What was found
ON TAKEOFF, RUDDER PEDALS VERY STIFF. CONFIRMED YAW DAMPER OFF. RETURNED. RUDDER BIAS CHECKED NORMAL ON TAXI. AFTER LANDING, ON TAXI IN, CHECKED RUDDER STIFFNESS AND FOUND NORMAL AT IDLE POWER BUT RUDDER BECAME PROGRESSIVELY STIFFER AS POWER ADVANCED. COULD NOT DUPLICATE AFTER COMPLETE RUDDER BIAS SYS OPS CHECK, INSTALLED O/H RUDDER BIAS SHUTOFF VALVE. OPS CHECKED GOOD IAW MM 27-20-05.