ENH: add option to enter sweep angle in Rocket.addTrapezoidalFins

rocketpy/Rocket.py

@@ -483,6 +483,7 @@ def addTrapezoidalFins(
         distanceToCM,
         cantAngle=0,
         sweepLength=None,
+        sweepAngle=None,
         radius=None,
         airfoil=None,
     ):
@@ -514,6 +515,13 @@ def addTrapezoidalFins(
             parallel to the rocket centerline. If not given, the sweep length is
             assumed to be equal the root chord minus the tip chord, in which case the
             fin is a right trapezoid with its base perpendicular to the rocket's axis.
+            Cannot be used in conjunction with sweepAngle.
+        sweepAngle : int, float, optional
+            Fins sweep angle with respect to the rocket centerline. Must
+            be given in degrees. If not given, the sweep angle is automatically
+            calculated, in which case the fin is assumed to be a right trapezoid with
+            its base perpendicular to the rocket's axis.
+            Cannot be used in conjunction with sweepLength.
         radius : int, float, optional
             Reference radius to calculate lift coefficient. If None, which
             is default, use rocket radius. Otherwise, enter the radius
@@ -545,11 +553,21 @@ def addTrapezoidalFins(
         """
         # Retrieves and convert basic geometrical parameters
         Cr, Ct = rootChord, tipChord
-        sweepLength = Cr - Ct if sweepLength is None else sweepLength
         s = span
         radius = self.radius if radius is None else radius
         cantAngleRad = np.radians(cantAngle)
 
+        # Check if sweep angle or sweep length is given
+        if sweepLength is not None and sweepAngle is not None:
+            raise ValueError("Cannot use sweepLength and sweepAngle together")
+        elif sweepAngle is not None:
+            sweepLength = np.tan(sweepAngle * np.pi / 180) * span
+        elif sweepLength is None:
+            sweepLength = Cr - Ct
+        else:
+            # Sweep length is given
+            pass
+
         # Compute auxiliary geometrical parameters
         d = 2 * radius
         Aref = np.pi * radius**2