A Semi-Analytical Weight Estimation Method for Oval Fuselages in Novel Aircraft Configurations

Abstract

Research in aircraft design is focusing on novel aircraft configurations in search for a step change in terms of overall transport efficiency. Aircraft design relies heavily on empirical methods, so-called Class 2 methods, to evaluate the performance of a design. Since these methods are based on statistical data their validity is limited when these are used for the design of novel aircraft. There is therefore a strong need for methods that are valid for the conceptual aircraft design of these novel aircraft. The method proposed in this thesis is a semi-analytical method for estimating the weight of a fuselage constructed using the oval fuselage concept. The oval fuselage is a concept for a wide unobstructed pressurized cabin specifically useful for Blended Wing Body aircraft. A parameterization of the oval fuselage is presented and it is demonstrated that the oval cross-section can be used for the design of conventional tube-and-wing aircraft with a single-deck or twin-deck layout as well as for blended-wing-body aircraft. It is also shown that the oval cross-section allows for additional design freedom of the fuselage shape without introducing any bending loads in the fuselage skin panels. Using this parameterization, a method is presented for estimating the weight of this fuselage when used in conventional and novel aircraft configurations. The weight estimation of the fuselage is based on the combination of pressurization loads, steady-state maneuver loads, aerodynamic loads and landing loads. Each of the structural members of the inner structure is sized based on two-dimensional structural analysis satisfying requirements on bi-axial strength, global buckling, crippling, dimpling, and wrinkling. The outer structure is sized using a global buckling criteria adapted from cylinders and a local buckling criteria based on buckling of slender plates. Empirical methods are used to calculate the nonstructural weight and additional weight. A verification of the structural analysis method by a finite-element analysis shows that the made assumptions for the analysis of the structure are valid within the application of aircraft fuselage design. The weight estimation method is compared with weight estimation methods from the open literature and with weight data of existing aircraft. The accuracy of the weight estimation is similar to that of empirical methods for circular fuselages. Examples are shown of oval fuselages in aircraft designs and weight estimations are performed on these fuselages to form a basis for future research on this subject.