Digital DATCOM Forces and Moments

Compute aerodynamic forces and moments using Digital DATCOM static and dynamic stability derivatives

Libraries:
Aerospace Blockset / Aerodynamics

Description

The Digital DATCOM Forces and Moments block computes the aerodynamic forces and moments about the center of gravity using aerodynamic coefficients from Digital DATCOM.

The Digital DATCOM Forces and Moments block port labels change based on the input and output units selected from the Units list.

Examples

Lightweight Airplane Design

Address the technical and process challenges of aircraft design using the design of a lightweight aircraft.

Open Live Script

Limitations

The Digital DATCOM Forces and Moments block supports only Digital DATCOM, which is the 1976 version of DATCOM.
The operational limitations of Digital DATCOM apply to the data contained in the Digital DATCOM structure parameter. For more information on Digital DATCOM limitations, see Section 2.4.5 of reference [1].
The Digital DATCOM structure parameters alpha, mach, alt, grndht, and delta must be strictly monotonically increasing to be used with the Digital DATCOM Forces and Moments block.
The Digital DATCOM structure coefficients must correspond to the dimensions of the breakpoints (alpha, mach, alt, grndht, and delta) to be used with the Digital DATCOM Forces and Moments block.

Ports

Input

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Port_1 — Angle of attack
scalar

Angle of attack, specified as a scalar.

Data Types: double

Port_2 — Sideslip angle
scalar

Sideslip angle, specified as a scalar, in radians.

Data Types: double

Port_3 — Mach number
scalar

Mach number, specified as a scalar.

Data Types: double

Port_4 — Altitude
scalar

Altitude, specified as a scalar, in selected length units.

Data Types: double

Port_5 — Dynamic pressure
scalar

Dynamic pressure, specified as a scalar, in selected pressure units.

Data Types: double

Port_6 — Velocity
three-element vector

Velocity, specified as a three-element vector, in selected velocity units and selected force axes.

Data Types: double

Port_7 — Angle of attack rate
scalar

Angle of attack rate, specified as a scalar, in radians per second.

Dependencies

Appears when DAMP Control Card is used in input to Digital DATCOM.

Data Types: double

Port_8 — Body angular rates
three-element vector

Body angular rates, specified as a three-element vector, in radians per second.

Dependencies

Appears when DAMP Control Card is used in input to Digital DATCOM.

Data Types: double

Port_9 — Ground height
scalar

Ground height, specified as a scalar, in select units of length.

Dependencies

Appears when GRNDEF Namelist is used in input to Digital DATCOM.

Data Types: double

Port_10 — Control surface deflection
scalar

Control surface deflection, specified as a scalar, in radians.

Dependencies

Appears when ASYFLP or SYMFLP and GRNDEF namelists are used in input to Digital DATCOM.

Data Types: double

Output

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Port_1 — Aerodynamic forces at the center of gravity
three-element vector

Aerodynamic forces at the center of gravity, returned as a three-element vector, in selected coordinate system: Body (F, F_{y_x}, and F_z), or Wind (F_D, F_y, and F_L).

Data Types: double

Port_2 — Aerodynamic moments at the center of gravity
three-element vector

Aerodynamic moments at the center of gravity, returned as a three-element vector, in body coordinates (M_x, M_y, and M_z).

Data Types: double

Parameters

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Units — Units
`Metric (MKS)` (default) | `English (Velocity in ft/s)` | `English (Velocity in kts)`

Input and output units, specified as:

Units	Force	Moment	Length	Velocity	Pressure
`Metric (MKS)`	Newton	Newton- meter	Meters	Meters per second	Pascal
`English (Velocity in ft/s)`	Pound	Foot-pound	Feet	Feet per second	Pound per square inch
`English (Velocity in kts)`	Pound	Foot-pound	Feet	Knots	Pound per square inch

Programmatic Use

Block Parameter: units

Type: character vector

Values:

'Metric
									(MKS)'

'English (Velocity in
									ft/s)'

'English (Velocity in
									kts)'

Default:

'Metric
									(MKS)'

Digital DATCOM structure — Digital DATCOM data structure
`factstruct{1}` (default) | structure

MATLAB^® structure containing the digital DATCOM data. This structure is generated by the datcomimport function. To include dynamic derivatives in the generated output file, call the datomimport function with the damp keyword.

For more information on creating the digital DATCOM structure, see Import from USAF Digital DATCOM Files. This example shows how to bring United States Air Force (USAF) Digital DATCOM files into the MATLAB environment using the Aerospace Toolbox software.

Programmatic Use

Block Parameter: dcase

Type: character vector

Values: factstruct{1} | structure

Default: factstruct{1}

Force axes — Coordinate system for aerodynamic force
`Body` (default) | `Wind`

Coordinate system for aerodynamic force, specified as Body or Wind.

Programmatic Use

Block Parameter: fmode

Type: character vector

Values: 'Body' | 'Wind'

Default: 'Body'

Interpolation method — Interpolation method
`None - flat` (default) | `Linear`

Interpolation method, specified as None (flat) or Linear. The block uses the interpolation method to interpolate the static and dynamic stability coefficients in the Digital DATCOM structure.

Programmatic Use

Block Parameter: imethod

Type: character vector

Values:

'None
									(flat)'

| 'Linear'

Default:

'None
									(flat)'

Extrapolation method — Extrapolation method
`None - clip` (default) | `Linear`

Extrapolation method, specified as None (clip) or Linear. The block uses the extrapolation method to extrapolate the static and dynamic stability coefficients in the Digital DATCOM structure.

Programmatic Use

Block Parameter: emethod

Type: character vector

Values:

'None
									(flat)'

| 'Linear'

Default:

'None
									(flat)'

Process out-of-range input — Handle out-of-range input
`Clip to Range` (default) | `Linear Extrapolation`

Handle out-of-range input action, Linear Extrapolation or Clip to Range.

Programmatic Use

Block Parameter: rmethod

Type: character vector

Values:

'Clip to
									Range'

'Linear
								Extrapolation'

Default:

'Clip to
									Range'

Action for out-of-range input — Out-of-range block behavior
`None` (default) | `Warning` | `Error`

Out-of-range block behavior, specified as:

Action	Description
`None`	No action.
`Warning`	Warning in the Diagnostic Viewer, model simulation continues.
`Error` (default)	Error in the Diagnostic Viewer, model simulation stops.

Programmatic Use

Block Parameter: action

Type: character vector

Values: 'None' | 'Warning' | 'Error'

Default: 'Warning'

Algorithms

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Algorithms for calculating forces and moments build up the overall aerodynamic forces and moments (F and M) from data contained in the Digital DATCOM structure parameter:

F = F _static + F _dyn

(1)

M = M _static + M _dyn

(2)

F_static and M_static are the static contribution, and F_dyn and M_dyn the dynamic contribution, to the aerodynamic coefficients. If the dynamic characteristics are not contained in the Digital DATCOM structure parameter, their contribution is set to zero.

Static Stability Characteristics

Static stability characteristics include the following.

Coefficient	Meaning
C _D	Matrix of drag coefficients. These coefficients are defined positive for an aft-acting load.
C _L	Matrix of lift coefficients. These coefficients are defined positive for an up-acting load.
C _m	Matrix of pitching-moment coefficients. These coefficients are defined positive for a nose-up rotation.
C _Yβ	Matrix of derivatives of side-force coefficients with respect to sideslip angle
C _nβ	Matrix of derivatives of yawing-moment coefficients with respect to sideslip angle
C _lβ	Matrix of derivatives of rolling-moment coefficients with respect to sideslip angle

These are the static contributions to the aerodynamic coefficients in stability axes.

C _{D static} = C _D

(3)

C _{y static} = C _Yβ β

(4)

C _{L static} = C _L

(5)

C _{l static} = C _lβ β

(6)

C _{m static} = C _M

(7)

C _{n static} = C _nβ β

(8)

Dynamic Stability Characteristics

Dynamic stability characteristics include the following.

Coefficient	Meaning
C _Lq	Matrix of lift force derivatives due to pitch rate
C _mq	Matrix of pitching-moment derivatives due to pitch rate
C _Ldα/dt	Matrix of lift force derivatives due to rate of angle of attack
C _mdα/dt	Matrix of pitching-moment derivatives due to rate of angle of attack
C _lp	Matrix of rolling-moment derivatives due to roll rate
C _Yp	Matrix of lateral force derivatives due to roll rate
C _np	Matrix of yawing-moment derivatives due to roll rate
C _nr	Matrix of yawing-moment derivatives due to yaw rate
C _lr	Matrix of rolling-moment derivatives due to yaw rate

These are the dynamic contributions to the aerodynamic coefficients in stability axes.

$\begin{array}{l} C_{D}_{dyn} = 0 \\ C_{y}_{dyn} = C_{yp} p (b_{ref} / 2 V) \\ C_{L}_{dyn} = (C_{L}_{q} q + C_{L \dot{α}} \dot{α}) (c_{bar} / 2 V) \\ C_{l}_{dyn} = (C_{lp} p + C_{lr} r) (b_{ref} / 2 V) \\ C_{m}_{dyn} = (C_{mq} q + C_{m}_{\dot{a}} \dot{a}) (c_{bar} / 2 V) \\ C_{n}_{dyn} = (C_{np} p + C_{nr} r) (b_{ref} / 2 V) \end{array}$

References

[1] The USAF Stability and Control Digital Datcom, AFFDL-TR-79-3032, 1979.

[2] Etkin, B., and L. D. Reid. Dynamics of Flight Stability and Control, Hoboken, NJ: John Wiley & Sons, 1996.

[3] Roskam, J. "Airplane Design Part VI: Preliminary Calculation of Aerodynamic, Thrust and Power Characteristics", Roskam Aviation and Engineering Corporation, Ottawa, Kansas: 1987.

[4] Stevens, B. L., and F. L. Lewis. Aircraft Control and Simulation, Hoboken, NJ: John Wiley & Sons, 1992.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2006b

Digital DATCOM Forces and Moments

Description

Examples

Lightweight Airplane Design

Limitations

Ports

Input

Port_1 — Angle of attack scalar

Port_2 — Sideslip angle scalar

Port_3 — Mach number scalar

Port_4 — Altitude scalar

Port_5 — Dynamic pressure scalar

Port_6 — Velocity three-element vector

Port_7 — Angle of attack rate scalar

Dependencies

Port_8 — Body angular rates three-element vector

Dependencies

Port_9 — Ground height scalar

Dependencies

Port_10 — Control surface deflection scalar

Dependencies

Output

Port_1 — Aerodynamic forces at the center of gravity three-element vector

Port_2 — Aerodynamic moments at the center of gravity three-element vector

Parameters

Units — Units Metric (MKS) (default) | English (Velocity in ft/s) | English (Velocity in kts)

Programmatic Use

Digital DATCOM structure — Digital DATCOM data structure factstruct{1} (default) | structure

Programmatic Use

Force axes — Coordinate system for aerodynamic force Body (default) | Wind

Programmatic Use

Interpolation method — Interpolation method None - flat (default) | Linear

Programmatic Use

Extrapolation method — Extrapolation method None - clip (default) | Linear

Programmatic Use

Process out-of-range input — Handle out-of-range input Clip to Range (default) | Linear Extrapolation

Programmatic Use

Action for out-of-range input — Out-of-range block behavior None (default) | Warning | Error

Programmatic Use

Algorithms

Static Stability Characteristics

Dynamic Stability Characteristics

References

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using Simulink® Coder™.

Version History

See Also

Topics

Port_1 — Angle of attack
scalar

Port_2 — Sideslip angle
scalar

Port_3 — Mach number
scalar

Port_4 — Altitude
scalar

Port_5 — Dynamic pressure
scalar

Port_6 — Velocity
three-element vector

Port_7 — Angle of attack rate
scalar

Port_8 — Body angular rates
three-element vector

Port_9 — Ground height
scalar

Port_10 — Control surface deflection
scalar

Port_1 — Aerodynamic forces at the center of gravity
three-element vector

Port_2 — Aerodynamic moments at the center of gravity
three-element vector

Units — Units
`Metric (MKS)` (default) | `English (Velocity in ft/s)` | `English (Velocity in kts)`

Digital DATCOM structure — Digital DATCOM data structure
`factstruct{1}` (default) | structure

Force axes — Coordinate system for aerodynamic force
`Body` (default) | `Wind`

Interpolation method — Interpolation method
`None - flat` (default) | `Linear`

Extrapolation method — Extrapolation method
`None - clip` (default) | `Linear`

Process out-of-range input — Handle out-of-range input
`Clip to Range` (default) | `Linear Extrapolation`

Action for out-of-range input — Out-of-range block behavior
`None` (default) | `Warning` | `Error`

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.