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In this paper, a powerful optimization framework is proposed to design highly efficient winged unmanned aerial vehicle (UAV) that is powered by electric motors. In the proposed approach, the design of key UAV parameters including both aerodynamic configurations, (e.g. wing span, sweep angle, chord, taper ratio, cruise speed and angle of attack) and the propulsion systems (e.g. propeller, motor and battery) are cast into an unified optimization problem, where the optimization objective is the design goal (e.g. flight range, endurance). Moreover, practical constraints are naturally incorporated into the design procedures as constraints of the optimization problem. These constraints may arise from the preliminary UAV shape and layout determined by industrial design, weight constraints, etc. The backend of the optimization based UAV design framework are highly accurate aerodynamic models and propulsion system models proposed in this paper and verified by actual experiment data. The optimization framework is inherently non-convex and involves both continuous variables (e.g. the aerodynamic configuration parameters) and discrete variables (e.g. propulsion system combinations). To solve this problem, a novel coordinate descent method is proposed. Trial designs show that the proposed method works rather efficiently, converging in a few iterations. And the returned solution is rather stable with different initial conditions. Finally, the entire approach is applied to design a quadrotor tail-sitter VTOL UAV. The designed UAV is validated by both CFD simulations and intensive real-world flight tests.

The past few decades have witnessed a dramatically growth of unmanned aerial vehicle (UAV) market. Such an increasing requirement of UAV also caused fierce competition among UAV companies all over the world. For these UAV manufactures and relative researchers, optimization of UAV design is critical to improve performance of UAVs. Compare to all other configurations of UAVs, winged UAV is the most complex and difficult to optimize during the design progress. That is not only because of the involved complex aerodynamic model, but also due to the coupling of aerodynamic model and propulsion system model, which composed by several sub-models, such as battery model, propeller model and motor model. In this thesis, a powerful model based optimization framework is proposed to design highly efficient winged UAVs powered by electric motors. In the proposed approach, the models of aerodynamic configurations and propulsion system are built and cast into an unified optimization problem, where the optimization objective is the design goal (e.g. flight range, endurance). To evaluate the models, the key design variables are parameterized as two groups, which respectively denote the aerodynamic model (e.g. wing span, sweep angle, chord, taper ratio, cruise speed and angle of attack) and the propulsion systems model (e.g. propeller, motor and battery). Moreover, practical constraints are naturally incorporated into the design procedures as constraints of the optimization problem. These constraints may arise from the preliminary UAV shape and layout determined by industrial design, weight constraints, etc. The optimization framework is inherently non-convex and involves both continuous variables (e.g. the aerodynamic configuration parameters) and discrete variables (e.g. propulsion system combinations). To solve this problem, a novel coordinate descent method is proposed. Trial designs show that the proposed method works rather efficiently, converging in a few iterations. And the ret

Hybrid VTOL UAVs such as tail-sitters allow several key maneuvers such as vertical takeoff, landing, and hovering while at the same time maintaining superior aerodynamic efficiency at level flight. However, the large wing area of a tail-sitter at hovering makes it rather sensitive to the cross wind. In this letter, we present a disturbance observer (DOB) based control method to improve its hovering accuracy in presence of external disturbances such as cross wind. The presented DOB, operating on top of the aircraft baseline position controller, is designed in frequency domain using H ∞ synthesis techniques and is guaranteed to stabilize the closed loop system with robustness to model uncertainties. In addition, it admits nonminimum phase system model, as the case of our tail-sitter platform, and does not require much hand tuning work on the Q-filter. Comparison study with existing UAV disturbance rejection method is conducted under different wind disturbances. Results show that the presented DOB control technique can effectively estimate various types of wind disturbances and lead to improved hovering accuracy of the tail-sitter UAV.

In this paper, we present an optimization framework for the conceptual design of electric-powered unmanned aerial vehicles (UAVs) with wings, to meet the community's ever increasing interest in developing novel efficient winged UAVs. In our framework, the UAV design is formulated as an optimization problem with a user-defined objective. It also accepts various constraints, such as restricted aircraft size, weight, and preliminary wing (and fuselage) shape determined by industrial design, limited availability of propulsion systems, etc. Such a framework is particularly suitable for the design of small UAVs with many practical limitations, such as portability, size, cost, etc. In evaluating a given aircraft configuration (e.g., wing, fuselage, landing gears, etc.), we adopt various empirical aerodynamic models that have been commonly used in aviation history. We also retrieve hundreds of propeller and motor data from their manufacturers and fit them to constitute a high-fidelity propulsion system database. Wind tunnel testing on existing airframe data shows that our aerodynamic models fit the measurements very well. Propeller testing is also carried out to validate the fitted propeller model. With the ability to evaluate a given aircraft and propulsion, we propose a coordinate descent method that nicely decouples the optimization for the aircraft configuration, which involves continuous variables, and the propulsion system, which involves discrete variables (e.g., motor index, propeller index). With the presented optimization framework and coordinate descent method, a quadrotor tail-sitter vertical takeoff and landing (VTOL) UAV is designed, manufactured and tested.

This paper presents the modeling, simulation, and control of a small-scale electric powered quadrotor tail-sitter vertical take-off and landing unmanned aerial vehicle. In the modeling part, a full attitude wind tunnel test is performed on the full-scale unmanned aerial vehicle to capture its aerodynamics over the flight envelope. To accurately capture the degradation of motor thrust and torque at the presence of the forward speed, a wind tunnel test on the motor and propeller is also carried out. The extensive wind tunnel tests, when combined with the unmanned aerial vehicle kinematics model, dynamics model and other practical constraints such as motor saturation and delay, lead to a complete flight simulator that can accurately reveal the actual aircraft dynamics as verified by actual flight experiments. Based on the developed model, a unified attitude controller and a stable transition controller are designed and verified. Both simulation and experiments show that the developed attitude controller can stabilize the unmanned aerial vehicle attitude over the entire flight envelope and the transition controller can successfully transit the unmanned aerial vehicle from vertical flight to level flight with negligible altitude dropping, a common and fundamental challenge for tail-sitter vertical take-off and landing aircrafts. Finally, when supplied with the designed controller, the tail-sitter unmanned aerial vehicle can achieve a wide flight speed envelope ranging from stationary hovering to fast level flight. This feature dramatically distinguishes our aircraft from conventional fixed-wing airplanes.

We present the design and implementation of a quadrotor tail-sitter Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV). The VTOL UAV combines the advantage of a quadrotor, vertical take-off and landing and hovering at a stationary point, with that of a fixed-wing, efficient level flight. We describe our vehicle design with special considerations on fully autonomous operation in a real outdoor environment where the wind is present. The designed quadrotor tail-sitter UAV has insignificant vibration level and achieves stable hovering and landing performance when a cross wind is present. Wind tunnel test is conducted to characterize the full envelope aerodynamics of the aircraft, based on which a flight controller is designed, implemented and tested. MATLAB simulation is presented and shows that our vehicle can achieve a continuous transition from hover flight to level flight. Finally, both indoor and outdoor flight experiments are conducted to verify the performance of our vehicle and the designed controller. © 2017 IEEE.

We present a hierarchical control approach that can be used to fulfill autonomous flight, including vertical take-off, landing, hovering, transition, and level flight, of a quadrotor tail-sitter vertical take-off and landing unmanned aerial vehicle (VTOL UAV). A unified attitude controller, together with a moment allocation scheme between elevons and motor differential thrust, is developed for all flight modes. A comparison study via real flight tests is performed to verify the effectiveness of using elevons in addition to motor differential thrust. With the well-designed switch scheme proposed in this paper, the aircraft can transit between different flight modes with negligible altitude drop or gain. Intensive flight tests have been performed to verify the effectiveness of the proposed control approach in both manual flight mode and fully autonomous flight mode.

This paper presents the design and implementation of a cost-effective, lightweight, yet power efficient tail-sitter Vertical Take-off and Landing (VTOL) unmanned aerial vehicle (UAV). The UAV consists a pair of wings for efficient level flight and four rotors for attitude control. The aerodynamic and mechanical configurations of the UAV are designed and implemented from scratch to meet the required power efficiency, and subsequently optimized to enhance the stability and maneuverability. The developed VTOL UAV has a weight and cost comparable to a typical quadrotor, while consuming only half power, as shown by real flight tests. In addition, it can achieve all key VTOL maneuvers, including vertical take-off, landing, hovering, cruising and transition.

In this paper, we present the design and verification of a hybrid vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAV) of the type named dualsystem or extra propulsion VTOL UAV. This paper features the comprehensive system development of such VTOL UAVs from all aspects, including the aircraft design and implementation, onboard devices integration, ground station support, and long distance communication. We proceed with aerodynamic analysis, mechanical design, and controller development. Finally, we verify by experiment that this hybrid VTOL UAV has the desired aerodynamic performance, flight stability, endurance and range. In addition, with the designed flight controller, the VTOL UAV can achieve full autonomous flight in a real outdoor environment. It serves a good platform for future research, such as vision-based precise landing, motion planing and quick 3D mapping, as well as service applications, such as medicine delivery.

This paper presents the modeling and simulation of a quad rotor tail-sitter VTOL UAV. The VTOL UAV is configured with four rotors for full attitude control and thrust generation for both vertical and forward fight. In the modeling process, a full attitude wind tunnel test was performed on the full scale UAV to capture the UAV aerodynamics. In our model, we explicitly consider the degradation of motor thrust and torque at the presence of forward speed, which is usually neglected in most multi-rotor models. Quaternion based attitude representation is utilized to drive the dynamics of the aircraft. When monitoring and commanding the UAV attitude, ZXY Euler angles are used to avoid the singularity at pitching angle of 90 degrees of commonly used ZYX Euler angles. Other minor considerations include motor dynamics, gyroscopic effect, etc. Such a model captures the UAV kinematics, dynamics, aerodynamics and actuator dynamics, and serves a good reference model for flight controller design and verification. As a testimony of the presented model, an attitude controller with an altitude holding loop will be presented. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.