Similitude augmentation in sub-scale flight test model design: An MDAO based similarity maximization approach

By 2050, the aviation industry is expected to grow by 250-300% of its current air traffic. If left unchecked, the corresponding increase in atmospheric and noise pollution will have a catastrophic impact on the environment. Thus, improvements in aircraft design are urgently needed for a sustainable growth of the aviation industry. The performance and behaviour of existing tube-and-wing aircraft have been refined and improved so much in the past decades that further improvements are barely possible. Consequently, by 2050, breakthrough solutions in the form of unconventional design configurations, novel propulsion systems and operation models are required to meet the ambitious goals stated in Europe’s vision for Aviation. However, the design of unconventional aircraft is particularly challenging as it often involves integrated multi-functional components for which legacy data is unavailable. Thus, appropriate means to assess their performance and behaviour are needed to lower their industrial development risk. Sub-scale Flight Testing (SFT), an experimental approach involving the free-flight testing of sub-scale models with an on-board powerplant, shows promise in the evaluation of the in-flightmotion of a given aircraft configuration and its response to control inputs. In the past, SFT has been used in a wide-range of flight tests to study the effect of novel technologies on the aircraft flight behavior, to assess systems integration feasibility and as a proof-of concept for unconventional designs. The actual benefit and validity of SFT mainly depends on the design of the SFT model used for the test. A well designed SFT model can show a similar behaviour to the fullscale aircraft such that any observation on the scaled device can be directly used to predict the full-scale performance. However, ensuring similarity between SFT model and full-scale aircraft is challenging due to the differences in their size and flight conditions. In addition to guaranteeing similitude, SFT model must comply with multidisciplinary design requirements such as safe completion of the mission, adhering to restrictions imposed by local authorities and selecting suitable flight-control and measurement equipment...