import numpy as np
from rocketpy.plots.aero_surface_plots import _TrapezoidalFinsPlots
from rocketpy.prints.aero_surface_prints import _TrapezoidalFinsPrints
from .fins import Fins
[docs]
class TrapezoidalFins(Fins):
"""Class that defines and holds information for a trapezoidal 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
----------
TrapezoidalFins.n : int
Number of fins in fin set.
TrapezoidalFins.rocket_radius : float
The reference rocket radius used for lift coefficient normalization, in
meters.
TrapezoidalFins.airfoil : tuple
Tuple of two items. First is the airfoil lift curve.
Second is the unit of the curve (radians or degrees).
TrapezoidalFins.cant_angle : float
Fins cant angle with respect to the rocket centerline, in degrees.
TrapezoidalFins.changing_attribute_dict : dict
Dictionary that stores the name and the values of the attributes that
may be changed during a simulation. Useful for control systems.
TrapezoidalFins.cant_angle_rad : float
Fins cant angle with respect to the rocket centerline, in radians.
TrapezoidalFins.root_chord : float
Fin root chord in meters.
TrapezoidalFins.tip_chord : float
Fin tip chord in meters.
TrapezoidalFins.span : float
Fin span in meters.
TrapezoidalFins.name : string
Name of fin set.
TrapezoidalFins.sweep_length : float
Fins sweep length in meters. By sweep length, understand the axial
distance between the fin root leading edge and the fin tip leading edge
measured parallel to the rocket centerline.
TrapezoidalFins.sweep_angle : float
Fins sweep angle with respect to the rocket centerline. Must
be given in degrees.
TrapezoidalFins.d : float
Reference diameter of the rocket, in meters.
TrapezoidalFins.ref_area : float
Reference area of the rocket, in m².
TrapezoidalFins.Af : float
Area of the longitudinal section of each fin in the set.
TrapezoidalFins.AR : float
Aspect ratio of each fin in the set
TrapezoidalFins.gamma_c : float
Fin mid-chord sweep angle.
TrapezoidalFins.Yma : float
Span wise position of the mean aerodynamic chord.
TrapezoidalFins.roll_geometrical_constant : float
Geometrical constant used in roll calculations.
TrapezoidalFins.tau : float
Geometrical relation used to simplify lift and roll calculations.
TrapezoidalFins.lift_interference_factor : float
Factor of Fin-Body interference in the lift coefficient.
TrapezoidalFins.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.
TrapezoidalFins.cpx : float
Fin set local center of pressure x coordinate. Has units of length and
is given in meters.
TrapezoidalFins.cpy : float
Fin set local center of pressure y coordinate. Has units of length and
is given in meters.
TrapezoidalFins.cpz : float
Fin set local center of pressure z coordinate. Has units of length and
is given in meters.
TrapezoidalFins.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.
TrapezoidalFins.clalpha : float
Lift coefficient slope. Has units of 1/rad.
"""
[docs]
def __init__(
self,
n,
root_chord,
tip_chord,
span,
rocket_radius,
cant_angle=0,
sweep_length=None,
sweep_angle=None,
airfoil=None,
name="Fins",
):
"""Initialize TrapezoidalFins class.
Parameters
----------
n : int
Number of fins, must be larger than 2.
root_chord : int, float
Fin root chord in meters.
tip_chord : int, float
Fin tip chord in meters.
span : int, float
Fin span in meters.
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.
sweep_length : int, float, optional
Fins sweep length in meters. By sweep length, understand the axial
distance between the fin root leading edge and the fin tip leading
edge measured 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 sweep_angle.
sweep_angle : 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 sweep_length.
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
"""
super().__init__(
n,
root_chord,
span,
rocket_radius,
cant_angle,
airfoil,
name,
)
# Check if sweep angle or sweep length is given
if sweep_length is not None and sweep_angle is not None:
raise ValueError("Cannot use sweep_length and sweep_angle together")
elif sweep_angle is not None:
sweep_length = np.tan(sweep_angle * np.pi / 180) * span
elif sweep_length is None:
sweep_length = root_chord - tip_chord
else:
# Sweep length is given
pass
self._tip_chord = tip_chord
self._sweep_length = sweep_length
self._sweep_angle = sweep_angle
self.evaluate_geometrical_parameters()
self.evaluate_center_of_pressure()
self.evaluate_lift_coefficient()
self.evaluate_roll_parameters()
self.prints = _TrapezoidalFinsPrints(self)
self.plots = _TrapezoidalFinsPlots(self)
@property
def tip_chord(self):
return self._tip_chord
@tip_chord.setter
def tip_chord(self, value):
self._tip_chord = value
self.evaluate_geometrical_parameters()
self.evaluate_center_of_pressure()
self.evaluate_lift_coefficient()
self.evaluate_roll_parameters()
@property
def sweep_angle(self):
return self._sweep_angle
@sweep_angle.setter
def sweep_angle(self, value):
self._sweep_angle = value
self._sweep_length = np.tan(value * np.pi / 180) * self.span
self.evaluate_geometrical_parameters()
self.evaluate_center_of_pressure()
self.evaluate_lift_coefficient()
self.evaluate_roll_parameters()
@property
def sweep_length(self):
return self._sweep_length
@sweep_length.setter
def sweep_length(self, value):
self._sweep_length = value
self.evaluate_geometrical_parameters()
self.evaluate_center_of_pressure()
self.evaluate_lift_coefficient()
self.evaluate_roll_parameters()
[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.sweep_length / 3) * (
(self.root_chord + 2 * self.tip_chord) / (self.root_chord + self.tip_chord)
) + (1 / 6) * (
self.root_chord
+ self.tip_chord
- self.root_chord * self.tip_chord / (self.root_chord + self.tip_chord)
)
self.cpx = 0
self.cpy = 0
self.cpz = cpz
self.cp = (self.cpx, self.cpy, self.cpz)
[docs]
def evaluate_geometrical_parameters(self): # pylint: disable=too-many-statements
"""Calculates and saves fin set's geometrical parameters such as the
fins' area, aspect ratio and parameters for roll movement.
Returns
-------
None
"""
# pylint: disable=invalid-name
Yr = self.root_chord + self.tip_chord
Af = Yr * self.span / 2 # Fin area
AR = 2 * self.span**2 / Af # Fin aspect ratio
gamma_c = np.arctan(
(self.sweep_length + 0.5 * self.tip_chord - 0.5 * self.root_chord)
/ (self.span)
)
Yma = (
(self.span / 3) * (self.root_chord + 2 * self.tip_chord) / Yr
) # Span wise coord of mean aero chord
# Fin–body interference correction parameters
tau = (self.span + self.rocket_radius) / self.rocket_radius
lift_interference_factor = 1 + 1 / tau
lambda_ = self.tip_chord / self.root_chord
# Parameters for Roll Moment.
# Documented at: https://docs.rocketpy.org/en/latest/technical/
roll_geometrical_constant = (
(self.root_chord + 3 * self.tip_chord) * self.span**3
+ 4
* (self.root_chord + 2 * self.tip_chord)
* self.rocket_radius
* self.span**2
+ 6 * (self.root_chord + self.tip_chord) * self.span * self.rocket_radius**2
) / 12
roll_damping_interference_factor = 1 + (
((tau - lambda_) / (tau)) - ((1 - lambda_) / (tau - 1)) * np.log(tau)
) / (
((tau + 1) * (tau - lambda_)) / (2)
- ((1 - lambda_) * (tau**3 - 1)) / (3 * (tau - 1))
)
roll_forcing_interference_factor = (1 / np.pi**2) * (
(np.pi**2 / 4) * ((tau + 1) ** 2 / tau**2)
+ ((np.pi * (tau**2 + 1) ** 2) / (tau**2 * (tau - 1) ** 2))
* np.arcsin((tau**2 - 1) / (tau**2 + 1))
- (2 * np.pi * (tau + 1)) / (tau * (tau - 1))
+ ((tau**2 + 1) ** 2)
/ (tau**2 * (tau - 1) ** 2)
* (np.arcsin((tau**2 - 1) / (tau**2 + 1))) ** 2
- (4 * (tau + 1))
/ (tau * (tau - 1))
* np.arcsin((tau**2 - 1) / (tau**2 + 1))
+ (8 / (tau - 1) ** 2) * np.log((tau**2 + 1) / (2 * tau))
)
# Store values
self.Yr = Yr
self.Af = Af # Fin area
self.AR = AR # Aspect Ratio
self.gamma_c = gamma_c # Mid chord angle
self.Yma = Yma # Span wise coord of mean aero chord
self.roll_geometrical_constant = roll_geometrical_constant
self.tau = tau
self.lift_interference_factor = lift_interference_factor
self.λ = lambda_ # pylint: disable=non-ascii-name
self.roll_damping_interference_factor = roll_damping_interference_factor
self.roll_forcing_interference_factor = roll_forcing_interference_factor
self.evaluate_shape()
def evaluate_shape(self):
if self.sweep_length:
points = [
(0, 0),
(self.sweep_length, self.span),
(self.sweep_length + self.tip_chord, self.span),
(self.root_chord, 0),
]
else:
points = [
(0, 0),
(self.root_chord - self.tip_chord, self.span),
(self.root_chord, self.span),
(self.root_chord, 0),
]
x_array, y_array = zip(*points)
self.shape_vec = [np.array(x_array), np.array(y_array)]
[docs]
def info(self):
self.prints.geometry()
self.prints.lift()
[docs]
def all_info(self):
self.prints.all()
self.plots.all()
def to_dict(self, include_outputs=False):
data = super().to_dict(include_outputs)
data["tip_chord"] = self.tip_chord
if include_outputs:
data.update(
{
"sweep_length": self.sweep_length,
"sweep_angle": self.sweep_angle,
"shape_vec": self.shape_vec,
"Af": self.Af,
"AR": self.AR,
"gamma_c": self.gamma_c,
"Yma": self.Yma,
"roll_geometrical_constant": self.roll_geometrical_constant,
"tau": self.tau,
"lift_interference_factor": self.lift_interference_factor,
"roll_damping_interference_factor": self.roll_damping_interference_factor,
"roll_forcing_interference_factor": self.roll_forcing_interference_factor,
}
)
return data
@classmethod
def from_dict(cls, data):
return cls(
n=data["n"],
root_chord=data["root_chord"],
tip_chord=data["tip_chord"],
span=data["span"],
rocket_radius=data["rocket_radius"],
cant_angle=data["cant_angle"],
airfoil=data["airfoil"],
name=data["name"],
)
