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4 Answers

Forward CG the airplane more stable i know that when the CG in front of center of pressure the airplane become stable but why ????

Asked by: 2693 views Aerodynamics

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4 Answers

  1. Best Answer

    Mark Kolber on Feb 14, 2014

    I don’t know how technical an answer you want so I’ll use the simple one I use with my students.

    Do you ski? Skateboard? If so, try sitting or standing all the way back and see how stable it is. Now move forward and try it.

    Or maybe you have a car? Load the trunk with cinder blocks or bricks so the CG of the car is way back. Then drive around a bit (but not too far!). More or less stable?

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  2. reza zare on Feb 15, 2014

    because when an airplane’s CG is located in front of the airplane makes an airplane nose heavy and when a nose heavy airplane stalls the airplane tends to decrease the angle of attack because of CG forward .

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  3. Mohammad Adaileh on Feb 16, 2014

    Thank you for the feedback.

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  4. Brian on Feb 22, 2014

    “when an airplane’s CG is located in front of the airplane makes an airplane nose heavy”

    This is a poor and inaccurate way to think of CG and is all too common. It comes from an inaccurate connection between a weight on a fixed fulcrum to the weighting of an aircraft. In the case of a ground object with a fixed rotation point (a fulcrum), the weight applied to one side can be said to make that side heavier. This is because the point of rotation is a fixed point; not the CG.

    In an airplane, however, the CG is the point of rotation. The lifting force on the wing acts behind the CG and acts upward. This causes a nose down rotation. The arm between the lifting force and the CG determine the strength of this rotation. The tail, to counter this forward rotation, provides a tail down force. The arm between the CG and the tail, as well as the surface area of the tail, determine the strength of rotation the tail can handle.

    So how does this explain a forward CG making the pilot think the plane is nose heavy? When the CG moves forward the arm between lifting force on the wing and the CG increase. Since the main wing lift force is quite strong, even a small shift forward will mean a much greater rotational force being present. When the CG is moved too far forward this forward rotation force becomes so great that the tail of the airplane can no longer produce a great enough rotational force to overcome it.

    So we conclude that the airplane is too nose heavy when really it’s the point of rotation (CG) being too far from the main wing lifting force for the tail to overcome the rotation created by the lifting wing. If we could somehow slide the wing forward, or move the tail farther back/increase it’s size, then we would be alright again. So it isn’t the weight being forward that is causing us to feel nose heavy, it is the rotational force created by the location of the CG that gives this result.


    Here is a pic that gives a bit more detail than what Mark provide; should you be interested. http://apstraining.com/wp-content/uploads/Figure-1-Tail-Down-Force-Balancing-Wing-Moment.jpg

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