This report addresses a project conducted at Saab Aeronautics during the spring of 2018. The goal of the project was to investigate aircraft weight estimations in the conceptual design phase. The work was divided into two major parts: finding new weight estimation techniques and implementing an existing technique called the Berry Weight Estimation in to the Pacelab APD software. Several weight estimation techniques were found during an extensive literature review but in the end, only one was chosen for further investigation. The chosen technique was the NASA Wing Weight Build-Up which proposed calculations for wing weights based on aircraft statistics. It contained material data tables for determining so called K-factors that were used to essentially scale the individual wing weight formulas. The data tables did not include K-factors up to a load factor of 9 which was a requirement from Saab. Extrapolations of the material data tables were done to approximate the missing values. The NASA wing weight build-up showed promising results with little deviation from the actual wing weight for a few chosen aircraft. This weight estimation technique was consequently chosen as a worthy candidate for a future implementation in the Pacelab APD software. The task of implementing the Berry Weight Estimation in Pacelab APD was divided into a fuselage- and a wing part. This was done to ease the implementation since it would resemble the original description of the method. The wing and fuselage weights were both calculated in two steps. The first step was to calculate a gross shell weight. This is the weight of an idealized structure without cut-outs or imperfections. The second step was to add so called weight penalties for various components within the wing or fuselage. Typical aircraft components had associating weight penalty functions described in the Berry Weight Estimation. Most of the implemented calculations used Pacelab APD to get involved parameters automatically. However, some of the needed parameters had to be user specified for the implemented Berry Weight Estimation to work. Once the implementation task was finished, several sensitivity studies were made to establish a perception about the involved parameters impact on the Berry Weight Estimation results. The new implementation gave benefits compared with the Berry Weight Estimation in Bex. One of these was the ability to perform extensive trade- and sensitivity studies. The sensitivity studies gave verdicts on the most influencing parameters of the implemented code and guide lines on future improvements of the calculations. These sensitivity studies show, among other things, that is recommended to increase the number of wing and fuselage stations significantly in order to get a converged result for the Berry Weight Estimation.

<p>Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies. Hence, a comparative value is required which is used for the evaluation of a design solution in terms of cost and weight. The direct operating cost (DOC) can be used as this comparative value; it captures all costs that arise when the aircraft is flown. In this work, a cost/weight optimization framework for composite structures is proposed. It takes into account manufacturing cost, non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the DOC as the objective function.</p><p>First, the different phases in the design of an aircraft are explained. It is then focused on the advantages and drawbacks of composite structures, the design constraints and allowables, and non-destructive inspection. Further, the topics of multiobjective optimization and the combined optimization of cost and weight are addressed. Manufacturing cost can be estimated by means of different techniques; here, feature-based cost estimations and parametric cost estimations proved to be most suitable for the proposed framework. Finally, a short summary of the appended papers is given.</p><p>The first paper contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty, defined as the specific lifetime fuel burn, is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof.</p><p>The second paper proposes the inclusion of non-destructive testing cost in the design process of the component, and the adjustment of the design strength of each laminate according to the inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the (guaranteed) laminate quality. It is shown that the direct operating cost can be lowered when the quality level of the laminate is assigned and adjusted in an early design stage.</p>

Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies. Hence, a comparative value is required which is used for the evaluation of a design solution in terms of cost and weight. The direct operating cost (DOC) can be used as this comparative value; it captures all costs that arise when the aircraft is flown. In this work, a cost/weight optimization framework for composite structures is proposed. It takes into account manufacturing cost, non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the DOC as the objective function. First, the different phases in the design of an aircraft are explained. It is then focused on the advantages and drawbacks of composite structures, the design constraints and allowables, and non-destructive inspection. Further, the topics of multiobjective optimization and the combined optimization of cost and weight are addressed. Manufacturing cost can be estimated by means of different techniques; here, feature-based cost estimations and parametric cost estimations proved to be most suitable for the proposed framework. Finally, a short summary of the appended papers is given. The first paper contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty, defined as the specific lifetime fuel burn, is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof. The second paper proposes the inclusion of non-destructive testing cost in the design process of the component, and the adjustment of the design strength of each laminate according to the inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the (guaranteed) laminate quality. It is shown that the direct operating cost can be lowered when the quality level of the laminate is assigned and adjusted in an early design stage. / QC 20101112