Source code for rocketpy.rocket.aero_surface.fins.free_form_fins
from rocketpy.plots.aero_surface_plots import _FreeFormFinsPlots
from rocketpy.prints.aero_surface_prints import _FreeFormFinsPrints
from rocketpy.rocket.aero_surface.fins._geometry import _FreeFormGeometry
from .fins import Fins
[docs]
class FreeFormFins(Fins):
"""Class that defines and holds information for a free form fin set.
This class inherits from the Fins 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
--------
Fins
Attributes
----------
FreeFormFins.n : int
Number of fins in fin set.
FreeFormFins.rocket_radius : float
The reference rocket radius used for lift coefficient normalization, in
meters.
FreeFormFins.airfoil : tuple
Tuple of two items. First is the airfoil lift curve.
Second is the unit of the curve (radians or degrees).
FreeFormFins.cant_angle : float
Fins cant angle with respect to the rocket centerline, in degrees.
FreeFormFins.cant_angle_rad : float
Fins cant angle with respect to the rocket centerline, in radians.
FreeFormFins.root_chord : float
Fin root chord in meters.
FreeFormFins.span : float
Fin span in meters.
FreeFormFins.name : string
Name of fin set.
FreeFormFins.rocket_diameter : float
Reference diameter of the rocket, in meters.
FreeFormFins.reference_area : float
Reference area of the rocket, in m².
FreeFormFins.Af : float
Area of the longitudinal section of each fin in the set.
FreeFormFins.AR : float
Aspect ratio of each fin in the set
FreeFormFins.gamma_c : float
Fin mid-chord sweep angle.
FreeFormFins.Yma : float
Span wise position of the mean aerodynamic chord.
FreeFormFins.roll_geometrical_constant : float
Geometrical constant used in roll calculations.
FreeFormFins.tau : float
Geometrical relation used to simplify lift and roll calculations.
FreeFormFins.lift_interference_factor : float
Factor of Fin-Body interference in the lift coefficient.
FreeFormFins.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.
FreeFormFins.cpx : float
Fin set local center of pressure x coordinate. Has units of length and
is given in meters.
FreeFormFins.cpy : float
Fin set local center of pressure y coordinate. Has units of length and
is given in meters.
FreeFormFins.cpz : float
Fin set local center of pressure z coordinate. Has units of length and
is given in meters.
FreeFormFins.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.
FreeFormFins.clalpha : float
Lift coefficient slope. Has units of 1/rad.
FreeFormFins.mac_length : float
Mean aerodynamic chord length of the fin set.
FreeFormFins.mac_lead : float
Mean aerodynamic chord leading edge x coordinate.
"""
[docs]
def __init__(
self,
n,
shape_points,
rocket_radius,
cant_angle=0,
airfoil=None,
name="Fins",
):
"""Initialize FreeFormFins class.
Parameters
----------
n : int
Number of fins, must be larger than 2.
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 fin set.
Returns
-------
None
"""
root_chord, span = _FreeFormGeometry.infer_dimensions(shape_points)
super().__init__(
n,
root_chord,
span,
rocket_radius,
cant_angle,
airfoil,
name,
)
self.geometry = _FreeFormGeometry(self, shape_points)
self._update_geometry_chain()
self.evaluate_shape()
self.prints = _FreeFormFinsPrints(self)
self.plots = _FreeFormFinsPlots(self)
[docs]
def evaluate_center_of_pressure(self):
"""Calculates and returns the center of pressure of the fin set in local
coordinates. The center of pressure position is saved and stored as a
tuple.
Returns
-------
None
"""
# Center of pressure position in local coordinates
cpz = self.mac_lead + 0.25 * self.mac_length
self.cpx = 0
self.cpy = 0
self.cpz = cpz
self.cp = (self.cpx, self.cpy, self.cpz)
@property
def shape_points(self):
return self.geometry.shape_points
def to_dict(self, **kwargs):
data = super().to_dict(**kwargs)
data.update(
self.geometry.get_data(include_outputs=kwargs.get("include_outputs", False))
)
return data
@classmethod
def from_dict(cls, data):
return cls(
n=data["n"],
shape_points=data["shape_points"],
rocket_radius=data["rocket_radius"],
cant_angle=data["cant_angle"],
airfoil=data["airfoil"],
name=data["name"],
)