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The unsteady aerodynamic forces and moments of an oscillating airfoil for the fixed wing case were determined by Theodorsen along with the development of a lift deficiency function. Loewy subsequently developed an analogous lift deficiency function for the rotary wing case in which there are an infinite number of layers of shed vorticity, or wakes, below the reference airfoil. With the advent of computer panel codes that calculate the time histories of the wakes generated by oscillating airfoils, a theory is developed for the rotary wing case in which there are a finite number of layers of shed vorticity below the reference airfoil. This theory includes a lift deficiency function that is completely analogous to Loewy and Theodorsen. It has long been recognized that an airfoil oscillating in pure plunge produces a propulsive force ( Katzmayr effect ). Garrick used Theodorsen's work to develop equations for the propulsive force that include the lift deficiency function as a parameter. When either Loewy's lift deficiency function or the finite wake lift deficiency function is used, the effect of the propulsive force is greatly enhanced with the proper phase relationship of the wakes. The finite wake theory along with Garrick's work is used to describe the performance characteristics of Higher Harmonic Control. Specifically for the OH-6A, coupled pitch-plunge motion results in a propulsive force that significantly reduces the rotor drag force. Helicopter, Rotary wing, Unsteady aerodynamics, Wake, Propulsive force, Higher harmonic control, Hummingbird, http://archive.org/details/finitewaketheory00couc, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

This thesis is intended to be a reference for solid modeling and Computer Aided Design (CAD) tailored specifically for the Naval Postgraduate School's capstone helicopter design course, AA 4306. The goal is to present the use of AutoCAD R13 software as a central design tool throughout the conceptual design phase of the American Helicopter Society (AHS) Graduate Design Competition project. The specifics of AutoCAD that are essential to performing the design project are explored through examples of model construction and lessons learned from the 1997 VIPER design effort. The usage of solid modeling as a design tool for design team integration is investigated. It is intended for this work to allow future classes to acquire sufficient proficiency with Computer Aided Design and solid modeling. Maximizing the practical usage of CAD techniques in a single quarter will provide an improved learning experience in a more realistic design environment., http://archive.org/details/solidmodelingfor1094531920, NA, NA, U.S. Navy (U.S.N.) author., Approved for public release; distribution is unlimited.

The need for improved pilot aids has become a high priority item for pilots and aircrews operating at sea and ashore. Pilot aids such as the moving map display, GPWS, collision, and vortex ring state (VRS) warning systems will significantly enhance aircrew situational awareness and safety. Many more of today's aircraft mishaps are a result of pilot error, which includes a loss of situational awareness. The moving map display provides relatively easy incorporation of sophisticated pilot aids without operational flight program (OFP) modification. This thesis discusses, examines and selects a vortex ring state prediction algorithm to be incorporated in the GADGHT unit. A program was written that manipulated required aircraft performance data from the ARINC 429 data bus and compared this data to vortex ring state boundaries predicted by the algorithm. The GADGHT unit provides an audible and visual warning to the pilots when the aircraft has penetrated the VRS boundaries. This warning system will provide increased safety and situational awareness to helicopter crews operating in increasingly demanding 0perational environments, http://archive.org/details/developmentofhel1094526475, Lieutenant Commander, United States Navy, Approved for public release; distribution is unlimited.

The Hummingbird is a 15()-lb. gross weight, remotely piloted helicopter (RPH) with a 50-lb. payload and a rotor radius of 10.25 ft. It is powered by a 25 h.p. air cooled two-cylinder Westlake engine. As such it represents one of the largest RPH's in the world. It was purchased from Gorham Model Products in 1992 to provide a suitable rotor craft research flight test platform for the Department of Aeronautics and Astronautics at the Naval Postgraduate School. The helicopter was delivered disassembled and was accompanied by an ample supply of replacement and spare parts. Also included was a second helicopter in a partially assembled condition that had been previously flown. Assemblies provided comprised the chassis, main rotor transmission, rotor head assembly and tailboom with tail rotor gear box and rotor. The task undertaken by this thesis was to fabricate one complete fully operable RPH and to design, fabricate and install whatever new assemblies that were required for its NPS mission and to make up for deficiencies in the previous design. The work completed required: (1) Design, fabrication and installation of a new skid-type landing gear system; (2) Redesign, and incorporation of a new engine mount system; (3) Modification of the engine and main rotor transmission coupling; (4) Upgrade of the electrical system and elongation of the nose section; and (5) Initial engine testing. Recommendations for future modifications to the helicopter and laboratory facilities, and development of a static hover test fixture are also included, http://archive.org/details/acquisitiondesig1094526844, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

This thesis is part of the helicopter research program established at The Naval Postgraduate School (NPS). NPS currently has two OH-6A light observation helicopters which were obtained from the U.S. Army. One of these is dedicated to ground vibration testing and dynamics research. Previous research on the OH-6A at NPS established baseline vibration test data. The data includes natural frequencies, principal mode shapes and damping characteristics. This thesis continues previous research of the OH-6A and develops a detailed finite element model to be used in future helicopter dynamics research at NPS. The model is based on an MSC/NASTRAN finite element model of a similar aircraft obtained from the McDonnell Douglas Helicopter Company. Both the nose and empennage were modified to represent the structural characteristics of the test article. Due to lack of structural design data, model mass updating was performed using previously obtained test data and a design sensitivity approach. The updated model natural frequencies agree well with the test data, http://archive.org/details/developmentcorre1094526468, Approved for public release; distribution is unlimited.

The Department of Aeronautics and Astronautics at the Naval Postgraduate School (NPS) is conducting a research program in methods of higher harmonic control (HHC) for reduction of helicopter vibrations. The program at NPS uses remotely piloted helicopters (RPH) to study HHC effects on vibration and blade load reduction. The scope of this master's thesis was to measure the baseline vibration profile of the RPH test vehicles prior to the installation of a HHC system. This goal was met by the development of a data instrumentation and recording system and by conducting a ground and flight test program for the RPH test vehicles. From the results of these tests it was concluded that: a) the data instrumentation and recording system was of sufficient sensitivity to detect vibrations experienced within the RPH airframe; and b) the RPH exhibited a vibration profile similar to that of a full scale helicopter. It is recommended that a HHC system be designed, fabricated, and installed on the RPH so that the effects of HHC on helicopter performance may be evaluated., http://archive.org/details/baselinevibratio1094526396, Approved for public release; distribution is unlimited.

e model is obtained through use of commercial off-the-shelf software that is incorporated in a low-cost flight simulator, which is marketed as FLIGHTLAB. The FLIGHTLAB development system facilitates rapid design and analysis of a high fidelity helicopter model using non-linear dynamic modeling techniques. The simulator model of the Hughes OH-6A helicopter is presented and its fidelity is compared to actual fight test data conducted at the U.S. Naval Test Pilot School in Patuxent River, MD. Advancements in electromagnetic actuators and visual rendering systems are also presented to provide insight into the direction simulator technology is progressing., http://archive.org/details/modelingohausing109456038, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

The Department of Aeronautics and Astronautics at the Naval Postgraduate School (NPS) is expanding its helicopter research capabilities in order to facilitate present and future research demands. The rapidly changing needs have already out paced available assets. Therefore it was necessary to design and develop a new remotely piloted helicopter (RPH) that would meet present needs, NOTAR and HHC, and be flexible enough to meet future needs. The research efforts encompassed by this thesis are defining the present needs, investigating what type/size of RPH would fulfill these needs, procuring this asset, and analyzing its capabilities. Based on a defined payload, helicopter trends are analyzed to determine an estimate of the overall RPH size (gross weight) and engine size required. A preliminary design process validates these figures. Choosing to procure an RPH instead of building one, a detailed performance analysis is conducted on the main rotor system. This analysis includes blade vibration analysis, retreating blade stall analysis, and power required analysis. Modification of the RPH's main rotor hub, drive train, and landing gear are studied and recommendations presented. This research effort is a continuation of a long- term program to provide NPS with robust assets to support present and future rotorcraft research efforts., http://archive.org/details/rphpreliminaryde1094524030, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

This thesis develops a technique for formulating the full nonlinear equations of motion for a coupled rotor-fuselage system utilizing the symbolic processing software MAPLE(registered). The symbolic software is further utilized to automatically convert the equations of motion into C, Fortran or MATLAB(registered) source code formatted specifically for numerical integration. The compiled source code can be accessed and numerically integrated by the dynamic simulation software SIMULINK(registered). SIMULINK(registered) is utilized to generate time history plots of blade and fuselage motion. These time traces can be used to explore the effects of damping nonlinearities, structural nonlinearities, active control, individual blade control, and damper failure on ground resonance. In addition, a MATLAB(registered) program was developed to apply the Moving Block Technique for determining modal damping of the rotor- fuselage system from the time marching solutions, http://archive.org/details/modelingndnalysi109458686, Lieutenant United States Navy, Approved for public release; distribution is unlimited.

Motivation to expand the understanding of a helicopter rotor descending into the vortex ring state (VRS) stems from the aircraft mishaps that have plagued the helicopter community. The V-22 has become the most recent victim of encounters with VRS. The onset of VRS is associated with the collapse of the helical vortex wake in the plane of the rotor. The resulting wake disturbances develop an irregular and aperiodic flow. Rotor blade interaction with the disturbed vortices causes large variations in the blade spanwise aerodynamic load distribution. Harmonic analysis of the loading indicates that higher harmonic content becomes prevalent in this state. The dynamic flow similarities achieved in a water tunnel are used to explore flow visualization and conduct vibration analysis of a rotor system operating in the VRS. A scaled rotor system was operated in the NPS Aeronautical Engineering Department's water tunnel. Sensors were used to gather thrust and vibration power spectrum data when operating in VRS. Experimental results correlate with full scale flight data and show a significant increase in the vibration levels of the even multiples of the blade passage frequency. The relative strength of these higher harmonics can be used as an indicator of impending VRS encounters., http://archive.org/details/awatertunnelinve10945915, Major, United States Marine Corps, Approved for public release; distribution is unlimited.

The Army RAH-66 Comanche Helicopter made its first flight in January of 1996. Its current structural configuration, however does not meet the Army's requirements for radar signature. Structural configurations of the tailcone that meet radar cross-section requirements tend to lack sufficient structural stiffness due to the presence of Kevlar in place of graphite on the outer mold line. This thesis investigates potential structural design modifications to the Comanche tailcone that would move the design closer to meeting both its structural and radar signature requirements. Geometry modifications with baseline (current configuration) materials increased torsional stiffness by nine percent. Structural geometry modifications using radar signature compliant materials reduced torsional stiffness by 10 percent. The geometry changes analyzed produce structural performance improvements insufficient to allow the use of radar-compliant materials without further geometry changes, http://archive.org/details/analysisofpotent109457940, Major, United States Army, Approved for public release; distribution is unlimited.

The strain pattern analysis (SPA) method is applied to estimate rotor blade torsional deflections. The SPA technique requires calculated mode shapes for the tested rotor blade and strain measurements from the rotor's wind tunnel or flight test. The Holzer method is developed to calculate the required mode shapes from rotor blade stiffness and mass properties and the torsional equation of motion. The Holzer method is tested with numerous theoretical and experimental cases and is proven accurate. The strain measurements are from wind tunnel tests conducted by the Army, NASA, United Technologies Research Center (UTRC) and Sikorsky at DNW with a (1:5.73) model-scale UH-60A rotor blade with an advance ratio of 0.301, an advancing tip Mach number of 0.8224 and an average Reynolds number of 1,278,729. The SPA method predicts slightly larger torsional deflections that compare well with the overall trend and range of UTRC static method integrated deflections. The SPA method was evaluated to determine the tolerance to change in the number of measurements and the modes applied, errors in the measurements, and errors in rotor blade stiffness and mass properties. The method is tolerant to all effects except a decrease in the number of measurements and modes., http://archive.org/details/estimationofroto109456003, Captain, U.S. Army, U.S. Army (USA) author, Approved for public release; distribution is unlimited.

The Army RAH-66 ComancheHelicopter is currently undergoing developmental flight testing. Theempennage of the aircraft isexperiencing buffeting where the horizontal and vertical tail vibrate at resonant frequencies. These high buffet loads are manifested in higher than anticipated fitting loads, particularly on the tail, and vibrations in the crew stations and at the nose cone where the targeting sensors are located. Significant effort has been devoted to identifying the sources of excitation and the nature of the structural response. This thesis determines the location andmagnitude of empennage vibratory airloads. Because the nature of the excitation is a random function, spectral analysis is used. To obtain the loads, a three step process was utilized. First, from aircraft differential pressure transducers and accelerometers, the spectral content of theresponse and excitation was determined. Then, using aNASTRAN model modified to replicate the flight test aircraft, frequency response functions were determined between selected points on the aircraft's tail and the accelerometers. Finally, using this information, a solution was obtained for the vibratory airloads. Having provided information on the nature of the driving forces, structural modifications can be made that move the natural frequencies away from thefrequencies of the applied airloads, http://archive.org/details/identificationof109458486, Major, United States Army, Approved for public release; distribution is unlimited.

This thesis presents a fully coupled, quasi-3D analysis of rotor blade flutter that can accommodate forward flight conditions. The rotor blade is modeled as a uniform beam, taking the average characteristics of a real blade between 20% and 90% of its length. Applying Rayleigh's method, the first few bending and torsion normal mode shapes and natural frequencies are determined, and then adjusted for the rotating case. With this data, force and moment equations of motion are developed using Lagrange's equation along with a normal mode analysis. Theodorsen coefficients are calculated over a range of forward velocities (input as reduced frequencies) for a specified number of elements along the blade model. Incorporating these coefficients into the equations of motion, a square matrix is generated from which complex eigenvalues can be derived. These eigenvalues provide the aeroelastic natural frequencies and damping coefficients for each coupled mode. The forward velocity at which one of the modes produces a positive damping coefficient gives the value of reduced frequency for the flutter point. The resulting forward speed and blade tip speed can then be determined., http://archive.org/details/adtheodorsenbase109454580, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

Until recently, computer simulations of helicopter rotor dynamics have employed equations of motion that have been linearized or simplified. These modified equations of motion did not allow for the evaluation of nonlinear material properties in the rotor since higher order terms in the dynamics had been modified in the simplification process. With recent advances in both computer simulation hardware and symbolic mathematic manipulation software, the full nonlinear equations of motion may be utilized in helicopter rotor simulations. This dissertation reports on the use of the full nonlinear equations of motion in the analysis of rotor blade lead/lag motion and its effect on rotor hub and rigid body fulselage motion. Nonlinear modeling methods are implemented using Maple symbolic mathematic manipulation software and Matlab and Simulink computer simulation environments. Results are compared to the RAH- 66 Comanche Froude scale wind tunnel article and new methodologies evaluated in the search for a damperless rotor system that is free of ground and air resonance mechanical instabilities, http://archive.org/details/nonlineardynamic109458740, Naval Postgraduate School author., Approved for public release; distribution is unlimited.

The Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) computer program has been developed at the Naval Postgraduate School to aid in the preliminary design of rotorcraft and has been updated to include a Graphical User Interface (Gul). This thesis is a continuation of the program focusing on stability and control analysis. The trim solution for a specified flight condition is computed from the Performance module of the program. This trim solution is then used to compute stability derivatives for the specified flight condition and a linear state space model is created. This solution can then be used to perform various time and frequency domain analyses or can be saved to a file for future use, http://archive.org/details/stabilityndcontr109459003, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

The RAH-66 Comanche's stealth design requires the use of radar- absorbing material (RAM) on the outer skin of the aircraft. The reduced stiffness properties of RAM produce insufficient tail torsional stiffness, necessitating the use of non-radar-absorbing graphite on the outer skin of the tail section. This thesis investigates structural design modifications to increase the tail section's stiffness to allow the use of RAM on the outer skin and still meet all structural requirements. An original model represents the prototype aircraft at first flight. The goal is to create a model using RAM on the outer skin that watches the structural stiffness of the original model. This thesis builds on earlier work conducted at the Naval Postgraduate School (NPS). Two new design modifications to the tailbone are developed. The best modification increases the torsional stiffness of a baseline model by six percent. Integrating earlier NPS modifications increases torsional stiffness by 12 percent. When RAM is applied to the outer skin of the modified model, torsional stiffness is reduced by only six percent from the baseline as compared to a 24 percent reduction with no modifications. Additional modifications to the vertical and horizontal stabilizers further increase structural stiffness and reduce weight, http://archive.org/details/structuraldesign109459020, Major, United States Army, Approved for public release; distribution is unlimited.

Historically, helicopter and load combinations have been qualified through flight testing, requiring considerable time and cost. With advancements in simulation and flight test techniques, there is potential to substantially reduce costs and increase the safety of helicopter sling load certification. Validated simulation tools make possible accurate prediction of operational flight characteristics before initial flight tests. Real time analysis of test data improves the safety and efficiency of the testing programs. To advance these concepts, the US Army and NASA, in cooperation with the Israeli Air Force and Technion, under a Memorandum of Agreement, seek to develop and validate a numerical model of the UH-60 with sling load and demonstrate a method of near real time flight test analysis. This thesis presents results from flight tests of a US Army Black Hawk helicopter with various external loads. Tests were conducted as the US first phase of this MOA task. The primary load was a container express box (CONEX), which contained a compact instrumentation package. The flights covered the airspeed range from hover to 70 knots. Primary maneuvers were pitch and roll frequency sweeps, steps, and doublets. Results of the test determined the effect of the suspended load on both the aircraft's handling qualities and it's control system's stability margins. Included were calculations of the stability characteristics of the load's pendular motion. Utilizing CIFER software, a method for near-real time system identification was also demonstrated during the flight test program, http://archive.org/details/flighttestingndr109458414, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.

An experimental investigation was made to determine the ultimate tensile strength and elastic modulus of IM6-3501-6 graphite epoxy laminated specimens exposed to temperatures from 70°F to 600°F. Specimens were layered (0°), (90", 0"), (90 ° , 0° , 90° ) . The coupons used are candidate materials for advanced tactical missile airframe design. A Material Testing System (MTS) testing machine with 100,000 lb. maximum load capacity was used to apply the programmed uniaxial tensile loading. A Research Incorporated quad elliptical heating chamber, together with temperature and power controller, were used for maintaining the elevated temperatures. A Measurements Group data acquisition system 4000 was used for data acquisition and data reduction. The ultimate strength of the 12 plied composite specimen was determined at two temperatures, 70 °F and 138 °F. The failure of the grips precluded the determination of the modulus at higher temperatures. The overall modulus was obtained for the same type of specimen at several temperatures up to 400 °F., http://archive.org/details/compositemateria1094522962, Lieutenant Commander, United States Navy, Approved for public release; distribution is unlimited.

This thesis provides a MATLAB (copyright) code and graphical user interface (GUI) which rapidly estimates the bending frequencies of rotating beams from the knowledge of bending frequencies of nonrotating beams. The approach is based on the Rayleigh energy method developed by Yntema. The beams may be rotating or nonrotating, cantilever or hinged, uniform or with linear mass and stiffness distributions, with or without root offsets from the axis of rotation; or uniform with or without tip mass. Especially, the frequencies of both nonrotating and rotating cases can be estimated for (a) beams with and without offset which have mass and stiffness distributions which can be approximated by linear relations and (b) beams with uniform mass and stiffness distributions plus a concentrated mass at the tip. Also, as a part of the MATLABʼ code, the bending frequencies of rotating beams with arbitrary stiffness and mass distributions can be estimated given that the stiffness and mass distributions as well as mode shapes of the rotating beam are provided. In latter case, the mode shapes of nonrotating beams may be used to get rough estimations. The code also presents the nonrotating bending-mode shapes in conjunction with the bending frequencies. The code and GUI are intended for use as a subprogram of JANRAD computer program developed at the Naval Postgraduate School, but can also be used as a stand-alone MATLABʼ program., http://archive.org/details/acomputercodefor109455553, First Lieutenant, Turkish Army, Approved for public release; distribution is unlimited.

Blade Dynamics Analysis is a major portion of a helicopter design. The success of the design is strictly related to accuracy of the blade dynamic calculations. The natural frequencies and the mode shapes are not only difficult to calculate but also can be a time consuming procedure. The Myklestad Extension Method gives the designer the opportunity of calculating correct values of the natural frequencies and the mode shapes when centrifugal forces are present. This thesis provides a transfer matrix Myklestad analysis programmed in MATLABʼ and a Graphical User Interface (GUI) tool built in the MATLABʼ programming language version 6.1, to implement the Myklestad Extension Method. The generated code and the GUI are designed to be a part of 'Blade Dynamics Module' of Joint Army/Navy Rotorcraft Analysis Design (JANRAD). For comparison, nonrotating and uniform beam data from Young and Felgar and the actual data of an H-3 (S-61) helicopter blade are used. Results of the comparison show that the accuracy and robustness of the program are very good, which would make this generated code a valuable part of the helicopter designer's toolbox., http://archive.org/details/developmentofmyk109454691, First Lieutenant, Turkish Army, Approved for public release; distribution is unlimited.

This thesis presents a method for the dynamic system identification and simulation model development of a small rotary wing UAV. Using aerodynamic parameterization and linear state-space modeling techniques, the Bergen Industrial UAV was modeled for computer simulation to analyze its inherent stability and control characteristics. The NPS designed JANRAD software was utilized to determine the stability and control derivatives used in the simulation model. The identification of the UAV dynamic model will aid in the development of closed-loop controllers capable of autonomous UAV control. The fidelity of the simulation model was verified by comparing the simulation responses with data collected from on-board sensors during test flight, http://archive.org/details/dynamicsystemide109458282, Approved for public release; distribution is unlimited, Major, United States Marine Corps, Approved for public release; distribution is unlimited.

Described is the behavior of a rotorcraft equipped with Higher Harmonic Stall Control (HHSC) and a Reverse Velocity Rotor (RVR). Current rotorcraft are limited in forward flight speed by retreating blade stall and compressibility effects on the advancing blade. Stall occurs as the blade encounters increasingly severe reverse flow. HHSC enables conventional rotor systems to fly on the forward and aft sections of the rotor disk, greatly reducing reliance on the mixed flow regions defined by the advancing and retreating blades. Employment of the RVR allows lift generation while the rotor is experiencing reverse flow. A similar type of two per revolution (2/rev) input can be tailored to deliver maximum benefit to RVR equipped rotorcraft. Modification of the Joint Army Navy Rotorcraft Analysis and Design (JANRAD) computer program allows 2/rev cyclic input, use of the RVR, and analysis using high fidelity graphical output to examine angle of attack, coefficient of lift, and air load. Computational results show performance gains in conventional helicopters and high speed flight potential for RVR equipped aircraft. The RVR is applied to the Joint Heavy Vertical Lift (JVHL) aircraft conceptual design for preliminary analysis. This conceptual design can be used as an indicator of the performance of a high speed RVR equipped aircraft.

Motivation to expand the understanding of a helicopter rotor descending into the vortex ring state (VRS) stems from the aircraft mishaps that have plagued the helicopter community. The V-22 has become the most recent victim of encounters with VRS. The onset of VRS is associated with the collapse of the helical vortex wake in the plane of the rotor. The resulting wake disturbances develop an irregular and aperiodic flow. Rotor blade interaction with the disturbed vortices causes large variations in the blade spanwise aerodynamic load distribution. Harmonic analysis of the loading indicates that higher harmonic content becomes prevalent in this state. The dynamic flow similarities achieved in a water tunnel are used to explore flow visualization and conduct vibration analysis of a rotor system operating in the VRS. A scaled rotor system was operated in the NPS Aeronautical Engineering Department's water tunnel. Sensors were used to gather thrust and vibration power spectrum data when operating in VRS. Experimental results correlate with full scale flight data and show a significant increase in the vibration levels of the even multiples of the blade passage frequency. The relative strength of these higher harmonics can be used as an indicator of impending VRS encounters.

This thesis presents a fully coupled, quasi-3D analysis of rotor blade flutter that can accommodate forward flight conditions. The rotor blade is modeled as a uniform beam, taking the average characteristics of a real blade between 20% and 90% of its length. Applying Rayleigh's method, the first few bending and torsion normal mode shapes and natural frequencies are determined, and then adjusted for the rotating case. With this data, force and moment equations of motion are developed using Lagrange's equation along with a normal mode analysis. Theodorsen coefficients are calculated over a range of forward velocities (input as reduced frequencies) for a specified number of elements along the blade model. Incorporating these coefficients into the equations of motion, a square matrix is generated from which complex eigenvalues can be derived. These eigenvalues provide the aeroelastic natural frequencies and damping coefficients for each coupled mode. The forward velocity at which one of the modes produces a positive damping coefficient gives the value of reduced frequency for the flutter point. The resulting forward speed and blade tip speed can then be determined.

This thesis provides a MATLAB (copyright) code and graphical user interface (GUI) which rapidly estimates the bending frequencies of rotating beams from the knowledge of bending frequencies of nonrotating beams. The approach is based on the Rayleigh energy method developed by Yntema. The beams may be rotating or nonrotating, cantilever or hinged, uniform or with linear mass and stiffness distributions, with or without root offsets from the axis of rotation; or uniform with or without tip mass. Especially, the frequencies of both nonrotating and rotating cases can be estimated for (a) beams with and without offset which have mass and stiffness distributions which can be approximated by linear relations and (b) beams with uniform mass and stiffness distributions plus a concentrated mass at the tip. Also, as a part of the MATLABʼ code, the bending frequencies of rotating beams with arbitrary stiffness and mass distributions can be estimated given that the stiffness and mass distributions as well as mode shapes of the rotating beam are provided. In latter case, the mode shapes of nonrotating beams may be used to get rough estimations. The code also presents the nonrotating bending-mode shapes in conjunction with the bending frequencies. The code and GUI are intended for use as a subprogram of JANRAD computer program developed at the Naval Postgraduate School, but can also be used as a stand-alone MATLABʼ program.

e model is obtained through use of commercial off-the-shelf software that is incorporated in a low-cost flight simulator, which is marketed as FLIGHTLAB. The FLIGHTLAB development system facilitates rapid design and analysis of a high fidelity helicopter model using non-linear dynamic modeling techniques. The simulator model of the Hughes OH-6A helicopter is presented and its fidelity is compared to actual fight test data conducted at the U.S. Naval Test Pilot School in Patuxent River, MD. Advancements in electromagnetic actuators and visual rendering systems are also presented to provide insight into the direction simulator technology is progressing.

The strain pattern analysis (SPA) method is applied to estimate rotor blade torsional deflections. The SPA technique requires calculated mode shapes for the tested rotor blade and strain measurements from the rotor's wind tunnel or flight test. The Holzer method is developed to calculate the required mode shapes from rotor blade stiffness and mass properties and the torsional equation of motion. The Holzer method is tested with numerous theoretical and experimental cases and is proven accurate. The strain measurements are from wind tunnel tests conducted by the Army, NASA, United Technologies Research Center (UTRC) and Sikorsky at DNW with a (1:5.73) model-scale UH-60A rotor blade with an advance ratio of 0.301, an advancing tip Mach number of 0.8224 and an average Reynolds number of 1,278,729. The SPA method predicts slightly larger torsional deflections that compare well with the overall trend and range of UTRC static method integrated deflections. The SPA method was evaluated to determine the tolerance to change in the number of measurements and the modes applied, errors in the measurements, and errors in rotor blade stiffness and mass properties. The method is tolerant to all effects except a decrease in the number of measurements and modes.

The work of this thesis was to investigate the probability distributions of test data taken for aluminum 7050-T7451, and to attempt to develop a probability based model from the variation of the 4 fatigue life constants ( , f ̤, ' f ,Ì b,c). The goal was to create strain-life-probability curves that would more accurately describe the likelihood of failure at a given strain amplitude. The investigator determined that the test data did not demonstrate any consistent known probability density function. The investigator cautioned against assuming a normal distribution before it could be completely established as the predominate probability density function. Possible consequences of invalid assumptions were presented. Attempts were made to explain the disparity of sample data between two different laboratories testing of the same material. Assuming random behavior within an established range, probability based models were developed using the 4 strain- life constants. It was determined that in order to create a complete probability based model, an accurate regression of the test data must fit all strain levels to include the intermediate strain level's "knee". In an attempt to solve that problem, 8 parameter equations were explored. Methods to predict the 8 parameters included random number simulation combined with non- least squares curve fits, evolutionary algorithms and genetic algorithms.

Blade Dynamics Analysis is a major portion of a helicopter design. The success of the design is strictly related to accuracy of the blade dynamic calculations. The natural frequencies and the mode shapes are not only difficult to calculate but also can be a time consuming procedure. The Myklestad Extension Method gives the designer the opportunity of calculating correct values of the natural frequencies and the mode shapes when centrifugal forces are present. This thesis provides a transfer matrix Myklestad analysis programmed in MATLABʼ and a Graphical User Interface (GUI) tool built in the MATLABʼ programming language version 6.1, to implement the Myklestad Extension Method. The generated code and the GUI are designed to be a part of 'Blade Dynamics Module' of Joint Army/Navy Rotorcraft Analysis Design (JANRAD). For comparison, nonrotating and uniform beam data from Young and Felgar and the actual data of an H-3 (S-61) helicopter blade are used. Results of the comparison show that the accuracy and robustness of the program are very good, which would make this generated code a valuable part of the helicopter designer's toolbox.

The Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) computer program has been developed at the Naval Postgraduate School to aid in the preliminary design of rotorcraft and has been updated to include a Graphical User Interface (Gul). This thesis is a continuation of the program focusing on stability and control analysis. The trim solution for a specified flight condition is computed from the Performance module of the program. This trim solution is then used to compute stability derivatives for the specified flight condition and a linear state space model is created. This solution can then be used to perform various time and frequency domain analyses or can be saved to a file for future use

The need for improved pilot aids has become a high priority item for pilots and aircrews operating at sea and ashore. Pilot aids such as the moving map display, GPWS, collision, and vortex ring state (VRS) warning systems will significantly enhance aircrew situational awareness and safety. Many more of today's aircraft mishaps are a result of pilot error, which includes a loss of situational awareness. The moving map display provides relatively easy incorporation of sophisticated pilot aids without operational flight program (OFP) modification. This thesis discusses, examines and selects a vortex ring state prediction algorithm to be incorporated in the GADGHT unit. A program was written that manipulated required aircraft performance data from the ARINC 429 data bus and compared this data to vortex ring state boundaries predicted by the algorithm. The GADGHT unit provides an audible and visual warning to the pilots when the aircraft has penetrated the VRS boundaries. This warning system will provide increased safety and situational awareness to helicopter crews operating in increasingly demanding 0perational environments

Until recently, computer simulations of helicopter rotor dynamics have employed equations of motion that have been linearized or simplified. These modified equations of motion did not allow for the evaluation of nonlinear material properties in the rotor since higher order terms in the dynamics had been modified in the simplification process. With recent advances in both computer simulation hardware and symbolic mathematic manipulation software, the full nonlinear equations of motion may be utilized in helicopter rotor simulations. This dissertation reports on the use of the full nonlinear equations of motion in the analysis of rotor blade lead/lag motion and its effect on rotor hub and rigid body fulselage motion. Nonlinear modeling methods are implemented using Maple symbolic mathematic manipulation software and Matlab and Simulink computer simulation environments. Results are compared to the RAH- 66 Comanche Froude scale wind tunnel article and new methodologies evaluated in the search for a damperless rotor system that is free of ground and air resonance mechanical instabilities

Helicopter/slung load systems are two body systems in which the slung load adds its rigid body dynamics, aerodynamics, and sling stretching dynamics to the helicopter. The slung load can degrade helicopter handling qualities and reduce the flight envelope of the helicopter. Confirmation of system stability parameters and envelope is desired, but flight test evaluation is time consuming and costly. A simulation model validated for handling quality assessments would significantly reduce resources expended in flight testing while increasing efficiency, productivity, and safety by aiding researchers, designers, and pilots to understand factors affecting helicopter-slung load handling qualities. This thesis describes a comprehensive dynamics and aerodynamics model for slung load simulation, obtained by integrating the NASA Ames Gen Hel UH-60A simulation with slung load equations of motion. Frequency domain analysis is used to compare simulation to flight test frequency responses and key system stability parameters. Results are given for no load, a 4K lb Block, and a 4K lb CONEX load. Handling quality parameters, stability margins, and load pendulum motion roots for cases without load aerodynamics and with static wind tunnel data were compared. Results illustrated state-of-the-art simulation modeling of helicopter/slung load dynamics and its accuracy in predicting key dynamic parameters of interest.

Adapting the Naval Postgraduate School full nonlinear simulation model of coupled rotor/fuselage response to the 11-3 Sea King, the concentration of this work rests on validating the rotor simulation against an actual rotorcraft. The parameters of the 11-3 from the characteristic equation of a modeled mass-spring- damper system are inputted into a five-bladed model initially utilizing MAPLE to process LaGrange's equation defining the helicopter's full set of nonlinear equations of motion. Results are converted to MATLAB and are then processed in SIMULINK returning time history plots of blade/ fuselage motion. Conclusions are in accordance with literature of Coleman, Fein old and Deutsch.

The Army RAH-66 ComancheHelicopter is currently undergoing developmental flight testing. Theempennage of the aircraft isexperiencing buffeting where the horizontal and vertical tail vibrate at resonant frequencies. These high buffet loads are manifested in higher than anticipated fitting loads, particularly on the tail, and vibrations in the crew stations and at the nose cone where the targeting sensors are located. Significant effort has been devoted to identifying the sources of excitation and the nature of the structural response. This thesis determines the location andmagnitude of empennage vibratory airloads. Because the nature of the excitation is a random function, spectral analysis is used. To obtain the loads, a three step process was utilized. First, from aircraft differential pressure transducers and accelerometers, the spectral content of theresponse and excitation was determined. Then, using aNASTRAN model modified to replicate the flight test aircraft, frequency response functions were determined between selected points on the aircraft's tail and the accelerometers. Finally, using this information, a solution was obtained for the vibratory airloads. Having provided information on the nature of the driving forces, structural modifications can be made that move the natural frequencies away from thefrequencies of the applied airloads

A Graphical User Interface (Gul) was developed and implemented as the front end of the NPS software Joint Army/Navy Rotorcraft Analysis and Design (JANRAD). The original JANRAD computer program was developed to aid in the analysis of helicopter rotor performance, stability and control and rotor dynamics. An interactive program, JANRAD was capable of accurately and quickly solving helicopter design problems at the preliminary design level. The addition of the Gul greatly simplified the use of the program but added considerable complexity to the original MAThAB0 M-File code. Because of the increased complexity, only the Performance Analysis module of the program was modified. The use of several new features of MAThAB0 version 5.1, such as the GUIDE0 and Structure functions, simplified the construction of the Gul environment and enhanced the tie between the user interface and performance calculation routines. Although initiated from the MAThAB command line, the program can now be worked entirely from the "Windows'1 environment. The performance routines weremodified extensively to connect the user input with the existing analysis routines. However, the fundamental method of analysis remains unchanged. Several cases of Sikorsky UH-60A Black Hawk input data were run and results compared with those from JANRAD version 3.1(1995). The results correlated exactly. A users Guide was developed and is included in Appendix A.

This thesis presents a method for the dynamic system identification and simulation model development of a small rotary wing UAV. Using aerodynamic parameterization and linear state-space modeling techniques, the Bergen Industrial UAV was modeled for computer simulation to analyze its inherent stability and control characteristics. The NPS designed JANRAD software was utilized to determine the stability and control derivatives used in the simulation model. The identification of the UAV dynamic model will aid in the development of closed-loop controllers capable of autonomous UAV control. The fidelity of the simulation model was verified by comparing the simulation responses with data collected from on-board sensors during test flight

The Joint Army/Navy Rotorcraft Analysis and Design (JANRAD) computer program was developed at the Naval Postgraduate School to perform performance, stability and control, and rotor dynamics analysis during preliminary helicopter design efforts. This thesis is the continuation of a previous work in which a Graphical User Interface (GUI) was developed and implemented as the front end of the NPS program. Due to the complexity of the GUI design, only the Performance module of JANRAD was completed by the prior student. This thesis expands the capabilities of the Performance module, and the JANRAD code, by adding graphical output of performance results, improved rotor sizing capabilities, resources for user defined blade elements and non-linear blade twist, airfoil meshing capabilities, and additional reference airfoil data corrected for compressibility effects. It contains the basic architecture for the Stability and Control module GUI. Additionally, utilizing actual UH-60A Black Hawk airfoil and test flight data as inputs, JANRAD version 5.0 was run to validate its output with the test flight results, and those produced in a prior hesis by JANRAD version 3.1 (1995). Excellent agreement was demonstrated in all flight regimes. Utilizing airfoil data corrected for compressibility effects, high altitude runs resulted in much better correlation with test flight results than those experienced in 1995 using uncorrected airfoil data. A JANRAD Users Guide was updated and is included in Appendix A.

The Army RAH-66 Comanche Helicopter made its first flight in January of 1996. Its current structural configuration, however does not meet the Army's requirements for radar signature. Structural configurations of the tailcone that meet radar cross-section requirements tend to lack sufficient structural stiffness due to the presence of Kevlar in place of graphite on the outer mold line. This thesis investigates potential structural design modifications to the Comanche tailcone that would move the design closer to meeting both its structural and radar signature requirements. Geometry modifications with baseline (current configuration) materials increased torsional stiffness by nine percent. Structural geometry modifications using radar signature compliant materials reduced torsional stiffness by 10 percent. The geometry changes analyzed produce structural performance improvements insufficient to allow the use of radar-compliant materials without further geometry changes

The RAH-66 Comanche's stealth design requires the use of radar- absorbing material (RAM) on the outer skin of the aircraft. The reduced stiffness properties of RAM produce insufficient tail torsional stiffness, necessitating the use of non-radar-absorbing graphite on the outer skin of the tail section. This thesis investigates structural design modifications to increase the tail section's stiffness to allow the use of RAM on the outer skin and still meet all structural requirements. An original model represents the prototype aircraft at first flight. The goal is to create a model using RAM on the outer skin that watches the structural stiffness of the original model. This thesis builds on earlier work conducted at the Naval Postgraduate School (NPS). Two new design modifications to the tailbone are developed. The best modification increases the torsional stiffness of a baseline model by six percent. Integrating earlier NPS modifications increases torsional stiffness by 12 percent. When RAM is applied to the outer skin of the modified model, torsional stiffness is reduced by only six percent from the baseline as compared to a 24 percent reduction with no modifications. Additional modifications to the vertical and horizontal stabilizers further increase structural stiffness and reduce weight

Historically, helicopter and load combinations have been qualified through flight testing, requiring considerable time and cost. With advancements in simulation and flight test techniques, there is potential to substantially reduce costs and increase the safety of helicopter sling load certification. Validated simulation tools make possible accurate prediction of operational flight characteristics before initial flight tests. Real time analysis of test data improves the safety and efficiency of the testing programs. To advance these concepts, the US Army and NASA, in cooperation with the Israeli Air Force and Technion, under a Memorandum of Agreement, seek to develop and validate a numerical model of the UH-60 with sling load and demonstrate a method of near real time flight test analysis. This thesis presents results from flight tests of a US Army Black Hawk helicopter with various external loads. Tests were conducted as the US first phase of this MOA task. The primary load was a container express box (CONEX), which contained a compact instrumentation package. The flights covered the airspeed range from hover to 70 knots. Primary maneuvers were pitch and roll frequency sweeps, steps, and doublets. Results of the test determined the effect of the suspended load on both the aircraft's handling qualities and it's control system's stability margins. Included were calculations of the stability characteristics of the load's pendular motion. Utilizing CIFER software, a method for near-real time system identification was also demonstrated during the flight test program

This thesis develops a technique for formulating the full nonlinear equations of motion for a coupled rotor-fuselage system utilizing the symbolic processing software MAPLE(registered). The symbolic software is further utilized to automatically convert the equations of motion into C, Fortran or MATLAB(registered) source code formatted specifically for numerical integration. The compiled source code can be accessed and numerically integrated by the dynamic simulation software SIMULINK(registered). SIMULINK(registered) is utilized to generate time history plots of blade and fuselage motion. These time traces can be used to explore the effects of damping nonlinearities, structural nonlinearities, active control, individual blade control, and damper failure on ground resonance. In addition, a MATLAB(registered) program was developed to apply the Moving Block Technique for determining modal damping of the rotor- fuselage system from the time marching solutions

This thesis is intended to be a reference for solid modeling and Computer Aided Design (CAD) tailored specifically for the Naval Postgraduate School's capstone helicopter design course, AA 4306. The goal is to present the use of AutoCAD R13 software as a central design tool throughout the conceptual design phase of the American Helicopter Society (AHS) Graduate Design Competition project. The specifics of AutoCAD that are essential to performing the design project are explored through examples of model construction and lessons learned from the 1997 VIPER design effort. The usage of solid modeling as a design tool for design team integration is investigated. It is intended for this work to allow future classes to acquire sufficient proficiency with Computer Aided Design and solid modeling. Maximizing the practical usage of CAD techniques in a single quarter will provide an improved learning experience in a more realistic design environment.

This thesis is part of the helicopter research program established at The Naval Postgraduate School (NPS). NPS currently has two OH-6A light observation helicopters which were obtained from the U.S. Army. One of these is dedicated to ground vibration testing and dynamics research. Previous research on the OH-6A at NPS established baseline vibration test data. The data includes natural frequencies, principal mode shapes and damping characteristics. This thesis continues previous research of the OH-6A and develops a detailed finite element model to be used in future helicopter dynamics research at NPS. The model is based on an MSC/NASTRAN finite element model of a similar aircraft obtained from the McDonnell Douglas Helicopter Company. Both the nose and empennage were modified to represent the structural characteristics of the test article. Due to lack of structural design data, model mass updating was performed using previously obtained test data and a design sensitivity approach. The updated model natural frequencies agree well with the test data

Efforts to establish a helicopter research program in structural dynamics at NPS were greatly enhanced when the U. S. Army donated two OH-6A light observation helicopters. One of the helicopters is reserved for ground vibration testing and dynamics research. Vibration measurements are extremely important in predicting and understanding an aircraft's dynamic behavior and durability. A comparison of a helicopters natural frequencies and those frequencies transmitted to the airframe through the rotor system can alert the designer/evaluator to possible dynamic problems. This thesis establishes a baseline vibration test program on the OH-6A helicopter for future testing and comparison to analytic models. The goal of the research is to establish natural frequencies (eigenvalues) principal mode shapes (eigenvectors), and damping characteristics of the OH-6A and to compare these values to test and analytical data obtained from the McDonnell Douglas Helicopter Company.

Originally designed as a target drone for the U.S. Army, the NPS hummingbird has undergone several modifications to convert it into a reliable research platform. The 163 pound remotely piloted helicopter (RPH) is powered by a Weslake Aeromarine Engines Limited (WAEL) 342 two stroke, twin cylinder, 25 hp, gasoline engine. An engine failure due to cylinder overheating halted research efforts until investigation as to the cause and subsequent corrections could be made. Costing approximately $3000 per engine, another failure is unacceptable. The tasks undertaken in this thesis were to investigate the cause of the overheat failure and improve the engine cooling system. Cooling system corrections required total redesigns of the engine cooling and engine start systems. Additionally, research of the RPH's history revealed a need for a torsional shock absorber to be incorporated in the drive train to increase component life. The changes made to Hummingbird provide a decrease in empty weight, minimal center of gravity change and, most importantly, an increase in user safety finishing the Department of Aeronautics and Astronautics with a dependable vehicle for rotary wing research.

An analysis was made of the aircrew centered system design aspects for the MH-53E helicopter. These aircrew centered design features included changes in the cockpit, aircraft weight, and drag coefficient. The cockpit evaluation compared the current MH-53E cockpit configuration with design changes currently under review by the Navy. This evaluation suggests that the proposed cockpit design display change may reduce aircrew load stress and improve mission effectiveness. Changes in subsystem components may either increase or decrease the weight of the MH-53E. Similarly, changes in crew tasking may result in a need for more or less fuselage volume size. Therefore, the sensitivity of MH-53E performance to generic changes in weight and drag was investigated in order to make source assessment of equipment and crew tasking changes upon MH-53E mission effectiveness

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 inter-active, 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.