What was found
AFTER TAKEOFF, DURING RIGHT TURN AIRCRAFT HAD STUDDERING, TURNING OUT OF TURN SAME BUFFETING EFFECT IN AIRFRAME. DID NOT FEEL IN YOKE, NO VISIBLE ENGINE INDICATIONS OF MALFUNCTION. NO LEFT TURNS MADE). FOUND RUDDER PRESSURE REDUCER VALVE BYPASSING. REMOVED AND REPLACED RUDDER PRESSURE REDUCER VALVE, LEAK AND OPS CHECK GOOD ON GROUND.