... More on the Sink Rate Difference Between Short and Long Line Segments

Graig Spolek (a fly fisherman, author of multiple published articles on fly fishing equipment, and Professor of Mechanical and Materials Engineering at Portland State University) sent us the following e-mail on the sink rate difference for short (1"-2") line segments compared to the longer ones actually used for fishing.

"This phenomenon that Jim Havstad alludes to is a well-known end effect issue, due to vortices that roll over the end of objects subject to immersed flow. Much work has been performed to document the magnitude of this effect on aircraft wings, since the effect works to reduce wing lift and increase wing drag (for a short segment of sinking line, reducing lift leads to faster sinking). Wings on aircraft routinely now incorporate some sort of wing tip "winglet," usually a turned up end or a section of airfoil normal to the wing plane, to reduce this effect. Theory shows that the magnitude of this end effect scales with the wing plane area (L D for lines) divided by the length squared, or the scaling factor is L/D for lines. So for aircraft to have very high lift (slow sink rate for lines), the wings are very long with relatively short span. Spy planes that fly at very high altitudes, gliders, and albatrosses all have long, narrow wings.

The argument can be made, then, that sinking line tests should use long, narrow specimens (large L/D ratio)."