**5. Discussion**

As mentioned in the discussion of the first workshop [12], a full-scale data-based validation of this AMA stage is hardly possible for such studies, considering the lacking experimental data on the morphing attributes. For this purpose, the relative positioning of the option implementation is qualitatively verified. For instance, the definitive flight performance advantage of an entire morphable wing over separate morphable sections confirms the logical expectation. Similarly, mechanical extensions such as flaps and slats exhibit slightly less system complexity than the other morphing mechanisms included in the MM. However, as stated in the previous section, the difference among solutions involving certain options is seen to be relatively weak, which is reflected in the small solution translations along the axes. This might speak for two things: (a) prominent epistemic uncertainty (lack of knowledge on these options) or/and (b) overly general definition of the options preventing the experts from focusing on the most relevant aspects. Based on these observations, one could declare a partial reliability of the results.

The expert feedback also plays a key role as a partial method validation. In this context, the aspects put forward by the participants not only indicate more space for improvement possibilities. Together with a global workshop conduction analysis, these also point out further dimensions of SEJE integration with the AMA design process. Such is, for example, the purpose of group discussions. On the one hand, a significant number of profound professional arguments have been heard when deciding on the best options for the sub-criteria. On the other hand, the purpose of "re-convincing" the expert to possibly correct their evaluation was rejected by the majority of the DMs. Its influence on the results has been assessed as low by the researchers as well. This brings forward the following questions:


Furthermore, based on the results and the participant feedback, the following improvement proposals have been drawn:


#### **6. Conclusions**

The present paper describes the definition and application of the technology evaluation stage of the AMA design process based on expert workshops. In particular, the derivation and integration of SEJE techniques in the conceptual aircraft design with the AMA. The following research objectives have been fulfilled: (a) justification for the development of a SEJE approach adapted to the AMA needs and (b) the extraction of use case results and expert feedback for further method development from a second conducted workshop.

In order to justify the derived methodology, an extensive literature review on SEJE has been conducted first. As a result, the most prominent SEJE methods (the Classical Method, the SHELF framework and the IDEA protocol) were summarized, compared and used for the identification of common SEJE components. Further important aspects for the preparation and conduction of such elicitation have been researched and commented, namely the role of bias, the remote and personal formats as well as qualitative and quantitative elicitation variables. Additionally, the integration of these aspects and the combination of SEJE methods with MCDM frameworks were considered. The importance of such approaches is underlined by SEJE application examples in aerospace. This analysis was used for the development of a SEJE methodology adopted specifically for conceptual aircraft design within the AMA design framework and its positioning in the scientific context.

The second part of the paper is dedicated to the description and application of this methodology in the form of a second AMA workshop. Its design took into account the lessons learned from the first workshop (see Reference [12]). The consideration of novel technologies was implemented by selecting the design of wing morphing concepts as a use case for the workshop. In particular, it studied the influence of morphing technologies and their integration in different airfoil and wing sections. During the workshop, these were compared by the expert panel regarding the criteria flight performance, system complexity, and energy input by entering their fuzzy numbers in the specially developed software platform. The expert weighting was based on their self-designated expertise and did not show any significant influence on the results. This might be due either to the homogeneity of the panel's professional background or to an undiscovered methodological flaw. The workshop consisted of two main steps: individual evaluation of the options and group discussions. The latter aimed to combine ideas and help the experts correct their evaluations, thus reducing bias and increasing results objectivity.

After applying the FAHP, the AMA software was used to generate the solution space. On the one hand, it confirmed some expected trends, e.g., the flight performance advantage of an entirely morphable wing referred to only partial morphing. On the other hand, it revealed the unexpectedly low difference of some option scores, mostly among the morphing mechanisms. The reason for this might be the very similar evaluations given by the experts as a result of lacking knowledge on this very specific topic (epistemic uncertainty).

Along with the various visual results presentation and their analysis, a vital outcome of the work was the participants' feedback. It serves not only as a partial validation source of the methodology, but also as a valuable guideline for its further development.

Based on these results, improvement proposals for future work on the project have been drawn. These refer mostly to ambiguity in the definition of technology options and criteria. The need for additional use case structuring and definition was pointed out along with the necessity for preliminary preparation on specialized topics. Furthermore, the full capacity of expert panel discussions should be used by restructuring these and defining clearer purpose and deliverables.

Although based on a thorough literature study on SEJE methods and the corresponding biases, a deeper look into technology assessments and scenario workshops for a better process structuring is required. Future studies would benefit not only from the lessons learned through the current work. Potential workshops would also profit from widening their purpose, namely by extending the pure technical assessment of technologies to their integration with the environment and society.

The findings are not only an integral part of the AMA enhancement process, but can also serve as a solid basis for technology evaluation via SEJE methods focused mostly on technical qualities of the solutions, which is rarely found in the existing literature. This work represents a "stand-alone" methodological component for similar studies in the aerospace domain and beyond.

The major elicitation components that were added to the methodology take the extended workshop concept to a new level. It exhibits not only the development of a full-scale SEJE method, but most importantly its integration into the early stages of conceptual aircraft design. This has been achieved by the appropriate definition of attributes, options, and criteria, as well as by orienting the elicitation towards the problematic of aircraft architecture design. In particular, the evaluations required references to specific aspects from design and operational point of view. Additionally, the group discussions aimed to broaden the experts' horizon on a certain technology group by gathering different views from various engineering disciplines in order to obtain results with increased objectivity.

In a global perspective, the AMA, the qualitative evaluation approach, and the corresponding expert workshops are seen as a step prior to the application of "classical" MDAO algorithms. The flexible definition of the MM and the workshops implies the qualitative multi-criteria comparison of options from possibly different aircraft classes (e.g., aerostatic lift generation against fixed wings), otherwise hardly feasible within a single MDAO framework. The resulting exhaustive solution space allows the consideration of solutions possibly let out of scope during conventional idea generation.

**Author Contributions:** Conceptualization, V.T.T., D.R. and A.B.; methodology, V.T.T. and D.R.; software, V.T.T.; validation, V.T.T. and A.B.; formal analysis, V.T.T.; investigation, V.T.T.; resources, D.R. and A.B.; data curation, V.T.T.; writing—original draft preparation, V.T.T. and D.R.; writing—review and editing, D.R. and A.B.; visualization, V.T.T.; supervision, D.R. and A.B.; project administration, A.B.; funding acquisition, A.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) grant number 443831887.

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Data can be made available on demand.

**Conflicts of Interest:** The authors declare no conflict of interest.
