the fasteners. This approved sticky-back tape helps prevent  the fabric from tearing.  [Figure 3-23]  Then, screws, rivets,  and clips simply attach into the predrilled holes in the rib caps  to hold the fabric to the caps. Rib lacing is a more involved  process whereby the fabric is attached to the ribs with cord. The amount polyester fabric shrinks is directly related to  the temperature applied. Polyester fabric can shrink nearly  5 percent at 250 °F and 10 percent at 350 °F. It is customary  to shrink the fabric in stages, using a lower temperature first,  before finishing with the final temperature setting. The first  shrinking is used to remove wrinkles and excess fabric. The  final shrinking gives the finished tautness desired. Each  process has its own temperature regime for the stages of  tautening. Typically ranging from 225 °F to 350 °F, it is  imperative to follow the process instructions. Not all fabric  covering processes use the same temperature range and  maximum temperature. Ensure irons are calibrated to prevent  damage at high temperature settings. There are two kinds of rib lacing cord. One has a round  cross-section and the other flat. Which to use is a matter  of preference based on ease of use and final appearance.  Only approved rib lacing cord can be used. Unless a rib is  unusually deep from top to bottom, rib lacing uses a single  length of cord that passes completely through the wing from  the upper surface to the lower surface thereby attaching the  top and bottom skin to the rib simultaneously.  Once the fabric has been tautened, covering processes vary.  Some require a sealing coat be applied to the fabric at this  point. It is usually put on by brush to ensure the fibers are  saturated. Other processes seal the fabric later. Whatever  the process, the fabric on wings must be secured to the wing  ribs with more than just cement. The forces caused by the  airflow over the wings are too great for cement alone to hold  the fabric in place. As described in the materials section,  screws, rivets, clips and lacing hold the fabric in place on  manufactured aircraft. Use the same attach method as used by  the original aircraft manufacturer. Deviation requires a field  approval. Note that fuselage and empennage attachments  may be used on some aircraft. Follow the methodology for  wing rib lacing described below and the manufacturer’s  instructions for attach point locations and any possible  variations to what is presented here. Holes are laid out and pre-punched through the skin as  close to the rib caps as possible to accept the lacing cord.  [Figure 3-24]  This minimizes leverage the fabric could  develop while trying to pull away from the structure and  prevents tearing. The location of the holes is not arbitrary.  The spacing between lacing holes and knots must adhere  to manufacturer’s instructions, if available. STC lacing  guidance refers to manufacturer’s instructions or to that  shown on the chart in  Figure 3-25  which is taken from AC  43.13-1. Notice that because of greater turbulence in the area  of the propeller wash, closer spacing between the lacing is  required there. This slipstream is considered to be the width  of the propeller plus one additional rib. Ribs are normally  laced from the leading edge to the trailing edge of the wing.  Rib lacing is done with a long curved needle to guide the  cord in and out of holes and through the depth of the rib.  The knots are designed not to slip under the forces applied  and can be made in a series out of a single strand of lacing.  Stitching can begin at the leading edge or trailing edge. A  Care must always be taken to identify and eliminate any sharp  edges that might wear through the fabric. Reinforcing tape of  the exact same width as the rib cap is installed before any of  3-18 Figure 3-24.  A premarked location for a lacing hole, which is  punched through the fabric with a pencil.  Figure 3-23.  Reinforcing tape the same width as the wing ribs is  applied over all wing ribs. Rib Lacing Attaching Fabric to the Wing Ribs