Mujahid Abdulrahim

Flight Characteristics of Shaping the Membrane Wing of a Micro Air Vehicle

Biologically inspired concepts are rapidly expanding the range of aircraft technology. Consideration is given to merging two biologically-inspired concepts, morphing and micro air vehicles, and the resulting flight characteristics are investigated. Specifically, wing shaping is used to morph the membrane wings of a micro air vehicle. The micro air vehicle has poor lateral control because hinges, and consequently ailerons, are difficult to install on a membrane wing. Instead, a set of torque rods, aligned along the wings, are used to twist the membrane and shape the wing. The resulting morphing is shown to provide significant control authority for lateral dynamics. A set of flight tests are undertaken to determine the flight characteristics by commanding pulses and doublets to the control actuation. The vehicle demonstrates excellent roll performance in response to wing shaping. Futhermore, the vehicle demonstrates several types of spin behavior related to combinations of elevator deflection and the wing shaping.

ROLL CONTROL FOR A MICRO AIR VEHICLE USING ACTIVE WING MORPHING

A micro air vehicle is a ight system being designed for operation within urban environments. Such vehicles are small and highly agile but often have limited control authority. This paper investigates the use of morphing as an effector to provide control authority. Simple mechanisms for morphing are designed to twist the wings of a 24 in vehicle and to curl the wings of a 12 in vehicle. Flight tests show the morphing is an excellent strategy to command roll maneuvers. The resulting vehicles are relatively easy to y and consequently are suitable for autopilot design and mission deployment.

Flight Dynamics of a Morphing Aircraft Utilizing Independent Multiple-Joint Wing Sweep:

Morphing, which changes the shape and configuration of an aircraft, is being adopted to expand mission capabilities of aircraft. The introduction of biologically-inspired morphing is particularly attractive in that highly-agile birds present examples of aerodynamically-effective shapes. This paper introduces an aircraft with a multiple-joint design that allows variations in sweep to mimic some shapes observed in birds. These variations are independent on the left and right wings along with on the inboard and outboard sections. The aircraft is designed and analyzed to demonstrate the range of flight dynamics which result from the morphing. In particular, the vehicle is shown to have enhanced turning capabilities and crosswind rejection which are certainly critical metrics for the urban environments in which these aircraft are anticipated to operate.

Investigation of Membrane Actuation for Roll Control of a Micro Air Vehicle

A class of micro air vehicles uses a flexible membrane wing for weight savings and passive shape adaptation. Such a wing is not amenable to conventional aileron mechanisms for roll control, due to a lack of internal wing structure. Therefore, morphing (in the form of asymmetric twisting) is implemented through the use of a torque-actuated wing structure with thousands of discrete design permutations. A static aeroelastic model of the micro air vehicle is developed and validated to optimize the performance of the torque-actuated wing structure. Objective functions include the steady-state roll rate and the lift-to-drag ratio incurred during such a maneuver. An optimized design is obtained through the use of a genetic algorithm presenting significant improvements in both performance metrics compared with the baseline design.

Flight Testing A Micro Air Vehicle Using Morphing For Aeroservoelastic Control

Micro air vehicles are able to y in environments with little maneuvering room; however, such ight requires high agility and precision maneuvering. A current class of micro air vehicle is constructed with only rudder and elevator for control authority. Such surfaces are not optimal for ight control but ailerons can not be installed on the membrane used for wings on these vehicles. Morphing is used as an aeroservoelastic effector for control. Vehicles are constructed using threads to command a curl of the wings and using torque rods to command a twist of the wings. In each case, ight tests demonstrate the actuation causes sufcient deformation of the wing to result in signicant control authority. The ight dynamics show turns and spins can be repeatedly performed using this aeroservoelastic control. I. Introduction Micro air vehicles (MAV) are rapidly gaining attention in the ight test community. The small size and light weight of these vehicles make them especially attractive for some missions. The vehicles are quite portable so may be easily transported to remote locations. A MAV is inherently stealthy because of its size and quiet because of its electric propulsion. Furthermore, many types of sensors are being miniaturized and would t within the payload capabilities of a MAV. Some areas of operation, such as urban environments, require a vehicle that is small but also extremely agile. Agility is obviously needed so the vehicle can maneuver within small areas and between obstacles in a dense environment. The vehicle must also be highly responsive to reject disturbances like wind gusts which may be considerable near buildings. The concept of aeroservoelastic tailoring through morphing is being studied for control on many vehicles. The basic concept of this approach involves actively changing the shape of a vehicle to affect the aerodynamics and, consequently, the ight dynamics. Such control inherently uses the control and actuation through the structural dynamics to affect the aerodynamics as an aeroservoelastic system. The resulting system has difcult dynamics so design and analysis of aeroservoelastic control is a challenge. 1

Control and Simulation of a Multi-Role Morphing Micro Air Vehicle

The practical application of UAV technology will be dependent on how well the aircraft can perform a wide range of missions. Morphing aircraft are of particular interest because the shape change can achieve a range of performance and dynamic characteristics beyond the capability of conventional aircraft. However, a significant challenge exists in the control and stabilization of such a vehicle, where the plant model is expected to change considerably throughout the flight. The approach in the current study is based on an aircraft which achieves a 2-DOF, biologically-inspired wing morphing. The morphing allows the wings to be reconfigured to achieve a set of desired dynamics. This reconfiguration is computed in the control design process by finding the morphing condition which minimizes the differences relative to the desired dynamics for a certain flight condition. H∞ model-following controllers are computed to match the output of the plant model to the desired mission dynamics, which include cruise, maneuvering, steep descent, and sensor-pointing. Simulation results are presented for each mission.

On Low Altitude Flight Through The Atmospheric Boundary Layer

Major challenges to low speed micro flight are the transient and time-averaged velocities arising from the Atmospheric Boundary Layer (ABL), particularly turbulence a few metres above the ground. In this paper, existing data from meteorologists and wind engineers are reviewed and measurements dedicated to understanding the spatial and temporal velocity fields that MAVs experience are briefly described. Data from a wide variety of terrains are analysed, with the majority of data obtained in relatively well mixed turbulent flow (i.e. away from local effects such as buildings) and for conditions of nominally neutral stability. Spectra for data well removed from local effects exhibited the expected 5/3rds Kolmogorov law. Transient flow pitch angles were investigated (obtained from four small laterally displaced probes), in order to understand the possible roll and pitch inputs to MAVs. It was noted that for all data obtained the variation with lateral separation decreased relatively slowly with reducing separation down to the closest inter-probe spacing of 14mm. This effect is thought to explain the increasing piloting difficulties experienced in maintaining good roll control for decreasing scales of craft when any appreciable atmospheric winds are present.

On the Dynamics of Automobile Drifting

Driving at large angles of sideslip does not necessarily indicate terminal loss of control, rather, it is the fundamental objective of the sport of drifting. Drift racing challenges drivers to navigate a course in a sustained sideslip by exploiting coupled nonlinearities in the tire force response. The current study explores some of the physical parameters affecting drift motion, both in simulation and experiment. Combined-slip tire models are used to develop nonlinear models of a drifting vehicle in order to illustrate the conditions necessary for stability. Experimental drift testing is conducted to observe the dynamics featured in the track data. An accelerometer array on the test vehicle measures the acceleration vector field in order to estimate the vehicle states throughout the drift testing. Neural networks are used to identify the patterns in the accelerations that correspond to sideslip excursions during drifts. These estimates combined with computations of angular acceleration, yaw rate, and lateral acceleration build a framework for identifying the dynamics in terms of physical parameters and stability and control derivatives. The research developments are intended to support a future study quantifying the effects of vehicle configuration changes on drift capability as related to performance potential and handling qualities.

Waypoint navigation for a micro air vehicle using vision-based attitude estimation

Missions envisioned for micro air vehicles may require a high degree of autonomy to operate in unknown environments. As such, vision is a critical technology for mission capability. This paper discusses an autopilot that uses vision coupled with GPS and altitude sensors for waypoint navigation. The vision processing analyses a horizon to estimate roll and pitch information. The GPS and altitude sensors then command values to roll and pitch for navigation between waypoints. A flight test of a MAV using this autopilot demonstrates the resulting closed-loop system is able to autonomously reach several waypoints. The vehicle actually uses a telemetry link to a ground station on which all vision processing and related guidance and control is performed. Several issues, such as estimating heading to account for slow updates, are investigated to increase performance.

Flight Performance Characteristics of a Biologically-Inspired Morphing Aircraft

Despite the past century of innovation in aircraft technology, the versatility of modern aircraft remains far worse than airborne biological counterparts. The shape changing accomplished by birds and bats in ight stands as one of the few examples of true morphing. As such, the aircraft community is devoting considerable attention to the study of biological systems and how they might be implemented on a ight vehicle. Much of this work addresses static aerodynamic and aeroelastic effects. However, this limited focus leaves the entire areas of dynamics, control, stability, and ight performance unstudied. This paper presents a simple approach to morphing based on existing vehicle designs and actuators. The aircraft is modied to mimic basic morphing mechanisms commonly observed on bird wings, namely twisting the wingtips for roll control and varying the gull wing angle. The latter mechanism is used as a quasi-static effector, where the wing shape is changed from one position to another. The aircraft employs a thin-undercambered wing and a skeletal spar structure to achieve wing morphing. Results from a series of ight tests are presented to highlight the effect of the morphing control on the vehicle dynamics. Command and response data analysis indicates a marked change in the vehicle’s handling qualities for different levels of morphing. Additionally, the morphing has been shown to have an effect on ight performance metrics such as climb rate, glide angle, and stall characteristics.