Joel A. Hetrick

Design and application of compliant mechanisms for morphing aircraft structures

Morphing aircraft structures can significantly enhance air vehicle performance. This paper highlights ongoing work to design novel compliant mechanisms that efficiently morph aircraft structures in order to exploit aerodynamic benefits. Computational tools are being developed to design structures that deform into specified shapes given simple actuator inputs. In addition, these synthesis methods seek to optimize the stiffness of the structure to minimize actuator effort and maximize the stiffness with respect to the environment (external loading). These tools have been used to study two different types of morphing systems: (i) variable geometry wings and (ii) high-frequency vortex generators for active flow control. Several case studies are presented which highlight the design approach and computational and experimental results of these morphing aircraft systems.

Flight testing of Mission Adaptive Compliant Wing

This paper describes flight test results of a “Mission Adaptive Compliant Wing” (MACWing) variable geometry trailing edge flap in conjunction with a natural laminar flow airfoil. The MAC-Wing technology provides lightweight, low power, variable geometry reshaping of the upper and lower flap surface with no seams or discontinuities. In this particular program, the airfoil-flap system is optimized to maximize the laminar boundary layer extent over a broad lift coefficient range for endurance aircraft applications. The expanded “laminar bucket” capability allows the endurance aircraft to significantly extend their range (15% or more) by continuously optimizing the wing L/D throughout the mission. The wing was tested at full-scale dynamic pressure, full scale Mach, and reduced-scale Reynolds Numbers on Scaled Composites’ White Knight aircraft. Test results confirmed laminar flow regime up to approximately 60% chord for much of the lift range. Analysis and test results suggest significant fuel savings, weight savings and a higher control authority. Preliminary drag results, future aerodynamic applications and vehicle performance projections are discussed.

A tilt and roll device for automated correction of rotational setup errors.

A tilt and roll device has been developed to add two additional degrees of freedom to an existing treatment table. This device allows computer-controlled rotational motion about the inferior-superior and left-right patient axes. The tilt and roll device comprises three supports between the tabletop and base. An automotive type universal joint welded to the end of a steel pipe supports the center of the table. Two computer-controlled linear electric actuators utilizing high accuracy stepping motors support the foot of table and control the tilt and roll of the tabletop. The current system meets or exceeds all pre-design specifications for precision, weight capacity, rigidity, and range of motion.

Active flow control using high-frequency compliant structures

Flow control to avoid or delay boundary-layer separation on a wing can dramatically improve the performance of most air vehicles in strategic parts of their individual flight envelopes. Previous aerodynamic experiments and computations have indicated that unsteady excitation at the appropriate frequency can delay boundary-layer separation and wing stall more effectively than steady flow perturbations and that these unsteady perturbations, when generated in an optimum frequency range, maximize the extent of flow separation control for specific flight conditions. Preliminary aerodynamic experiments have been performed on a deflected trailing-edge flap to evaluate turbulent boundary layer separation control with a deployable high-frequency micro-vortex-generator (HiMVG) array. The HiMVG design tested incorporated emerging displacement amplification compliant structures technology that deployed micro-vortex-generator blades 5 mm, through a range of frequencies between 30 and 70 Hz, when driven by an appropriately sized voice‐coil actuator. The mechanical HiMVG system tested produced an oscillatory stream of boundary-layer embedded vortices that proved effective in mitigating flow separation on the upper surface of a deflected flap when a similar array of static vortex generators could not. A second-generation HiMVG design driven by a piezoelectric actuator was also conceptualized. Candidate flow control applications for this second-generation design are discussed.

Synthesizing high-performance compliant stroke amplification systems for MEMS

We have recently designed, fabricated, demonstrated a new class of compliant stroke amplification mechanisms that are exceptionally well suited for MEMS applications. Manufactured in Sandias advanced 5-level surface micromachining technology known as SUMMiT-V, these computer generated structures provide high work and area efficiency in designs that are highly compatible with the fabrication process. The actual devices display outstanding yield, robustness, endurance, and resistance to surface adhesion effects during the final release process. One device has been driven to a 20-/spl mu/m output displacement at resonance for more than 10/sup 10/ cycles with no apparent fatigue. This paper focuses on the unique methodology employed to design and analyze these compliant stroke amplification systems. The same approach, however, can be used to design many other compliant structures for fabrication in a MEMS technology. Compliance in design leads to creation of jointless, no-assembly, monolithic mechanical device.

The Quest for Efficient Transonic Cruise

*† ‡ § This paper details the history of the transonic drag reduction flight test programs that have been conducted in the Air Force Research Laboratory over the past thirty years. We begin with the Transonic Aircraft Technology (TACT) program, which looked at utilizing supercritical airfoils on tactical aircraft, then the follow-on Mission Adaptive Wing (MAW) program, which investigated using active flight control for tactical utility, and most recently the Mission Adaptive Compliant Wing (MACW), that tested a lightweight, low power, variable geometry system that has no seams or discontinuities on either the upper or lower wing surface. The application of these technologies to military and commercial aircraft offers significant performance potential that can be exploited in next generation aircraft. Nomenclature A = aspect ratio CL = lift coefficient CD = drag coefficient M� = Mach number MDD = drag divergence Mach number p� = ambient static pressure q� = ambient dynamic pressure � = angle of attack Λ = wing sweep, referenced to leading edge, deg. δ = control surface deflection, deg.

An Adaptive Structures Electro -Mechanical Device for Dynamic Flow Control Applications

Flow control to prevent or delay boundary layer separation can dramatically improve the performance of air vehicles in critical regions of the flight envelope. Prior aerodynamic experim ents have shown that unsteady excitation, at the appropriate frequency, can delay boundary layer separation more effectively than steady flow perturbations. An electro - mechanical flow control device, with a substantial deployment frequency bandwidth, has been developed and tested in both static and dynamic flow control environments. The device couples a high frequency piezostack actuator with a sixty five -to -one displacement amplification mechanism to oscillate sixteen vortex generating blades at rates up t o two hundred hertz. Conceptual design of the piezostack -compliant mechanism is discussed. Flow separation control results are presented and device performance issues including dynamic characteristics are addressed.