Development of a Tilt-Rotor Aircraft Model Using System Identification Technique

Authors: Antonio Vitale, Nicola Genito, Giovanni Cuciniello, Ferdinando Montemari

Abstract:

The introduction of tilt-rotor aircraft into the existing civilian air transportation system will provide beneficial effects due to tilt-rotor capability to combine the characteristics of a helicopter and a fixed-wing aircraft into one vehicle. The disposability of reliable tilt-rotor simulation models supports the development of such vehicle. Indeed, simulation models are required to design automatic control systems that increase safety, reduce pilot's workload and stress, and ensure the optimal aircraft configuration with respect to flight envelope limits, especially during the most critical flight phases such as conversion from helicopter to aircraft mode and vice versa. This article presents a process to build a simplified tilt-rotor simulation model, derived from the analysis of flight data. The model aims to reproduce the complex dynamics of tilt-rotor during the in-flight conversion phase. It uses a set of scheduled linear transfer functions to relate the autopilot reference inputs to the most relevant rigid body state variables. The model also computes information about the rotor flapping dynamics, which are useful to evaluate the aircraft control margin in terms of rotor collective and cyclic commands. The rotor flapping model is derived through a mixed theoretical-empirical approach, which includes physical analytical equations (applicable to helicopter configuration) and parametric corrective functions. The latter are introduced to best fit the actual rotor behavior and balance the differences existing between helicopter and tilt-rotor during flight. Time-domain system identification from flight data is exploited to optimize the model structure and to estimate the model parameters. The presented model-building process was applied to simulated flight data of the ERICA Tilt-Rotor, generated by using a high fidelity simulation model implemented in FlightLab environment. The validation of the obtained model was very satisfying, confirming the validity of the proposed approach.

Keywords: Flapping Dynamics, Flight Dynamics, System Identification, Tilt-Rotor Modeling and Simulation.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1132667

References:

[1] L. A. Young et al., “Civil Tiltrotor Aircraft Operations”, 11th AIAA Aviation Technology, Integration and Operations (ATIO) Conference, AIAA 2011-6898, 2011.
[2] M. Foster, “The Future Evolution of the Tiltrotor”, AIAA/ICAS International Air and Space Symposium and Exposition, AIAA 2003-2652, 2003.
[3] R. R. Reber, “Civil TiltRotor Transportation for the 21st Century”, AIAA International Powered Lift Conference, AIAA 93-7475, 1993.
[4] W. Johnson, G. Yamauchi and M. E. Watts, “NASA Heavy Lift Rotorcraft Systems Investigation”, NASA/TP 213467, December 2005.
[5] M. Miller, J. Narkiewicz, “Tiltrotor Modelling for Simulation in Various Flight Conditions”, Journal of Theoretical and Applied Mechanics, Vol. 44, N° 4, pp. 881-906, Warsaw 2006.
[6] L. Yuan, W. Zhang, X. Wen, “Study on Model and Simulation of the Tilt Rotor Aircraft in Transition Mode”, International Conference on Advances in Mechanical Engineering and Industrial Informatics, AMEII, 2015.
[7] S. W. Ferguson, “A Mathematical Model for Real Time Flight Simulation of a Generic Tilt-Rotor Aircraft”, NASA-CR-166536, September 1988.
[8] L. Haixu, Q. Xiangju, W. Weijun, “Multi-body Motion Modeling and Simulation for Tilt Rotor Aircraft”, Chinese Journal of Aeronautics Vol. 23, 2010, pp. 415-422.
[9] O. Juhasz, “Flight Dynamics Simulation Modeling and Control of a Large Flexible Tiltrotor Aircraft”, PhD Dissertation Thesis, University of Maryland, 2014.
[10] P. Masarati, G. L. Ghiringhelli, M. Lanz, and P. Mantegazza, “Experiences of Multibody Multidisciplinary Rotorcraft Analysis”, XVI Congresso Nazionale AIDAA, Palermo, IT, September 2001
[11] R. W. Du Val, “A Real-Time Multi-Body Dynamics Architecture for Rotorcraft Simulations”, RAeS and AHS International Conference on the Challenge of Realistic Rotorcraft Simulation, London, UK, November 2001.
[12] FlightLab Theory Manual, Vol. One, Advanced Rotorcraft Technology, Inc., Mountain View CA, 2006.
[13] W. Johnson, CAMRAD II Comprehensive Analytical Model of Rotorcraft Aeromechanics and Dynamics - Theory Manual, Johnson Aeronautics Palo Alto, CA, June 1993.
[14] G. D. Padfield, Helicopter Flight Dynamics – The Theory and Application of Flying Qualities and Simulation Modelling, Second Edition, Oxford, UK, Blackwell Publishing Ltd, 2007, ch. 3.
[15] B. L. Stevens and F. L. Lewis, Aircraft Control and Simulation, Second Edition, John Wiley & Sons Inc., Hoboken, New Jersey, 2003.
[16] H. Garnier, M. Mensler and A. Richard, “Continuous-time Model Identification from Sampled Data: Implementation Issues and Performance Evaluation" International Journal of Control, Vol. 76, Issue 13, 2003, pp 1337–1357.
[17] L. Ljung, System Identification Toolbox User's Guide, The Mathworks Inc., 2012.
[18] D. E. Wells, E. J. Krakiwsky, The Method of Least Squares, Lecture Notes 18, University of New Brunswick, Canada, 1997.
[19] P. Alli, F. Nannoni, M. Cicalè, “ERICA: the European Tiltrotor Design and Critical Technology Projects”, AIAA/ICAS International Air and Space Symposium and Exposition, Dayton, OH, July 2003.