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Research Papers

Helicopter Ground Resonance Phenomenon With Blade Stiffness Dissimilarities: Experimental and Theoretical Developments

[+] Author and Article Information
Leonardo Sanches

Faculty of Mechanical Engineering,
Federal University of Uberlândia,
Av. João Naves de Ávila, 2121—Bloco 1R,
Santa Mônica, Uberlândia, MG 38400-902, Brazil
e-mail: ls.leonardosanches@gmail.com

Guilhem Michon

Institut Clémant Ader, ISAE,
Université de Toulouse,
Toulouse 31055,France
e-mail: guilhem.michon@isae.fr

Alain Berlioz

Insitut Clémant Ader, UPS,
Université de Toulouse,
Toulouse 31077,France
e-mail: alain.berlioz@univ-tlse3.fr

Daniel Alazard

Département Mathématique,
Informatique et Automatique, ISAE,
Université de Toulouse,
Toulouse 31055,France
e-mail: daniel.alazard@isae.fr

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received September 19, 2012; final manuscript received March 23, 2013; published online June 28, 2013. Assoc. Editor: Olivier A. Bauchau.

J. Vib. Acoust 135(5), 051028 (Jun 28, 2013) (7 pages) Paper No: VIB-12-1263; doi: 10.1115/1.4024217 History: Received September 19, 2012; Revised March 23, 2013

Recent works have studied ground resonance in helicopters under the aging or damage effects. Indeed, blade lead-lag stiffness may vary randomly with time and differ from blade to blade. The influence of stiffness dissimilarities between blades on the stability of the ground resonance phenomenon was determined through numerical investigations into the periodic equations of motion, treated using Floquet's theory. A stability chart highlights the appearance of new instability zones as a function of the perturbation introduced on the lead-lag stiffness of one blade. In order to validate the theoretical results, a new experimental setup was designed and developed. The ground resonance instabilities were investigated using different rotors and the boundaries of stability were determined. A good correlation between both theoretical and experimental results was obtained and the new instability zones, found in asymmetric rotors, were verified experimentally. The temporal responses of the measured signals highlighted the exponential divergence in the instability zones.

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References

Coleman, R. P., and Feingold, A. M., 1957, “Theory of Self-Excited Mechanical Oscillations of Helicopter Rotors With Hinged Blades,” NASA Technical Report TN 3844.
Wang, J., and Chopra, I., 1992, “Dynamics of Helicopters in Ground Resonance With and Without Blade Dissimilarities,” AIAA Dynamics Specialists Conference, Dallas, TX, April 16–17, AIAA Paper No. 92-1208, pp. 273–291. [CrossRef]
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Sanches, L., Michon, G., Berlioz, A., and Alazard, D., 2011, “Instability Zones for Isotropic and Anisotropic Multibladed Rotor Configurations,” Mech. Mach. Theory, 46(8), pp. 1054–1065. [CrossRef]
Sanches, L., Michon, G., Berlioz, A., and Alazard, D., 2012, “Parametrically Excited Helicopter Ground Resonance Dynamics With High Blade Asymmetries,” J. Sound Vib., 331(16), pp. 3897–3913. [CrossRef]
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Skjoldan, P., and Hansen, M., 2009, “On the Similarity of the Coleman and Lyapunov-Floquet Transformations for Modal Analysis of Bladed Rotor Structures,” J. Sound Vib., 327(3–5), pp. 424–439. [CrossRef]
Sanches, L., Michon, G., Berlioz, A., and Alazard, D., 2009, “Modélisation Dynamique d'un Rotor sur Base Flexible,” Congress Français de Mécanique, Marseille, France, August 24–28.
Bauchau, O., and Nikishkov, Y., 2001, “An Implicit Floquet Analysis for Rotorcraft Stability Evaluation,” J. Am. Helicopter Soc., 46(3), pp. 200–209. [CrossRef]
Floquet, G., 1883, “Sur les Équations Différentielles Linéaires à Coefficients Périodiques,” Ann. Sci. Ećole Norm. Sup., 2(12), pp. 47–88.
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Figures

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Fig. 1

Representation of the mechanical model

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Fig. 2

The final design of the experimental helicopter for ground resonance analysis

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Fig. 3

The experimental setup: (a) global view and (b) detailed view

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Fig. 4

Blade oscillations with set 1 of blade laminas in panel (a) and its frequency spectrum diagram in panel (b)

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Fig. 5

Comparison between the numerical and experimental instability prediction for IR configuration

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Fig. 6

Time history of the experimental helicopter with IR configuration at Ω ≈ 7.5 Hz; (a) blades and (b) fuselage accelerations

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Fig. 7

Rotor deformation shape for the experimental helicopter EH with IR at Ω ≈ 7.5 Hz

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Fig. 8

Comparison between the numerical and experimental instability prediction for AR configuration

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Fig. 9

Time history of the experimental helicopter with AR configuration at Ω ≈ 2.5 Hz; (a) blades and (b) fuselage accelerations

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