FreeFormFin Class#

class rocketpy.FreeFormFin[source]#

Class that defines and holds information for a free form fin set.

This class inherits from the Fin class.

Note

Local coordinate system:

  • Origin located at the top of the root chord.

  • Z axis along the longitudinal axis of symmetry, positive downwards (top -> bottom).

  • Y axis perpendicular to the Z axis, in the span direction, positive upwards.

  • X axis completes the right-handed coordinate system.

See also

Fin

Variables:

  • FreeFormFin.n (int) – Number of fins in fin set.

  • FreeFormFin.rocket_radius (float) – The reference rocket radius used for lift coefficient normalization, in meters.

  • FreeFormFin.airfoil (tuple) – Tuple of two items. First is the airfoil lift curve. Second is the unit of the curve (radians or degrees).

  • FreeFormFin.cant_angle (float) – Fins cant angle with respect to the rocket centerline, in degrees.

  • FreeFormFin.cant_angle_rad (float) – Fins cant angle with respect to the rocket centerline, in radians.

  • FreeFormFin.root_chord (float) – Fin root chord in meters.

  • FreeFormFin.span (float) – Fin span in meters.

  • FreeFormFin.name (string) – Name of fin set.

  • FreeFormFin.rocket_diameter (float) – Reference diameter of the rocket, in meters.

  • FreeFormFin.reference_area (float) – Reference area of the rocket, in m².

  • FreeFormFin.Af (float) – Area of the longitudinal section of each fin in the set.

  • FreeFormFin.AR (float) – Aspect ratio of the fin.

  • FreeFormFin.gamma_c (float) – Fin mid-chord sweep angle.

  • FreeFormFin.Yma (float) – Span wise position of the mean aerodynamic chord.

  • FreeFormFin.roll_geometrical_constant (float) – Geometrical constant used in roll calculations.

  • FreeFormFin.tau (float) – Geometrical relation used to simplify lift and roll calculations.

  • FreeFormFin.lift_interference_factor (float) – Factor of Fin-Body interference in the lift coefficient.

  • FreeFormFin.cp (tuple) – Tuple with the x, y and z local coordinates of the fin set center of pressure. Has units of length and is given in meters.

  • FreeFormFin.cpx (float) – Fin set local center of pressure x coordinate. Has units of length and is given in meters.

  • FreeFormFin.cpy (float) – Fin set local center of pressure y coordinate. Has units of length and is given in meters.

  • FreeFormFin.cpz (float) – Fin set local center of pressure z coordinate. Has units of length and is given in meters.

  • FreeFormFin.cl (Function) – Function which defines the lift coefficient as a function of the angle of attack and the Mach number. Takes as input the angle of attack in radians and the Mach number. Returns the lift coefficient.

  • FreeFormFin.clalpha (float) – Lift coefficient slope. Has units of 1/rad.

  • FreeFormFin.mac_length (float) – Mean aerodynamic chord length of the fin set.

  • FreeFormFin.mac_lead (float) – Mean aerodynamic chord leading edge x coordinate.

__init__(angular_position, shape_points, rocket_radius, cant_angle=0, airfoil=None, name='Free Form Fin')[source]#

Initialize FreeFormFin class.

Parameters:

  • angular_position (float) – Angular position of the fin in degrees measured as the rotation around the symmetry axis of the rocket relative to one of the other principal axis. See Angular Position Inputs

  • shape_points (list) – List of tuples (x, y) containing the coordinates of the fin’s geometry defining points. The point (0, 0) is the root leading edge. Positive x is rearwards, positive y is upwards (span direction). The shape will be interpolated between the points, in the order they are given. The last point connects to the first point, and represents the trailing edge.

  • rocket_radius (int, float) – Reference radius to calculate lift coefficient, in meters.

  • cant_angle (int, float, optional) – Fins cant angle with respect to the rocket centerline. Must be given in degrees.

  • airfoil (tuple, optional) – Default is null, in which case fins will be treated as flat plates. Otherwise, if tuple, fins will be considered as airfoils. The tuple’s first item specifies the airfoil’s lift coefficient by angle of attack and must be either a .csv, .txt, ndarray or callable. The .csv and .txt files can contain a single line header and the first column must specify the angle of attack, while the second column must specify the lift coefficient. The ndarray should be as [(x0, y0), (x1, y1), (x2, y2), …] where x0 is the angle of attack and y0 is the lift coefficient. If callable, it should take an angle of attack as input and return the lift coefficient at that angle of attack. The tuple’s second item is the unit of the angle of attack, accepting either “radians” or “degrees”.

  • name (str) – Name of the free form fin.

Return type:

None

evaluate_center_of_pressure()[source]#

Calculates and returns the center of pressure of the fin in local coordinates. The center of pressure position is saved and stored as a tuple.

Return type:

None