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Angle of attack from pitch angle acceleration

  1. Sep 18, 2012 #1
    I am analyzing the landing of an aircraft with the following assumptions:

    - I consider the main and the nose landing gear wheels as skids, in order to ignore the tyre deflection;

    - I have a 3 DOF aircraft model, with X and Y-axis indicating the forces acting respectively horizontally and vertically and the theta angle positive clockwise. This frame of reference is referred to the center of gravity;

    - I assume that the plane has already touched the ground, so I don't consider the gliding phase towards the runway.

    Now the summation of moments aroung the c.g. gives:

    ƩMcg = Iyy[itex]\ddot{\vartheta}[/itex]= RNLG * Ln - RMLG * Lm - hcg * [itex]\mu[/itex]Fvert

    [itex]\ddot{\vartheta}[/itex] is the angular acceleration of the pitch moment;
    RNLG and RMLG are the vertical reactions of the nose and of the main landing gear shock absorber;
    Ln and Lm are the distances respectively of the nose landing gear and of the main landing gear from the c.g.;
    [itex]\mu[/itex] is the friction coefficient;
    hcg is the vertical distance between the runway and the c.g.;
    Fvert is the resultant of the vertical forces.

    Knowing the value of Iyy, which is the airplane pitch moment of intertia I can then compute [itex]\ddot{\vartheta}[/itex].

    From this angular acceleration of the pitch angle I want to find the angle of attack, which is the difference from the pitch angle and the flight path angle:
    A.o.A. -> α = θ - γ

    My questions are:

    1) Can I assume γ = 0 (flight path angle), since the plane has already touched the ground when I start my computations?

    2) If so, how do I integrate [itex]\ddot{\vartheta}[/itex] in order to get the picth angle? What are my intitial conditions?

    I hope that everything is clear and sorry for the long post.
    Last edited: Sep 18, 2012
  2. jcsd
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