Source code for RCAIDE.Library.Methods.Aerodynamics.Common.Drag.asymmetry_drag
# ----------------------------------------------------------------------
# Imports
# ----------------------------------------------------------------------
# RCAIDE Imports
from RCAIDE import *
from RCAIDE.Library.Components import Wings
# ----------------------------------------------------------------------
# Compute asymmetry drag due to engine failure
# ----------------------------------------------------------------------
[docs]
def asymmetry_drag(state, geometry, engine_out_location = 0, single_engine_thrust = 0, windmilling_drag_coefficient = 0.):
"""
Computes asymmetry drag coefficient due to engine failure and resulting trim requirements.
Parameters
----------
state : Data
Flight conditions and aerodynamic state containing:
- conditions.freestream.dynamic_pressure : float
Freestream dynamic pressure [Pa]
- conditions.aerodynamics.coefficients.drag.windmilling.total : float, optional
Windmilling drag coefficient [unitless]
geometry : Data
Vehicle geometry containing:
- reference_area : float, optional
Reference area for drag coefficient calculation [m²]
- mass_properties.center_of_gravity : array
Center of gravity location [m]
- networks : list
List of propulsion networks containing:
- number_of_engines : int
Total number of engines [unitless]
- wings : list
List of wing objects containing:
- tag : str
Unique identifier for the wing
- sref : float
Reference area of the wing [m²]
- spans.projected : float
Projected span of the wing [m]
- aerodynamic_center : array
Aerodynamic center location [m]
- origin : array
Wing origin location [m]
- vertical : bool
Flag indicating if wing is vertical tail
engine_out_location : float, optional
Lateral distance of failed engine from aircraft centerline [m]
single_engine_thrust : float, optional
Thrust produced by remaining operational engine [N]
windmilling_drag_coefficient : float, optional
Windmilling drag coefficient for failed engine [unitless]
Returns
-------
asymm_trim_drag_coefficient : float
Asymmetry trim drag coefficient [unitless]
Notes
-----
This function calculates the additional drag required to trim the aircraft when one engine
fails, creating an asymmetric thrust condition. The calculation accounts for the drag caused by yawing
moment created by the asymmetric thrust and the counteracting moment from the vertical tail.
**Major Assumptions**
* Two-engine aircraft configuration
* Vertical tail provides the primary yawing moment for trim
* Linear relationship between trim drag and asymmetric thrust moment
* Windmilling drag contributes to the asymmetric moment
**Theory**
The asymmetry drag is calculated from the trim requirement to balance the yawing moment:
:math:`D_{trim} = \\frac{(y_{engine})^2 (T_{single} + D_{windmilling})^2}{q_{\\infty} \\pi (h_{vt} \\cdot l_{vt})^2}`
where:
- :math:`y_{engine}` is the lateral distance of the failed engine [m]
- :math:`T_{single}` is the thrust of the remaining engine [N]
- :math:`D_{windmilling}` is the windmilling drag force [N]
- :math:`q_{\\infty}` is the freestream dynamic pressure [Pa]
- :math:`h_{vt}` is the vertical tail height [m]
- :math:`l_{vt}` is the moment arm of the vertical tail [m]
The windmilling drag force is:
:math:`D_{windmilling} = C_{D,windmilling} \\cdot q_{\\infty} \\cdot S_{ref}`
The asymmetry drag coefficient is:
:math:`C_{D,asymmetry} = \\frac{D_{trim}}{q_{\\infty} \\cdot S_{ref}}`
**Definitions**
'Asymmetry Drag'
Additional drag required to trim the aircraft when thrust is asymmetric due to engine failure.
'Windmilling Drag'
Drag produced by a failed engine that continues to rotate due to incoming airflow.
'Trim Drag'
Drag increment required to maintain aircraft equilibrium in asymmetric flight conditions.
References
----------
[1] Unknown source
See Also
--------
RCAIDE.Library.Components.Wings.Main_Wing
RCAIDE.Library.Methods.Aerodynamics.Common.Drag.windmilling_drag
"""
# ==============================================
# Unpack
# ==============================================
vehicle = geometry
wings = vehicle.wings
dyn_press = state.conditions.freestream.dynamic_pressure
# Defining reference area
if vehicle.reference_area:
reference_area = vehicle.reference_area
else:
n_wing = 0
for wing in wings:
if not (isinstance(wing,Wings.Main_Wing) or isinstance(wing,Wings.Blended_Wing_Body)): continue
n_wing = n_wing + 1
reference_area = wing.sref
if n_wing > 1:
print(' More than one Main_Wing in the vehicle. Last one will be considered.')
elif n_wing == 0:
print('No Main_Wing defined! Using the 1st wing found')
for wing in wings:
if not isinstance(wing,Wings.Wing): continue
reference_area = wing.sref
break
# getting cg x position
xcg = vehicle.mass_properties.center_of_gravity[0]
# finding vertical tail
for idx,wing in enumerate(wings):
if not wing.vertical: continue
vertical_idx = wing.tag
break
# if vertical tail not found, raise error
try:
vertical_idx
except AttributeError:
print(' No vertical tail found! Error calculating one engine inoperative drag')
# getting vertical tail data (span, distance to cg)
vertical_height = wings[vertical_idx].spans.projected
vertical_dist = wings[vertical_idx].aerodynamic_center[0] + wings[vertical_idx].origin[0][0] - xcg[0]
# colculating windmilling drag
if windmilling_drag_coefficient == 0:
try:
windmilling_drag_coefficient = state.conditions.aerodynamics.coefficients.drag.windmilling.total
except: pass
windmilling_drag = windmilling_drag_coefficient * dyn_press * reference_area
# calculating Drag force due to trim
trim_drag = (engine_out_location**2 * (single_engine_thrust+windmilling_drag)**2 ) / \
(dyn_press * 3.141593* (vertical_height*vertical_dist)**2)
# Compute asymmetry trim drag coefficient
asymm_trim_drag_coefficient = trim_drag / dyn_press / reference_area
# dump data to state
state.conditions.aerodynamics.coefficients.drag.asymmetry_trim.total = asymm_trim_drag_coefficient
return asymm_trim_drag_coefficient
