Digital DATCOM Forces and Moments

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

• Library:

• 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.

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

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

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_yx, 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

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 Importing from USAF Digital DATCOM Files (Aerospace Toolbox). 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 follows.

Action	Description
None	No action.
Warning	Warning in the MATLAB Command Window, model simulation continues.
Error (default)	MATLAB returns an exception, model simulation stops.

Programmatic Use

Block Parameter: action

Type: character vector

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

Default: 'None'

Model Examples

Lightweight Airplane Design

How to use MathWorks® products to address the technical and process challenges of aircraft design using the design of a lightweight aircraft.

Open Model

Algorithms

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.

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

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.