RCAIDE.Library.Methods.Aerodynamics.Common.Drag.trim_drag
trim_drag#
- trim_drag(state, settings, geometry)[source]#
Computes trim drag and updates aerodynamic coefficients due to control surface deflections.
- Parameters:
state (Data) –
- Flight conditions and aerodynamic state of aircraft containing:
- conditions.aerodynamics.coefficients.drag.parasite.totalfloat
Parasite drag coefficient [unitless]
- conditions.aerodynamics.coefficients.drag.induced.totalfloat
Induced drag coefficient [unitless]
- conditions.aerodynamics.coefficients.drag.compressible.totalfloat
Compressibility drag coefficient [unitless]
- conditions.aerodynamics.coefficients.drag.form.totalfloat
Form drag coefficient [unitless]
- conditions.control_surfaces.flap.deflectionfloat
Flap deflection angle [degrees]
settings (dict) – Aerodynamic analysis settings and parameters
geometry (Data) –
- Aircraft geometry containing:
- wingslist
List of wing objects with control_surfaces attribute - control_surfaces : list
List of control surface objects (Spoiler, Flap, etc.) - deflection : float
Control surface deflection angle [degrees]
- chord_fractionfloat
Fraction of wing chord occupied by control surface [unitless]
- typestr
Type of flap (‘split’, ‘plain’, ‘single_slotted’, ‘flowler’, ‘double_slotted’)
- Returns:
Results are stored in state.conditions.aerodynamics.coefficients.drag.trim.total
- Return type:
None
Notes
This function calculates the additional drag and aerodynamic effects caused by control surface deflections, particularly spoilers and flaps. The calculations are based on empirical correlations from wind tunnel testing and flight data.
- Major Assumptions
Linear relationship between control surface deflection and drag increment
Control surface effects are additive to baseline aerodynamic coefficients
Empirical coefficients are valid across typical flight conditions
Theory
For spoilers, the drag increment is calculated as:
\(\Delta C_D = 0.0011 \frac{\delta_{spoiler}}{1°}\)
where \(\delta_{spoiler}\) is the spoiler deflection angle in degrees.
For flaps, the drag increment follows:
\(\Delta C_D = c_f \cdot A \cdot \left(\frac{\delta_{flap}}{1°}\right)^B\)
where: - \(c_f\) is the chord fraction of the flap - \(A\) and \(B\) are empirical coefficients that depend on flap type - \(\delta_{flap}\) is the flap deflection angle in degrees
The lift and moment effects for spoilers are:
\(\Delta C_L = -0.0075 \frac{\delta_{spoiler}}{1°}\)
\(\Delta C_M = 0.0053 \frac{\delta_{spoiler}}{1°}\)
Definitions
- ‘Trim Drag’
Additional drag caused by control surface deflections required to maintain aircraft equilibrium.
- ‘Spoiler’
Control surface that reduces lift and increases drag by disrupting airflow over the wing.
- ‘Flap’
High-lift device that increases wing camber and chord to improve low-speed performance.
References
[1] Croom, D. R. (1976). “Low-speed wind-tunnel investigation of various segments of flight spoilers as trailing-vortex-alleviation devices on a transport aircraft model.” NASA-TN-D-8162. [2] Sadraey, M. H. (2017). “Aircraft performance: an engineering approach.” CRC Press.