Experimental Investigation of Aerodynamic Hysteresis Using a Five-Degree-of-Freedom Wind-Tunnel Maneuver Rig

Abstract

The high incidence aerodynamics of a lightweight jet trainer aircraft model has been investigated using a novel five degree-of-freedom (DoF) dynamic manoeuvre rig, recently updated with improved actuation and data acquisition systems, in the 7 × 5 closed-section low-speed wind tunnel at the University of Bristol. The major focus was to identify the nonlinear and unsteady aerodynamic characteristics specific to the stall region and which affect free-to-move aircraft model behaviour. First, the unstable equilibrium states in the limit cycle regions were stabilized, and so observed, over a wide range of angles of attack using a simple elevator feedback control law based on pitch angle and pitch-rate sensor measurements. Tests with two degrees-of-freedom, namely the aircraft model and rig arm pitch angles, revealed the existence of static hysteresis in the normal force acting on the aircraft model in the stall region. Unlocking the aircraft model in roll and yaw accompanied by feedback stabilization of the lateral-directional modes of motion demonstrated onset of asymmetric aerodynamic rolling and yawing moments in this four degree-of-freedom configuration. This observation implicitly indicates a link between the static hysteresis in the normal aerodynamic force with an onset of aerodynamic asymmetry. The experimental results show the efficiency of the updated multi-degree-of-freedom actively controlled manoeuvre rig in providing insight into complicated aerodynamic effects within the stall region. Nomenclature C L = aircraft model lift coefficient

Capturing nonlinear time-dependent aircraft dynamics using a wind tunnel manoeuvre rig

“…It also allows for separate estimation of α and q stability derivatives. Furthermore, even without a load cell, static lift loads can be estimated through the compensator model when the latter is used to balance the system [15]. When the model is driven by its onboard control surfaces or excited by an external device such as a gust generator, the compensator can be used to apply compensation for the influence of the rig on model behaviour or alternatively to force model motions (e.g.…”

“…the compensation of roll motion using the aerodynamic compensator (Figure 1a) [3], investigating aerodynamic hysteresis utilising a feedback control law to track the aircraft's equilibria [15] and studying the effects of geometric constraints on the coupled rig/aircraft dynamics by feedback of load cell reaction force measurements to the compensator control surfaces [27].…”

“…However, a new feature has been identified here: the results suggest the existence of an inner LCO within the hysteretic region of the high α LCO. The hysteresis phenomena in this region were studied in [15] and found to be associated with an asymmetric separated flow structure on the wings. It was shown in [1], by testing at nonzero model yaw angles, that this hysteretic behaviour is sustained over a range of sideslip angles (although their extent does vary noticeably); this suggests that the existence of these structures is robust to the flow conditions but their characteritics are dependent on them.…”

An Innovative Experimental Approach to Lateral-Directional Flying Quality Investigation for Tailless Aircraft

“…The results of the free flight test validated the designed control laws and indicated satisfactory flight behavior. One can see that the main idea is to allow the scaled tailless aircraft to fly in a wind tunnel working section freely or with partially constrained motion imposed by a dynamic rig [17], which has previously been used for identification and control investigations of conventional aircraft [18]- [22].…”

Post-stall flight dynamics of commercial transport aircraft configuration: A nonlinear bifurcation analysis and validation

“…The motivation for this research stems from the recognition that the advanced wind tunnel virtual flight test 16–19 that could closely replicate real aircraft motions is a promising way to be an alternative for validation in high-risk conditions. A series of low-speed static and dynamic wind tunnel tests of a common research model over an extended angle of attack/sideslip envelope was conducted and the dynamic wind tunnel data from rotary balance and forced oscillation testing with static wind tunnel data was blended to achieve the aerodynamic model.…”