1974. An Improved Methodology for Estimating Advanced Composite Airframe Weights During Conceptual and Preliminary Design
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Paper
Abstract
Current projections indicate an increased application of advanced composites in next-generation aircraft. With the stringent requirements on improved performance of these aircraft, an early and accurate estimate of the composite e weight is needed for a timely assessment of their performance/mission capabilities. Also, in order to minimize weight driven problems during preliminary design, a more accurate method of estimating the weight of a composite and/or hybrid airframe is needed beginning with conceptual design level. With the emergence of ultra light weight composite utilizing high modulus/strength carbon fibers, the current data base lacks the support of existing aircraft utilizing such materials. As a result, the conventional weight estimation methods for composite airframes are based on parametric relationships, established from correlations of existing metallic aircraft weights, and adjusted by empirical ”Material Factors” to account for the use of composites. A number of industry-wide studies have used weight ratio methodologies based on existing metallic structures to estimate the weight reductions associated with the use of composites. However, the highly directional/anisotropic properties of these materials lead to different behaviors of these materials in a number of failure modes. As a result, the existing weight ratio methods are invalid and need proper adjustments to account for the unique behavior of composite materials. A modified ”Weight Ratio Methodology” that could accurately quantify the weight changes due to metal-to composite material substitutions will result in more rationally defined ”Material Factors.” These rational ”Material Factors” will allow the evaluation and development of more reliable and comprehensive parametric methods for estimating composite airframe weights of next-generation aircraft. This paper will discuss the development of ”Material Factors” for a conventional graphite/epoxy system such as AS4/3501-6 as well as emerging high strength/modulus carbon fiber composites currently being evaluated in ”Ultra light weight Airframe” studies.
