start packagification

3 files changed, 768 insertions, 0 deletions

diff --git a/tools/creator.py b/tools/creator.py
new file mode 100644
index 0000000..810df09
--- /dev/null
+++ b/tools/creator.py
@@ -0,0 +1,416 @@
+# 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()
diff --git a/tools/evaluator.py b/tools/evaluator.py
new file mode 100644
index 0000000..ad1f873
--- /dev/null
+++ b/tools/evaluator.py
@@ -0,0 +1,288 @@
+# 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 evaluator.py module contains a single Evaluator class,
+which knows all the attributes of a specified Airfoil instance,
+and contains functions to analyse the airfoil's geometrical
+& structural properties.
+"""
+
+import sys
+import os.path
+import numpy as np
+from math import sqrt
+import matplotlib.pyplot as plt
+
+
+class Evaluator:
+    """Performs structural evaluations for the airfoil passed as argument."""
+
+    def __init__(self, airfoil):
+        # Evaluator knows all geometrical info from evaluated airfoil
+        self.airfoil = airfoil
+        self.spar = airfoil.spar
+        self.stringer = airfoil.stringer
+        # Global dimensions
+        self.chord = airfoil.chord
+        self.semi_span = airfoil.semi_span
+        # Mass & spanwise distribution
+        self.mass_total = float(airfoil.mass
+                                + airfoil.spar.mass
+                                + airfoil.stringer.mass)
+        self.mass_dist = []
+        # Lift
+        self.lift_rectangular = []
+        self.lift_elliptical = []
+        self.lift_total = []
+        # Drag
+        self.drag = []
+        # centroid
+        self.centroid = []
+        # Inertia terms:
+        self.I_ = {'x': 0, 'z': 0, 'xz': 0}
+
+    def __str__(self):
+        return type(self).__name__
+
+    def info_print(self, round):
+        """Print all the component's evaluated data to the terminal."""
+        name = '    EVALUATOR 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 = 'airfoil_{}_eval.txt'.format(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
+
+    # All these functions take integer arguments and return lists.
+
+    def get_lift_rectangular(self, lift):
+        L_prime = [lift / (self.semi_span * 2) for x in range(self.semi_span)]
+        return L_prime
+
+    def get_lift_elliptical(self, L_0):
+        L_prime = [
+            L_0 / (self.semi_span * 2) * sqrt(1 - (y / self.semi_span)**2)
+            for y in range(self.semi_span)
+        ]
+        return L_prime
+
+    def get_lift_total(self):
+        F_z = [(self.lift_rectangular[_] + self.lift_elliptical[_]) / 2
+               for _ in range(len(self.lift_rectangular))]
+        return F_z
+
+    def get_mass_distribution(self, total_mass):
+        F_z = [total_mass / self.semi_span for x in range(0, self.semi_span)]
+        return F_z
+
+    def get_drag(self, drag):
+        # Transform semi-span integer into list
+        semi_span = [x for x in range(0, self.semi_span)]
+
+        # Drag increases after 80% of the semi_span
+        cutoff = round(0.8 * self.semi_span)
+
+        # Drag increases by 25% after 80% of the semi_span
+        F_x = [drag for x in semi_span[0:cutoff]]
+        F_x.extend([1.25 * drag for x in semi_span[cutoff:]])
+        return F_x
+
+    def get_centroid(self):
+        """Return the coordinates of the centroid."""
+        stringer_area = self.stringer.area
+        cap_area = self.spar.cap_area
+
+        caps_x = [value for spar in self.spar.x for value in spar]
+        caps_z = [value for spar in self.spar.z for value in spar]
+        stringers_x = self.stringer.x
+        stringers_z = self.stringer.z
+
+        denominator = float(len(caps_x) * cap_area
+                            + len(stringers_x) * stringer_area)
+
+        centroid_x = float(sum([x * cap_area for x in caps_x])
+                           + sum([x * stringer_area for x in stringers_x]))
+        centroid_x = centroid_x / denominator
+
+        centroid_z = float(sum([z * cap_area for z in caps_z])
+                           + sum([z * stringer_area for z in stringers_z]))
+        centroid_z = centroid_z / denominator
+
+        return (centroid_x, centroid_z)
+
+    def get_inertia_terms(self):
+        """Obtain all inertia terms."""
+        stringer_area = self.stringer.area
+        cap_area = self.spar.cap_area
+
+        # Adds upper and lower components' coordinates to list
+        x_stringers = self.stringer.x
+        z_stringers = self.stringer.z
+        x_spars = self.spar.x[:][0] + self.spar.x[:][1]
+        z_spars = self.spar.z[:][0] + self.spar.z[:][1]
+        stringer_count = range(len(x_stringers))
+        spar_count = range(len(self.spar.x))
+
+        # I_x is the sum of the contributions of the spar caps and stringers
+        # TODO: replace list indices with dictionary value
+        I_x = sum([cap_area * (z_spars[i] - self.centroid[1])**2
+                   for i in spar_count])
+        I_x += sum([stringer_area * (z_stringers[i] - self.centroid[1])**2
+                    for i in stringer_count])
+
+        I_z = sum([cap_area * (x_spars[i] - self.centroid[0])**2
+                   for i in spar_count])
+        I_z += sum([stringer_area * (x_stringers[i] - self.centroid[0])**2
+                    for i in stringer_count])
+
+        I_xz = sum([cap_area * (x_spars[i] - self.centroid[0])
+                    * (z_spars[i] - self.centroid[1])
+                    for i in spar_count])
+        I_xz += sum([stringer_area * (x_stringers[i] - self.centroid[0])
+                     * (z_stringers[i] - self.centroid[1])
+                     for i in stringer_count])
+        return (I_x, I_z, I_xz)
+
+    def get_dx(self, component):
+        return [x - self.centroid[0] for x in component.x_start]
+
+    def get_dz(self, component):
+        return [x - self.centroid[1] for x in component.x_start]
+
+    def get_dP(self, xDist, zDist, V_x, V_z, area):
+        I_x = self.I_['x']
+        I_z = self.I_['z']
+        I_xz = self.I_['xz']
+        denom = float(I_x * I_z - I_xz ** 2)
+        z = float()
+        for _ in range(len(xDist)):
+            z += float(-area * xDist[_] * (I_x * V_x - I_xz * V_z)
+                       / denom
+                       - area * zDist[_] * (I_z * V_z - I_xz * V_x)
+                       / denom)
+        return z
+
+    def analysis(self, V_x, V_z):
+        """Perform all analysis calculations and store in class instance."""
+        self.drag = self.get_drag(10)
+        self.lift_rectangular = self.get_lift_rectangular(13.7)
+        self.lift_elliptical = self.get_lift_elliptical(15)
+        self.lift_total = self.get_lift_total()
+        self.mass_dist = self.get_mass_distribution(self.mass_total)
+        self.centroid = self.get_centroid()
+        self.I_['x'] = self.get_inertia_terms()[0]
+        self.I_['z'] = self.get_inertia_terms()[1]
+        self.I_['xz'] = self.get_inertia_terms()[2]
+        spar_dx = self.get_dx(self.spar)
+        spar_dz = self.get_dz(self.spar)
+        self.spar.dP_x = self.get_dP(spar_dx, spar_dz,
+                                     V_x, 0, self.spar.cap_area)
+        self.spar.dP_z = self.get_dP(spar_dx, spar_dz,
+                                     0, V_z, self.spar.cap_area)
+        return None
+
+
+def plot_geom(evaluator):
+    """This function plots analysis results over the airfoil's geometry."""
+    # Plot chord
+    x_chord = [0, evaluator.chord]
+    y_chord = [0, 0]
+    plt.plot(x_chord, y_chord, linewidth='1')
+    # Plot quarter chord
+    plt.plot(evaluator.chord / 4, 0,
+             '.', color='g', markersize=24, label='Quarter-chord')
+    # Plot airfoil surfaces
+    x = [0.98 * x for x in evaluator.airfoil.x]
+    y = [0.98 * z for z in evaluator.airfoil.z]
+    plt.fill(x, y, color='w', linewidth='1', fill=False)
+    x = [1.02 * x for x in evaluator.airfoil.x]
+    y = [1.02 * z for z in evaluator.airfoil.z]
+    plt.fill(x, y, color='b', linewidth='1', fill=False)
+
+    # Plot spars
+    try:
+        for _ in range(len(evaluator.spar.x)):
+            x = (evaluator.spar.x[_])
+            y = (evaluator.spar.z[_])
+            plt.plot(x, y, '-', color='b')
+    except AttributeError:
+        print('No spars to plot.')
+    # Plot stringers
+    try:
+        for _ in range(0, len(evaluator.stringer.x)):
+            x = evaluator.stringer.x[_]
+            y = evaluator.stringer.z[_]
+            plt.plot(x, y, '.', color='y', markersize=12)
+    except AttributeError:
+        print('No stringers to plot.')
+
+    # Plot centroid
+    x = evaluator.centroid[0]
+    y = evaluator.centroid[1]
+    plt.plot(x, y, '.', color='r', markersize=24, label='centroid')
+
+    # Graph formatting
+    plt.xlabel('X axis')
+    plt.ylabel('Z axis')
+
+    plot_bound = max(evaluator.airfoil.x)
+    plt.xlim(-0.10 * plot_bound, 1.10 * plot_bound)
+    plt.ylim(-(1.10 * plot_bound / 2), (1.10 * plot_bound / 2))
+    plt.gca().set_aspect('equal', adjustable='box')
+    plt.gca().legend()
+    plt.grid(axis='both', linestyle=':', linewidth=1)
+    plt.show()
+    return None
+
+
+def plot_lift(evaluator):
+    x = range(evaluator.semi_span)
+    y_1 = evaluator.lift_rectangular
+    y_2 = evaluator.lift_elliptical
+    y_3 = evaluator.lift_total
+    plt.plot(x, y_1, '.', color='b', markersize=4, label='Rectangular lift')
+    plt.plot(x, y_2, '.', color='g', markersize=4, label='Elliptical lift')
+    plt.plot(x, y_3, '.', color='r', markersize=4, label='Total lift')
+
+    # Graph formatting
+    plt.xlabel('Semi-span location')
+    plt.ylabel('Lift')
+
+    plt.gca().legend()
+    plt.grid(axis='both', linestyle=':', linewidth=1)
+    plt.show()
+    return None
diff --git a/tools/generator.py b/tools/generator.py
new file mode 100644
index 0000000..0213828
--- /dev/null
+++ b/tools/generator.py
@@ -0,0 +1,64 @@
+# 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 generator.py module contains a single Population class,
+which represents a collection of randomized airfoils.
+"""
+
+from tools import creator
+
+
+def default_airfoil():
+    """Generate the default airfoil."""
+    airfoil = creator.Airfoil.from_dimensions(100, 200)
+    airfoil.add_naca(2412)
+    airfoil.add_mass(10)
+
+    airfoil.spar = creator.Spar()
+    airfoil.spar.add_coord(airfoil, 0.23)
+    airfoil.spar.add_coord(airfoil, 0.57)
+    airfoil.spar.add_spar_caps(0.3)
+    airfoil.spar.add_mass(10)
+    airfoil.spar.add_webs(0.4)
+
+    airfoil.stringer = creator.Stringer()
+    airfoil.stringer.add_coord(airfoil, 3, 6, 5, 4)
+    airfoil.stringer.add_area(0.1)
+    airfoil.stringer.add_mass(5)
+    airfoil.stringer.add_webs(0.1)
+
+    return airfoil
+
+
+class Population(creator.Airfoil):
+    """Collection of random airfoils."""
+
+    def __init__(self, size):
+        af = creator.Airfoil
+        # print(af)
+        self.size = size
+        self.gen_number = 0  # incremented for every generation
+
+    def mutate(self, prob_mt):
+        """Randomly mutate the genes of prob_mt % of the population."""
+
+    def crossover(self, prob_cx):
+        """Combine the genes of prob_cx % of the population."""
+
+    def reproduce(self, prob_rp):
+        """Pass on the genes of the fittest prob_rp % of the population."""
+
+    def fitness():
+        """Rate the fitness of an individual on a relative scale (0-100)"""