Transitional Vertical Take-off and Landing Aircraft (TVA) are systems capable of flying as Fixed-Wing (FW) aircraft and rotorcraft as well as transition between these flight modes. Responding to the technology advancement and impetus by the emerged mission needs, TVA have recently gained much interest in the aviation industry and many current/future aircraft are required/envisioned to have both the FW and rotorcraft capabilities in diverse potential applications. However, consolidating the characteristics of FW aircraft and rotorcraft increases the challenges when designing aircraft for which solutions currently do not exist. The number of Design Requirements (DRs) needed to be achieved and the number of contradictory Design Parameters (DPs) involved in the design process, further complicates the design process of TVA compared with traditional design methods for either FW aircraft or rotorcraft. Despite the maturity in the field of design for conventional FW aircraft and rotorcraft, considerable design work, techniques, and methodologies need to be specifically developed to tackle the challenges that exist in TVA design. Generally, the earlier design steps are the most important within any aircraft design and development process as significant decisions/calculations about the aircraft configuration are made with a somewhat limited knowledge about the aircraft.

This thesis discusses the challenges/difficulties associated with the early design steps of TVA and introduces a newly developed conceptual design framework to tackle them.

First, a systematic concept development methodology is developed with all necessary mathematical formulations and complementary benchmarks that integrates well-known methods/tools in a novel way suitable for TVA concept development. The proposed approach allows managing multiple conflicting criteria and coupled decisions. Furthermore, the methodology enables efficient exploration of a very large design space with different alternatives and complex design hierarchies to generate the most relevant aircraft configurations responding to a set of DRs and selecting the one that best meets the requirements. The proposed approach allows designers to examine more alternatives than what is feasible with traditional design methods and prevents designers from either choosing poor concepts due to the lack of experience or overlooking valuable ones.

Second, a generalized formal sizing methodology for TVA is developed by modifying several assumptions typically made when using the available and well-known FW and rotorcraft performance equations. From such an approach, a new set of equations is developed to enable the simultaneous calculation of the adequate sizing parameters such that TVA satisfy the DRs in all of the three flight modes (i.e., FW, transition, and rotorcraft).

In order to demonstrate and validate the capabilities and adaptation of the developed framework, the approach is applied to the conceptual design of an advanced unmanned highly-maneuverable TVA having challenging DRs (e.g., requirement to perform maneuvers not possible by traditional aircraft like pitch-hover and transition to FW flight mode at any attitude). The obtained results revealed that the proposed framework can be applied to TVA conceptual design with a reasonable level of confidence in its accuracy. The formulations and tools developed reduce the time typically needed to develop aircraft concepts and increase the chances to generate a final aircraft with high performance meeting the initial DRs.