Installing flexible ducts correctly is essential for optimal air flow. If not pulled tight, the inside of the duct will be uneven and compressed, resulting in poor air flow and increased sagging over time. Additionally, it is important to ensure that the duct has a well-fitting inner lining. The friction speed increases significantly if the duct is not pulled tight. According to the diagram below, if a flexible duct has 15% longitudinal compression, the friction velocity doubles.
With a longitudinal compression of 30%, the friction velocity quadruples. To avoid this issue, it is important to stretch the flexible ducts as hard as possible. When connecting the flexible ducts to the trunk or at takeoff, it is important to stretch them again and remove any excess core. Once this is done, the other end can be connected and the installation can be completed.