Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Vita. / Includes bibliographical references. / by John Shaw. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1982. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / by Paul Michael Stremel. / M.S.

Chen, Yipin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 81-83). / Abstracts in English and Chinese. / Abstract --- p.1 / 摘要 --- p.2 / Table of Contents --- p.3 / Acknowledgements --- p.4 / Nomenclature --- p.5 / List of Figures --- p.9 / Chapter 1 --- Introduction / Chapter 1.1 --- Motivation and Literature Review --- p.11 / Chapter 1.2 --- Background --- p.13 / Chapter 1.3 --- Research Overview --- p.14 / Chapter 1.4 --- Thesis Outline --- p.15 / Chapter 2 --- Kinematic and Dynamic Modeling / Chapter 2.1 --- Helicopter Dynamics --- p.16 / Chapter 2.2 --- Kinematics of Point Feature Projection --- p.19 / Chapter 2.3 --- Kinematics of Line Feature Projection --- p.22 / Chapter 3 --- Adaptive Visual Servoing with Uncalibrated Camera / Chapter 3.1 --- On-line Parameter Estimation --- p.25 / Chapter 3.2 --- Controller Design --- p.28 / Chapter 3.3 --- Stability Analysis --- p.30 / Chapter 3.4 --- Simulation --- p.33 / Chapter 4 --- Adaptive Control with Unknown IMU Position / Chapter 4.1 --- Control Strategies --- p.47 / Chapter 4.1.1 --- Dynamic Model with Rotor Dynamics --- p.47 / Chapter 4.1.2 --- p.50 / Chapter 4.2 --- Stability Analysis --- p.55 / Chapter 4.3 --- Simulation --- p.57 / Chapter 5 --- Conclusions / Chapter 5.1 --- Summary --- p.64 / Chapter 5.2 --- Contributions --- p.65 / Chapter 5.3 --- Future Research --- p.65 / Chapter A --- Inertial Matrix of the Helicopter --- p.66 / Chapter B --- Induced Torque --- p.69 / Chapter C --- Unknown Parameter Vectors and Initial Estimation Values --- p.72 / Chapter D --- Cauchy Inequality --- p.74 / Chapter E --- Rotor Dynamics --- p.77 / Bibliography --- p.81

The primary objective of the research reported in this thesis was the improvement of safety in helicopters by identifying and, where necessary, developing vibration analysis techniques for the detection and diagnosis of safety critical faults in helicopter transmission systems. A review and, where necessary, expansion of past research is made into (a) the mechanisms involved in the production of vibrations in mechanical systems, (b) the failure modes experienced in geared transmission systems, (c) which failure modes are critical to the safety of helicopters, (d) how the safety critical failure modes affect the vibration signature, and e) the vibration analysis techniques currently used to detect safety critical failures. The effectiveness of the currently available vibration analysis techniques is investigated using in-flight vibration data from Royal Australian Navy helicopters and seeded fault data from a purpose built spur gear test rig. Detailed analysis of techniques for synchronous signal averaging of gear vibration data is undertaken, which includes the development of new methods of modelling and quantifying the effects of synchronous averaging on non-synchronous vibration. A study of digital resampling techniques is also made, including the development of two new methods which provide greater accuracy and/or efficiency (in computation) over previous methods. A new approach to fault diagnosis is proposed based on time-frequency signal analysis techniques. It is shown that these methods can provide significant improvement in diagnostic capabilities over existing vibration analysis techniques. Some limitations of general time-frequency analysis techniques are identified and a new technique is developed which overcomes these limitations. It is shown that the new technique provides a significant improvement in the concentration of energy about the instantaneous frequency of the individual components in the vibration signal, which allows the tracking of small short term amplitude and frequency modulations with a high degree of accuracy. The new technique has the capability of 'zooming' in on features which may span only a small frequency range, providing an enhanced visual representation of the underlying structure of the signal.

Throughout the evolution of rotorcraft design, great advancements have been made in developing performance analysis and sizing tools to assist designers during the preliminary and detailed design phases. However, very few tools exist to assist designers during the conceptual design phase. Most performance analysis tools are very discipline or concept specific, and many are far too cumbersome to use for comparing vastly different concepts in a timely manner. Consequently, many conceptual decisions must be made qualitatively. A need exists to develop a single software tool which is capable of modeling any type of feasible rotorcraft concept using different levels of detail and accuracy in order to assist in the decision making throughout the conceptual and preliminary design phases. This software should have a very intuitive and configurable user interface which allows users of different backgrounds and experience levels to use it, while providing a broad capability of modeling traditional, innovative, and highly complex design concepts. As an illustration, a newly developed Concept Independent Rotorcraft Analysis and Design Software (CIRADS) will be presented to prove the applicability of such software tools. CIRADS is an object oriented application with a Graphical User Interface (GUI) for specifying mission requirements, aircraft configurations, weight component breakdowns, engine performance, and airfoil characteristics. Input files from the GUI are assembled to form analysis and design project files which are processed using algorithms developed in MATLAB but compiled as a stand alone executable and imbedded in the GUI. The performance calculations are based primarily upon a modified momentum theory with empirical correction factors and simplified blade stall models. The ratio of fuel (RF) sizing methodology is used to size the aircraft based on the mission requirements specified by the user. The results of the analysis/design simulations are then displayed in tables and Text Fields in the GUI. The intent for CIRADS is to become a primary conceptual sizing and performance estimation tool for the Georgia Institute of Technology rotorcraft design teams for use in the annual American Helicopter Society Rotorcraft Design Competition.

Dynamic stall has proven to be a complex problem in helicopter aerodynamics because it limits the helicopter flight regime. Dynamic stall is characterized by drastic increases in lift and a delay of stall due to rapid pitching motions of aerodynamic surfaces. Prediction and control of dynamic stall requires an understanding of the leading edge flow structure. An investigation was conducted of dynamic stall near the leading edge of a large-scale Sikorsky SSC-A09 airfoil, dynamically pitching about its quarter chord, under realistic helicopter flight conditions (M_infinity = 0.1, k = 0.1, Re_c = 1.0 x 10^6). A testing model with a chord of 0.46 m and a span of 2.13 m was designed and constructed for experimentation in the Dynamic Stall Facility at Texas A&M University. Particle image velocimetry data were recorded for the first 15% of the airfoil chord. Mean velocities, Reynolds stresses, and vorticity were computed. Analyses revealed that during the upstroke, stall onset is delayed in the leading edge region and the first indications of separation are observed at 18 degree angle of attack. The edge of the boundary layer has been characterized for alpha = 18 degrees. The roles of the Reynolds stresses and vorticity are examined.

Rotorcraft transmission design is limited by empirical weight trends that are proportional to the power/torque raised to the two-thirds coupled with the relative inexperience industry has with the employment of variable speed transmission to heavy lift helicopters of the order of 100,000 lbs gross weight and 30,000 installed horsepower. The advanced rotorcraft transmission program objectives are to reduce transmission weight by at least 25%, reduce sound pressure levels by at least 10 dB, have a 5000 hr mean time between removal, and also incorporate the use of split torque technology in rotorcraft drivetrains of the future. The major obstacle that challenges rotorcraft drivetrain design is the selection, design, and optimization of a variable speed transmission in the goal of achieving a 50% reduction in rotor speed and its ability to handle high torque with light weight gears, as opposed to using a two-speed transmission which has inherent structural problems and is highly unreliable due to the embodiment of the traction type transmission, complex clutch and brake system. This thesis selects a nontraction pericyclic continuously variable transmission (P-CVT) as the best approach for a single main rotor heavy lift helicopter to target the above mentioned obstacle for drivetrain design and provides advancement in the state of the art of drivetrain design over existing planetary and split torque transmissions currently used in helicopters. The goal of the optimization process was to decrease weight, decrease noise, increase efficiency, and increase safety and reliability. The objective function utilized the minimization of the weight and the constraint is the tooth bending stress of the facegears. The most important parameters of the optimization process are weight, maintainability, and reliability which are cross-functionally related to each other, and these parameters are related to the torques and operating speeds. The analysis of the split torque type P-CVT achieved a weight reduction of 42.5% and 40.7% over planetary and split torque transmissions respectively. In addition, a 19.5 dB sound pressure level reduction was achieved using active gear struts, and also the use of fabricated steel truss like housing provided a higher maintainability and reliability, low cost, and low weight over cast magnesium housing currently employed in helicopters. The static finite element analysis of the split torque type P-CVT, both 2-D and 3-D, yielded stresses below the allowable bending stress of the material. The goal of the finite element analysis is to see if the designed product has met its functional requirements. The safety assessment of the split torque type P-CVT yielded a 99% probability of mission success based on a Monte Carlo simulation using stochastic- petri net analysis and a failure hazard analysis. This was followed by an FTA/RBD analysis which yielded an overall system failure rate of 140.35 failures per million hours, and a preliminary certification and time line of certification was performed. The use of spherical facegears and pericyclic kinematics has advanced the state of the art in drivetrain design primarily in the reduction of weight and noise coupled with high safety, reliability, and efficiency.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 47-49). Also available on the World Wide Web.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Rudolph Darken, Joseph A. Sullivan. Includes bibliographical references (p. 103-104). Also available online.

Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Hodges, Dewey; Committee Member: Bauchau, Olivier; Committee Member: Sankar, Lakshmi. Part of the SMARTech Electronic Thesis and Dissertation Collection.