Modeling and characterization of the impact of control surface free-play on flutter for an all moving surface

Abstract

Dynamics of flutter is an important consideration in the design of aircraft structures. Flutter is an unstable selfexcitation of the structure due to an undesirable coupling of structural elasticity and aerodynamics. Flutter is very difficult to predict and its occurrence can lead to catastrophic structural failure. The dynamics of flutter are affected by several factors including nonlinearities in structural stiffness, damping, and free-play in control surfaces. The free-play nonlinearity in control surfaces mechanisms is similar to the backlash in gears. Such nonlinearity introduces persistent limit cycle oscillations (LCO's) and significantly affects the onset of flutter. The impact of free-play on the flutter speed and frequency is not fully understood and is an active area of research. Historically, very conservative estimates have been used for the allowable freeplay. The current military specification limit for free-play is based on the wind tunnel tests performed in 1950's at the Wright Air Development Center (WADC). The key contribution of this paper lies in gaining deeper understanding of free-play dynamics to enable more accurate modeling of free-play and predict its impact on flutter speed and frequency. The proposed modeling methodology is validated via close agreement of the simulation with WADC test data. Energy-based novel approach is presented for life cycle assessment and to predict flutter instability.

Understanding Energy Transfer in Aeroelastic Flutter

“…Data was collected for varying speeds until LCO and/or divergence was observed. Different combinations of free-play settings were used and data was collected to see the LCO onset velocity dependence on the free-play magnitude 1,11 . The experimental tests conducted by VSI Aerospace, Inc. produced large amounts of data indicating relationship between onset flow speed, free-play, and flutter onset velocity.…”

Understanding energy transfer in aeroelastic flutter and exploiting free-play induced flutter for energy harvesting

“…As a result, the study is focussed on the energy recovery from aeroelastic response of the structure. The work in this thesis leverages the previous results given in Asjes (2015), Whitmer et al (2012) and Asjes et al (2014). The work demonstrating flutter dependence on free-play parameter, development of 2D system, modelling free-play as hyperbolic nonlinearity and wind tunnel experimental results presented before are used as the foundation for this thesis.…”

“…After gaining insights into energy transfer phenomena taking place in 2D configuration, high fidelity 3D computational model is developed. The wind tunnel experimental results from previous studies [Whitmer et al (2012)] is used as a reference for the 3D computational model development to establish two way coupled system simulation. The energy evolution data obtained from 3D simulations was then studied in detail similar to the 2D case.…”

“…, Asjes et al (2014) andWhitmer et al (2012) on free-play nonlinearity modelling and its theoreticalexperimental study of how flutter is affected by free-play. This work gives a systematic approach to characterize free-play effects for an accurate prediction of stability and performance boundaries.…”

Nonlinear analysis of a two- and three-degree-of-freedom aeroelastic system with rotational stiffness free-play

“…In work related to this research, Whitmer et al (2012) present results of a three-dimensional (3D) modeling methodology for the all-moving control surface with rotational free-play. In this study, a full 3D model is constructed using a segmented, lumped parameter structure, and the free-play nonlinearity is implemented as a piecewise linear switching scheme that transitions the system between an inner state and an outer state (i.e., inside the deadband and outside the deadband, respectively).…”