A survey of hybrid Unmanned Aerial Vehicles

Since October 2005, the T-wing tail-sitter unmanned air vehicle has undergone an extensive program of flight tests, resulting in a total of more than 50 flights, many under autonomous control from takeoff to landing. Starting in August 2006, free flights with conversion between vertical and horizontal flight modes have also been undertaken. Although the latter flights have required some guidance-level ground-pilot input, significant portions of them were performed in autonomous mode, including the transitions between horizontal and vertical flight. This paper considers the overall control architecture of the vehicle, including the different control modes that the vehicle was flown under during the recent series of tests. Although the individual controllers for each flight mode are unremarkable in themselves, it is notable that the aggregate system allows the vehicle to fly throughout its entire flight envelope, which is considerably broader than that of conventional fixed- or rotary-wing vehicles. The performance of the controllers for the different flight modes will also be considered, with a particular focus on hover dispersion results, in differing wind conditions. The majority of these flights were performed on a tether test rig during autonomous control development, to ensure vehicle safety with minimal impact on vehicle dynamics. The demonstration of autonomous flight under the constraints imposed by the tether system in winds up to 18 kt is a significant achievement Results from the more recent horizontal flight tests with conversions between vertical and horizontal flight are also presented. Most important, these results confirm the basic feasibility of tail-sitter vehicles that use control surfaces submerged in propeller wash for vertical flight control.

Flight Testing of the T-Wing Tail-Sitter Unmanned Air Vehicle

This paper details the control and guidance architecture for the T-wing tail-sitter unmanned air vehicle, (UAV). The T-wing is a vertical take off and landing (VTOL) UAV that is capable of both wing-born horizontal flight and propeller born vertical mode flight including hover and descent. During low-speed vertical flight the T-wing uses propeller wash over its aerodynamic surfaces to effect control. At the lowest level, the vehicle uses a mixture of classical and LQR controllers for angular rate and translational velocity control. These low-level controllers are directed by a series of proportional guidance controllers for the vertical, horizontal and transition flight modes that allow the vehicle to achieve autonomous waypoint navigation. The control design for the T-wing is complicated by the large differences in vehicle dynamics between vertical and horizontal flight; the difficulty of accurately predicting the low-speed vehicle aerodynamics; and the basic instability of the vertical flight mode. This paper considers the control design problem for the T-wing in light of these factors. In particular it focuses on the integration of all the different types and levels of controllers into a full flight-vehicle control system.

Control architecture for a tail-sitter unmanned air vehicle

http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/3881.pdf

Autonomous Hovering of a Noncyclic Tiltrotor UAV: Modeling, Control and Implementation

This paper describes the modeling, control and hardware implementation of an experimental tilt-rotor aircraft. This vehicle combines the high-speed cruise capabilities of a conventional airplane with the hovering capabilities of a helicopter by tilting their four rotors. Changing between cruise and hover flight modes in mid-air is referred to transition. Dynamic model of the vehicle is derived both for vertical and horizontal flight modes using Newtonian approach. Two nonlinear control strategies are presented and evaluated at simulation level to control, the vertical and horizontal flight dynamics of the vehicle in the longitudinal plane. An experimental prototype named Quad-plane was developed to perform the vertical flight. A low-cost DSP-based Embedded Flight Control System (EFCS) was designed and built to achieve autonomous attitude-stabilized flight.

https://hal.archives-ouvertes.fr/hal-00923129/document

Quad-Tilting Rotor Convertible MAV: Modeling and Real-Time Hover Flight Control

This paper considers the aerodynamic modeling of a twin-engine tail-sitter unmanned air vehicle that relies on wing- and fin-mounted control surfaces submerged in the propeller slipstreams for control during low-speed vertical flight The aerodynamic forces on this vehicle are predicted using a full azimuthal blade-element solution for the propellers combined with a fixed-wake panel-method model of the vehicle itself. When the flow components determined from the propeller solution are superimposed on the external flowfield and integrated with the panel-method model, the aerodynamic forces can be determined for the full vehicle, including slipstream effects, which are dominant in low-speed flight. The modeling described in this paper has been used extensively for multidisciplinary optimization work, as well as in the construction of a comprehensive aerodynamic database for the vehicle. This database encompasses all the aerodynamic force and moment coefficients and their derivatives for over 4300 separate flight conditions and has been extensively used for vehicle simulation and control design purposes.

R. Hugh Stone

Papers

Flight Testing of the T-Wing Tail-Sitter Unmanned Air Vehicle

Aerodynamic Modeling of the Wing-Propeller Interaction for a Tail-Sitter Unmanned Air Vehicle

Aerodynamic Modelling of a Wing-in-Slipstream Tail-Sitter UAV

The T-Wing Tail-Sitter Research UAV

Modelling and Control of a Tandem-Wing Tail-Sitter UAV