  We report measurements of turbulent drag reduction of two different
polyelectrolyte solutions: DNA and hydrolyzed Polyacrylamide. Changing the salt
concentration in the solutions allows us to change the flexibility of the
polymer chains. For both polymers the amount of drag reduction was found to
increase with the flexibility. Rheological studies reveal that the elongational
viscosity of the solutions increases simultaneously. Hence we conclude that the
elongational viscosity is the pertinent macroscopic quantity to describe the
ability of a polymer to cause turbulent drag reduction.
