def v_equil(alpha, cli, cdi):
    """Calculate the equilibrium glide velocity.

    Parameters
    ----------
    alpha : float
        Angle of attack in rad
    cli : function
        Returns Cl given angle of attack
    cdi : function
        Returns Cd given angle of attack

    Returns
    -------
    vbar : float
        Equilibrium glide velocity
    """

    den = cli(alpha)**2 + cdi(alpha)**2
    return 1 / den**(.25)