed to sewn seams. They are simple  and easy to make and provide excellent strength, elasticity,  durability, and appearance. When using the blanket method,  seam overlap is specified in the covering instructions and  the FAA-certificated A&P mechanic must adhere to these  specifications. Typically, a minimum of two to four inches  of fabric overlap seam is required where ends of fabric are  joined in areas of critical airflow, such as the leading edge of  a wing. One to two inches of overlap is often the minimum  in other areas.  When using the blanket method, options exist for deciding  where to overlap the fabric for coverage. Function and the  final appearance of the covering job should be considered.  For example, fabric seams made on the wing’s top surface  of a high wing aircraft are not visible when approaching the  aircraft. Seams on low wing aircraft and many horizontal  stabilizers are usually made on the bottom of the wing for  the same reason.  [Figure 3-20] When the airframe is primed and ready for fabric installation,  it must receive a final inspection by an A&P with IA.  When approved, attachment of the fabric may begin. The  manufacturer’s or STC’s instructions must be followed  without deviation for the job to be airworthy. The following  are the general steps taken. Each approved process has its  own nuances.  During installation, the fabric is overlapped and seamed  together. Primary concerns for fabric seams are strength,  elasticity, durability, and good appearance. Whether using the  blanket method or envelope method, position all fabric seams  over airframe structure to which the fabric is to be adhered  during the covering process, whenever possible. Unlike the  blanket method, fabric seam overlap is predetermined in the  envelope method. Seams sewn to the specifications in AC  43.13-1, the STC under which the work is being performed,  or the manufacturer’s instructions should perform adequately.  A polyester fabric covering is cemented or glued to the  airframe structure at all points where it makes contact. Special  formula adhesives have replaced nitrate dope for adhesion  in most covering processes. The adhesive (as well as all  subsequent coating materials) should be mixed for optimum  characteristics at the temperature at which the work is being  performed. Follow the manufacturer’s or STC’s guidance  when mixing. Fabric Cement Seams Attaching Polyester Fabric to the Airframe Top fabric Bottom fabric Top fabric Bottom fabric 2" typical overlap on the leading edge 2" typical overlap on the leading edge 1" typical overlap on the trailing edge 1" typical overlap on the trailing edge Fabric overlap covering a low wing aircraft Fabric overlap covering a high wing aircraft Figure 3-20.  For appearance, fabric can be overlapped differently on high wing and low wing aircraft.  3-16