ENH: change of variables between rocket and motor

rocketpy/Motor.py

@@ -115,6 +115,7 @@ def __init__(
         self,
         thrustSource,
         burnOut,
+        distanceNozzlePropellant,
         nozzleRadius=0.0335,
         throatRadius=0.0114,
         reshapeThrustCurve=False,
@@ -137,6 +138,12 @@ def __init__(
             Function. See help(Function). Thrust units are Newtons.
         burnOut : int, float
             Motor burn out time in seconds.
+        distanceNozzlePropellant : int, float
+            Distance from nozzle outlet to the motor reference point, which
+            for Solids and Hybrids is the center of mass of the solid propellant,
+            in meters. Generally positive, meaning a positive position in the
+            z axis which has an origin in the rocket's center of mass (without
+            propellant) and points towards the nose cone.
         nozzleRadius : int, float, optional
             Motor's nozzle outlet radius in meters. Used to calculate Kn curve.
             Optional if the Kn curve is not interesting. Its value does not impact
@@ -166,6 +173,9 @@ def __init__(
         self.interpolate = interpolationMethod
         self.burnOutTime = burnOut
 
+        # Geometric parameters
+        self.distanceNozzlePropellant = distanceNozzlePropellant
+
         # Check if thrustSource is csv, eng, function or other
         if isinstance(thrustSource, str):
             # Determine if csv or eng
@@ -275,7 +285,8 @@ def reshapeThrustCurve(
         # Reshape thrust - set total impulse
         if oldTotalImpulse is None:
             oldTotalImpulse = self.evaluateTotalImpulse()
-        self.thrust.source[:, 1] = (totalImpulse / oldTotalImpulse) * thrustArray
+        self.thrust.source[:, 1] = (
+            totalImpulse / oldTotalImpulse) * thrustArray
         self.thrust.setInterpolation(self.interpolate)
 
         # Store total impulse
@@ -472,7 +483,8 @@ def importEng(self, fileName):
                         description = line.strip().split(" ")
                     else:
                         # Extract thrust curve data points
-                        time, thrust = re.findall(r"[-+]?\d*\.\d+|[-+]?\d+", line)
+                        time, thrust = re.findall(
+                            r"[-+]?\d*\.\d+|[-+]?\d+", line)
                         dataPoints.append([float(time), float(thrust)])
 
         # Return all extract content
@@ -589,7 +601,8 @@ def allInfo(self):
         print("Grain Outer Radius: " + str(self.grainOuterRadius) + " m")
         print("Grain Inner Radius: " + str(self.grainInitialInnerRadius) + " m")
         print("Grain Height: " + str(self.grainInitialHeight) + " m")
-        print("Grain Volume: " + "{:.3f}".format(self.grainInitialVolume) + " m3")
+        print("Grain Volume: " +
+              "{:.3f}".format(self.grainInitialVolume) + " m3")
         print("Grain Mass: " + "{:.3f}".format(self.grainInitialMass) + " kg")
 
         # Print motor details
@@ -724,6 +737,7 @@ def __init__(
         self,
         thrustSource,
         burnOut,
+        distanceNozzlePropellant,
         grainNumber,
         grainDensity,
         grainOuterRadius,
@@ -793,6 +807,9 @@ def __init__(
         self.interpolate = interpolationMethod
         self.burnOutTime = burnOut
 
+        # Geometric parameters
+        self.distanceNozzlePropellant = distanceNozzlePropellant
+
         # Check if thrustSource is csv, eng, function or other
         if isinstance(thrustSource, str):
             # Determine if csv or eng
@@ -973,9 +990,11 @@ def geometryDot(y, t):
             grainMassDot = self.massDot(t) / self.grainNumber
             rI, h = y
             rIDot = (
-                -0.5 * grainMassDot / (density * np.pi * (rO**2 - rI**2 + rI * h))
+                -0.5 * grainMassDot /
+                    (density * np.pi * (rO**2 - rI**2 + rI * h))
             )
-            hDot = 1.0 * grainMassDot / (density * np.pi * (rO**2 - rI**2 + rI * h))
+            hDot = 1.0 * grainMassDot / \
+                (density * np.pi * (rO**2 - rI**2 + rI * h))
             return [rIDot, hDot]
 
         # Solve the system of differential equations
@@ -1045,7 +1064,8 @@ def evaluateBurnRate(self):
         burnRate : Function
         Rate of progression of the inner radius during the combustion.
         """
-        self.burnRate = (-1) * self.massDot / (self.burnArea * self.grainDensity)
+        self.burnRate = (-1) * self.massDot / \
+            (self.burnArea * self.grainDensity)
         self.burnRate.setOutputs("Burn Rate (m/s)")
         return self.burnRate
 
@@ -1253,7 +1273,8 @@ def allInfo(self):
         print("Grain Outer Radius: " + str(self.grainOuterRadius) + " m")
         print("Grain Inner Radius: " + str(self.grainInitialInnerRadius) + " m")
         print("Grain Height: " + str(self.grainInitialHeight) + " m")
-        print("Grain Volume: " + "{:.3f}".format(self.grainInitialVolume) + " m3")
+        print("Grain Volume: " +
+              "{:.3f}".format(self.grainInitialVolume) + " m3")
         print("Grain Mass: " + "{:.3f}".format(self.grainInitialMass) + " kg")
 
         # Print motor details
@@ -1388,14 +1409,15 @@ def __init__(
         self,
         thrustSource,
         burnOut,
+        distanceNozzlePropellant,
         grainNumber,
         grainDensity,
         grainOuterRadius,
         grainInitialInnerRadius,
         grainInitialHeight,
         oxidizerTankRadius,
         oxidizerTankHeight,
-        oxidizerInitialPresure,
+        oxidizerInitialPressure,
         oxidizerDensity,
         oxidizerMolarMass,
         oxidizerInitialVolume,
@@ -1438,10 +1460,10 @@ def __init__(
             Oxidizer Tank inner radius.
         oxidizerTankHeight :
             Oxidizer Tank Height.
-        oxidizerInitialPresure :
-            Initial presure of the oxidizer tank, could be equal to the pressure of the source cylinder in atm.
+        oxidizerInitialPressure :
+            Initial pressure of the oxidizer tank, could be equal to the pressure of the source cylinder in atm.
         oxidizerDensity :
-            Oxidizer theoretical density in liquit state, for N2O is equal to 1.98 (Kg/m^3).
+            Oxidizer theoretical density in liquid state, for N2O is equal to 1.98 (Kg/m^3).
         oxidizerMolarMass :
             Oxidizer molar mass, for the N2O is equal to 44.01 (g/mol).
         oxidizerInitialVolume :
@@ -1481,6 +1503,9 @@ def __init__(
         self.interpolate = interpolationMethod
         self.burnOutTime = burnOut
 
+        # Geometric parameters
+        self.distanceNozzlePropellant = distanceNozzlePropellant
+
         # Check if thrustSource is csv, eng, function or other
         if isinstance(thrustSource, str):
             # Determine if csv or eng
@@ -1519,6 +1544,7 @@ def __init__(
         # Grain and nozzle parameters
         self.nozzleRadius = nozzleRadius
         self.throatRadius = throatRadius
+        # Propellant parameters
         self.grainNumber = grainNumber
         self.grainSeparation = grainSeparation
         self.grainDensity = grainDensity
@@ -1527,7 +1553,7 @@ def __init__(
         self.grainInitialHeight = grainInitialHeight
         self.oxidizerTankRadius = oxidizerTankRadius
         self.oxidizerTankHeight = oxidizerTankHeight
-        self.oxidizerInitialPresure = oxidizerInitialPresure
+        self.oxidizerInitialPressure = oxidizerInitialPressure
         self.oxidizerDensity = oxidizerDensity
         self.oxidizerMolarMass = oxidizerMolarMass
         self.oxidizerInitialVolume = oxidizerInitialVolume
@@ -1675,9 +1701,11 @@ def geometryDot(y, t):
             grainMassDot = self.massDot(t) / self.grainNumber
             rI, h = y
             rIDot = (
-                -0.5 * grainMassDot / (density * np.pi * (rO**2 - rI**2 + rI * h))
+                -0.5 * grainMassDot /
+                    (density * np.pi * (rO**2 - rI**2 + rI * h))
             )
-            hDot = 1.0 * grainMassDot / (density * np.pi * (rO**2 - rI**2 + rI * h))
+            hDot = 1.0 * grainMassDot / \
+                (density * np.pi * (rO**2 - rI**2 + rI * h))
             return [rIDot, hDot]
 
         # Solve the system of differential equations
@@ -1747,7 +1775,8 @@ def evaluateBurnRate(self):
         burnRate : Function
         Rate of progression of the inner radius during the combustion.
         """
-        self.burnRate = (-1) * self.massDot / (self.burnArea * self.grainDensity)
+        self.burnRate = (-1) * self.massDot / \
+            (self.burnArea * self.grainDensity)
         self.burnRate.setOutputs("Burn Rate (m/s)")
         return self.burnRate
 

rocketpy/Rocket.py

@@ -40,10 +40,11 @@ class Rocket:
         Rocket.distanceRocketNozzle : float
             Distance between rocket's center of mass, without propellant,
             to the exit face of the nozzle, in meters. Always positive.
-        Rocket.distanceRocketPropellant : float
+        Rocket.distanceRocketMotorReference : float
             Distance between rocket's center of mass, without propellant,
-            to the motor reference point, which for solid and hybrid motors
-            is the center of mass of solid propellant, in meters. Always positive.
+            to the motor reference point, for solid and hybrid motor
+            the reference point is the center of mass of solid propellant,
+            in meters. Always positive.
 
         Mass and Inertia attributes:
         Rocket.mass : float
@@ -113,7 +114,6 @@ def __init__(
         inertiaZ,
         radius,
         distanceRocketNozzle,
-        distanceRocketPropellant,
         powerOffDrag,
         powerOnDrag,
     ):
@@ -125,12 +125,12 @@ def __init__(
         motor : Motor
             Motor used in the rocket. See Motor class for more information.
         mass : int, float
-            Unloaded rocket total mass (without propelant) in kg.
+            Unloaded rocket total mass (without propellant) in kg.
         inertiaI : int, float
             Unloaded rocket lateral (perpendicular to axis of symmetry)
-            moment of inertia (without propelant) in kg m^2.
+            moment of inertia (without propellant) in kg m^2.
         inertiaZ : int, float
-            Unloaded rocket axial moment of inertia (without propelant)
+            Unloaded rocket axial moment of inertia (without propellant)
             in kg m^2.
         radius : int, float
             Rocket biggest outer radius in meters.
@@ -139,12 +139,12 @@ def __init__(
             in meters. Generally negative, meaning a negative position in the
             z axis which has an origin in the rocket's center of mass (without
             propellant) and points towards the nose cone.
-        distanceRocketPropellant : int, float
+        distanceRocketMotorReference : int, float
             Distance from rocket's unloaded center of mass to the motor reference
-            point, which for solid and hybrid motor the is the center of mass of
-            solid propellant, in meters. Generally negative, meaning a negative
-            position in the z axis which has an origin in the rocket's center of
-            mass (with out propellant) and points towards the nose cone.
+            point, for solid and hybrid motor the reference point is the center
+            of mass of solid propellant, in meters. Generally negative, meaning a negative
+            position in the z axis which has an origin in the rocket's center
+            of mass (with out propellant) and points towards the nose cone.
         powerOffDrag : int, float, callable, string, array
             Rocket's drag coefficient when the motor is off. Can be given as an
             entry to the Function class. See help(Function) for more
@@ -162,22 +162,30 @@ def __init__(
         -------
         None
         """
+        # Define motor to be used
+        self.motor = motor
+
+        # Center of mass distance to points of interest
+        self.distanceRocketNozzle = distanceRocketNozzle
+        self.distanceRocketMotorReference = (
+            self.distanceRocketNozzle + self.motor.distanceNozzlePropellant
+        )
+
         # Define rocket inertia attributes in SI units
         self.mass = mass
         self.inertiaI = inertiaI
         self.inertiaZ = inertiaZ
+
         self.centerOfMass = (
-            (distanceRocketPropellant - motor.yCM) * motor.mass / (mass + motor.mass)
+            (self.distanceRocketMotorReference - self.motor.yCM)
+            * motor.mass
+            / (mass + motor.mass)
         )
 
         # Define rocket geometrical parameters in SI units
         self.radius = radius
         self.area = np.pi * self.radius**2
 
-        # Center of mass distance to points of interest
-        self.distanceRocketNozzle = distanceRocketNozzle
-        self.distanceRocketPropellant = distanceRocketPropellant
-
         # Eccentricity data initialization
         self.cpEccentricityX = 0
         self.cpEccentricityY = 0
@@ -213,9 +221,6 @@ def __init__(
             "constant",
         )
 
-        # Define motor to be used
-        self.motor = motor
-
         # Important dynamic inertial quantities
         self.reducedMass = None
         self.totalMass = None
@@ -963,7 +968,7 @@ def allInfo(self):
         )
         print(
             "Rocket Center of Mass - Motor reference point: "
-            + str(self.distanceRocketPropellant)
+            + str(self.distanceRocketMotorReference)
             + " m"
         )
         print(