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Thread: Q no. 16433 about pitching moment coefficient Cm versus angle of attack diagram

  1. #1
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    Q no. 16433 about pitching moment coefficient Cm versus angle of attack diagram

    http://i.imgur.com/1hPDxQq.png

    Hi there , could anyone help me with how to read the diagram plz ?

    Number: 16433

    Which statement is correct regarding the pitching moment coefficient Cm versus angle of attack diagram?


    A-Line 4 shows an aeroplane with reducing static longitudinal stability at very high angles of attack.

    B-Line 4 shows an aeroplane with greater static longitudinal stability at low angles of attack than that in shown line 3.

    C-Line 1 shows an aeroplane with increasing static longitudinally instability at very high angles of attack.

    D-Line 3 shows an aeroplane with reducing static longitudinal stability at high angles of attack.4
    Last edited by subsky; 03-06-2014 at 06:52 AM. Reason: adding photo

  2. #2
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    Hi Subsky,

    I have added an explanation to question 16433.

    ATPLS

  3. #3
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    you need to understand when the line go down mean stable, up unstable and horizontally mean neutral

    the answer here is D, because if u look the graphic you will see the line 3, at high AoA(angle of attack) the slope is reduces to being a horizontally line, so line 3 are neutral at high AoA

    to understand this graph in another way try to compare line 4 and 1, the line 1 is an aircraft with the cg at aft(or maybe exceed the limit) limit, if u increase the AoA the aircraft, it will pith up more and more because the weight are aft, so it tends to pitch up without any imput, so this is unstable situation.
    Therefore the line 4 is an aircraft with the CG at forward limit, if u try to climb it try to return in the straight flight, or from another point of view if u try to climb the weight of the aircraft tend to push the nose down, so when you try to increase the AoA the aircraft try to decrease it, thats are a stable situation

    i hope my explanation will help you

    Cpt. Baraa
    Last edited by Cpt.Baraa; 10-08-2014 at 09:16 AM.

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