Maximum Control Surface Freeplay, Design and Flight Testing Approach on the F-22

Anderson, Wallace L.; Mortara, Sean

doi:10.2514/6.2007-1767

Cited by 17 publications

(6 citation statements)

References 2 publications

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“…Also notable is an exercise carried out on the F-22 to establish safe limits for control surface freeplay based on allowable LCO response levels, which were then confirmed by flight testing [10]. A theoretical and experimental study of LCO in a wing-store combination was reported in [11], where a von Karman nonlinear plate model of the wing was coupled to linear vortex lattice aerodynamics for the wing and slender body aerodynamics for the store.…”

Section: Introductionmentioning

confidence: 89%

Store-Induced Limit-Cycle Oscillations Due to Nonlinear Wing-Store Attachment

Padmanabhan

Dowell

Thomas

et al. 2016

Journal of Aircraft

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Several high-performance fighter aircraft exhibit store-induced limit-cycle oscillations, leading to pilot discomfort, potential structural fatigue, and flight envelope restrictions. The roles of various aerodynamic and structural factors causing the limit-cycle oscillation are not sufficiently understood, and their numerical exploration via time marching is computationally expensive. In this paper, the effects of nonlinear stiffness and damping in the wing-store attachments of the F-16 aircraft are examined, in the presence of steady flow aerodynamic nonlinearity, using the computationally efficient harmonic balance method. Structural mechanisms including cubic restoring force of both softening and hardening types, freeplay, and Coulomb friction are systematically evaluated, and the most likely among these are identified by comparing the computed limit-cycle oscillation results to flight data. An extension of the harmonic balance method to handle nonlinear unsteady aerodynamics along with structural nonlinearity is also proposed to enable rapid and accurate limit-cycle oscillation assessment of candidate store configurations.

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Section: Introductionmentioning

confidence: 89%

Store-Induced Limit-Cycle Oscillations Due to Nonlinear Wing-Store Attachment

Padmanabhan

Dowell

Thomas

et al. 2016

Journal of Aircraft

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“…As will be shown later, the sensitivity to e/d of the two models exhibited varies in both nature and severity, and therefore the value chosen in each case requires dedicated discussion. Following consultation of other freeplay studies which are informed by the examination of real-world systems, a value of 0.1°for the deadband half-width d is, though small, deemed to be representative of wear accrued during the service life of an aerospace system [16,38] and is therefore suitable for use in the present work. While the matrix format of the equations is retained in both models through their adaptation, the arctangent expression is integrated by calculating its value separately and adding the result into the relevant element of the matrix product KX, where K has had the original linear term (K p ) removed so that it does not feature in the multiplication.…”

Section: Freeplay Adaptationmentioning

confidence: 99%

Stability analysis of whirl flutter in rotor-nacelle systems with freeplay nonlinearity

2021

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Tiltrotor aircraft are growing in prevalence due to the usefulness of their unique flight envelope. However, aeroelastic stability—particularly whirl flutter stability—is a major design influence that demands accurate prediction. Several nonlinearities that may be present in tiltrotor systems, such as freeplay, are often neglected for simplicity, either in the modelling or the stability analysis. However, the effects of such nonlinearities can be significant, sometimes even invalidating the stability predictions from linear analysis methods. Freeplay is a nonlinearity that may arise in tiltrotor nacelle rotation actuators due to the tension–compression loading cycles they undergo. This paper investigates the effect of a freeplay structural nonlinearity in the nacelle pitch degree of freedom. Two rotor-nacelle models of contrasting complexity are studied: one represents classical whirl flutter (propellers) and the other captures the main effects of tiltrotor aeroelasticity (proprotors). The manifestation of the freeplay in the systems’ dynamical behaviour is mapped out using Continuation and Bifurcation Methods, and consequently the change in the stability boundary is quantified. Furthermore, the effects on freeplay behaviour of (a) model complexity and (b) deadband edge sharpness are studied. Ultimately, the freeplay nonlinearity is shown to have a complex effect on the dynamics of both systems, even creating the possibility of whirl flutter in parameter ranges that linear analysis methods predict to be stable. While the size of this additional whirl flutter region is finite and bounded for the basic model, it is unbounded for the higher complexity model.

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“…Therefore, modern advanced fighters and tactical missiles generally regard high maneuverability and agility as one of their key characteristics. For example, the fourth generation fighter (such as F-22) has post-stall maneuverability, requiring rapid nose pointing ability [1]. The future unmanned combat aircraft will have much higher mobility and agility than the present manned combat aircraft due to the removal of physiological overload restrictions.…”

Section: Introductionmentioning

confidence: 99%

Minimum Parameters Learning-Based Dynamic Surface Control for Advanced Aircraft at High Angle of Attack

et al. 2019

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Aiming at the difficulty of post-stall maneuvering control modeling and control of advanced aircraft under unsteady aerodynamics, a control method with high control accuracy and fast computation speed is proposed based on Radial Basis Function (RBF) network with minimum parameters learning (MPL) and dynamic surface control (DSC) method. Firstly, the aerodynamic characteristics of post-stall maneuvers are analyzed based on the experimental data of large-scale oscillation wind tunnels, and the key factors affecting the unsteady aerodynamic forces are obtained. Then, an accurate unsteady aerodynamic model is established based on the improved extreme learning machine (ELM) method. Secondly, the influence of unsteady aerodynamic forces on the control of post-stall maneuvers is considered. For the uncertainty of advanced aircraft model, high angle of attack flight control laws based on RBF-DSC are designed. In order to improve the calculation speed of the above control law and optimize the parameters, a post-stall maneuver control law method based on MPL-RBF-DSC is designed, and the stability of the method is proved. The coordinated allocation of the conventional aerodynamic surfaces and thrust vectors is realized based on the daisy chain method. Finally, the typical maneuver simulation of ''Cobra'' is carried out, which highlights the advantages of the design method in this paper, such as high control accuracy, short calculation time and strong robustness.INDEX TERMS Flight control, high angle of attack, wind tunnel test, unsteady aerodynamics modeling, MPL-RBF-DSC method.

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Maximum Control Surface Freeplay, Design and Flight Testing Approach on the F-22

Cited by 17 publications

References 2 publications

Store-Induced Limit-Cycle Oscillations Due to Nonlinear Wing-Store Attachment

Store-Induced Limit-Cycle Oscillations Due to Nonlinear Wing-Store Attachment

Stability analysis of whirl flutter in rotor-nacelle systems with freeplay nonlinearity

Minimum Parameters Learning-Based Dynamic Surface Control for Advanced Aircraft at High Angle of Attack

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