Remote control actuated wind tunnel models: design and testing best practices

Abstract

Remote Control Actuation (RCA) of wind tunnel models provides a paradigm shift in wind tunnel testing. Traditional wind tunnel testing involves fabricating and testing numerous fixed parts requiring time consuming model changes in order to test configurations of interest. RCA wind tunnel models seek to replace these fixed wind tunnel parts with moving, controllable parts. Thus RCA enables increased productivity, improved data quality, and reduced cost of wind tunnel testing. An international team from Boeing, Deharde Maschinenbau, European Transonic Windtunnel (ETW), and NASA Langley Research Center has developed and tested multiple RCA models in high speed cryogenic wind tunnels in order to demonstrate, scope, and validate the technology. Over the last decade, multiple RCA enabled wind tunnel models were designed, built, and tested at cryogenic high speed tunnels such as NASA Langley and ETW enabling the technology to mature with each iteration, Figure 1. Tests of multiple models are described here along with design and testing best practices. A 2D airfoil with a controllable spoiler provided an efficient platform to develop and demonstrate RCA capabilities. The spoiler system included an integrated solid-state actuator using Shape Memory Alloy (SMA), mechanisms for torque transmission and braking, integrated sensors and electronics, and advanced controls. The spoiler airfoil was designed to incorporate a suite of sensors, including pressure taps, thermocouples, spoiler position sensors, and strain gages for load sensing. The team designed, built, assembled, and laboratory tested the 2D spoiler test article prior to operational testing in Pilot European Transonic Windtunnel (PETW) and NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel (TCT). Later improvements to the model were made to increase rate and precision. Modifications included highly robust, next generation Nickel-Titanium-Hafnium SMA actuation elements, efficient induction heating, and an improved control system. The system was tested at NASA TCT in 2021 demonstrating a 10x rate improvement, more precise spoiler angle control down to 0.1 degrees, and robust disturbance rejection. The system performance was remarkably stable over the five day test period and provided a performance expectation for future wind tunnel models. The RCA technology was validated for cryogenic high-speed wind tunnel testing during production-type testing of a modified 4.5% 787-8 half-model with multiple RCA surfaces at ETW main tunnel. Three primary RCA surfaces: aileron, outboard spoiler (OB Spoiler) and inboard spoiler (IB spoiler) were designed, built and tested based on lessons learned and best practices from previous tests over the preceding 4+ years, in particular the initial testing of the 2D inboard Spoiler. The test demonstrated a 90% reduction in wind tunnel test time using RCA surface rather than changing out traditional fixed parts. The test identified challenges for RCA wind tunnel testing, including the ability to hold position under rapidly changing loads. Subsequent development and testing of the 2D Spoiler model demonstrated technical solutions to these challenges. The improved 787 model will be tested at the NASA Langley National Transonic Facility (NTF) in early 2023. RCA wind tunnel testing has matured over multiple design, build, test iterations resulting in a commercial ready technology that is fundamentally changing wind tunnel testing. This presentation describes the design and testing of these wind tunnel models and provides a glimpse at the future of the technology that will provide significant benefits to aerospace vehicle development.