Russell F. Osborn

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.

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.

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.

High energy crystal field excitations in Pr x Y1−x Ba2Cu3O7−δ

We have measured the high energy crystalline electric field transitions in samples of PrxY1−xBa2Cu3O7−δ withx ≈ 0·5 andx ≈ 1. The fully Pr-doped samples exhibits three strong transitions with excitation energies of about 65, 85 and 105 meV, plus three more weaker ones at 113, 123 and 132meV. Magnetic intensity is observed in the same energy range in thex=0.5 sample but is largely structureless in character, with only one clear peak at about 109meV. The large number of transitions would seem to indicate a Pr valence of 3+, rather than 4+, but the intrinsically broad character of the excitations is evidence for a dynamically mixed valence state.

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.

Crystal field excitations in electron superconductors

We have measured the complete crystalline electric field (CEF) spectrum of Nd3+ in superconducting Nd1·85Ce0·15CuO4 and Nd2CuO3·7F0·3, and in the non-superconducting parent compound, Nd2CuO4, by neutron inelastic scattering. The best description of the ground-state excitations for both compounds is achieved by the addition of a molecular field parameter to the CEF hamiltonian that takes account of exchange interactions from Nd or Cu spin ordering.