Agamemnon L. Crassidis

Methodologies for Adaptive Flight Envelope Estimation and Protection

This paper reports the latest development of several techniques for adaptive flight envelope estimation and protection system for aircraft under damage upset conditions. Through the integration of advanced fault detection algorithms, real-time system identification of the damage/faulted aircraft and flight envelop estimation, real-time decision support can be executed autonomously for improving damage tolerance and flight recoverability. Particularly, a bank of adaptive nonlinear fault detection and isolation estimators were developed for flight control actuator faults; a real-time system identification method was developed for assessing the dynamics and performance limitation of impaired aircraft; online learning neural networks were used to approximate selected aircraft dynamics which were then inverted to estimate command margins. As off-line training of network weights is not required, the method has the advantage of adapting to varying flight conditions and different vehicle configurations. The key benefit of the envelope estimation and protection system is that it allows the aircraft to fly close to its limit boundary by constantly updating the controller command limits during flight. The developed techniques were demonstrated on NASA s Generic Transport Model (GTM) simulation environments with simulated actuator faults. Simulation results and remarks on future work are presented.

Wing kinematics and aerodynamics of a hovering flapping Micro Aerial Vehicle

Biological Inspiration for the design of flapping wing vehicles has been the source of numerous design efforts in the field of Micro Aerial Vehicle (MAV) development. For flapping flight in small birds and insects, high lift generation is typically a result of unsteady fluid flow phenomena. Our previous studies have conceptualized and demonstrated how a dragonfly inspired Quad-Winged Vehicle (QV) can produce higher energy efficiency and increase payload capacity on-board an MAV. The objective of this paper is to further improve on the in-flight aerodynamic efficiency of MAVs and propose improved flapping configuration and kinematics of a light weight wing to enhance lift and aerodynamic efficiency during hovering flight. This paper presents a series of experimental and computational results in the form of performance plots comparing the effects of wing orientation, flapping kinematics: frequency / amplitude and wing feathering, all of which influence the lift and drag generated by the MAV.

Longitudinal Rate Gyro Bias and Pitch Attitude Estimation Utilizing an Accelerometer Array

In this paper, a novel attitude estimation device is proposed utilizing cost-efiective rate and acceleration measurement sensors. The device combines a rate gyroscope with an accelerometer array and algorithm to estimate and eliminate the rate gyro bias online for accurate real-time aircraft longitudinal attitude tracking. Proper vehicle operation is predicated on accurate attitude determination algorithms that are dependent on instantaneous and accurate measurements of translational and rotational body rates for precise estimation of vehicle orientation in three-dimensional space. Measurement error of instantaneous rate sensors, gyroscopes, is introduced via inherent biases and signal noise resulting in gyro drift. Integration of the rate signal for instantaneous net displacement calculation amplifles even minute measurement errors leading to an inaccurate and unreliable attitude estimate. The proposed device is a departure from typical attitude observers and bias estimators due to reliance on accelerometers measuring the local gravitational vector in lieu of additional magnetic fleld sensors or GPS. The end result is a longitudinal attitude estimation device able to compute a rate gyro bias in real-time for accurate vehicle pitch angle tracking while subjected to simulated aircraft ∞ight conditions. The efiectiveness of the newly constructed attitude estimation algorithm is demonstrated by comparison of attitude and rate gyro bias estimates produced from noise corrupted and biased sensors with the actual attitude of a nonlinear aircraft model and true rate gyro bias.

Verification and Validation of a Theoretical Model of an Integrated Actuator Package for Primary Flight Control

This paper presents a benchmark study on fault diagnosis of electrohydraulic servoa uators (EHSA). EHSA are considered to be affected by faults and disturbances. The linear mathematical model of the EHSA is given. Two differe t design methods for fault diagnosis are studied. The first method considers the strategy of parity space design, and observer-based implementation, in which a perfect disturbance decoupling is achieved. The second method considers the linear EHSA model with polytopic uncertainties in order to design a residual signal using fault detecti n filter (FDF) theory, and to calculate a threshold. Linear matrix inequalities (LMI) are used to obtain the problem solutions.

The Applicability of Unsteady Vortex Panel Methods to the Design of Hovering Flapping-Wing Micro Air Vehicles

An unsteady 2D vortex panel code is developed based on potential flow methods. The code is written in MATLAB and allows for arbitrary motion of an airfoil through a stationary, inviscid fluid. The surface of the airfoil is represented by a series of vortex panels, each having a linear distribution of circulation across its length; the wake is represented by discrete vortices shed from the trailing edge which move with the local velocity field. The panel code is validated against a similar code being used by researchers at the Naval Postgraduate School with excellent agreement. The code is then used to simulate an airfoil undergoing flapping oscillations in hovering mode and to evaluate the forces generated. The results are compared with results from FLUENT, a commercially available CFD code, in order to assess the applicability of vortex panel methods to the design of hovering flapping-wing Micro Air Vehicles. The results of the study show that the panel code compares fairly well with CFD predictions, though it is unable to capture viscous effects such as leading-edge vortices. If the code is extended to three dimensions and the leading-edge vortex can be modeled, vortex panel codes could prove very beneficial to designers of flapping-wing MAVs.

An Intelligent Robotic System Platform for Autonomous Mapping and Sensor Data Gathering of Non-GPS Friendly Environments

This paper presents results of a novel intelligent robotic system using a re-configurable platform for autonomous mapping and sensor data gathering of non-Global Positioning System (GPS) friendly, unknown and hazardous enclosed environments such as caves, underground and underwater tunnel networks, building floors, and spaces within a collapsed building rubble field. The work developed here forms a basis for a swarm of mini/micro robotic vehicles capable of autonomous routing and control with a self-contained navigation system that does not rely on GPS information. A robotic prototype capable of autonomously mapping a floor plan (such as hallways within a building) has been developed. The robot navigates autonomously without the use of GPS and gathers absolute position information developing a 2-dimensional map of the hallway network using a novel Mini Inertial Measurement/Navigation System (MIMNS) developed at RIT. Also, enhancements to the MIMNS unit are presented for estimating attitude orientation of the robot using an accelerometer based device allowing for non-flat plane mapping using the MIMNS unit. The paper presents the concepts of the robot hardware and software, results of a 2-dimensional mapping of a flat plane, and introduces simulation results of an accelerometer based attitude orientation device.Copyright

Computational Approaches to Design and Analysis of Small-Scale Flapping Wings

Micro air vehicles promise to play an important part in public, private, and military arenas in the coming years. Small, lightweight, agile, and inexpensive, these flying machines are of interest in domestic search-and-rescue operations, law enforcement, reconnaissance, mapping, and urban combat operations. Nature demonstrates that flapping wings are an extremely effective solution to the problem of hovering flight with good agility in close quarters. However, the highly unsteady, largely separated character of the flow complicates aerodynamic analysis of these vehicles, and these challenges are magnified in a design setting when the sensitivities to many geometric and kinematic parameters must be assessed. In this paper, computational fluid dynamics simulation is applied as a means to evaluate kinematic parameters of flapping wings for a four-wing, dragonfly-like micro air vehicle. It is shown that high-frequency, moderate-amplitude flapping is preferred for wings flapping in a vertical stroke plane, and...

Center of Gravity Estimation of an Aircraft Solely Using Standard Aircraft Measurement Sensors

In this paper, a novel approach to center of gravity estimation for an aircraft will be investigated. Three separate algorthms have been developed using a physics based approach to optimize center of gravity estimates under dynamic loading conditions on a vehicle. Rigid body motion relationships and aircraft dynamics will be exposed to create estimates of numerous aircraft parameters. Errors between estimates and sensor measurements provide the basis for center of gravity improvement. The first algorithm involves calculation and elimination of imposed loading on the airframe, allowing for determination of new attitude estimates. The second algorithm requires comparison of aircraft estimates of position and velocity in the Earth-fixed coordinate system to GPS and INS information. The third algorithm includes analysis using air data measurements available from onboard sensors to calculated estimates. These innovative approaches to center of gravity estimation remove dependence on detailed and expensive aerodynamic models that require level and steady flight conditions for operation, and limit the introduction of human error that occurs in hand calculation methods. Such improved knowledge can improve aircraft control response, reduce conservative safety factors placed on airframe fatigue calculators, and ensure safe loading scenarios throughout the flight envelope. Simulations using measurement collections from a high performance aircraft for each individual algorithm were performed and included. Additionally a combined algorithm incorporating all three methods was simulated. Each resulted in successful center of gravity localization.

Dynamic Inversion Control for Non-Square Systems with Application to Aircraft Longitudinal Control

This paper presents a novel method for control of non-square dynamical systems using a model-following approach. Control methodologies such as dynamic inversion and sliding mode control require an inversion of the input influence matrix. However, if the system input influence matrix is non-square direct inversion is not possible. Pseudo inversion of the input influence matrix may be performed for control allocation. However, the pseudo inversion limits the control to states where the controller is directly applied. The pseudoinverse method does not permit the engineer to designate a particular state to control or track. When accurate tracking of the remaining states is required the pseudo inversion method is not useful. Current methods such as dynamic extension can be used to generate a square input influence matrix, essentially, creating an input influence matrix that is invertible. However, this method is tedious for large systems. In this paper, a new transformation is applied to the original dynamical system model to develop an input influence matrix that is square. Assuming the system is controllable, the proposed transformation allows for accurate tracking of selectable states. Selection of the new transformation matrix is used to develop accurate tracking of certain states compared to the remaining states. A method based on optimal control theory is used to define the transformation matrix. The new approach is first applied to control a two mass system with simulation results presented showing the advantage of the proposed new control strategy. Finally, simulation results are presented for longitudinal control of an aircraft using one control input.

Modeling and Control of a Recoverable Balloon System for Launch of Small Payloads to Low Earth Orbit

This paper presents system modeling and simulation results of a balloon system for the purpose of launching small payloads into low earth orbit using rockets . The system uses a balloon attached to a platform containing a rocket capable of maneuvering b y an actuation device relative to the platform . The balloon propels the system into the upper atmosphere where the rocket is launched and a parachute is employed to retrieve the system after launch to be reused for other missions . This paper focuses on dev eloping a “systems” based model including the rocket launch system (a DC -motor actuation system is assumed for pointing of the rocket) and the platform where the rocket is mounted . A linear state -space model is developed using Lagrange’s equations . The sta te -space model is non dimensionalized by defining characteristic parameters to quantify interaction effects of the motor -platform system a nd power requirements using non dimensional parameter analysis . Two control laws are implemented on the system model inc luding PID control and dynamic inversion . Simulation results indicate both control law algorithms provide sufficient tracking control for the rocket maneuver module . However, power requirements for an optimal system confi guration based on open -loop non dime nsional analysis are minimal for the dynamic inversion Control closed -law system.