Source code for RCAIDE.Library.Methods.Aerodynamics.Common.Drag.miscellaneous_drag
# RCAIDE/Library/Methods/Aerodynamics/Common/Drag/miscellaneous_drag.py
#
# Created: Jun 2025, M. Clarke
# ----------------------------------------------------------------------------------------------------------------------
# IMPORT
# ----------------------------------------------------------------------------------------------------------------------
from RCAIDE.Framework.Core import Data
# package imports
import numpy as np
# ----------------------------------------------------------------------------------------------------------------------
# Miscellaneous Drag Total
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[docs]
def miscellaneous_drag(state,settings,geometry):
"""
Computes the miscellaneous drag coefficient associated with aircraft components and configurations.
Parameters
----------
state : Data
Flight conditions containing:
- conditions.freestream.mach_number : float
Freestream Mach number [unitless]
settings : dict
Aerodynamic analysis settings and parameters
geometry : Data
Aircraft geometry containing:
- reference_area : float
Reference area for drag coefficient calculation [m²]
- landing_gears : list
List of landing gear objects containing:
- gear_extended : bool
Flag indicating if landing gear is deployed
- fairing : bool
Flag indicating if landing gear has fairings
- wheels : int
Number of wheels on the landing gear
- tire_diameter : float
Diameter of landing gear tires [m]
- tire_width : float
Width of landing gear tires [m]
- wings : list
List of wing objects containing:
- areas.wetted : float
Wetted area of the wing [m²]
- fuselages : list
List of fuselage objects containing:
- areas.wetted : float
Wetted area of the fuselage [m²]
- booms : list
List of boom objects containing:
- areas.wetted : float
Wetted area of the boom [m²]
- networks : list
List of propulsion networks containing propulsors
- propulsors : list
List of propulsor objects with nacelle attributes
- nacelle : Nacelle, optional
Nacelle object containing:
- areas.wetted : float
Wetted area of the nacelle [m²]
- diameter : float
Diameter of the nacelle [m]
Returns
-------
None
Results are stored in state.conditions.aerodynamics.coefficients.drag.miscellaneous.total
Notes
-----
This function calculates the miscellaneous drag coefficient including landing gear drag,
subsonic miscellaneous drag based on wetted area, and supersonic nacelle base drag and
fuselage upsweep drag. The calculation method varies between subsonic and supersonic
flight regimes.
**Major Assumptions**
* Landing gear drag is proportional to tire frontal area
* Subsonic miscellaneous drag correlates with total wetted area
* Supersonic drag includes nacelle base drag and fuselage upsweep effects
* Landing gear fairings reduce drag by approximately 50%
* Basic empirical correlations are valid for typical transport aircraft
**Theory**
Landing Gear Drag:
The landing gear drag coefficient is calculated as:
:math:`C_{D,LG} = \\sum_{i=1}^{n} N_{wheels,i} \\cdot C_{D,i} \\cdot \\frac{D_i \\cdot W_i}{S_{ref}}`
where:
- :math:`N_{wheels,i}` is the number of wheels on landing gear :math:`i`
- :math:`C_{D,i}` is 0.15 for faired landing gear or 0.30 for unfaired
- :math:`D_i` and :math:`W_i` are the tire diameter and width [m]
- :math:`S_{ref}` is the reference area [m²]
Subsonic Miscellaneous Drag:
For Mach ≤ 1.0, the miscellaneous drag is:
:math:`C_{D,misc} = \\frac{0.40(0.0184 + 0.000469 S_{wet} - 1.13 \\times 10^{-7} S_{wet}^2)}{S_{ref}}`
where :math:`S_{wet}` is the total wetted area [m²].
Supersonic Miscellaneous Drag:
For Mach > 1.0, the drag includes nacelle base drag and fuselage upsweep:
:math:`C_{D,nacelle} = \\sum_{i=1}^{n} \\frac{0.5}{12} \\pi D_i \\cdot 0.2 / S_{ref}`
:math:`C_{D,upsweep} = \\frac{0.006}{S_{ref}}`
:math:`C_{D,misc} = C_{D,nacelle} + C_{D,upsweep}`
**Definitions**
'Miscellaneous Drag'
Drag component not accounted for by other drag categories, including landing gear, nacelle base, and fuselage upsweep effects.
'Landing Gear Drag'
Additional drag caused by deployed landing gear, proportional to tire frontal area.
'Nacelle Base Drag'
Drag caused by the base area of nacelles in supersonic flow.
References
----------
[1] Stanford AA241 Course Notes. http://aerodesign.stanford.edu/aircraftdesign/aircraftdesign.html
"""
conditions = state.conditions
S_ref = geometry.reference_area
Mach = conditions.freestream.mach_number
# landing gear drag
landing_gear_drag = np.zeros_like(Mach)
for landing_gear in geometry.landing_gears:
if landing_gear.gear_extended == True:
if landing_gear.fairing:
cd_lg = 0.15
else:
cd_lg = 0.30
landing_gear_drag[:,0] += landing_gear.wheels * cd_lg * (landing_gear.tire_diameter * landing_gear.tire_width) /S_ref
# subsonic
miscellaneous_drag = np.zeros_like(Mach)
swet_tot = 0.
for wing in geometry.wings:
swet_tot += wing.areas.wetted
for fuselage in geometry.fuselages:
swet_tot += fuselage.areas.wetted
for boom in geometry.booms:
swet_tot += boom.areas.wetted
for network in geometry.networks:
for propulsor in network.propulsors:
if propulsor.nacelle != None:
swet_tot += propulsor.nacelle.areas.wetted
miscellaneous_drag[:,0] = (0.40* (0.0184 + 0.000469 * swet_tot - 1.13*10**-7 * swet_tot ** 2)) / S_ref
# supersonic
fuselage_upsweep_drag = 0.006 /S_ref
miscellaneous_drag[Mach>1] = fuselage_upsweep_drag
# total misc drag
total_miscellaneous_drag = miscellaneous_drag + landing_gear_drag
# Store results
conditions.aerodynamics.coefficients.drag.miscellaneous = Data( total = total_miscellaneous_drag)
return
