def natural_wavelength(gamma_factor, E, I, delta_f, W_sub):
    """Return the factored natural wavelength [m] i.e. the distance from prop to
    touchdown - JIP. 

    :param float E: Young's Modulus [Pa]
    :param float I: Second moment of area [m^4]
    :param float delta_f: Imperfection height [m]
    :param W_sub float: Submerged pipe weight [kg/m^3]
    """
    return gamma_factor * (72 * E * I * delta_f / W_sub) ** (1 / 4)
