Landing Gear Conceptual Design and Structural Optimization of a Large Blended Wing Body Aircraft
The Blended-Wing-Body (BWB) is a revolutionary concept for commercial aircraft .In the past years a number of design suggestions have been proposed for the BWB such as several wing planforms or a number of distributed propulsion system. However, there have been only few proposals for BWB landing gear configurations despite its significant effect on the overall aircraft performance. The landing gear system is one of the largest aircraft systems which contributes a large part to the overall aircraft weight. Landing gear attachment loads are usually design load cases of major airframe parts such as the rear fuselage and the wing center section. As a result, a well-considered conceptual design of the landing gear system plays a significant role in the final design of the aircraft. The state-of-the-art landing gear conceptual design process is based on experience from existing aircrafts. This process reaches its limitation, however, if the landing gear system must be designed for an unconventional aircraft like the BWB, where no data is available for comparison. Because of these reasons the objective of this work is to propose a design process for the conceptual design of the BWB landing gear system. The work focuses on the following design aspects: a BWB ground loads determination, a BWB landing gear weight estimation, the assessment of the ground loads effect on the aircraft structure and finally the proposal of a conceptual landing gear configuration. This work introduces a new integrated Multidisciplinary Optimization process to investigate these design issues. There are two essential elements proposed in this process. The first element is the determination of the unknown dynamical ground loads for a BWB. The Multi-Body Simulation, MBS, method is selected for this task. Figure 1 shows an example of the landing gear MBS model for the ground load determination. The second element is the landing gear weight determination. An analytical conceptual design method is implemented to design each landing gear component individually for the weight determination. The capability of the new process is validated by a conceptual redesign of the landing gear system of an aircraft comparable to the implemented BWB. The process is then implemented for the landing gear conceptual design of a large (MTOW~700t) BWB transport aircraft. Figure 2 shows the implemented BWB aircraft. Four different configurations of different numbers of main landing gears (MLG) of 4, 6, 8 and 12 are designed, analysed and optimized. According to the results from the validation design case, the process has been proven to be able to realistically predict the ground loads for the BWB. It has been found that the lateral ground loads from the asymmetric landing case play a significant role for the landing gear design. The MLGs must be positioned in a triangle-like topology in order to distribute the landing energy from this landing case. Figure 3a shows an example of the landing gear topology result. Concerning the total system weight result, it has been discovered that the total system weight is reduced with an increase in the number of MLG. The weight reduction comes from the lower ground loads of the high MLG number configurations. However if the number of MLG is too high this advantage will be outstripped by too many MLG components. As the result, the concept with 8 MLGshas an optimum total system weight for the given BWB configuration. Figure 3b shows the total system weight result. This study of the total system weight trend as the function of MLG number and position is not possible before with the classical conceptual design method where mostly the MTOW is the only parameter used for the weight determination. Finally, the obtained knowledge, the new process accomplishments and open problems are discussed.