Enh/parachute

rocketpy/__init__.py

@@ -41,3 +41,4 @@
 from .SolidMotor import SolidMotor
 from .Rocket import Rocket
 from .Flight import Flight
+from .utilities import *

rocketpy/utilities.py

@@ -0,0 +1,35 @@
+# -*- coding: utf-8 -*-
+
+__author__ = "Franz Masatoshi Yuri"
+__copyright__ = "Copyright 20XX, Projeto Jupiter"
+__license__ = "MIT"
+
+
+def compute_CdS_from_drop_test(
+    terminal_velocity, rocket_mass, air_density=1.225, gravity=9.80665
+):
+    """Returns the parachute's CdS calculated through its final speed, air
+    density in the landing point, the rocket's mass and the force of gravity
+    in the landing point.
+
+    Parameters
+    ----------
+    terminal_velocity : float
+        Rocket's speed in m/s when landing.
+    rocket_mass : float
+        Rocket's mass in kg.
+    air_density : float, optional
+        Air density, in kg/m^3, right before the rocket lands. Default value is 1.225.
+    gravity : float, optional
+        Gravitational acceleration experienced by the rocket and parachute during
+        descent in m/s^2. Default value is the standard gravity, 9.80665.
+
+    Returns
+    -------
+    CdS : float
+        Number equal to drag coefficient times reference area for parachute.
+
+    """
+
+    CdS = 2 * rocket_mass * gravity / ((terminal_velocity ** 2) * air_density)
+    return CdS

tests/test_utilities.py

@@ -0,0 +1,4 @@
+from rocketpy import utilities
+
+def test_compute_CdS_from_drop_test():
+    assert utilities.compute_CdS_from_drop_test(31.064,18,1.0476) == 0.3492311157844522