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Gust alleviation and flutter suppression are essential elements of an effective fly-by-feel system. Knowledge of real-time forces and moments can have huge effect on designing an effective controller for flutter suppression and gust rejection. One unique method of predicting forces and moments is to use distributed arrays of artificial hair sensors that are capable of sensing the environment and therefore capturing important flow features. In this paper, the local flow measurement from the artificial hair sensor is used with feed-forward neural network to predict the aerodynamic parameters (angle of attack, freestream velocity, lifte coefficient and moment coefficient per unit span, and flap angle) on an airfoil containing control surface. These aerodynamic parameters can be combined with the airfoil’s physical parameters to predict the real time lift and moment. Also, the effect of artificial hair sensor integration location on prediction of aerodynamic parameters is studied.

Aircraft propulsion system noise can be a large contributor to ground level noise. Mounting the propulsor above the wing can reduce ground level noise below the vehicle. The level of acoustic shielding is dependent on wing planform dimensions and vehicle shape. Two different modeling approaches to predict noise shielding by tapered wings were investigated for use in an automated aircraft system modeling framework. The first approach uses the commercial code Virtual Lab (BEM, FEM, and Ray acoustics methods), and the second is the Maggi-Rubinowicz diffraction potential solution to the Kirchhoff Integral. Results from Virtual Lab were compared to two experimental results found in literature. Good agreement between Virtual Lab and experiment were obtained using the FEM. Acoustic shielding by tapered wings was calculated using FEM for the case of a single monopole noise source mounted on center just above the wing and compared to the Maggi-Rubinowicz diffraction potential method. Model development, analysis, and post processing were automated for both approaches so that they could be used as part of an aircraft system modeling framework. The FEM in Virtual Lab offers higher fidelity but higher computational cost, while the Maggi-Rubinowicz diffraction potential method is relatively lower fidelity since it is limited to use in diffraction problems with relatively simple geometry, and higher frequencies. A difference in shielding of several dB between the Maggi-Rubinowicz diffraction potential method compared with the FEM solution was noted, however, the diffraction potential method captures the correct trends in shielding and has much faster computational speed compared to FEM, which is beneficial for automated vehicle design routines.

Two wing self-noise modeling methods were used to predict the effect of airfoil camber and thickness on wing self-noise and their relationship with lift. Both a semi-empirical airfoil self-noise prediction code called NAFNoise, and a noise metric which uses steady RANS models were used for the investigation. Development and previous validations of the NAFNoise code with experimental measurements are summarized to understand the limitations of the code. Predictions were made at low speed and moderate Reynolds number similar to the environment of a small unmanned aerial system. Self-noise predictions are plotted with lift coefficient for a series of camber and thickness changes. The boundary layer was tripped and left untripped to understand the effect boundary layer transition has on airfoil noise versus airfoil aerodynamic performance. Analysis indicated that increasing airfoil camber leads to higher overall sound level at lower angles of attack. An increase in airfoil camber increases lift at lower angles of attack. NAFnoise models with untripped boundary layers predict that increasing airfoil thickness leads to higher overall sound level, with largest increase in overall sound level at lower angles of attack. Results were inconclusive as to whether increasing camber is an effective way to increase lift coefficient and lift over drag without significantly increasing airfoil noise, because the conclusion was dependent on modeling methodology. NAFNoise models with untripped boundary layers indicated that increasing camber would result in a beneficial increase in section lift coefficient & lift over drag (up to about 8% camber) with minimal increase in noise production. RANS based noise metric and exclusion of the laminar boundary layer vortex shedding model from NAFNoise predictions indicated an increase in noise with section lift coefficient independent of airfoil camber.

An aerodynamic study is presented that focuses on the longitudinal characteristics of a small radio controlled glider aircraft with particular emphasis given to the contribution of control surface deflections to lift, drag, and pitching moment coefficients. The location and orientation of the aircraft and its control surfaces were measured in-flight using a 60 camera motion capture system while performing pitch up maneuvers related to perching. The result is a simple model of the vehicle lift, drag, and pitching moment coefficients based on traditional component buildup methods.

This paper describes the design of bio-mimetic remote controlled airplanes and experiments in perching them. The goal of this research is the development of a biomimetic robotic bird that can alight and rest on a perch. Design starts with the overall architecture including airfoil selection and mass determination given performance requirements. Particular attention is given to the stability analysis since with a bird-like planform with the tail so close to the body and without a vertical tail surface many designs are unstable. The stability matrices are also the basis of the PID controller design. Several foamie planes were built to test different designs and control strategies. Most of the perching experiments used the Dreamflight® Alula glider because it was one of the most bird-like planforms that is available commercially. A catapult launcher and a perch were set up in the AFRL Aviari indoor flight facility which uses motion capture cameras to determine to vehicle state. This allows control algorithms to be developed off-board the plane saving on weight of sensors and on-board computers. Various control strategies were tested from mostly open loop flights, relatively simple PID controllers, to fuzzy logic and dynamic inversion. This paper is limited to the development and testing of the PID controllers.

This paper describes the development and use of a 3-D vortex particle method to rapidly model the time-dependent aerodynamics of wings performing perching manoeuvres where the angle of attack ranges from zero to well above stall. The focus is on bird size Micro Air Vehicles (MAVs) where highly three-dimensional flow can occur due to low aspect ratios, post-stall flight, wing flexibility, and planform changes, and strongly time dependent flows can occur due to rapid pitch manoeuvres and even flapping of the wing. To be used as a design tool to optimize trajectories, and the design of the vehicle itself, the aerodynamic model must be fast enough that many trajectories can be simulated in a few hours or days. Once developed the optimal perching trajectories using the 3-d vortex particle method were compared to optimal trajectories calculated using 2-d particle methods, timedelay calculations, and analytical models.

A biomimetic composite reconfigurable wing for small unmanned air systems has been designed and tested experimentally in a wind tunnel. Actuation of the wing results in a 30% reduction of wing planform area and 34% decrease in span mimicking wing sweeping motion used by birds for flight control. The wing uses a thin cambered airfoil along the span. Wing sweep motion of 56° was demonstrated under static aerodynamic loads at angles of attack between -5 and +15° at 10 m/s. The wing was fabricated using a variety of materials including carbon fiber and fiberglass composite morphing skins and direct manufactured plastic frame structures. The large shear displacement required by the skin to achieve large wing sweep angles was managed by folding large sections of the skin, similar to folding of bird feathers.

This paper presents a new mechanism concept for a perching micro air vehicle. In this concept, each wing is a three degree-of-freedom serial chain that enables wing pitching, sweeping and folding. The rst two motions are each driven by a servo motor through a four-bar linkage that is kinematically synthesized via the function generation technique. However the folding motion of the outer spar is designed to be a passive joint that is coupled with the sweeping motion through a pulley and cable system. A preliminary design of these mechanisms is obtained by rst applying a kinematic synthesis technique that requires the mechanism passes through a prescribed set of key positions. It is then optimized for two actuation quality measurements: transmission angle and mechanical advantage. At last a working prototype was built and tested with a servo controller. The preliminary results show that the concept can achieve the desired motion. This new concept and prototype facilitates future studies such as ight control for perching MAVs.

This work concerns the development of a biologically inspired methodology for multidisciplinary shape and topology optimization of aeroelastic MAV structures. The methodology is based on the map L systems modeling of cellular division to generate a structural topology. The topology thus generated is analyzed using the nite element method, and the rules that indirectly develop the topology are then evolved using a genetic algorithm for multi-objective optimization. The methodology is demonstrated by application to the aeroelastic design of a MAV wing. This example clearly shows the suitability of the proposed method for topology optimization of advanced engineering structures and systems.

This paper investigates the modeling of transient aerodynamic behaviour on micro air vehicles at angles of attack from zero to well above stall. These angles of attack are seen in extreme manoeuvres, in this case perching, where highly threedimensional flow can occur due to low aspect ratios, wing segmentation, planform changes, or other physical reconfigurations of the vehicle. The ultimate goal of this work is to develop a fast yet robust 3-D unsteady aerodynamic model to be used in trajectory simulations as part of a design tool to guide the design of control systems to perform highly acrobatic manoeuvres. This paper focuses on the development of a vortex particle method to model the unsteady flow of perching manoeuvres and comparison its results with experimental results and reduced order engineering models.

Morphing aircraft and reconfigurable structures are multidisciplinary systems that require efficient integration of actuation systems, mechanisms, and structures to achieve the desired functionality and the state change of the vehicle to accomplish a wide range of mission roles. Typically, the actuation required to achieve this functionality comes from an on-board energy source, converted to mechanical force and motion. In this case, the ability to operate in response to environment change requires radically new structural concepts for system level capability. This paper seeks to understand new concepts that utilize environmental thermal energy to trigger reconfiguration and employ a fundamental bistable effect of compliant mechanisms for shape change. For this study, available heat energy on the surface of the re-entry vehicle with a blunt fuselage shape is investigated including the duration of the heat generation to determine the best energy conversion. A compliant mechanism will be designed to change its configuration by opening the heat shield and deploying a folded wing as the induced heat load expands elements to reach an unfolded stable position. The size and shape of the mechanism are explored and analyzed using an energy method and the material selection of the flexible link is discussed.

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.

*† ‡ 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.

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.

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.

This paper presents a novel optimization approach for the design of mechanisms in morphing aircraft structures. The layout of the mechanism as well as the location and number of actuators and pivots are determined by an extended formulation of a material-based topology optimization. The design problem is modeled within an aeroelastic framework to directly assess aerodynamic performance criteria while optimizing the overall mechanized system. The proposed methodology is illustrated through the design optimization of a quasi 3-D section of an adaptive wing, where the approach is compared to a conventional two-step approach of rst optimizing the aerodynamic shape for one or multiple igh t conditions, then nding the mechanism that leads to this shape. The comparison shows that the interactions between o w, structural deformation, mechanism, and actuator must be considered to nd the optimal solution.

A study was conducted to investigate the applicability of active-aeroelastic-wing technology to a joined-wing sensorcraft configuration for the purpose of minimization of embedded antenna deformations. The study was performed using a half-span aeroelastic model of a joined-wing sensorcraft design with six control surfaces. These control surfaces were used concurrently to minimize the elastic deformations at structural nodes corresponding to the antenna tip, while trimming the aircraft to a required 1-g level flight, simultaneously satisfying constraints on the allowable hinge moments and maximum control surface deflections. Comparison of antenna displacements for the optimized and baseline cases (using one control surface at a time) demonstrates that the active-aeroelastic-wing concept can be used to significantly reduce the antenna displacements, potentially improving the performance of the embedded antenna system. Aeroelastic displacements from the trim-optimized system are an order-of-magnitude smaller than those of the baseline. These results demonstrate the feasibility of active-aeroelastic-wing technology for the improvement of embedded antenna performance caused by structural deformations.

This paper describes the wind tunnel research at Wright Laboratory continuing the validation effort in variable-stif fness tailored aeroelasticity for smart structures. To enhance aircraft performance, these structures employ flexible, adaptive, lightweight mechanisms to exploit rather than minimize static aeroelastic phenomena. While aircraft wings traditionally require added structure (and weight) to achieve adequate stiffness for roll control effectiveness, the variable stiffness design approach uses small changes in the wing stiffness to achieve the same roll control. This investigation examines the aeroelastic response to changes in stiffness to produce the desired roll effectiveness in a low speed wind tunnel. A simple, unswept, rectangular wing model is tested to explore the feasibility of using variable stiffness that is aeroelastically tailored to act as a force multiplier in conjunction with a small, outboard, trailing edge control surface (CS). This wind tunnel model is configured to simulate variable stiffness that may be employed both in the wing- fuselage attachments area and in the wing structural box itself. The model's aeroelastic response to changes in the aileron CS deflection is measured over a range of dynamic pressures at two different stiffnesses. The results obtained from this series of tests are used to evaluate the control potential of variable stiffness. Results indicate beneficial