Adrian Hiliuta

Approximation of Unsteady Aerodynamic Forces Q(k, M) by Use of Fuzzy Techniques

The unsteady aerodynamic forces acting on an F/A-18 aircraft are calculated in the frequency domain using a doublet-lattice method (subsonic regime) or a constant-pressure method (supersonic regime). To study the effects of the control laws on a flexible fly-by-wire aircraft structure and calculate the flutter velocities and frequencies, these aerodynamic forces must be approximated in the Laplace domain. We show here that in the case where the aerodynamic forces data are calculated for a range of unevenly spaced reduced frequencies, a combination of fuzzy clustering and shape-preserving techniques can be used to obtain a very good approximation of these unsteady aerodynamic forces. Because the approximation of these forces by this new method remains actually in the frequency domain, we could easily further use for their conversion from the frequency domain into Laplace domain, classical methods such as least squares or minimum state. Finally, care must be used in the choice of reduced frequencies range, to determine the method to be deployed.

Ground dynamics model validation by use of landing flight test

[Abstract] In this paper, a new formulation for a ground dynamics model of a commercial two-engine helicopter is validated after touchdown. The inputs of the ground dynamics model are the velocities and angles at touchdown, and its outputs are the forces and moments produced by the ground on the helicopter. Expressions for forces and moments, which depend on the ground contact force, the friction coefficient between the skids and the ground, and the system stiffness and damping are determined. . The system stiffness and damping are defined between the touchdown point and the center of gravity in each of the helicopter’s degree of freedom. Expressions for the stiffness, damping and friction coefficients are validated for two kinds of landing situations: one-engine inoperative and autorotation. The ground dynamics of the Bell-427 helicopter model are then used to build and certify a level-D flight simulator.

Rigid and Control Modes Aerodynamic Unsteady Forces Aeroservoelastic Modeling

An important aspect of aeroservoelasticity is the analysis of interactions between rigid, elastic, and control modes. The stability and control derivatives were determined for a high number (90) of flight test conditions expressed in terms of Mach number, altitudes, and angles of attack. In this paper, the rigid and control mode aerodynamic forces for an F/A-18 aircraft are calculated and validated by two methods (numerical and analytical). The results obtained here were found to be identical for all flight test conditions.

Flight dynamics helicopter model validation based on flight test data

Abstract In the current paper, a new technique for a helicopter model estimation based on flight test data is presented. The state space helicopter models, for different flight conditions, are computed. The method is automatic and is applied when one knows the motion parameters types x, y, and u of a real helicopter and in the absence of any seed matrices. The method is highly convergent, and very good results are obtained for all flight cases. In the introductory part, a bibliographic research is carried on, and the necessary data collection is presented. In the next step, the preliminary estimation of seed matrices, for state-space representation is performed using a non-linear model and small perturbation theory. The last paragraph deals with the seed optimization with respect to different flight conditions. In the end, the model validation and the conclusion on possibilities to further develop and use the present methodology is investigated.

Aeroservoelastic flutter and frequency response interactions on the CL-704 aircraft

Two methods for the aerodynamic forces conversions from frequency into Laplace domain were conceived and validated: Least Squares LS and Minimum State MS, on the Bombardier CL-604 aircraft. A new feature was added in these two methods consisting in the writing of the error calculated by LS and MS classical methods under an analytical form similar to the LS and MS form of approximated aerodynamic forces; this error was once again minimized. Then, new methods using this new feature were called: Corrected Least Squares CLS and Corrected Minimum State CMS methods (as error was once again corrected). All these four methods were programmed in Matlab to approximate the unsteady aerodynamic forces from frequency domain to Laplace domain.

Validation of a Ground Dynamics Model Formulation By use of Landing Data

In this paper, a new formulation for a ground dynamics model for a commercial two engines helicopter is validated after touchdown. The inputs of the ground dynamics model are the velocities and angles at touchdown, while its outputs are the forces and moments produced by the ground on the helicopter. Expressions for forces and moments depending on the friction coefficient between the skids and the ground and the system stiffness and damping are presented. The system stiffness and damping are defined between the touchdown point and the center of mass in each of the helicopter degree of freedom. Expressions for the stiffness, damping and friction coefficients are derived to validate one engine inoperative and autorotation landing cases. The ground dynamics model is validated by use of landing flight test data collected on the B-427 helicopter and is further used in the building and in the certification of a level D simulator

New technique for a helicopter flight model estimation based on flight test data

In this paper, a new technique for a helicopter model estimation based o n flight test data is presented. The state space helicopter models, for each flight condition, are presented. The method is automatic and is applied when one knows the motion parameters types x, y and u of a real helicopter and in the absence of any seed m atrices. The method is highly convergent, and very good results are obtained for all flight cases. In the introductory part, a bibliographic research is carried on, and the necessary data collection is presented. In the next step, the preliminary estimatio n of seed matrices, for state -space representation is performed using a non -linear model and small perturbation theory. The last paragraph deals with the seed optimization with respect to different flight conditions. In the end, the conclusion on possibili ties to further develop and use the presented methodology is investigated.

Aerodynamic forces formulation for aircraft aeroservoelasticity studies

An important aspect of aeroservoelastic interactions studies is the common aerodynamic forces formulation for servo -control studies on rigid aircraft and for aeroelastic studies on flexible aircraft. Aerodynamic generalized forces are calculated for aeroelasticity studies on a flexible aircraft from purely oscillatory mot ion of each mode for a range of reduced frequencies and Mach numbers. Aerodynamic forces are calculated for servo -control studies on six degrees of freedom rigid aircraft by use of Newton’s equations of motion. For aeroservoelasticity studies, we replace a erodynamic forces calculated in aeroelasticity studies for rigid / control interactions with forces calculated by rigid body Newton’s theory for servo -control analysis. In aircraft stability and control analysis, we observe the dependency of small variatio ns on parameters defining aircraft’s motion around the trim point, such as linear and angular coordinates, velocities and accelerations. Calculation of forces implies calculation of longitudinal and lateral stability and control derivatives. The relationsh ip between generalized force coefficients in the inertial axis system and aircraft body axis non dimensional stability and control derivatives is here summarized. Longitudinal (symmetric mode) and lateral (anti -symmetric mode) stability and control coeffic ients are here calculated for the generalized stiffness and damping matrices.