Gregory W. Reich

Flexible Skin Development for Morphing Aircraft Applications via Topology Optimization

This article describes the development of engineered composite skins for morphing aircraft applications. Some of these applications suggest that materials with low in-plane stiffness and relatively high out-of-plane stiffness may be required. To this end, a two-step design process has been developed in order to synthesize skins to meet these requirements. The first step in the process is to determine bulk material properties for the skin and the layout of attachments between the skin and underlying substructure. This results in a distribution of bulk properties across the skin. The second step utilizes these property values as constraints to match the found bulk property in a multi-phase material optimization in order to determine the layout of a set of microscopic multi-phase material unit cells. As a first attempt, a 2D engineered skin design using a proposed two-step process is demonstrated in this article, and material fabrication process using a rapid prototyping (RP) technique and test result are discussed.

Aerodynamic Performace of a Notional Perching MAV Design

This paper describes a mechanized wing concept for a perching micro air vehicle, and the aerodynamic behavior of such a concept at wing angles of attack up to ninety degrees. The model has wings capable of rotating in pitch at two spanwise joints to simulate the motion of a bird’s wings during a perching maneuver. The advantage of a perching landing is that it allows the vehicle to land with approximately zero vertical and horizontal velocity on a tree branch, power line, or ledge. Wind tunnel tests are conducted to measure vehicle performance and ight control parameters for further development of a free-ying model. Static measurements of lift, drag, and pitching moments are correlated to wing section angles from zero to nearly ninety degrees angle of attack. Unsteady eects related to dynamic stall are also investigated by varying the speed at which the wing sections are actuated. In order to investigate actuation and mechanization designs for this concept, additional measurements are made to determine the amount of power required to achieve the wing motions.

Large-Area Aerodynamic Control for High-Altitude Long- Endurance Sensor Platforms

The use of large-area aerodynamic control schemes to enable high-altitude long-endurance sensor platforms is investigated. The focus is on a vehicle with a joined-wing design. The vehicle has two performance shortcomings that are considered typical of the broader class of high-altitude long-endurance vehicles. The first is minimum roll rate at landing due to the large amount of roll damping associated with these configurations. It is shown that multiple distributed control surfaces can help meet the roll rate requirements. The second is sensitivity of takeoff gross weight to maximum lift-to-drag ratio. Notional mission requirements drive the fuel fraction to high levels and small changes in lift-to-drag ratio can enable large changes in the vehicle weight through reduced fuel requirements. It is shown that the same technology used to satisfy the roll requirement can also be used to actively control the twist and camber during cruise and can have a moderate impact on the vehicle weight or endurance.

Dynamic Modeling, Testing, and Stability Analysis of an Ornithoptic Blimp

In order to study ornithopter flight and to improve a dynamic model of flapping propulsion, a series of tests are conducted on a flapping-wing blimp. The blimp is designed and constructed from mylar plastic and balsa wood as a test platform for aerodynamics and flight dynamics. The blimp, 2.3 meters long and 420 gram mass, is propelled by its flapping wings. Due to buoyancy the wings have no lift requirement so that the distinction between lift and propulsion can be analyzed in a flight platform at low flight speeds. The blimp is tested using a Vicon motion tracking system and various initial conditions are tested including accelerating flight from standstill, decelerating from an initial speed higher than its steady state, and from its steady-state speed but disturbed in pitch angle. Test results are used to estimate parameters in a coupled quasi-steady aerodynamics/Newtonian flight dynamics model. This model is then analyzed using Floquet theory to determine local dynamic modes and stability. It is concluded that the dynamic model adequately describes the vehicle’s nonlinear behavior near the steady-state velocity and that the vehicle’s linearized modes are akin to those of a fixed-wing aircraft.

Wing Mechanization Design and Analysis for a Perching Micro Air Vehicle

This paper describes the development of a mechanized wing concept for a perching micro air vehicle. The wings are capable of rotating at two spanwise joints to simulate the motion of a bird’s wings during a perching maneuver. This project focuses on the wing mechanization design and analysis as well as the structure/mechanism integration. The advantage of a perching type of landing is that it allows the vehicle to land with approximately zero vertical and horizontal velocity on a tree branch, power line, or ledge. The requirements to perform this maneuver were investigated, the structural design was developed, and the mechanization integration to achieve this motion was determined. A model was designed and manufactured to demonstrate the kinematic mechanism making this wing motion possible. Wind tunnel testing and analytical simulation were also completed to further develop the model.

Development of Skins for Morphing Aircraft Applications via Topology Optimization

*† ‡ This paper describes the development of engineered composite skins for morphing aircraft applications. Some of these applications suggest that materials with low in-plane stiffness and relatively high out-of-plane stiffness may be required. To this end, a two-step topology optimization process has been developed in order to design skins to meet these requirements. The first step in the process is to determine bulk material properties for the skin and the layout of attachments between the skin and underlying substructure. This results in a distribution of bulk properties across the skin. The second step utilizes these property values as objectives in a multi-phase material optimization in order to determine the composition and layout of a set of macroscopic multi-phase material unit cells.

Detection of flow separation and stagnation points using artificial hair sensors

Recent interest in fly-by-feel approaches for aircraft control has motivated the development of novel sensors for use in aerial systems. Artificial hair sensors (AHSs) are one type of device that promise to fill a unique niche in the sensory suite for aerial systems. In this work, we investigate the capability of an AHS based on structural glass fibers to directly identify flow stagnation and separation points on a cylindrical domain in a steady flow. The glass fibers are functionalized with a radially aligned carbon nanotube (CNT) forest and elicit a piezoresistive response as the CNT forest impinges on electrodes in a micropore when the hair is deflected due to viscous drag forces. Particle image velocimetry is used to measure the flow field allowing for the resulting moment and force acting on the hair to be correlated with the electrical response. It is demonstrated that the AHS provides estimates for the locations of both the stagnation and separation in steady flow. From this, a simulation of a heading estimation is presented to demonstrate a potential application for hair sensors. These results motivate the construction of large arrays of hair sensors for imaging and resolving flow structures in real time.

Origami Actuator Design and Networking Through Crease Topology Optimization

Origami structures morph between 2D and 3D conformations along predetermined fold lines that efficiently program the form of the structure and show potential for many engineering applications. However, the enormity of the design space and the complex relationship between origami-based geometries and engineering metrics place a severe limitation on design strategies based on intuition. The presented work proposes a systematic design method using topology optimization to distribute foldline properties within a reference crease pattern, adding or removing folds through optimization, for a mechanism design. Optimization techniques and mechanical analysis are co-utilized to identify an action origami building block and determine the optimal network connectivity between multiple actuators. Foldable structures are modeled as pin-joint truss structures with additional constraints on fold, or dihedral, angles. A continuous tuning of foldline stiffness leads to a rigid-to-compliant transformation of the local foldline property, the combination of which results in origami crease design optimization. The performance of a designed origami mechanism is evaluated in 3D by applying prescribed forces and finding displacements at set locations. A constraint on the number of foldlines is used to tune design complexity, highlighting the value-add of an optimization approach. Together, these results underscore that the optimization of function, in addition to shape, is a promising approach to origami design and motivates the further development of function-based origami design tools.

Simulation Tool for Analyzing Complex Shape-Changing Mechanisms in Aircraft

This paper describes the development of a simulation tool to study the time domain, in-flight behavior of aircraft morphing mechanisms. Limitations of existing tools are discussed leading to requirements for the new capability. The framework of the tool is discussed as well as the component analyses including control systems, aerodynamics, modal structural representations, and multibody kinematics. The basic capability of the tool is demonstrated through example simulations of a folding morphing wing.

Development of an Integrated Aeroelastic Multibody Morphing Simulation Tool

Abstract : This paper describes the development of a tool for simulating the flight of a morphing aircraft during the morphing process. Also discussed are current-generation tools for modeling vehicle flight and illustrations of how these tools are as yet too immature for modeling of the flight of an aircraft during morphing of the wings. A framework is developed for modeling vehicle flight that incorporates vehicle morphing. The procedures outlined in the paper are sufficiently general to accommodate aircraft utilizing changes in sweep, span, or area. The current state of the art and the planned developments are illustrated through their application to the flight of a folding-wing vehicle.