Optimal positioning of piezoelectric actuators on a smart fin using bio-inspired algorithms

Buffet is an aeroelastic phenomenon associated with high performance aircraft especially those with twin vertical tails. In particular, for the F/A-18 aircraft at high angles of attack, vortices emanating from wing/fuselage leading edge extensions burst, immersing the vertical tails in their wake. The resulting buffet loads on the vertical tails are a concern from fatigue and inspection points of view. Recently, a 1/6-scale F-18 wind-tunnel model was tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center as part of the Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program to assess the use of active controls in reducing vertical tail buffeting. The starboard vertical tail was equipped with an active rudder and the port vertical tail was equiped with piezoelectric actuators. The tunnel conditions were atmospheric air at Mach 0.10. By using single-input-single-output control laws at gains well below the physical limits of the actuators, the power spectral density of the root strains at the frequency of the first bending mode of the vertical tail was reduced by as much as 60 percent up to angles of attack of 37 degrees. Root mean square (RMS) values of root strain were reduced by as much as 19 percent. The results herein illustrate that buffet alleviation of vertical tails can be accomplished using simple active control of the rudder or poezoelectric actuators. In fact, as demonstrated herein, a fixed gain single input single output control law that commands piezoelectric actuators may be active throughout the high angle-of-attack maneuver without requiring any changes during the maneuver. Future tests are mentioned for accentuating the international interest in this area of research.

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Vertical Tail Buffeting Alleviation Using Piezoelectric Actuators - Some Results of the Actively Controlled Response Of Buffet-Affected Tails (ACROBAT) Program

The goal of this publication is to provide an overview of the topic of revolutionary research in aeronautics at Langley, including many examples of research efforts that offer significant potential benefits, but have not yet been applied. The discussion also includes an overview of how innovation and creativity is stimulated within the Center, and a perspective on the future of innovation. The documentation of this topic, especially the scope and experiences of the example research activities covered, is intended to provide background information for future researchers.

https://ntrs.nasa.gov/api/citations/20060005004/downloads/20060005004.pdf

Innovation in Flight: Research of the NASA Langley Research Center on Revolutionary Advanced Concepts for Aeronautics

Ongoing research in buffet loads alleviation has provided an application for recently developed piezoelectric actuators capable of higher force output than previously existing actuators could provide and that can be embedded within the vehicle s structure. These new actuators, having interdigitated electrodes, promise increased performance over previous piezoelectric actuators that were tested on the fin of an F/A-18 aircraft. Two new actuators being considered by the United States Air Force to reduce buffet loads on high performance aircraft were embedded into the fins of an F/A-18 wind-tunnel model and tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center. The purpose of this test program, called ENABLE (Evaluation of New Actuators in a Buffet Loads Environment), was to examine the performance of the new actuators in alleviating fin buffeting, leading to a systems -level study of a fin buffet loads alleviation system architecture being considered by the USAF, Boeing, and NASA for implementation on high performance aircraft. During this wind-tunnel test, the two actuators performed superbly in alleviating fin buffeting. Peak values of the power spectral density functions for tip acceleration were reduced by as much as 85 percent. RMS values of tip acceleration were reduced by as much as 40 percent while using less than 50 percent of the actuators capacity. Details of the wind-tunnel model and results of the wind-tunnel test are provided herein.

/pdf/evaluation-of-new-actuators-in-a-buffet-loads-environment-udg6z2ugnd.pdf

Evaluation of New Actuators in a Buffet Loads Environment

Smart structures have demonstrated a broad range of potential applications for performance enhancement for the aerospace industry. This paper focuses on applications of smart structures to aircraft...

Applications of Smart Structures to Aircraft for Performance Enhancement

In 1993, tail buffet tests were performed on a full-scale, production model F/A-18 in the 80- by 120-Foot Wind Tunnel at NASA Ames Research Center. Steady and unsteady pressures were recorded on both sides of the starboard vertical tail for an angle-of-attack range of 20 to 40 degrees and at a sideslip range of -16 to 16 degrees at freestream velocities up to 100 knots (Mach 0.15, Reynolds number 1.23*10super7). The aircraft was equipped with removable leading edge extension (LEX) fences that are used in Flight to reduce tail buffet loads. In 1995, tail buffet tests were performed on a 1/6-scale F-18 A/B model in the Transonic Dynamics Tunnel (TDT) at NASA Langley Research Center. Steady and unsteady pressures were recorded on both sides of both vertical tails for an angle-of-attack range of 7 to 37 degrees at freestream velocities up to 65 knots (Mach 0.10). Comparisons of steady and unsteady pressures and root bending moments are presented for these wind-tunnel models for selected test cases. Representative pressure and root bending moment power spectra are also discussed, as are selected pressure cross-spectral densities.

/pdf/a-comparison-of-pressure-measurements-between-a-full-scale-3pqg7m6q2f.pdf

Pendleton Ed

Papers

A Comparison of Pressure Measurements Between a Full-Scale and a 1/6-Scale F/A-18 Twin Tail During Buffet