Identification Of Helicopter Flight Dynamics Model And Investigation On Maneuver Flight

The flying quality is one of the most important design criteria of modern helicopters. The helicopter flight dynamics model is the basis of doing flying quality research. The accuracy of the flight dynamics model directly affects the precision of flying quality assessment. Since the aerodynamic phenomenon of main rotor is complex, there is aerodynamic interference among main rotor, fuselage, tail rotor, horizontal tail etc. and the coupling of each degree of freedom is serious, traditional modeling technique which is based on theoretical analyzing cannot provide models with high confidence. System identification technique that based on flight test data becomes an effective way of increasing the accuracy of helicopter flight dynamics model. Time domain identification technique is one of the main methods for the identification of helicopter flight dynamics model since it is convenient to deal with real signal in time domain.The current time domain identification methods can provide identification results with high accuracy when it has been used to identify longitudinal or lateral flight dynamics model without coupling, but the identification results are not good enough when it has been applied to longitudinal/lateral coupled flight dynamics model. The main reason is there are too many parameters to be identified in longitudinal/lateral coupled model, at the mean time, these parameters are coupled seriously and have large differences in sensitivity. All the above features will cause the Hessian information matrix ill heavily. In connection with this problem, a multi-step algorithm with different cost function selection in different identification step has been presented in this paper to implement the identification of longitudinal/lateral coupled helicopter flight dynamics model.With the requests of helicopter flying quality to the actual application higher and higher, 6 degrees of freedom rigid body flight dynamics model cannot meet the requirement of doing flying quality research. The high order flight dynamics model with rotor flap degree of freedom should be the basic model of investigating flying quality. But the time domain identification technique always provides unsatisfying identification results to high order model. The main reason is the time domain technique gives high weighting to the low frequency part of the model which decreases the identification accuracy of high frequency part, so that the whole identification accuracy is decreased. However, frequency domain identification technique can solve this problem. A fast frequency domain identification algorithm for the helicopter flight dynamics model has been presented in this paper. In this algorithm, the flight test data was transformed to frequency domain by using FFT with Hanning window. Then Bode sensitivity function was established and combined with theoretical analysis to determine the model structure for final identification. A fast optimization algorithm was created to speed up the whole identification procedure according to the fact that different parameters to be identified has different converge speed. After that, the identification model for rotor flap movement has been created and then the 6 degrees of freedom low order flight dynamics model has been extended to 9 degrees of freedom high order model. Identification of high order model has been executed by combing fast frequency identification algorithm and multi-step algorithm. The comparison between high order model and 6 degrees of freedom rigid body model was also implemented.Up till now, the identification methods both in time domain and frequency domain that have been used in engineering are all belongs to statistic based method. The statistic information about noise and random error like mean value, variance etc. is required for these methods. But it is difficult to obtain such information during helicopter flight test. A new identification method based on set-membership identification theory has been established in this paper. This method doesn't need the statistic information about noise but only requires the bound. Since the helicopter flight dynamics model has lots of heavily coupled parameters, it is difficult to obtain explicit relationship between model outputs and parameters to be identified. An indirect identification algorithm has been established to solve the set-membership identification problem of state-space formed model. The concept of generalized noise has been introduced, solved the difficulties of identifying helicopter flight dynamics model which caused by severe coupling and large differences in sensitivity of parameters to be identified. Then a two step method for the set-membership identification of helicopter flight dynamics model has been established.The maneuver flight performance of helicopter is one of the important contents in the flying quality research. The current way of investigating maneuver flight is using inverse method to calculate the control inputs to implement certain maneuver flight. The deficiencies of inverse method are: first, inverse method uses fixed flight path to describe certain maneuver task. The generality of this kind of description is not good enough since a lot of maneuver tasks are unable to define fixed flight path; second, inverse method need solve the flight dynamics equations inversely to obtain the controls for implementing certain maneuver task. The efficiency of such calculation is low since it needs iteration. This paper introduces navigation calculation model and control calculation model. It dose not only make the description of all kinds of maneuver tasks conveniently, but also increase the computation efficiency of calculating controls for implementing maneuver flight. The design of control law and navigation law began with initial value calculation through the design method of linear quadratic regulator, and then determined the final value by tuning. The state-space flight dynamics model required in the control law design can be obtained through system identification. At last, the control inputs for implementing slalom, pirouette and depart/abort maneuver of UH-60 helicopter has been calculated separately according to the performance standard specified in ADS-33E-PRF.