Robert A. McDonald

Improved Geometry Modeling for High Fidelity Parametric Design

Advanced multidisciplinary physics-based design and analysis capabilities are required to pursue the revolutionary vehicle and technology concepts needed to meet the goals of the aerospace industry for the next 10-30 years. The multidisciplinary physics critical to advancing aerospace technology all have one common bond, the shape, size, and form of the underlying aircraft its geometry. An aircraft shape is the natural starting point for multidisciplinary analysis and optimization (MDAO). Vehicle Sketch Pad (VSP) is an aircraft geometry tool for rapid evaluation of advanced design concepts which was developed by NASA and is available to industry at large. VSP allows designers to express their design in terms of engineering parameters. The results of design choices are presented in real-time to the designer. In this research, VSP has been extended in two major ways to improve the designer’s ability to include high fidelity geometry based analysis in the design process. The first ma jor improvement was the addition of a new high-quality surface meshing capability for VSP. The second ma jor improvement was the addition of intuitive parametric representations of internal structure for VSP including the ability to convey that representation to appropriate structural modeling tools.

Mission Performance Considered as Point Performance in Aircraft Design

DOI: 10.2514/1.C031290 The cruise or loiter performance of an aircraft is intimately tied to its wing loading and its thrust-to-weight ratio. Paradoxically, mission performance is often not considered when these fundamental aircraft parameters are determined in conceptual design. In this paper, the traditional constraint diagram is extended to include contours of range or endurance parameter. These performance metrics represent the mission-performance capability of the aircraft without sizing the aircraft to a particular mission. This gives the designer an immediate and intuitive understanding of the tradeoff between the point and mission performance of the aircraft. The potential freedom for the designer to choose the operating condition of the aircraft is also considered. This improved constraint diagram presents the designer with a more complete basis for understanding and weighing the consequences of decisions.

Lift Superposition and Aerodynamic Twist Optimization for Achieving Desired Lift Distributions

A method for achieving an arbitrary lift distribution with an arbitrary planform is presented. This is accomplished through optimizing aerodynamic twist for a given number of either known airfoils or airfoils to be designed. The spanwise locations of these airfoils are optimized to get as close to the desired lift distribution as possible. Airfoils are linearly interpolated between these points. After aerodynamic twist, the planform is twisted geometrically using radial basis functions to model the twist distribution. The aerodynamic influence of each twist distribution is determined and all are superimposed to determine the function weights of each twist function, yielding the optimal twist to match the given lift. This method has been shown to match both an elliptical and a triangular lift distribution for an arbitrary planform. This method can also be used with any fidelity model, creating a powerful design tool.

Multidisciplinary Design Optimization of an Extreme Aspect Ratio HALE UAV

Development of High Altitude Long Endurance (HALE) aircraft systems is part of a vision for a low cost communications/surveillance capability. Applications of a multi payload aircraft operating for extended periods at stratospheric altitudes span military and civil genres and support battlefield operations, communications, atmospheric or agricultural monitoring, surveillance, and other disciplines that may currently require satellite-based infrastructure. The central goal of this research was the development of a multidisciplinary tool for analysis, design, and optimization of HALE UAVs, facilitating the study of a novel configuration concept. Applying design ideas stemming from a unique WWII-era project, a “pinned wing” HALE aircraft would employ self-supporting wing segments assembled into one overall flying wing. When wrapped in an optimization routine, the integrated design environment shows potential for a 17.3% reduction in weight when wing thickness to chord ratio, aspect ratio, wing loading, and power to weight ratio are included as optimizer-controlled design variables. Investigation of applying the sustained day/night mission requirement and improved technology factors to the design shows that there are potential benefits associated with a segmented or pinned wing. As expected, wing structural weight is reduced, but benefits diminish as higher numbers of wing segments are considered. For an aircraft consisting of six wing segments, a maximum of 14.2% reduction in gross weight over an advanced technology optimal baseline is predicted.

Formulation, Realization, and Demonstration of a Process to Generate Aerodynamic Metamodels for Hypersonic Cruise Vehicle Design

Presented at the 5th World Aviation Congress and Exposition, San Diego, CA, October 10-12, 2000.

Establishing Mission Requirements Based on Consideration of Aircraft Operations

The design requirements for a next-generation commercial aircraft can do much to secure its fate as a success or failure. New aircraft are often designed to meet or surpass the capabilities of an existing aircraft they are intended to replace. However, in the case of unconventional aircraft, this could lead to significant overdesign resulting in nonviable concepts. Instead, a method of analyzing observed aircraft use is presented with the intent of establishing a set of requirements based on replacing aircraft utility instead of capability. Two aircraft in the commercial fleet are used as example cases, and launch customers for each aircraft are assumed. Data originating from diverse sources are combined to present a probabilistic representation of aircraft use. The data collected include the payloads carried, ranges flown, and assigned cruise altitudes as well as the field length, elevation, and hot day characteristics of the airports used, and the launch customers’ fleet size history. Quantitative and q...

Parameter Estimation of Fundamental Technical Aircraft Information Applied to Aircraft Performance

Inverse problems can be applied to aircraft in many areas. One of the disciplines within the aerospace industry with the most openly published data is in the area of aircraft performance. Many aircraft manufacturers publish performance claims, flight manuals and Standard Aircraft Characteristic (SAC) charts without any mention of the more fundamental technical information such as CD0 . With accurate tools, generalized aircraft models and a few curve-fitting techniques, it is possible to evaluate vehicle performance and estimate these technical parameters. With this goal a program has been written in Matlab to calculate the fundamental information behind a general aircraft. The current results are promising with more work underway to further improve them. The results shown are for the Northrop F-5. While the results look good, the overall accuracy of the program is only as good as the data provided. For example, the maximum speed reported by a company may assume that the aircraft is in a dive with engines at full throttle. Or, the measurements may be overly optimistic, with an important characteristic such as ground friction during takeoff left out of the picture. If this information is not reported then an accurate analysis is not possible. Nomenclature

Senior Design at Cal Poly: A Recipe for Success

The Aerospace Engineering Department at Cal Poly has, over the years, evolved a unique recipe for Senior Design. This recipe has been applied to the capstone Aircraft and Spacecraft design courses and will soon be extended to an Unmanned Aerial Vehicle design course. This recipe consists primarily of a year long design sequence with a great deal of participation from the region’s aerospace industry. The Cal Poly recipe has proven to be both flexible and effective. The authors believe it could be adapted and applied in a similar manner at other institutions with a similar degree of success.

A User Friendly Interface for Gaussian Process Metamodeling

As research into metamodeling and using advanced metamodeling techniques continues, it is important to remember design engineers who need to use these advancements. Even experienced engineers may not be well versed in the material and mathematical background that is currently required to generate and fully comprehend advanced complex metamodels. A user friendly metamodeling environment is being developed to help bridge the gap that is currently growing between the research community and the design engineers. This tool allows users to easily create, modify, and assess the quality of metamodels. I. Introduction ODERN day engineers are continually given new and complex grand challenges, including simultaneously reducing emissions, noise and cost, all while developing multi-mission aircraft. Those engineers striving to develop further complex systems continually heighten the demands placed on modern computing resources. Thankfully, we expect computing resources to become faster and more powerful; however, the designer cannot put progress on hold while we wait for the ultimate computer. The increasing complexity of systems and the tightening environmental, economic, and performance demands placed on them drive the need for a continual increase in the fidelity of analysis throughout the design process. Naturally, running numerous complex models in the design process quickly becomes prohibitive. Another problem plaguing engineers, specifically those working in a multidisciplinary design optimization field, is the problem of size 1 . Koch points out that traditional parametric design approaches which work well for small, simple problems, become inefficient and inappropriate when applied to large scale, complex systems. Three specific issues that are related to size are: the number of variables and responses, computational expense, and multiple objectives with uncertainty. As the number of input variables and responses increase, traditional methods of holding variables constant while changing others become extremely inefficient and do not provide deep insight to the problem space. As mentioned earlier, as computational power increases, the need for complex codes will continue to increase. In a preliminary design there might be a level of uncertainty associated with the requirements, which drives the need for regions of good designs instead of an optimal design point, which becomes increasingly complex as data and variables are added 1 . These continuing challenges have led designers to adopt approximate surrogates for high fidelity models known as metamodels. Unfortunately, developing good engineering metamodels comes with its own set of challenges. Metamodeling (the process of building metamodels) has produced new and improved developments as research has continued in this field. However, as pointed out by Wang 2 , a gap appears to be growing between the research community and design engineers. Wang suggests that this widening gap is due to the mathematical involvement of metamodeling and that metamodeling evolves with information from multiple disciplines. Because of this, the research community needs to move its focus on metamodeling towards the needs of the design engineers. The goal with this research is to make not only building and using, but understanding metamodels easier for an entry level design engineer.

Error Allocation in Complex Systems Design

A fidelity trade environment was conceived, formulated, developed, and demonstrated. This development relied on the advancement of enabling techniques including error propagation, metamodeling, and information management. These techniques were integrated with an existing commercial systems design framework and an intuitive graphical interface to create a fidelity trade environment. A sensitivity approach to the propagation of error through complex systems was developed. This approach relied on the system sensitivity matrix to model the behavior of a complex system as a whole. In verification tests, the sensitivity approach provided approximate results substantially similar to a Monte Carlo approach that was many orders of magnitude more expensive. The rapid sensitivity approach to modeling error propagation enabled the responsive analysis required for an interactive environment. In a case study, a notional transport aircraft was modeled in the fidelity trade environment. The system was decomposed and the fidelity trade environment was used to integrate the system. Then, a scenario was described where a decision maker used the fidelity trade environment at the beginning of a complex systems design problem. Using the environment, the designer was able to make design decisions while considering error and he was able to make decisions regarding required tool fidelity as the design problem continues. These decisions could not be made in a quantitative manner before the fidelity trade environment was developed. The need for a new complex systems design technique was identified. A fidelity trade environment was conceived, establishing the need for advancement of three enabling techniques: error propagation, metamodeling, and information management. All of these techniques were integrated with an existing systems design architecture and an intuitive graphical interface, thereby creating the fidelity trade environment. This environment was applied to a representative complex system, thereby demonstrating its effectiveness in providing a new capability to the designer.