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+# This file is part of Marius Peter's airfoil analysis package (this program).
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+"""
+The creator.py module contains class definitions for coordinates
+and various components we add to an airfoil (spars, stringers, and ribs).
+
+Classes:
+    Airfoil: instantiated with class method to provide coordinates to heirs.
+    Spar: inherits from Airfoil.
+    Stringer: also inherits from Airfoil.
+
+Functions:
+    plot_geom(airfoil): generates a 2D plot of the airfoil & any components.
+"""
+
+import sys
+import os.path
+import numpy as np
+from math import sin, cos, atan
+import bisect as bi
+import matplotlib.pyplot as plt
+
+
+class Airfoil:
+    """This class represents a single NACA airfoil.
+
+    Please note: the coordinates are saved as two lists
+    for the x- and z-coordinates. The coordinates start at
+    the leading edge, travel over the airfoil's upper edge,
+    then loop back to the leading edge via the lower edge.
+
+    This method was chosen for easier future exports
+    to 3D CAD packages like SolidWorks, which can import such
+    geometry as coordinates written in a CSV file.
+    """
+
+    # Defaults
+    chord = 100
+    semi_span = 200
+
+    def __init__(self):
+        # mass and area
+        self.mass = float()
+        self.area = float()
+        # Component material
+        self.material = str()
+        # Coordinates
+        self.x = []
+        self.z = []
+
+    @classmethod
+    def from_dimensions(cls, chord, semi_span):
+        """Create airfoil from its chord and semi-span."""
+        if chord > 20:
+            cls.chord = chord
+        else:
+            cls.chord = 20
+            print('Chord too small, using minimum value of 20.')
+        cls.semi_span = semi_span
+        return Airfoil()
+
+    def __str__(self):
+        return type(self).__name__
+
+    def add_naca(self, naca_num):
+        """Generate surface geometry for a NACA airfoil.
+
+        The nested functions perform the required steps to generate geometry,
+        and can be called to solve the geometry y-coordinate for any 'x' input.
+        Equation coefficients were retrieved from Wikipedia.org.
+
+        Parameters:
+        naca_num: 4-digit NACA wing
+
+        Return:
+        None
+        """
+        # Variables extracted from 'naca_num' argument passed to the function
+        self.naca_num = naca_num
+        m = int(str(naca_num)[0]) / 100
+        p = int(str(naca_num)[1]) / 10
+        t = int(str(naca_num)[2:]) / 100
+        # x-coordinate of maximum camber
+        p_c = p * self.chord
+
+        def get_camber(x):
+            """
+            Returns camber z-coordinate from 1 'x' along the airfoil chord.
+            """
+            z_c = float()
+            if 0 <= x < p_c:
+                z_c = (m / (p ** 2)) * (2 * p * (x / self.chord)
+                                        - (x / self.chord) ** 2)
+            elif p_c <= x <= self.chord:
+                z_c = (m / ((1 - p) ** 2)) * ((1 - 2 * p)
+                                              + 2 * p * (x / self.chord)
+                                              - (x / self.chord) ** 2)
+            return (z_c * self.chord)
+
+        def get_thickness(x):
+            """Return thickness from 1 'x' along the airfoil chord."""
+            x = 0 if x < 0 else x
+            z_t = 5 * t * self.chord * (
+                + 0.2969 * (x / self.chord) ** 0.5
+                - 0.1260 * (x / self.chord) ** 1
+                - 0.3516 * (x / self.chord) ** 2
+                + 0.2843 * (x / self.chord) ** 3
+                - 0.1015 * (x / self.chord) ** 4)
+            return z_t
+
+        def get_theta(x):
+            dz_c = float()
+            if 0 <= x < p_c:
+                dz_c = ((2 * m) / p ** 2) * (p - x / self.chord)
+            elif p_c <= x <= self.chord:
+                dz_c = (2 * m) / ((1 - p) ** 2) * (p - x / self.chord)
+            theta = atan(dz_c)
+            return theta
+
+        def get_upper_coord(x):
+            x = x - get_thickness(x) * sin(get_theta(x))
+            z = get_camber(x) + get_thickness(x) * cos(get_theta(x))
+            return (x, z)
+
+        def get_lower_coord(x):
+            x = x + get_thickness(x) * sin(get_theta(x))
+            z = get_camber(x) - get_thickness(x) * cos(get_theta(x))
+            return (x, z)
+
+        # Densify x-coordinates 10 times for first 1/4 chord length
+        x_chord_25_percent = round(self.chord / 4)
+
+        x_chord = [i / 10 for i in range(x_chord_25_percent * 10)]
+        x_chord.extend(i for i in range(x_chord_25_percent, self.chord + 1))
+        # Reversed list for our lower airfoil coordinate densification
+        x_chord_rev = [i for i in range(self.chord, x_chord_25_percent, -1)]
+        extend = [i / 10 for i in range(x_chord_25_percent * 10, -1, -1)]
+        x_chord_rev.extend(extend)
+
+        # Generate our airfoil geometry from previous sub-functions.
+        self.x_c = []
+        self.z_c = []
+        for x in x_chord:
+            self.x_c.append(x)
+            self.z_c.append(get_camber(x))
+            self.x.append(get_upper_coord(x)[0])
+            self.z.append(get_upper_coord(x)[1])
+        for x in x_chord_rev:
+            self.x.append(get_lower_coord(x)[0])
+            self.z.append(get_lower_coord(x)[1])
+        return None
+
+    def add_mass(self, mass):
+        self.mass = mass
+
+    def info_print(self, round):
+        """Print all the component's coordinates to the terminal."""
+        name = '    CREATOR DATA FOR {}    '.format(str(self).upper())
+        num_of_dashes = len(name)
+        print(num_of_dashes * '-')
+        print(name)
+        for k, v in self.__dict__.items():
+            if type(v) != list:
+                print('{}:\n'.format(k), v)
+        print(num_of_dashes * '-')
+        for k, v in self.__dict__.items():
+            if type(v) == list:
+                print('{}:\n'.format(k), np.around(v, round))
+        return None
+
+    def info_save(self, save_path, number):
+        """Save all the object's coordinates (must be full path)."""
+        file_name = '{}_{}.txt'.format(str(self).lower(), number)
+        full_path = os.path.join(save_path, file_name)
+        try:
+            with open(full_path, 'w') as sys.stdout:
+                self.info_print(6)
+                # This line required to reset behavior of sys.stdout
+                sys.stdout = sys.__stdout__
+                print('Successfully wrote to file {}'.format(full_path))
+        except IOError:
+            print('Unable to write {} to specified directory.\n'
+                  .format(file_name),
+                  'Was the full path passed to the function?')
+        return None
+
+
+class Spar(Airfoil):
+    """Contains a single spar's location."""
+
+    def __init__(self):
+        super().__init__()
+        self.x_start = []
+        self.x_end = []
+        self.thickness = float()
+        self.z_start = []
+        self.z_end = []
+
+    def add_coord(self, airfoil, x_loc_percent):
+        """Add a single spar at the % chord location given to function.
+
+        Parameters:
+        airfoil: gives the spar access to airfoil's coordinates.
+        x_loc_percent: spar's location as a % of total chord length.
+
+        Return:
+        None
+        """
+
+        # Scaled spar location with regards to chord
+        loc = x_loc_percent * self.chord
+        # bi.bisect_left: returns index of first value in airfoil.x > loc
+        # This ensures that spar geom intersects with airfoil geom.
+        # Spar upper coordinates
+        spar_x = bi.bisect_left(airfoil.x, loc) - 1
+        x = [airfoil.x[spar_x]]
+        z = [airfoil.z[spar_x]]
+        # Spar lower coordinates
+        spar_x = bi.bisect_left(airfoil.x[::-1], loc)
+        x += [airfoil.x[-spar_x]]
+        z += [airfoil.z[-spar_x]]
+        self.x.append(x)
+        self.z.append(z)
+        return None
+
+    def add_spar_caps(self, spar_cap_area):
+        self.cap_area = spar_cap_area
+        return None
+
+    def add_mass(self, mass):
+        self.mass = len(self.x) * mass
+        return None
+
+    def add_webs(self, thickness):
+        """Add webs to spars."""
+        for _ in range(len(self.x)):
+            self.x_start.append(self.x[_][0])
+            self.x_end.append(self.x[_][1])
+            self.z_start.append(self.z[_][0])
+            self.z_end.append(self.z[_][1])
+        self.thickness = thickness
+        return None
+
+
+class Stringer(Airfoil):
+    """Contains the coordinates of all stringers."""
+
+    def __init__(self):
+        super().__init__()
+        self.x_start = []
+        self.x_end = []
+        self.thickness = float()
+        self.z_start = []
+        self.z_end = []
+        self.area = float()
+
+    def add_coord(self, airfoil,
+                  stringer_u_1, stringer_u_2,
+                  stringer_l_1, stringer_l_2):
+        """Add equally distributed stringers to four airfoil locations
+        (upper nose, lower nose, upper surface, lower surface).
+
+        Parameters:
+        airfoil_coord: packed airfoil coordinates
+        spar_coord: packed spar coordinates
+        stringer_u_1: upper nose number of stringers
+        stringer_u_2: upper surface number of stringers
+        stringer_l_1: lower nose number of stringers
+        stringer_l_2: lower surface number of stringers
+
+        Returns:
+        None
+        """
+
+        # Find distance between leading edge and first upper stringer
+        interval = airfoil.spar.x[0][0] / (stringer_u_1 + 1)
+        # initialise first self.stringer_x at first interval
+        x = interval
+        # Add upper stringers from leading edge until first spar.
+        for _ in range(0, stringer_u_1):
+            # Index of the first value of airfoil.x > x
+            i = bi.bisect_left(airfoil.x, x)
+            self.x.append(airfoil.x[i])
+            self.z.append(airfoil.z[i])
+            x += interval
+        # Add upper stringers from first spar until last spar
+        # TODO: stringer placement if only one spar is created
+        interval = (airfoil.spar.x[-1][0]
+                    - airfoil.spar.x[0][0]) / (stringer_u_2 + 1)
+        x = interval + airfoil.spar.x[0][0]
+        for _ in range(0, stringer_u_2):
+            i = bi.bisect_left(airfoil.x, x)
+            self.x.append(airfoil.x[i])
+            self.z.append(airfoil.z[i])
+            x += interval
+
+        # Find distance between leading edge and first lower stringer
+        interval = airfoil.spar.x[0][1] / (stringer_l_1 + 1)
+        x = interval
+        # Add lower stringers from leading edge until first spar.
+        for _ in range(0, stringer_l_1):
+            i = bi.bisect_left(airfoil.x[::-1], x)
+            self.x.append(airfoil.x[-i])
+            self.z.append(airfoil.z[-i])
+            x += interval
+        # Add lower stringers from first spar until last spar
+        interval = (airfoil.spar.x[-1][1]
+                    - airfoil.spar.x[0][1]) / (stringer_l_2 + 1)
+        x = interval + airfoil.spar.x[0][1]
+        for _ in range(0, stringer_l_2):
+            i = bi.bisect_left(airfoil.x[::-1], x)
+            self.x.append(airfoil.x[-i])
+            self.z.append(airfoil.z[-i])
+            x += interval
+        return None
+
+    def add_area(self, area):
+        self.area = area
+        return None
+
+    def add_mass(self, mass):
+        self.mass = len(self.x) * mass + len(self.x) * mass
+        return None
+
+    def add_webs(self, thickness):
+        """Add webs to stringers."""
+        for _ in range(len(self.x) // 2):
+            self.x_start.append(self.x[_])
+            self.x_end.append(self.x[_ + 1])
+            self.z_start.append(self.z[_])
+            self.z_end.append(self.z[_ + 1])
+        self.thickness = thickness
+        return None
+
+    def info_print(self, round):
+        super().info_print(round)
+        print('Stringer Area:\n', np.around(self.area, round))
+        return None
+
+
+def plot_geom(airfoil, view: False):
+    """This function plots the airfoil's + sub-components' geometry."""
+    fig, ax = plt.subplots()
+
+    # Plot chord
+    x = [0, airfoil.chord]
+    y = [0, 0]
+    ax.plot(x, y, linewidth='1')
+    # Plot quarter chord
+    ax.plot(airfoil.chord / 4, 0,
+            '.', color='g', markersize=24,
+            label='Quarter-chord')
+    # Plot mean camber line
+    ax.plot(airfoil.x_c, airfoil.z_c,
+            '-.', color='r', linewidth='2',
+            label='Mean camber line')
+    # Plot airfoil surfaces
+    ax.plot(airfoil.x, airfoil.z,
+            color='b', linewidth='1')
+
+    # Plot spars
+    try:
+        for _ in range(len(airfoil.spar.x)):
+            x = (airfoil.spar.x[_])
+            y = (airfoil.spar.z[_])
+            ax.plot(x, y, '-', color='y', linewidth='4')
+    except AttributeError:
+        print('No spars to plot.')
+    # Plot stringers
+    try:
+        for _ in range(0, len(airfoil.stringer.x)):
+            x = airfoil.stringer.x[_]
+            y = airfoil.stringer.z[_]
+            ax.plot(x, y, '.', color='y', markersize=12)
+    except AttributeError:
+        print('No stringers to plot.')
+
+    # Graph formatting
+    plot_bound = max(airfoil.x)
+    ax.set(title='NACA ' + str(airfoil.naca_num) + ' airfoil',
+           xlabel='X axis',
+           xlim=[- 0.10 * plot_bound, 1.10 * plot_bound],
+           ylabel='Z axis',
+           ylim=[- (1.10 * plot_bound / 2), (1.10 * plot_bound / 2)])
+
+    plt.grid(axis='both', linestyle=':', linewidth=1)
+    plt.gca().set_aspect('equal', adjustable='box')
+    plt.gca().legend(bbox_to_anchor=(1, 1),
+                     bbox_transform=plt.gcf().transFigure)
+
+    if view == True:
+        plt.show()
+    else:
+        pass
+    return fig, ax
+
+
+def main():
+    return None
+
+
+if __name__ == '__main__':
+    main()