Refined Method for Initial Design Point Parameters in Preliminary Aircraft Design

In Aircraft Sizing tools, commonly a rather simple algorithm is used to determine the design space and the initial design point for an aircraft sizing iteration loop. A basic aircraft constraint chart which typically covers equations for cruise performance, landing speed, takeoff distance and minimum climb angle with one engine inoperative (OEI) is used to reveal the design space. The design point offers the possibility of obtaining an outlook on thrust loading and wing loading to be expected from the final aircraft which fulfils the Top Level Aircraft Requirements (TLARs), before entering in a full preliminary aircraft design iteration. In most cases, the parameters used for the design chart equations are selected by the aircraft design engineer or tool user, based on statistical data. Depending on experience, luck, data source or try and error behavior, the quality of the revealed design space can vary a lot. Hence the quality of the initial design point which is coherent to the design space quality. With an improved assumption of the reference values, the constraint diagram and thus the design point can be determined more precisely. With an initial design point as the start of a design iteration, which more precisely matches the final aircraft design, computer-aided aircraft design environments, such as UNICADO in the present case, can deliver a converged result with fewer iterations. This increases the productivity of the software. In this work, a methodology for the selection of improved reference values used to determine the constraint diagram is presented. Moreover, the magnitude of the parameters’ influence on the resulting design space is investigated. Combining these results, the most significant design parameters and their range of values can be identified. These parameters are part of an initial sizing aircraft reference database the software can make use of. An algorithm is presented, enabling the selection of the most representative set of reference data within the database for the desired aircraft design project.