Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 139-144). Also available in electronic format on the Internet.

The purpose of this research was to develop parametric Design-to-Cost models for selected major subsystems of certain helicopters. This was accomplished by analyzing the relationships between historical production costs and certain design parameters which are available during the preliminary design phase of the life cycle. Several potential contributions are identified in the areas of academia, government, and industry. Application of the cost models will provide estimates beneficial to the government and DoD by allowing derivation of realistic Design-to-Cost estimates. In addition, companies in the helicopter industry will benefit by using the models for two key purposes: (1) optimizing helicopter design through cost-effective tradeoffs, and (2) justifying a proposal estimate.

Helicopter aeroelastic analysis is highly complex and multidisciplinary in nature; the flexibility of main rotor blades is coupled with aerodynamics, dynamics and control systems. A key component of an aeroelastic analysis is the vehicle trim procedure. Trim requires calculation of the main rotor and tail rotor controls and the vehicle attitude which cause the six steady forces and moments about the helicopter center of gravity to be zero. Trim simulates steady level flight of the helicopter. The trim equations are six nonlinear equations which depend on blade response and aerodynamic forcing through finite element analysis. Simulating the behavior of the helicopter in flight requires the solution of this system of nonlinear algebraic equations with unknowns being pilot controls and vehicle attitude angles. The nonlinear solution procedure is prone to slow convergence and occasional divergence causing problems in optimization and stochastic simulation studies. In this thesis, an attempt is made to efficiently solve the nonlinear equations involved in helicopter trim. Typically, nonlinear equations in mathematical physics and engineering are solved by linearizing the equations and forming various iterative procedures, then executing the numerical simulation. Helicopter aeroelasticity involves the solution of systems of nonlinear equations in a computationally expensive environment. The Newton method is typically used for the solution of these equations. Due to the expensive nature of each aeroelastic analysis iteration, Jacobian calculation at each iteration for the Newton method is not feasible for the trim problems. Thus, the Jacobian is calculated only once about the initial trim estimate and held constant thereafter. However, Jacobian modifications and updates can improve the performance of the Newton method. A comparative study is done in this thesis by incorporating different Jacobian update methods and selecting appropriate damping schemes for solving the nonlinear equations in helicopter trim. A modified Newton method with varying damping factor, Broyden rank-1 update and BFGS rank-2 update are explored using the Jacobian calculated at the initial guess. An efficient and robust approach for solving the strongly coupled nonlinear equations in helicopter trim based on the modified Newton method is developed. An appropriate initial estimate of the trim state is needed for successful helicopter trim. Typically, a guess from a simpler physical model such as a rigid blade analysis is used. However, it is interesting to study the impact of other starting points on the helicopter trim problem. In this work, an attempt is made to determine the control inputs that can have considerable effect on the convergence of trim solution in the aeroelastic analysis of helicopter rotors by investigating the basin of attraction of the nonlinear equations (set of initial guess points from which the nonlinear equations converge). It is illustrated that the three main rotor pitch controls of collective pitch, longitudinal cyclic pitch and lateral cyclic pitch have significant contribution to the convergence of the trim solution. Trajectories of the Newton iterates are shown and some ideas for accelerating the convergence of trim solution in the aeroelastic analysis of helicopter are proposed.

Helicopters are often used to transport supplies and equipment. When a heavy load is carried via suspension cables below a helicopter, the load oscillates in response to helicopter motion and disturbance forces, such as wind. This oscillation is dangerous and adversely affects control of the helicopter, especially when carrying large or heavy loads. By adding input shaping to the helicopter's flight controller, the suspended load oscillation caused by helicopter motion is greatly reduced. A significant benefit of this approach is that it does not require measurement of the load position. This thesis contains derivations and analysis of simple planar helicopter-load dynamic models, and these models are verified using experimental data from model-scale, radio-controlled helicopters. The effectiveness of input shaping at eliminating suspended load oscillation is then demonstrated on this experimental hardware. In addition, the design of an attitude command, near-hover flight controller that combines input shaping and a common flight control architecture is illustrated using dynamic models of a Sikorsky S-61 helicopter, and simulation results are shown for example lateral and longitudinal repositioning movements. Results show that applying input shaping to simulated pilot commands greatly improves performance when carrying a suspended load.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / The helicopter is a prime example of a nonlinear multi-body dynamic system that is subjected to numerous forces and motions to which the system must react. When a helicopter, with a conventionally articulated rotor head, is resting on the ground with its rotor spinning, a condition called ground resonance can develop. Ground resonance is a specific self-excited oscillation of the helicopter and is caused by the interaction between the main rotor blades and the fuselage structure. Inertia forces of the blades perform an out-of-phase lagging motion, which reacts with the elastic landing gear of the helicopter. For certain values of the main rotor angular velocity, the frequency of these inertia forces coincides with a natural vibration frequency of the fuselage structure. If this occurs, the inertia forces of the lagging blades produce oscillations of the fuselage, which then further excite the lagging motion of the blades. This interaction is responsible for an instability of conventionally articulated main rotor helicopters, which is called ground resonance. The ground resonance phenomenon is investigated by means of a classical analytical approach in which the ground resonance equations are derived from Euler-Bernoulli beam theory and verified with results in literature. These equations are required to discuss ground resonance stability in further detail and determine the specific regions in which the phenomenon occurs. These results are incorporated in a simplified numerical model using an elastic multiple-body dynamics analysis program called DYMORE to simulate the South African Rooivalk Combat Support Helicopter. DYMORE is a program that offers nonlinear multi-body dynamic analysis code, using the finite element method, which was specifically developed for helicopter modelling. The complexity of helicopter modelling generally requires large amounts of computing power to ensure reasonable processing time. In order to prevent excessive computational time, the numerical model will be simplified in terms of aerodynamic and structural aspects. The scope of the numerical investigation is, therefore, limited to the ground resonance phenomenon without the effect of aerodynamic forces and representing the fuselage as multi-body beam structures of specified stiffness.

Thesis (MEng) -- Stellenbosch University, 2000. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: This document contains the work done on the bearingless rotor hub for the 24% scale model of the Rooivalk Attack Helicopter situated at the CSIR in Pretoria. This work forms part of the MSc Ing degree of Johannes Steyn. This work was deemed necessary because of a movement away from the fully articulated rotor to one of hingeless and more recently bearingless rotors. The main emphasis of this thesis is to be a technology demonstrator more than the design of a fully working bearingless rotor hub. With this in mind the final design in this report is not an optimal one, but the procedures and methodology in getting to a design are laid out in this document. To verify the design, tests were identified and created. The procedures for these tests are also included in this document. For the fatigue test a test bench had to be designed and built. This document also includes the design of this test bench / AFRIKAANSE OPSOMMING: Die dokument lewer verslag van die aktiwiteite vir die ontwerp van ‘n laerlose rotor van die 24% skaal model van die Rooivalk Helikopter, gelee by die WNNR in Pretoria. Die werk gedoen vorm deel van die MSc Ing graad van Johannes Steyn. Die werk is nodig geag omdat daar ‘n tendens is om weg te beweeg van die volledig geartikuleerde rotor na die van ‘n skanierlose en meer huidig ‘n laerlose rotor. Die hoof klem van die tesis is om as tegnologie demonstrator op te tree, eerder as die daarstel van ‘n werkende laerlose rotor. Na aanleiding van bogenoemde stelling kan die finale ontwerp nie as optimaal beskou word nie. Die prosedures en metodiek wat gevolg is om die ontwerp te kry word uitgele in die dokument. Om die ontwerp te verifieer is toetse gei'dentifiseer. Die prosedures vir elk van die toetse word ook in die dokument ingesluit. Vir die uitputtingstoetse moes ‘n spesiale toetsbank ontwerp en gebou word. Die ontwerp van hierdie toetsbank is ook in die dokument.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: An experimental investigation was conducted usmg a cantilever beam to illustrate an understanding of vibration techniques and phenomena. The [Tee and forced vibration of the cantilever beam was investigated using various modelling strategies. Theoretical models such as the Lumped parameter, Myklestad, Distributed Parameter and Finite Element Methods were analysed and compared with experimental measurements. Excellent agreement of the natural frequencies, mode shapes and the harmonic transfer functions were found. To investigate tail boom vibration, a Finite Element Model of a simplified helicopter tail boom design was tested against experimentally measured data. The results correlated accurately and the model was used to evaluate the effectiveness of a vibration suppression system designed for the tail boom. The vibration suppression system was designed using two, parallel dynamic absorbers to reduce tail boom vibrations at its two dominant frequencies. For the purposes of this thesis, the dynamic absorbers were tuned to reduce the resonant peaks at the dominant excitation frequencies of the excitation force in-line with the thrust of the tail rotor only. This excitation force was estimated using a simplified tail rotor dynamic model, which when compared with actual vibration data was assumed to predict the basic frequency trends of the force, reliably. Incorporating the designed components into an accurate Lumped Parameter model of a cantilever beam structure and simulating the response of the structure at the dominant excitation frequencies of the calculated excitation force, tested the vibration suppression system. The results of this investigation proved the effectiveness of the design procedure and optimisation process of the design parameters. A similarly designed suppression system was incorporated into the Finite Element tail boom model and from the analytical results obtained it was shown to cause a fair reduction in the vibration response at the two dominant frequencies of the excitation force. Finally, two possible applications were suggested from the research presented in this thesis. The first application was the simplified configuration of a vibration monitoring system for the tail boom. The second application was the possible development of a system using the response of vibration suppression absorbers to predict the magnitudes of the excitation forces on the tail boom. / AFRIKAANSE OPSOMMING: 'n Experimentele ondersoek is ondemeem deur gebruik te maak van 'n ingeklemde balk om vibrasie tegnieke te illustreer. Die vrye en geforseerde vibrasie van die ingeklemde balk is ondersoek deur verskillende model tegnieke te gebruik. Teoretiese modelle soos die Lumped parameter, Myklestad, Distributed Parameter en Eindige Element Metodes was geanaliseer en vergelyk met die eksperimentele waardes. Uitstekende ooreenstemmings was gevind tussen die natuurlike frekwensies, die eievektore en die harmoniese oordragsfunk:sie. Om stert vibrasie te ondersoek, was'n eindige element model van 'n helikopter stert getoets teenoor die eksperimentele data. Die resultate het akuraat gekorreleer en dus was die model gebruik om die effektiwiteit van 'n vibrasie supressie sisteem te evalueer. Die vibrasie supressie sisteem was ontwerp deur gebruik te maak van twee parallele dinamiese absorbeerders om die helikopter stert se eerste twee dominante vibrasie frekwensies te minimeer. Vir die doel van hierdie tesis was die dinamiese absorbeerders ingestel om net die resonante pieke van die opgewende krag wat in lyn is met die drykrag van die stert rotor te minimeer Hierdie opgewende krag was, deur gebruik te maak van 'n basiese stert rotor dinamiese model, aanvaar om die basiese frekwensie tendense van die krag te voorspel. Die supressie sisteem wat ontwerp was, was getoets op die lumped parameter balk en het veroorsaak dat die voorspelde opgewende krag by al twee van sy dominante . frekwensies baie geminirneer was. Die effektiwiteit van die sisteem was dus bewys en die sisteem was gebruik om die respons van die eindige element model van die stert te verbeter. Die resultate het 'n aanvaarbare reduksie in die respons by die twee dominante frekwensies van die opgewende krag, gewys. Laastens, deur gebruik te maak van die resultate in hierdie tesis. was twee moontlikhede voorgestel. Die eerste een was die konfigurasie van 'n vibrasie moniterings sisteem vir die helikopter stert. Die tweede mmontlikheid was die moontlike ontwikkeling van 'n sisteem wat die grootte van die opgewende krag by die stert rotor kon voorspel, deur gebruik te maak van die vibrasie suppressie absorbeerders.

It is important to ensure that Transpower is prepared to deliver upcoming transmission tower refurbishment projects that are located on sites with difficult access. This project reviews the availability, capability and cost of utilising alternative construction methods and any associated wider issues. The focus of this report is on how Transpower can more effectively utilise helicopters and gin poles for transmission tower erection and material delivery on remote sites.

The requirement for low-level navigation flight conducted between 200 and 500 feet above ground level is something unique to the military helicopter pilot. Each novice helicopter pilot is introduced to this skill early and in a limited number of flights or flight hours. A low situational awareness (SA)is historically noted among the novice pilots during their first few flights within this flight regime. To that end, this thesis continues with the work conducted earlier to develop a trainer that places the pilot in an immersive and familiar cockpit environment for training through the use of chromakeyed technology as employed in the Virtual Environment Helicopter System (VEHELO). The pilot will then be able to learn and exercise required piloting tasks and multi-place aircraft communications as authentically and as meticulously as in actual flight. The focus of this thesis is to continue validation of the ChrAVE/VEHELO system. This will be accomplished by comparison of data obtained from data collected by pilots flying the ChrAVE and flying the actual aircraft during initial navigational training flights. Additionally this thesis will attempt to show that the latest version of the system has a previously unrecognized ability to improve pilot performance. The system is capable of teaching novice pilots the important skill of Crew Resource Management (CRM) and the appropriate communication skills. The original Chromakey Augmented Virtual Environment (ChrAVE) helicopter flight simulation system was developed to substantiate the feasibility of having embedded trainers for helicopters. Both the ChrAVE and VEHELO are comprised of commercial off the shelf (COTS) equipment in a mobile wheeled box. To determine the effectiveness of the ChrAVE as an instructional tool, the opinions of pilots and pilot instructors will be collected for analysis. The subject pilots will be tasked with numerous realistic piloting tasks. Empirical data will be collected and evaluated according to the low-level navigation performance thresholds set forth by Marine Medium Helicopter Training Squadron 164 (HMMT- 164) which is the CH-46E Model Manager. / US Marine Corps (USMC) author.

Applying selected concepts of organizational theory to the Mayaguez incident of 1975 leads to a more comprehensive understanding of events and more accurate lessons learned. Application of organizational theory to the Mayaguez incident demonstrates the decision processes at the executive level left the military operation vulnerable to failure. Henry Mintzberg's structural contingency model and Lee Bowman and Terrence Deal's frames model are used and are applied to executive-level decisions. The rationale behind focusing on the executive level is twofold: first, it is where final critical decisions are made and second, military operations cannot take place without an executive-level authorization. The Mayaguez crisis was rife with potential pitfalls and, though President Ford was equipped with an organization of intelligent, competent personnel, the result was unnecessary loss of life. Publicly, the operation was a success and President Ford the savior of the Mayaguez crew. To the military, the operation was an embarrassment because of failures in the organizational structure and decision making. Application of organizational theory provides an avenue for analysis of the military operation within the Mayaguez rescue.