AERODYNAMIC CENTRE

AERODYNAMIC CENTER

IN ASYMMETRICAL AIRFOILS THE CENTER OF PRESSURE MOVES ALONG THE CHORD LINE WITH CHANGES IN ANGLE OF ATTACK. AS THE ANGLE OF ATTACK INCREASES THE CENTER OF PRESSURE MOVES TOWARDS THE LEADING EDGE AND WHEN IT DECREASES IT MOVES TOWARDS THE TRAILING EDGE. A NOSE DOWN PITCHING MOMENT IS ALWAYS PRESENT AND INCREASES IN INTENSITY WITH INCREASING ANGLES OF ATTACK. HOWEVER THERE IS A POINT ON THE CHORD LINE ABOUT WHICH THE PITCHING MOMENT REMAINS CONSTANT,REGARDLESS OF ANY CHANGE IN ANGLE OF ATTACK. THIS POINT IS CALLED AERODYNAMIC CENTER.

IN SUBSONIC AIRFLOW IT IS LOCATED AT A DISTANCE 25% FROM LEADING EDGE ON THE CHORD LINE. HOWEVER IN SUPERSONIC AIRFLOW IT IS CONSIDERED TO BE LOCATED ON 50 % FROM LEADING EDGE ON THE CHORD LINE. FOR DESIGN PURPOSES IT IS CONSIDERED TO BE OVERALL LIFT FORCE TO ACT ON THAT POINT COMBINED WITH A PITCHING MOMENT OF CONSTANT STRENGTH.

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