Incidence, Sideslip, & Airspeed

Calculate incidence, sideslip, and airspeed

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Libraries:
Aerospace Blockset / Flight Parameters

Description

The Incidence, Sideslip, & Airspeed block calculates the angles between the velocity vector and the body, and also the total airspeed from the velocity components in the body-fixed coordinate frame. For the equations used in the calculation, see Algorithms.

Note

• For fixed-wing aircraft, the angle, α, computed by the Incidence, Sideslip, & Airspeed block is the angle between the relative wind and the longitudinal axis of the airframe. This angle is denoted in many aerospace engineering references as angle of attack. Incidence, Sideslip, & Airspeed refers to this angle as the incidence angle.

• In the case of vertical takeoff and landing (VTOL) configurations, the equations used for computation are the same as that for fixed-wing aircraft [1]. However, in maneuvers involving transitions between cruise and hover, there are likely scenarios involving low or zero values of velocity resulting in incorrect incidence and side-slip angles. Therefore, the use of this block for analysis of VTOL configurations is not recommended. As an alternative, use the 6DOF Wind (Quaternion) or 6DOF Wind (Wind Angles) blocks, which provide α and β as outputs.

Examples

Fly the De Havilland Beaver

Model the De Havilland Beaver using Simulink^® and Aerospace Blockset™ software.

• Open Live Script

Ports

Input

V_b — Velocity of body

three-element vector

Velocity of the body, specified as a three-element vector, resolved into the body-fixed coordinate frame.

Data Types: double

Output

ɑ — Incidence angle

scalar

Incidence angle, returned as a scalar, in radians.

Data Types: double

β — Sideslip angle

scalar

Sideslip angle, returned as a scalar, in radians.

Data Types: double

V — Airspeed

scalar

Airspeed of the body, returned as a scalar.

Data Types: double

Algorithms

To calculate the angles between the velocity vector and the body, and the total airspeed, the block uses these equations:

$$\alpha ={\tan }^{-1}\left(\frac{w}{u}\right)$$

$$\beta ={\sin }^{-1}\left(\frac{v}{V}\right)={\tan }^{-1}(\frac{v}{\sqrt{u^2+w^2}})$$

The block uses the tan-1 formulation for β to prevent division by 0.

$$V=\sqrt{u^2+v^2+w^2}$$

References

[1] C. Venkatesan, Fundamentals of Helicopter Dynamics: CRC Press, 261. Boca Raton, FL 2015.

Extended Capabilities

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

Version History

Introduced before R2006a

R2022b: Updated to Reduce Divide by Zero Issues

The Incidence, Sideslip, & Airspeed block now reduces the potential for divide by zero issues caused by aircraft hovering without forward movement. In previous releases, hovering without forward movement might cause divide by zero issues.