S. Chad Gibbs

Aeroelastic Model of Multisegmented Folding Wings: Theory and Experiment

Morphing-wing research has garnered much attention in the aerospace community over the last decade, and the folding wing is a promising concept that can improve aircraft performance over multiple types of missions. Several high-fidelity analyses of folding-wing aeroelastic stability have been published, but most analyses are specifi ct o certain wing planforms or a fixed number of wing segments. This paper presents a general aeroelastic model that predicts the flutter speed and flutter frequency of a folding wing with simplified geometry but with an arbitrary numberof wingsegments. Thebeam-theory structuralmodelandthe strip-theoryunsteadyaerodynamic modelare coupled using Lagrange’s equations. Three experimental models are constructed, and flutter tests are performed over a wide range of fold angles. The theoretical predictions for flutter speeds are within 10% of experimentally measured values for most configurations. In general, the results show that the essential physics of the problem is captured by the present first-principles model. Furthermore, data show that increasing the fold angle causes up to 30% increase in flutter speed, which has applications in extending the flutter boundaries of morphing aircraft.

Heliogyro Solar Sail Research at NASA

The recent successful flight of the JAXA IKAROS solar sail has renewed interest within NASA in spinning solar sail concepts for high-performance solar sailing. The heliogyro solar sail, in particular, is being re-examined as a potential game-changing architecture for future solar sailing missions. In this paper, we present an overview of ongoing heliogyro technology development and feasibility assessment activities within NASA. In particular, a small-scale heliogyro solar sail technology demonstration concept will be described. We will also discuss ongoing analytical and experimental heliogyro structural dynamics and controls investigations and provide an outline of future heliogyro development work directed toward enabling a low-cost heliogyro technology demonstration mission ca. 2020.

Solarelastic Stability of the Heliogyro

This article presents a methodology for analyzing the solarelastic stability of a solar sail spacecraft blade. This paper couples linear and non-linear rotating structural models with an optical solar radiation pressure model for a completely reflective surface. The resulting time varying ordinary differential equations are solved in a quasi-static sense, where an instantaneous stability boundary is determined. The quasi-static analysis with the linear model predicts a divergence type instability and slow and non-uniform modal convergence using parameters for a representative heliogyro spacecraft blade. The non-linear model predicts a flutter instability at a lower radiation pressure and has improved modal convergence characteristics. The paper uses the non-linear model to evaluate the stability of a NASA heliogyro concept design and explore the dependence of the stability boundary on the spacecraft rotation rate for the case of the sun directly overhead. Increasing the spin rate of the spacecraft improves the solarelastic stability, but must be traded off with decreased spacecraft maneuverability.

Stability of Rectangular Plates in Subsonic Flow with Various Boundary Conditions

The aeroelastic stability of rectangular plates in subsonic flow is well documented in literature. For example, the stability of a cantilever plate with a clamped edge parallel to the flow is well understood due to the similarity of this system to an aircraft wing. However, an ongoing push for lighter aerospace structures and novel designs requires advancing the understanding of the aeroelastic stability of plates with nonconventional boundary condition combinations. This paper summarizes the aeroelastic theory and experimental results on the flutter and/or divergence mechanisms of a rectangular plate with different sets of structural boundary conditions. The theory combines a linear plate structural model with a three-dimensional vortex lattice aerodynamic mode to create a high-fidelity frequency domain aeroelastic model. The paper also discusses the development of a modular experimental test bed to test the different boundary conditions. A pair of well-understood boundary condition configurations acts a...

Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on “rope ladder” membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

Aeroelastic Behavior of Noise-Reducing Membranes for Aircraft Lifting Surfaces Part I: Theory

xed, trailing edge free. This paper presents a theoretical study of the aeroelastic behavior of elastic plates with this boundary condition. Specically the paper discusses a vortex lattice aerodynamic model coupled with a classical plate/membrane model. The model is used to predict the linear utter boundary and utter characteristics of the panel while the support structure size, streamwise length, and normal direction tension are varied. The stability boundary is determined to be relatively insensitive to the support structure size, but varies non-simply with both the streamwise chord and the tension in the normal direction. Additionally the results are compared to previous aeroelastic simulations which suggested a higher mode utter which is not encountered in the current simulations. Experimental validation of the structural and aeroelastic models is presented in the companion paper.