Taking the results showed in the previous sections the following conclusions can be made.
5.1.
About R-GUI
About R-GUI, examining the results showed in R-GUI Validation section can be declared that R-GUI doesn’t cause changing of the results in the analysis performed. This is specifically demonstrated for the analysis previously reported but it can be extended for all analysis executable. Instead, the use of R-GUI versus the classical Command Prompt of Windows®, and so the application file “RSim_Caller.exe”, have brought a simplification in the RSim utilization and reduction of the time needed to perform any analysis.
As previously stated, the analysis executed using the application file “RSim_Caller.exe” needed a long preparation due to the writing of the FMI file, in ASCII format, containing the input data for the analysis. In order to resolve this problem and more general to improve the use of RSim, R-GUI has been developed. Therefore, it is used not only to call the standard RSim libraries, but it contained many functions, as showed in the Functions Implementation section, used to work easily with the simulation code, RSim. At the end R-GUI has been tested by the AW flight mechanics specialists who are showed themselves satisfied from the functions and the solutions developed for it.
In additional R-GUI is developed with an open source language program, which is free from taxes and licences. In this way, the cost of an innovative flight dynamic rotorcraft simulator is lower and more competitive than the commercial codes present in the aeronautical field.
For this reasons, R-GUI is the winning response for RSim in order to intensify its utilization in the AW Flight Mechanics department.
Conclusions and future developments
5.2.
Linear routine
In order to complete the function developed in R-GUI is also developed the linearization one. The relative function in RSim has not been developed yet. For this reason, firstly it has been developed in the simulation code (RSim) and then in R-GUI.
As previously stated in the Linear Analysis section, the function developed in RSim is able to define the matrixes of linearization in numerical way, through a numerical perturbation applied at every state for the matrix or every input for the matrix . The value of the numerical perturbation used to evaluate the matrixes has been defined with specific methods as explained in Definition of numerical perturbation section.
When the linear matrixes have been correctly defined the following step is the evaluation of the linear responses of the vehicle as function of the time history commands. These are evaluated in terms of state variables through the time integration of the derivates state as explained in Comparison of the responses section or through Equation 28. The linear responses have been evaluated in three flight conditions; hover, middle speed and high speed and for each one for four typical types of commands; collective doublet, longitudinal doublet, lateral doublet, pedal doublet.
The same thing has been done in the non linear analysis, using RSim in the standard way.
At the end, the two kinds of response have been compared in order to define the reliability of the linear analysis. Those are reported in the Comparison of the responses section where a good matching between the linear and non linear responses can be observed. Therefore, taking into consideration those results the linear analysis performed can be considerate as correct.
The final task of the linear analysis is the definition of the root locus in order to analyze the response of the vehicle as function of speed. This is described by the
movement of the poles (eigenvalues of matrix ) evaluated at several values of speed as explained in the Root Locus section.
As previously stated in the Graphical representation section, the root locus is useful to understand the behaviour both in short and long time of the rotorcraft. In additional it is used to evaluate the instability of the system and the time in which the several components of the response became important. At the same time, the components of the eigenvectors, defined in order to plot the root locus as explained in Eigenvectors section, are useful to define the pattern of the response at a specific value of speed, as confirmed by the free response evaluated in the previous section for three values of speed.
Thanks of this graphical representation, some discontinuity may be seen about the poles movements due to the inconsistency of the simulation code, the linear function or the rotorcraft model used.
In this case, an important discontinuity can be seen for the Pitch Oscillation mode. However, considering the good matching between the linear and not linear responses showed in Comparison of the response section, can be stated that the linearization function can be evaluated correctly the linear model of the vehicle, therefore some inconsistency have to investigate in the simulation code or in the rotorcraft model.
Exactly, the discontinuity showed in the root locus for the Pitch Oscillation mode nearby the highlights a possible inconsistency of the RSim code.
This unexpected behaviour can be related to aerodynamics loads of the lifting surfaces and more specifically to the definition of lifting component aerodynamics angles which have not been accurately validated in the version of RSim used in the present study.
5.3.
Future developments
In this work a pre-post processor has been developed to improve the utilization of a rotorcraft simulation code used in AW.
Conclusions and future developments
Moreover, a real time and linear analysis functions have been developed for real time analysis and linear model evaluation, respectively.
Taking into consideration the results defined in this work the future developments which may be applied are:
Updating of RSim; definition of an FCS.
The first point regards RSim in order to define and resolve the inconsistency showed in the previous analysis. Exactly the linear analysis has underlined an inconsistency probably due to a not correct evaluation of the aerodynamic loads of the lifting surfaces.
Therefore the next step may be the evaluation of the aerodynamic forces in several attitude condition, in order to define the relation between the loads and the attitude of the vehicle. These results will be compared with the same obtained by a simulation code already used in AW, in order to prove them reliability.
In additional, regarding the model used for all of the analysis, it is referred to a rotorcraft without any control system, indeed it appears how a unstable system. This is confirmed by the linear analysis which have showed some poles in the positive real plane as showed in the Figure 4.30 and in Figure 4.31. Obviously, if the model is unstable, the response will diverge in the time defined by the unstable poles. Therefore an interesting develop of R-GUI may be the implementation of a control system. The controller may be used to make stable the system in all of the flight conditions, at each value of speed, and also to improve the responses of the vehicle through the changing of its dynamics characteristics, for example increasing the damping of the Dutch Roll mode. However, R-GUI might implement several type of control system which are chosen by the user according to the analysis which will be executed.
[1]. AW_FMR_input_file_format_specification_v4.doc; (Internal documentation of AW).
[2]. RSim_DesignDoc.pdf; (Internal documentation of AW).
[3]. FMR_IN-OUT_Version_7.0.xlsx; (Internal documentation of AW).
[4]. Padfield, Gareth D. - Helicopter Flight Dynamics: The Theory and Application
of Flying Qualities and Simulation Modellin.
[5]. Jean Debord - Dmath; Math library for Delphi, FreePascal and Lzarus. [6]. Prof. E.Denti - Dispense dal corso di Dinamica del Volo.
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