"""CG calculation for load cases."""
# This file is part of FAST-OAD : A framework for rapid Overall Aircraft Design
# Copyright (C) 2021 ONERA & ISAE-SUPAERO
# FAST is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import numpy as np
import openmdao.api as om
[docs]class ComputeCGLoadCase(om.ExplicitComponent):
"""
Base class for computing load cases for CG calculations.
"""
@property
def output_name(self):
"""Builds name of the unique output from option "case_number"."""
return "data:weight:aircraft:load_case_%i:CG:MAC_position" % self.options["case_number"]
[docs] def initialize(self):
self.options.declare("case_number", 1, types=int)
self.options.declare("mass_per_pax", 80.0, types=float)
self.options.declare("mass_front_fret_per_pax", 0.0, types=float)
self.options.declare("mass_rear_fret_per_pax", 0.0, types=float)
self.options.declare("fuel_mass_variable", "", types=str, allow_none=True)
[docs] def setup(self):
self.add_input("data:geometry:wing:MAC:length", val=np.nan, units="m")
self.add_input("data:geometry:wing:MAC:at25percent:x", val=np.nan, units="m")
self.add_input("data:weight:payload:PAX:CG:x", val=np.nan, units="m")
self.add_input("data:weight:payload:rear_fret:CG:x", val=np.nan, units="m")
self.add_input("data:weight:payload:front_fret:CG:x", val=np.nan, units="m")
self.add_input("data:TLAR:NPAX", val=np.nan)
self.add_input("data:weight:aircraft_empty:CG:x", val=np.nan, units="m")
self.add_input("data:weight:aircraft_empty:mass", val=np.nan, units="kg")
if self.options["fuel_mass_variable"]:
self.add_input(self.options["fuel_mass_variable"], val=np.nan, units="kg")
self.add_input("data:weight:fuel_tank:CG:x", val=np.nan, units="m")
self.add_output(self.output_name)
[docs] def setup_partials(self):
self.declare_partials("*", "*", method="fd")
[docs] def compute(self, inputs, outputs, discrete_inputs=None, discrete_outputs=None):
l0_wing = inputs["data:geometry:wing:MAC:length"]
fa_length = inputs["data:geometry:wing:MAC:at25percent:x"]
x_cg_aircraft_empty = inputs["data:weight:aircraft_empty:CG:x"]
mass_aircraft_empty = inputs["data:weight:aircraft_empty:mass"]
mass_payload, x_cg_payload = self._get_payload_mass_and_cg(inputs)
x_cg_aircraft_with_payload = (
mass_aircraft_empty * x_cg_aircraft_empty + mass_payload * x_cg_payload
) / (mass_aircraft_empty + mass_payload)
cg_ratio_aircraft_with_payload = (
x_cg_aircraft_with_payload - fa_length + 0.25 * l0_wing
) / l0_wing
outputs[self.output_name] = cg_ratio_aircraft_with_payload
def _get_payload_mass_and_cg(self, inputs):
"""
:param inputs:
:return: tuple (payload mass, X-position of payload CG)
"""
cg_pax = inputs["data:weight:payload:PAX:CG:x"]
cg_rear_fret = inputs["data:weight:payload:rear_fret:CG:x"]
cg_front_fret = inputs["data:weight:payload:front_fret:CG:x"]
npax = inputs["data:TLAR:NPAX"]
mass_pax = npax * self.options["mass_per_pax"]
mass_front_fret = inputs["data:TLAR:NPAX"] * self.options["mass_front_fret_per_pax"]
mass_rear_fret = inputs["data:TLAR:NPAX"] * self.options["mass_rear_fret_per_pax"]
if self.options["fuel_mass_variable"]:
mass_fuel = inputs[self.options["fuel_mass_variable"]]
cg_fuel = inputs["data:weight:fuel_tank:CG:x"]
else:
mass_fuel = 0.0
cg_fuel = 0.0
mass_payload = mass_pax + mass_rear_fret + mass_front_fret + mass_fuel
x_cg_payload = (
mass_pax * cg_pax
+ mass_rear_fret * cg_rear_fret
+ mass_front_fret * cg_front_fret
+ mass_fuel * cg_fuel
) / mass_payload
return mass_payload, x_cg_payload