A self excitation and control system for wind tunnel dynamic stability measurements

The paper describes the design and development of a fast acting self-excitation and control system based on the principles of regenerative and negative feedback for phase resonance testing of aerodynamic models in wind tunnels. Simulation tests and analyses using a linearized model of the drive system are carried out, and results indicate that the system would function even if the system damping becomes neutral or negative. Experiments for dynamic stability measurements show that the control system meets all specifications and performs satisfactorily even in the presence of moderate amounts of turbulence in the air flow

Determination of model order for dynamical system

The problem of model order determination, which is an integral part of system identification for dynamical systems of auto-regressive and least square structures is investigated. Twelve model order testing criteria available in the literature are critically evaluated from simulated data and from two different physical processes: (1) human operator responses in compensatory tracking manual control; and (2) wind tunnel mounted model responses to tunnel flow instabilities. The study revealed that of all the criteria tested, only a subset is adequate to establish reliable model order. Based on this observation, a computationally effective working rule is proposed for model order determination for practical dynamical systems

EC 135 Rotorcraft System Identification - Estimation of Rigid Body and Extended Models from Simulated Data

At DLR, a new Active-Control-Technology/Flying Helicopter Simulator is being developed based on EC 135 helicopter. Accurate derivative models of EC 135 helicopter are required for the design of the model following control system. In the investigations reported in this document, system identification techniques are applied to obtain 6 DOF rigid body and 8 DOF extended models from EC 135 simulated data. Main rotor dynamics are explicitly included in estimation model and their effects on the helicopter on- and off axis response are investigated. Results from the identified models are presented and the obtainable benefits from the use of 8 DOF model are highlighted

Aircraft parameter estimation control and simulation (APES) computer: an Evaluation of quotations

Proposal of APES Computer system from the vendors are presented in this repor

Effects of flap position on longitudinal parameters of HFB-320

Parameter estimation results to evaluate the effects of small changes in flap position on the longitudinal derivatives of HFB-320 aircraft are presented. Maximum likelihood estimation procedure is used for kinematic consistency checking of flight test data and also for13; estimation of aerodynamic derivatives. Linear and nonlinear models are used to estimate dimensional and non-dimensional derivatives directly

Parametric identification of discontinuous nonlinearities

The present paper proposes a technique to identify systems with discontinuous nonlinearities. A well-established maximum likelihood estimation method has been suitably extended for this purpose. The technique enjoys the desired properties of consistency, efficiency, and unbiased estimates associated with the maximum likelihood estimation. The estimation method has been illustrated using a second-order dynamic system which incorporates specific nonlinear elements viz.: hysteresis and deadband plus saturation. Effects of additive noise on the parameter estimates have also been presented. Practical utility of the technique has been demonstrated in identifying from flight test data the discontinuous nonlinear effects in the control surface actuator system of an aircraft. (Author

Flight test plan/instrumentation system for MIG-21 aircraft parameter estimation

Various aspects of flight instrumentation system, comprising of aircraft motion sensors, data acquisition, signal conditioning unit and magnetic tape recorder, to be used for on-board flight test data acquisition have been discussed. Appropriate flight test programme has been worked out for MIG-21 aircraft to enable estimation of both longitudinal and lateral stability and control derivatives. A brief discussion about different types of control inputs suitable for parameter estimation has also been presented

Evaluation of recursive methods for aircraft parameter estimation

Three recursive algorithms: the Recursive Least Squares (RLS), Kalman Filter (EKF) and Discrete Fourier Transform (DFT) are formulated. A comparative study has been carried out in the off-line environment using simulated and flight data for longitudinal and lateral-directional modes of aircraft motion. The results from the standard iterative Output Error Method (OEM) form the basis for evaluating the performance of these recursive methods. All the recursive methods discussed in this document gave results matching with those from OEM. The overall performance of DFT method was found to be better than the RLS and EKF methods and and it is computationally simple. The DFT technique seems to be preferable for online identification purpose

Robust eigensystem assignment in multi input systems

Using simple geometric concepts it is shown that system sensitivity to parameter perturbation stems from the13; numerical ill conditioning of the normalised modal matrix (matrix of eigenvectors) to inversion, which is quantified by the absolute value of its determinant. By noting the freedom in partial selection of eigenvectors, beyond eigenvalue assignment in multi-input state feedback systems, an optimisation procedure is formulated to maximise the modal matrix determinant and thus minimise eigensystem sensitivity

Full scale fatigue control computer system software development-III

Generation of loading sequence on a random call basis13; starting from flight load envelope is discussed in this13; note for the special case when manoevres do not necessarily13; have trough gS below 19 level. The flight load envelope is13; usually generated by level excedences and hence does not .13; provide the information whether any excedence was a peak.13; or trough. The concept of associating all 'g' levels numerically below the chosen level as trough IgS, and all 'g' levels numerically above the chosen level as peak 'gS, is used. Modifications for the real time program which uses the generated load sequence to execute the loading on the aircraft through a tiactuator electrohydraulic loading system are discussed. These involve modifications for cycle formation, simple and complex manoevres and storage of loading sequence in core to avoid long term use of Electromechanical I/O devices