Effects of structural nonlinearities on limit cycle response of aerodynamic surfaces

The describing function method is used to analyze the flutter characteristics of the CF-18 aircraft with structural nonlinearities. The first nonlinearity studied is located at the CF-18 wing-fold hinge. From ground test data, this hinge can be represented by a bilinear spring. A flutter sensitivity study is carried out, which shows that when the hinge stiffness is reduced, divergent flutter involving the wing bending and torsion modes is replaced by limit-cycle flutter of the wing torsion and outer wing rotation modes. Another form of nonlinearity at the outboard leading-edge flap is also studied by treating it as a spring with free-play. Limit-cycle oscillations are possible only within a small range of velocities in the vicinity of its linear flutter velocity. The flutter modes remain unchanged and their frequencies are practically constant for hinge-stiffness values ranging from a few percent to its nominal value. Positive aileron angles are found to be more effective in alleviating limit-cycle flutter at the wing-fold than negative angles. Similar observations are made at the outboard leading-edge flap hinge where downward deflection of the aileron gives larger values of the preload and, hence, the equivalent stiffness than upward deflection. Nomenclature A = maximum positive displacement from equilibrium position AQ = midpoint of oscillation of nonlinear spring A i = amplitude of oscillation measured from A 0 K e = equivalent spring stiffness Ki,K 2 = stiffnesses of bilinear spring M = load MI = amplitude of sinusoidal load P = preload 2S = region where softer spring acts AIL = aileron LEF = leading-edge flap TEF = trailing-edge flap t = time x = displacement Xi = amplitude of sinusoidal displacement o> = frequency

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“…2) is set equal to zero. Using the method given by Laurenson et al, 5 preload can be derived to first-order accuracy as…”

Section: Equivalent Stiffness Approximationsmentioning

confidence: 99%

Effects of structural nonlinearities on flutter characteristics of the CF-18 aircraft

Lee

Tron

1989

Journal of Aircraft

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The Aeroelastic Response of a Two-Dimensional Airfoil with Bilinear and Cubic Structural Nonlinearities

Price

Alighanbari

Lee

1995

Journal of Fluids and Structures

161

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An Investigation of Stability in the Large Behaviour of a Control Surface With Structural Non-Linearities in Supersonic Flow

Lewis¹

2002

Journal of Sound and Vibration

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Effects of structural nonlinearities on limit cycle response of aerodynamic surfaces

Cited by 7 publications

References 2 publications

Effects of structural nonlinearities on flutter characteristics of the CF-18 aircraft

Effects of structural nonlinearities on flutter characteristics of the CF-18 aircraft

The Aeroelastic Response of a Two-Dimensional Airfoil with Bilinear and Cubic Structural Nonlinearities

An Investigation of Stability in the Large Behaviour of a Control Surface With Structural Non-Linearities in Supersonic Flow

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