An important consideration in the design of military aircraft is observability, or how visible an aircraft is to hostile weapons. One area of great importance to overall observability is an aircraft’s infrared signature, particularly the infrared emissions from the exhaust nozzle and plume. This creates the need for accurate modeling of the infrared signatures from these sources as a design aid or for comparison of candidate designs. To that end, a parametric model has been developed based on the General Electric F110-GE-129 jet engine. The basis of the model is a highly flexible Monte-Carlo ray-trace formulation which is capable of simulating real surface behavior, such as specular reflections, and allows for variation of input parameters such as temperature, surface properties, and geometry. For given input parameters, the model predicts the overall infrared signature due to surface radiation from the exhaust nozzle and interior components. It also indicates the relative contribution of each interior surface to the overall signature and predicts the image that would be seen using infrared imaging equipment. The basic principles of the simulation method and the theory behind the application are discussed. Results are presented, primarily in graphical format, and recommendations are made for further work. / Master of Science

A turbulent combustion noise model based on first principles is developed in this thesis. The model predicts (1) the pressure time series, (2) Sound Pressure Level (SPL) spectrum, (3) Over-All Sound Pressure Level (OASPL), (4) the thermoacoustic efficiency, (5) the peak frequency, and (6) the sound power of combustion generated noise. In addition, a correlation for sound power is developed based on fundamental burner and fuel variables known to affect the acoustic characteristics of turbulent combustion. The predicted pressure time series exhibits consistency with reality in that it has no steady component. It also confirms speculation in the literature that the predominant noise mechanism in open turbulent flames results from a "transition burning" phenomenon at the flame front. The predicted Sound Pressure Level spectrum, Over-All Sound Pressure Level, and the thermoacoustic efficiency are in excellent agreement with the results available in the literature. The shifts in the peak frequency with basic burner and fuel parameters are consistent with experimental observations from the literature. The disagreements between the predicted and the observed exponents of fuel and burner parameters for sound power are shown to be well within the standard deviation of the experimental observations. Certain areas for further analytical research on the combustion noise mechanism are identified. / Master of Science

published_or_final_version / abstract / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

This thesis presents an adaptive model reference controller for a highly maneuverable high performance aircraft, in particular, a modified F18. An adaptive controller is developed to maneuver an aircraft at a high angle of attack. Thus, the aircraft is required to fly over a highly nonlinear flight regime. The adaptive controller presented in this thesis can be viewed as a combination of a linear and a nonlinear controller. Around a fixed flight condition the adaptive controller converges to a linear controller; however, the controller remains a nonlinear controller during maneuvers. The contributions of this thesis lie in two areas. The first area is in control. A successful application of linear adaptive control is presented for a highly nonlinear system. A new method is used to generate the reference trajectory. The reference model uses output feedback to improve the reference trajectory. It is shown that this improvement is necessary because of the control limitations. This work is also important to the control of highly maneuverable high performance aircraft. A successful adaptive controller has been developed to rapidly maneuver an aircraft to a high angle of attack. The main focus of this thesis is adaptive control. / Graduation date: 1993

The two-noise source model for predicting jet noise claims that the radiated jet noise is composed of two distinct sources one associated with the small-scale turbulence and another associated with the large-scale turbulence. The former source is claimed to radiate noise predominantly at larger angles with respect to the downstream jet axis, whereas the large-scale turbulence radiates predominantly at the shallower angles. A key objective of this effort is to experimentally validate this model using correlation and coherence measurements. Upon the successful validation of the two-noise source model for jets exhausting from multiple nozzle geometries driven at Mach numbers ranging from subsonic to supersonic, a three-microphone signal enhancement technique is employed to separate the contribution of the small-scale turbulence from that of the large-scale turbulence in the far-field. This is the first-ever quantitative separation of the contributions of the turbulence scales in far-field jet noise measurements. Furthermore, by suitable selection of far-field microphone positions, the separation of the contribution of any internal or core noise from that of the jet-mixing noise is achieved. Using coherence-based techniques to separate the contributions of the small-scale turbulence, large-scale turbulence, and any internal or core noise from far-field exhaust noise measurements forms the backbone of this effort. In the application of coherence-based multiple-microphone signal processing techniques to separate the contributions of the small-scale turbulence, large-scale turbulence, and any internal or core noise in the far-field, research efforts focus on three techniques (1) the coherent output power spectrum using two microphones, (2) an ordinary coherence method using the three-microphone technique, and (3) the partial-coherence method using five microphones. The assumption of jet noise incoherence between correlating microphone is included in each of these methods. In light of the noise radiation mechanisms described within the framework of the two-noise source model and their spatial characteristics as experimentally determined in the far-field, the assumption of jet noise incoherence is evaluated through a series of experiments designed to study jet noise coherence across a variety of nozzle geometries and jet Mach numbers ranging from subsonic to supersonic. Guidelines for the suitable selection of far-field microphone locations are established.

Thesis (M.B.A.)--Naval Postgraduate School, December 2003. / "MBA professional report"--Cover. Joint authors: Robert K. DeGuzman Jr., Thomas S. Fulford III, Jesse E. Porter Sr. Thesis advisor(s): Donald R. Eaton, Kevin R. Gue, Mary A. Malina. Includes bibliographical references (p. 71-73). Also available online.

Approved for public release, distribution is unlimited / Presently, the required data file to be loaded onto the Radar Warning Receiver (RWR) onboard the F-16 aircraft is done manually by the aircraft technicians, two to three hours prior to the actual flight time. This process should be automated. As such there is a need to look into the use of wireless transmission technology to complement or replace the manual method of loading the critical data file from the command station onto every F-16 aircraft. The present wireless technology is relatively mature and stable. In this thesis, the feasibility of incorporating and adapting this technology for use in the flight line environment is examined. The propagation effect in wireless transmission is also studied and recommendations proposed with regards to the installation of wireless facilities in the flight line. In addition, the EDNA, a portable maintenance aid that comes with the F-16 aircraft for loading the data file, has to be upgraded. Hence, a system feasibility study is carried out to adapt or upgrade the present equipment to wireless transmission capability. / Major, Republic of Singapore Air Force

This thesis presents the design of various controllers for a highly maneuverable, high performance aircraft, namely the modified F-18. The aircraft was required to perform high angle-of-attack maneuvers, for which the aircraft behaves in as a highly nonlinear system. An adaptive PID controller was used to control the aircraft through these high angle-of-attack maneuvers. Several nonlinear controllers were then developed based on the adaptive PID control, and were tested for robustness. This thesis also looks at an improvement in the aircraft which may improve performance in high angle-of-attack maneuvers. The contributions of this thesis are in the areas of control, in general, and specifically in the area of aircraft control. Successful application of linear adaptive control and nonlinear control were presented. In the area of aircraft control, controllers were presented which produce good performance for high angle-of-attack maneuvers, while maintaining implementability. Also, some insight is gained into what aircraft changes could improve performance. / Graduation date: 1995