Sensors are crucial for the control of unmanned aerial vehicles (UAVs). However, sensor faults will inevitably appear over time. Therefore, it is important to develop a sensor fault detection approach for the reliability of UAV. This article presents a novel model-based UAV fault detection approach based on quadratic Kalman filter (QKF). First, an accurate kinematic and dynamic model of UAVs is established, where the model is linearized and discretized for Kalman filter (KF). Second, the first KF is used for denoising, the secondKF is used to detrend, and residuals are calculated for detection. It is worth mentioning that the second KF is a modified Sage–Husa adaptive KF, which can automatically estimate the measurement noise variance. Compared with traditional approaches, this approach has the advantages of noise reduction, self-adaptation, divergence avoidance, and high detection rate. Simulation and experimental results show the effectiveness of the proposed approach, which can accurately detect the abrupt and incipient fault of an inertial measurement unit (IMU) sensor. At the same time, it can get the higher fault detection rates (FDRs) compared with conventional KF. Furthermore, this approach also provides the leading information and foundation for UAV fault-tolerant control.

Urban Air Transportation (UAT) encompasses private aircraft, air taxis, and specialized missions. These missions include aerial sightseeing, logistics transportation, emergency response, and anti-terrorism operations. They impose stringent requirements on advanced air mobility (AAM) aircraft. These requirements include efficient hovering performance, high-speed cruising capability, and compliance with strict safety and clean energy standards. Consequently, one of the core vehicles for AAM is the efficient and reliable eVTOL (electric vertical take-off and landing) aircraft. Therefore, this paper presents a review of current research on eVTOL aircraft, and highlights potential research paths to advance this innovative field. We begin by classifying and analyzing the latest eVTOL aircraft configurations currently in production, offering an overview of their applications. Subsequently, we delve into key autonomous eVTOL aircraft technologies encompassing electric propulsion, flight control method, sensing & perception, decision-making, and safety & reliability, elucidating recent progress in each domain. Furthermore, we engage in a discourse on the regulatory and societal challenges, including a discussion on airworthiness regulations, that are pertinent to the integration and operation of autonomous eVTOL aircraft. Finally, we conclude by providing future trends and recommendations of autonomous eVTOL aircraft technology, focusing on its interaction with air traffic control system, the adaptation of urban infrastructure, and the design of efficient human-machine interaction protocols.

Urban air transportation (private aircraft, air taxi, etc.) and all kinds of special flight missions (aerial sightseeing, logistics transportation, disaster relief, anti-terrorism and anti-riot etc.) put forward high requirements for the flight performance of future urban aircraft. It not only demands high-efficiency hovering performance, but also demands the capability of high-speed cruising as well as high safety, clean energy and other characteristics. The maximum flight speed of conventional rotorcraft (such as helicopter, multi-rotor UAV, etc.) is limited by the fluid compressibility of advancing rotor blade and the airflow separation of retreating rotor blade, which makes further improvement of the flight speed more difficult. In order to overcome the fluid compressibility of rotor advancing side and stall of rotor retreating side encountered under high-speed, researchers have proposed many new concepts of advanced rotorcraft. This article sorts and analyses the current advanced VTOL (Vertical Take-Off and Landing) rotorcrafts with new configurations, and attempts to point out the feasible research direction in the future.