Affiliated faculty

Antônio B. Guimarães Neto

Ekkehard C. F. Schubert

Flávio J. Silvestre

Flávio L. Cardoso Ribeiro

Flávio L. de S. Bussamra

Guilherme Soares e Silva

Mauricio A. V. Morales

Roberto Gil A. da Silva

Students

Guilherme C. Barbosa (Doctoral student, ITA)

Juliano A. Paulino (Doctoral student, ITA)

Jéssica S. Martins (Doctoral student, ITA)

Pedro J. G. Ramirez (Doctoral student, ITA)

Rafael M. Bertolin (Doctoral student, ITA)

Augusto C. Sanches (Master of Science student, ITA)

Dirk Bradenburg (Undergrad student, TU Hamburg)

Richard Leiseder (Undergrad student, TU Hamburg)

Funding source

Inova Aerodefesa (FINEP/Embraer), project entitled “Flight physics” (2016-2020)

Embraer: DinaFlex project (2019)

Description

Higher aspect-ratio wings have a better aerodynamic performance due to induced drag reduction. Combined to the use of lightweight structures, this leads to more flexible wings and the frequency range of the aeroelastic dynamics is pushed toward the range of the flight dynamics modes.

The actual procedure for the design of flight control laws is based on the flight dynamics rigid-body approximation and the hight-frequency aeroelastic response is filtered in the measured parameters used for feedback with notch filters. Clearly, this procedure shall not work when flight and aeroelastic dynamics are close in frequency, and aeroservoelastic stability shall be an issue. For example, in the figure below, Silvestre (2013) shows aeroservoelastic instabilities (elastic modes getting unstable in closed loop) in the root-loci of a directional stability augmentation system. Therefore, new methodologies for flight control law design of these flexible aircraft, taking into account the aeroelastic dynamics, are being pursued.

For flight control law design of flexible aircraft, a unified formulation of the flight and aeroelastic dynamics is necessary. High-fidelity tools have been developed coupling CFD and FEM models in a flight mechanics solver environment. Due to their complexity, these tools are regarded to closed loop numerical validation rather than to flight control law design. In this scenario, simpler but still reliable models for aeroservoelastic applications are desired. Over the last years various simplified mathematical formulations have been proposed to represent flexible aircraft mathematically for simulation and stability analysis. These formulations have different levels of complexity model order, depending on the level of the aircraft flexibility to be taken into account. Therefore it is important to distinguish between very flexible and slightly flexible aircraft. Very flexible airframes undergo large elastic displacements, violating the assumptions that are necessary for the application of linear theories for the structural dynamics - an example of such formulation is the work of Patil, Hodges and Cesnik (2000), where the airframe is modeled in form of nonlinear beams. This formulation is enhanced in the works of Patil and Hodges (2006), Shearer and Cesnik (2007), and Su and Cesnik (2011). These models consist in a powerful simulation environment, where structural non-linearities can be analyzed. However, the increase on the number of degrees of freedom in the model can hardly limit its use in aeroservoelastic applications. Silvestre (2013) has proposed a unified model in the time domain for the dynamics of slightly flexible, high-aspect-ratio class of aircraft, which has been validated in an aeroelastic flight test campaign. The similarity to the rigid body model and low order of the model qualify it for the use in control law design.

In this research project, the following topics are addressed:

• validation of unified models of different complexities with flight tests, with a wing of varying aspect-ratio and flexibility
• methodology for flight control law design including aeroelastic effects and closed-loop validation with flight tests
• development of a unified, high-fidelity simulation tool for flexible aircraft, for numerical validation

These aspects shall be demonstrated with the modular, low-cost aeroelastic flight testing platform X-HALE, originally designed at the University of Michigan, which was built at ITA and is currently being tested.