The Butt Knows
I believe that much of the confusion comes from lack of understanding what the slip ball and yarn actually measure. The slip ball measures side forces at the location of the instrument in the aircraft. Side forces are a result of the sum of all dynamic forces on the machine. The yarn/slip string measures sideslip airflow at the location of the string not necessarily the actual sideslip of the machine. In flight test a boom is utilized to locate the pitot system clear of the rotor system thus measuring actual side slip. Like many who have responded on this site I have experienced the conflicts between what my butt says and what the instruments display. A good example is the EC-135. If the ball is in the middle my butt was hanging out and vice versa. The AS-350 was even more confusing. There you have two inputs (string and slip ball) versus your butt. In the end I allowed my butt to prevail and it has served me well.
Last edited by Jack Carson; 4th Aug 2013 at 22:44.