I teach, design, build and fly the unmanned aircraft systems of the future.

Purpose. High endurance fixed-wing UAVs powered by solar arrays or hydrogen fuel cells carry energy systems that cost more than the airframe itself and a single motor failure can end a multi-hour mission. This study aims to compare twin, trimotor and quad propulsion on measured data to find where the engine-out redundancy of each end.

Design/methodology/approach. Static thrust stand data for a 6.5 kg, 3.3 m airframe are transferred to flight with advance ratio dependent propeller coefficients. On a 1000 Wh budget, engine-out cases are scored against a two-level criterion of stopped propeller drag, trim drag and rudder authority.

Findings. All three configurations cruise at 18 m·s⁻¹ on 211–233 W and hold that airspeed after a motor loss with the tested motor and propeller combinations. What separates them is directional control. The quad and trimotor need under 12° of rudder and the trimotor loses its centerline motor with no yaw. The twin needs 73% of the rudder travel and cannot be trimmed below 12.8 m·s⁻¹, marginal against the 12 m·s⁻¹ minimum sustainable flight level.

Originality/value. For the tested components on this airframe, the twin-engine redundancy assumption inherited from manned practice does not carry over: the fin, sized for cruise stability, sets the redundancy of the twin and a minimum control speed after a motor loss belongs in the design case of such a layout.

Purpose. The current research conducts a comprehensive review on FishBAC (fishbone active camber morphing wing surfaces) for researchers and scientists and sheds light on challenges and opportunities of FishBAC development.

Design/methodology/approach. This is a review article and this study reviews previous research on FishBAC.

Findings. The current FishBAC applications could be upgraded into more efficient designs in materials, design and mechanisms with more perspectives involved. Then, this promising branch of morphing surface design could be integrated with rotor blades, unmanned aerial vehicle wings, general aviation aircraft surfaces and so on.

Research limitations/implications. This is a review article.

Practical implications. The contributions of the study are summarized as follows: to provide an overview of FishBAC research; to compare various approaches and trends in FishBAC designs; to address the research gap in the roadmap for FishBAC design; and to discuss the challenges and opportunities of FishBAC development.

Originality/value. To the best of the authors’ knowledge, this is the first review on a promising morphing method and an alternative for conventional flaps and ailerons.

The implementation of morphing wing applications in aircraft design has sparked significant interest as it enables the dimensional properties of the aircraft to be modified during flight. By allowing manipulation of the 2D and 3D parameters on the aircraft’s wings, tail surfaces, or fuselage, a variety of possibilities have arisen. Two primary schools of thought have emerged in the field of morphing wing applications: the mechanisms school and the smart surfaces approach that uses shape-memory materials and smart actuators. Among the research in this field, the Fishbone Active Camber (FishBAC) approach has emerged as a promising avenue for controlling the deflection of the wing’s trailing edge. This study revisits previous research on morphing wings and the FishBAC concept, evaluates the current state of the field, and presents an original design process flow that includes the design of a unique and innovative UAV called the Stingray within the scope of the study. A novel morphing concept developed for the Stingray UAV, Rear Spar Articulated Wing Camber (RSAWC), employs a fishbone-like morphing wing rib design with rear spar articulation in a cost-effective manner. The design process and flight tests of the RSAWC are presented and directly compared with a conventional wing. Results are evaluated based on performance, weight, cost, and complexity. Semi-empirical data from the flight testing of the concept resulted in approximately a 19% flight endurance increment. The study also presents future directions of research on the RSAWC concept to guide the researchers.