Currently, Draper Laboratory is in the development stages of a gliding autogyro airdrop system. The goal of the project is to design a platform capable of placing small, high value items into urban terrain. Theoretically, autogyros can achieve descent rates and glide slopes similar to current parafoil based systems, but do so with greater precision. Over the past half-century most rotorcraft research has focused on helicopter design, only viewing autorotation as a means of achieving emergency landings. In contrast, this project utilized early rotor theory to develop algorithms which can predict unpowered rotor performance across the entire flight envelope. To validate these predictions, a vertical wind tunnel capable of testing rotors up to 4 feet in diameter at descent rates of up to 25 ft/s was constructed. Emphasis was also placed on developing deployment sequences that would allow the system to achieve stable autorotation autonomously. By varying parameters such as blade pitch angle and rotor solidity, it is shown that in the proper configuration, rotor based systems can match and even surpass parafoils in areas such as descent rate and glide slope. The autogyro also has the added capability of varying its lift-to-drag ratio in flight while maintaining reasonable descent speeds...
In recent years, high altitude unmanned aerial vehicles have been used to great success in combat operations, providing both reconnaissance as well as weapon launch platforms for time critical targets. Interest is now growing in extending autonomous vehicle operation to the low altitude regime. Because perfect threat knowledge can never be assumed in a dynamic environment, an algorithm capable of generating evasive trajectories in response to pop-up threats is required. Predetermination of contingency plans is precluded due to the enormity of possible scenarios; therefore, an on-line vehicle trajectory planner is desired in order to maximize vehicle survivability. This thesis presents a genetic algorithm based threat evasive response trajectory planner capable of explicitly leveraging terrain masking in minimizing threat exposure. The ability of genetic algorithms to easily incorporate line-of-sight effects, the inherent ability to trade off solution quality for reduced solution time, and the lack of off-line computation make them well suited for this application. The algorithm presented generates trajectories in three-dimensional space by commanding changes in velocity magnitude and orientation. A crossover process is introduced that links two parent trajectories while preserving their inertial qualities. Throughout the trajectory generation process vehicle maneuverability limits are imposed so that the resultant solutions remain dynamically feasible.; (cont.) The genetic algorithm derived provides solutions over a fixed time horizon...
This thesis presents a method for creating continuously parametrized maneuver classes for autonomous vehicles. These classes provide useful tools for motion planners, bundling sets of related vehicle motions based on a low-dimensional parameter vector that describes the fundamental high-level variations within the trajectory set. The method follows from a relaxation of nonlinear parametric programming necessary conditions that discards the objective function, leaving a simple coordinatized feasible space including all dynamically admissible vehicle motions. A trajectory interpolation algorithm uses projection and integration methods to create the classes, starting from arbitrary user-provided maneuver examples, including those obtained from standard nonlinear optimization or motion capture of human-piloted vehicle flights. The interpolation process, which can be employed for real-time trajectory generation, efficiently creates entire maneuver sets satisfying nonlinear equations of motion and nonlinear state and control constraints without resorting to iterative optimization. Experimental application to a three degree-of-freedom rotorcraft testbed and the design of a stable feedforward control framework demonstrates the essential features of the method on actual hardware. Integration of the trajectory classes into an existing hybrid system motion planning framework illustrates the use of parametrized maneuvers for solving vehicle guidance problems. The earlier relaxation of strict optimality conditions makes possible the imposition of affine state transformation constraints...
This paper presents vehicle models and test flight results for an autonomous fixed-wing airplane that is designed to take-off, hover, transition to and from level-flight modes, and perch on a vertical landing platform in a highly space constrained environment. By enabling a fixed-wing UAV to achieve these feats, the speed and range of a fixed-wing aircraft in level flight are complimented by hover capabilities that were typically limited to rotorcraft. Flight and perch landing results are presented. This capability significantly eases support and maintenance of the vehicle. All of the flights presented in this paper are performed using the MIT Real-time Autonomous Vehicle indoor test ENvironment (RAVEN).; AFOSR Grant FA9550-04-1-0458
The Boeing Company
A high-order discontinuous Galerkin finite element discretization and output-based adaptation scheme for the compressible Euler equations are presented and applied to an isolated rotor in hover. A simplex cut-cell mesh generation technique is used to support robust and autonomous creation of higher-order meshes. The calculations are performed using a parallel implementation of the DG discretization and the results are compared to experimental data. As accurate simulation of rotorcraft wakes and blade-vortex interactions continues to be a challenge, the output-based adaptation scheme is used with thrust as the output of interest to refine the mesh. The result is a solution with less than three million degrees of freedom that is capable of preserving a rotor tip vortex for three and a half revolutions.; by James M. Modisette.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.; Includes bibliographical references (p. 69-73).
Approved for public release; distribution is unlimited; Integrated Modular Avionics, or IMA, has been a notable trend in aircraft avionics for the past two decades, promising significant size, weight, and power-consumption (SWAP) gains, radically increased sensors fusion, and streamlined support costs. Despite the demonstrated success of IMA systems in commercial airliners such as the Airbus A380 and the Boeing 787, military rotorcraft in the service of the United States Joint services have yet to benefit significantly from this technology. At long last, that may be about to change. The Future Vertical Lift Family of Systems (FVL) initiative was launched in 2008, with the aim of re-inventing the entire U.S. rotary wing fleet. Within the FVL program’s projected timeline, many signs point to the emergence of a second-generation IMA technology (IMA2G), which will leverage extensive virtualization and software-defined functionality to deliver further SWAP gains, fault-tolerance, and system capability. Development efforts are indeed already underway to integrate such advanced IMA features into the FVL’s Joint Common Architecture. This thesis assesses the maturity of IMA2G critical path technologies, validates the alignment between IMA2G benefits and desired FVL attributes...
Approved for public release, distribution unlimited; Rotor Blade vibratory stresses are of utmost importance in helicopter design. A modified Myklestad-Prohl method for rotating beams has been coded to assist in preliminary helicopter rotor blade design. The rotor blade dynamics program is part of the Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) program which was developed to aid in the preliminary design and analysis of helicopter rotor performance, stability and control, and rotor dynamics. JANRAD is an interactive, user friendly program written in MATLAB version 4.0 programming language and has been used extensively in the Naval Postgraduate School's capstone helicopter design course (AA 4306). A sample case is run and results are discussed.; U.S. Navy (USN) author
Operational modal analysis differs from traditional experimental modal analysis in that it only requires information of the output responses and the modal parameters (in terms of natural frequencies damping ratios and mode shapes) are estimated under the assumption of white noise excitation. It presents several advantages including the availability of modal properties of structure in operation thus representing a closer picture of the structure and its boundary conditions (which are not that easy to realize in laboratory conditions). However, lack of input excitation force information presents several challenges as
well as the proper estimation of the frequency response functions and the accurate evaluation of modal parameters in presence of harmonic components in the excitation.
Several methodologies have been developed in the last years as described in this thesis and the main purpose of the research is to assess their application in aerospace such as the rotorcraft technology and the environmental testing. Solutions to the main operational modal analysis limitations are suggested and the implementation of the related algorithms allows the application on several test cases after their validation. Taking advantages of this improving in the experimental analysis capabilities...
Within the Integrated Defense Systems of The Boeing Company, aftermarket support of military aircraft serves as an increasingly large source of revenue. One of the newest contracts between Boeing and the U.S. Government created such a supply partnership at the Army Rotorcraft Repair Depot in Corpus Christi, Texas. At this depot, all Army helicopters, including Boeing's AH-64 Apache Attack helicopter and CH-47 Chinook Cargo helicopter undergo major repair and overhaul. In 2004, Boeing entered an agreement with the U.S. Government to assume responsibility of the repair depot's supply chain for aftermarket parts for Boeing rotorcraft. Over the last two years, Boeing has been creating and refining Corpus Christi's support structure to ensure that the required repair parts arrive when demanded. In establishing this new supply chain, Boeing has identified numerous inefficiencies as a result of inaccurate and highly volatile forecasts. This thesis examines the impact of volatility within the new support structure and creates flexible solutions to mitigate its negative effects on lead times, multiple sources of supply and inventory management.; (cont.) Efforts to increase communication flow across the supply chain are used to capitalize on economies of scale for cost reduction while safety stock recommendations are made for critical end-items. Monte Carlo simulations are employed to justify and validate the solutions. The results of the thesis reveal that a strategic selection of raw material safety stock can reduce procurement lead times by an average 61% for a subset of parts while maintaining financial responsibility. Additionally...
In this thesis, we propose a strategy for a team of Unmanned Aerial Vehicles (UAVs) to perform reconnaissance of an intended route while operating within aural and visual detection range of threat forces. The advent of Small UAVSs (SUAVs) has fundamentally changed the interaction between the observer and the observed. SUAVs fly at much lower altitudes than their predecessors, and the threat can detect the reconnaissance and react to it. This dynamic between the reconnaissance vehicles and the threat observers requires that we view this scenario within a game theoretic framework. We begin by proposing two discrete optimization techniques, a recursive algorithm and a Mixed Integer Linear Programming (MILP) model, that seek a unique optimal trajectory for a team of SUAVs or agents for a given environment. We then develop a set of heuristics governing the agents' optimal strategy or policy within the formalized game, and we use these heuristics to produce a randomized algorithm that outputs a set of waypoints for each vehicle. Finally, we apply this final algorithm to a team of autonomous rotorcraft to demonstrate that our approach operates flawlessly in real-time environments.; by Philip J. Root.; Thesis (S.M.)--Massachusetts Institute of Technology...
As UAV capabilities continue to improve the technology will spill out of the military sector and into commercial and civil applications. Already, UAVs have demonstrated commercial marketability in such diverse areas as scientific and environmental research, cross-seas shipping, communications relays, emergency management, border monitoring, agriculture, and aerial photography. Small-scale tactical UAVs in particular have an enormous potential to fulfill a number of roles within urban centers, transforming the way civil safety institutions carry out their jobs. A lack of established flight regulations is currently the greatest barrier to the standardized use of these vehicles. While the United States is currently the world's leader in UAV manufacturing, this position is tenuous given strong competitive threats from a variety of foreign countries who are already ahead in establishing a standardized regulatory environment for UAVs. As part of a larger research effort focused on the design, implementation, and demonstration of highly maneuverable rotorcraft UAVs, the primary objective of this work is to examine how UAVs might gain access to and function safely in civil and commercial markets. Despite the wide variety of existing UAVs in terms of size...
A rotorcraft-based unmanned aerial vehicle exhibits more complex properties
compared to its full-size counterparts due to its increased sensitivity to
control inputs and disturbances and higher bandwidth of its dynamics. As an
aerial vehicle with vertical take-off and landing capability, the helicopter
specifically poses a difficult problem of transition between forward flight and
unstable hover and vice versa. The LPV control technique explicitly takes into
account the change in performance due to the real-time parameter variations.
The technique therefore theoretically guarantees the performance and robustness
over the entire operating envelope. In this study, we investigate a new
approach implementing model identification for use in the LPV control
framework. The identification scheme employs recursive least square technique
implemented on the LPV system represented by dynamics of helicopter during a
transition. The airspeed as the scheduling of parameter trajectory is not
assumed to vary slowly. The exclusion of slow parameter change requirement
allows for the application of the algorithm for aggressive maneuvering
capability without the need of expensive computation. The technique is tested
numerically and will be validated in the autonomous flight of a small scale
helicopter.; Comment: 6 pages...