All aircraft must meet controllability requirements to be certified for commercial use or adopted by the mi1itary. Aircraft maneuverability is often 1imited by control authority. Thus, it is essential for designers to evaluate a candidate concept's control authority early in the conceptual design phase. In this thesis, a methodology for rapid control power evaluation of preliminary design configurations against requirements at the key flight conditions is established. First, a collection of critical flight conditions to be considered using this methodology is identified. To examine a variety of aircraft configurations and accelerate the process of estimating stability and control derivatives, a FORTRAN program using the Vortex-Lattice Method was written to estimate subsonic, low angle-of-attack aerodynamics. Then, a spreadsheet processes the aerodynamic data to check whether the design configuration possesses adequate control power to satisfy the requirements of the critical flight conditions. / Master of Science

The purpose of this research is to apply engineering-based knowledge to the field of combat aircraft survivability, and to create scenario-specific models in order to estimate the tradeoff between aircraft survivability and lethality metrics at the encounter and sortie levels. The development of scenario-specific models serves to identify and quantify technological changes that have Ieverage on the overall performance of the aircraft from a survivability point of view. Also, the models focus on the fighter aircraft susceptibility assessment and are capable of incorporating outputs from offline studies as inputs, such as in the area of vulnerability assessment where extensive databases are available. The mission scenario models are microscopic in nature and relate important conceptual aircraft design parameters such as thrust-to-mass ratio, wing loading, empty mass, maneuverability, etc. and operational parameters (e.g., weapon payload, range, loiter time, flight profiles, etc.) to the aircraft sortie survivability and lethality under various threat scenarios. This research proposes a methodology to estimate survivability and lethality aircraft performance at the sortie level where aircraft parameters can be implemented into scenario-specific models to assess their impact upon survivability-related metrics. While the project was conceived with naval aircraft in mind, the methodology, to the extent possible, is not to be aircraft-specific and thus could be applied to any particular design at the conceptual stage. / Ph. D.

A general inverse design procedure has been developed to use optimization techniques and generic surface descriptions for the purpose of aerodynamic shape design. A variety of flow regimes are examined from 2-D inviscid, subsonic cases to 3-D turbulent, supersonic problems. Surface descriptions have been generalized through the use of B-splines to model a variety of curves and shapes with a minimum of parameters. The process uses a computational fluid dynamics program, GASP (the General Aerodynamic Simulation Program), and several iterative and optimization techniques to examine bodies of interest. A 2-D inviscid, subsonic airfoil test case demonstrates the ability of the procedure to solve problems governed by elliptic equations. A 3-D, viscous, compressible flow over a forebody/canopy model of a supersonic fighter and its comparison to test data establishes the ability of the method to solve practical problems of interest. Several other test cases are performed, including an axi-symmetric power law body and a 3-D elliptic cone. Unconstrained multi-parameter optimizations have been quite successful in matching target pressure coefficients and reproducing target body shapes. / Ph. D.

Discussed is the development of two computer programs for the calculation of cross-sectional areas for existing aircraft and aircraft concepts. The first program allows the user to display aircraft described in Hess format, to restructure the data in a manner compatible with computational fluid dynamic codes for predicting viscous flow drag, and to compute and display the axial distribution of cross-sectional area normal to the free-stream airflow. The second program is an extension of an existing conceptual design code called ACSYNT /VPI. The extension allows calculation of areas of intersection between a cutting plane tilted at an arbitrary angle with the aircraft axis and the aircraft. The design of both codes is described in depth, and user's guides for the resulting programs are included in the appendices. / Master of Science

Conceptual and preliminary aircraft design codes have different geometry requirements. Conceptual design codes use component based models, while preliminary design codes require a more complete and integrated geometry. An automatic procedure to convert between the two types of models would prevent geometry inconsistencies and speed up the design process. This thesis describes some of the concepts and algorithms necessary to develop such a procedure. Specifically, the theory and development of C2 continuous fillets between aircraft components is discussed. B-spline surface generation from conceptual geometry data and the relimiting of e surfaces is also presented. / Master of Science

Flush repairs to military aircraft are expected to become more prevalent as more thick skin composites are used, particularly on the surface of the fuselage, wings and other external surfaces. The use of these repairs, whilst difficult to manufacture provide an aerodynamic, ???stealthy??? finish that is also more structurally efficient than overlap repairs. This research was undertaken to improve the design methodology of scarf repairs with reduced material removal and to investigate the damage tolerance of scarf repair to low velocity impact damage. Scarf repairs involve shallow bevel angles to ensure the shear stress in the adhesive does not exceed allowable strength. This is important when repairing structures that need to withstand hot and humid conditions, when the adhesive properties degrade. Therefore, considerable amounts of parent material must be machined away prior to repair. The tips of the repair patch and the parent laminate are very sharp, thus a scarf repair is susceptible to accidental damage. The original contributions include: ??? Developed analytic means of predicting the stresses within optimised scarf joints with dissimilar materials. New equations were developed and solved using numerical algorithms. ??? Verified using finite element modelling that a scarfed insert with dissimilar modulus subjected to uniaxial loading attracted the same amount of load as an insert without a scarf. As such, the simple analytic formula used to predict load attraction/diversion through a plate with an insert may be used to predict the load attraction/diversion into a scarf repair that contains a dissimilar adherend patch. ??? Developed a more efficient flush joint with a doubler insert placed near the mid line of the parent structure material. This joint configuration has a lower load eccentricity than external doubler joint. ??? Investigated the damage tolerance of scarf joints, with and without the external doubler. The results showed that scarf joints without external doublers exhibited a considerable strength reduction following low velocity impact. Based on the observations, the major damage mechanics in the scarf joint region following impact have been identified. These results demonstrated that it is important to incorporate damage tolerance in the design of scarf repairs.

Aircraft design has recently experienced a trend away from performance centric design towards a more balanced approach with increased emphasis on engineering an economically successful system. This approach focuses on bringing forward a comprehensive economic and life-cycle cost analysis, which can be addressed by the introduction of a dynamic method allowing the analysis of the future attractiveness of such a concept in the presence of uncertainty. One way of addressing this is through the use of a competitive market model. However, existing market models do not focus on the dynamics of the market, which results in poor predictive capabilities. The method proposed here focuses on a top-down approach that integrates a competitive model based on work in the field of system dynamics into the aircraft design process. The primary contribution is the demonstration of the feasibility of such integration. This integration is achieved through the use of surrogate models, which enabled not only the practical integration of analysis techniques, but also reduced the computational requirements so that interactive exploration as envisioned is actually possible. An example demonstration of this integration is built on the competition in the 250 seat large commercial aircraft market. Two aircraft models were calibrated to existing performance and certification data and then integrated into the system dynamics market model, which was then calibrated with historical market data. This calibration showed a much improved predictive capability as compared to the conventional logit regression models. The resulting market model was then integrated into a prediction profiler environment with a time variant Monte-Carlo analysis resulting in a unique trade-off environment. This environment was shown to allow interactive trade-off between aircraft design decisions and economic considerations while allowing the exploration potential market success in the light of varying external market conditions and scenarios. Another use of the existing outputs of the Monte-Carlo analysis was then realized by visualizing the model variables on a multivariate scatter plot. This enables the designer to define strategic market and return on investment goals for a number of scenarios and then directly see which specific aircraft designs meet these goals.

Internal combustion (IC) engines that consume hydrocarbon fuels have dominated the propulsion systems of air-vehicles for the first century of aviation. In recent years, however, growing concern over rapid climate changes and national energy security has galvanized the aerospace community into delving into new alternatives that could challenge the dominance of the IC engine. Nevertheless, traditional aircraft sizing methods have significant shortcomings for the design of such unconventionally powered aircraft. First, the methods are specialized for aircraft powered by IC engines, and thus are not flexible enough to assess revolutionary propulsion concepts that produce propulsive thrust through a completely different energy conversion process. Another deficiency associated with the traditional methods is that a user of these methods must rely heavily on experts experience and advice for determining appropriate design margins. However, the introduction of revolutionary propulsion systems and energy sources is very likely to entail an unconventional aircraft configuration, which inexorably disqualifies the conjecture of such connoisseurs as a means of risk management. Motivated by such deficiencies, this dissertation aims at advancing two aspects of aircraft sizing: 1) to develop a generalized aircraft sizing formulation applicable to a wide range of unconventionally powered aircraft concepts and 2) to formulate a probabilistic optimization technique that is able to quantify appropriate design margins that are tailored towards the level of risk deemed acceptable to a decision maker. A more generalized aircraft sizing formulation, named the Architecture Independent Aircraft Sizing Method (AIASM), was developed for sizing revolutionary aircraft powered by alternative energy sources by modifying several assumptions of the traditional aircraft sizing method. Along with advances in deterministic aircraft sizing, a non-deterministic sizing technique, named the Probabilistic Aircraft Sizing Method (PASM), was developed. The method allows one to quantify adequate design margins to account for the various sources of uncertainty via the application of the chance-constrained programming (CCP) strategy to AIASM. In this way, PASM can also provide insights into a good compromise between cost and safety.

The design process of aerospace systems is becoming more and more complex. As the process is progressively becoming enterprise-wide, it involves multiple vendors and encompasses the entire life-cycle of the system, as well as a system-of-systems perspective. The amount of data and information generated under this paradigm has increased exponentially creating a difficult situation as it pertains to data storage, management, and retrieval. Furthermore, the data themselves are not suitable or adequate for use in most cases and must be translated into knowledge with a proper level of abstraction. Adding to the problem is the fact that the knowledge discovery process needed to support the growth of data in aerospace systems design has not been developed to the appropriate level. In fact, important design decisions are often made without sufficient understanding of their overall impact on the aircraft's life, because the data have not been efficiently converted and interpreted in time to support design. In order to make the design process adapt to the life-cycle centric requirement, this thesis proposes a methodology to provide the necessary supporting knowledge for better design decision making. The primary contribution is the establishment of a knowledge engineering framework for design decision support to effectively discover knowledge from the existing data, and efficiently manage and present the knowledge throughout all phases of the aircraft life-cycle. The second contribution is the proposed methodology on the feature generation and exploration, which is used to improve the process of knowledge discovery process significantly. In addition, the proposed work demonstrates several multimedia-based approaches on knowledge presentation.

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