We present a global controller for tracking nominal trajectories with a flying wing tailsitter vehicle. The control strategy is based on a first-principles model of the vehicle dynamics that captures all relevant aerodynamic effects, and we apply an onboard parameter learning scheme in order to estimate unknown aerodynamic parameters. A cascaded control architecture is used: Based on position and velocity errors an outer control loop computes a desired attitude keeping the vehicle in coordinated flight, while an inner control loop tracks the desired attitude using a lookup table with precomputed optimal attitude trajectories. The proposed algorithms can be implemented on a typical microcontroller and the performance is demonstrated in various experiments.

A global controller for flying wing tailsitter vehicles

We present a nonlinear hover controller for a small flying wing tailsitter vehicle, which enables recovering to hover from a large set of initial conditions. The proposed attitude control law is obtained by solving an optimal control problem, with the objective of correcting large attitude errors by turning primarily around the vehicle’s strongly actuated axis. Solutions for a set of initial attitudes are precomputed and stored in a lookup table. For each controller update, the optimal inputs are read from this table, and applied to the system in an MPC-like manner. Simulation results indicate that this control method is able to perform recoveries to hover from any initial attitude, given that the initial velocity of the vehicle is below a certain limit. Further, the performance of the control strategy is demonstrated on a small tailsitter vehicle in the ETH Zurich Flying Machine Arena.

A Global Strategy for Tailsitter Hover Control

A vertical takeoff and landing, unmanned aerial vehicle is presented that features a quadrotor design for propulsion and attitude stabilization, and an annular wing that provides lift in forward flight. The annular wing enhances human safety by enshrouding the propeller blades. Both the annular wing and the propulsion units are fully characterized in forward flight via wind tunnel experiments. An autonomous control system is synthesized that is based on model inversion, and accounts for the aerodynamics of the wing. It also accounts for the dominant aerodynamics of the propellers in forward flight, specifically the thrust and rotor torques when subject to oblique flow conditions. The attitude controller employed is tilt-prioritized, as the aerodynamics are invariant to the twist angle of the vehicle. Outdoor experiments are performed, resulting in accurate tracking of the reference position trajectories at high speeds.

An Annular Wing VTOL UAV: Flight Dynamics and Control

An Automatic Flight Control System for VTOL Aircraft Supported by Ducted Fans

An investigation of the mutual interference effects of the ground, wing, deflected jet stream, and free stream of a semispan delta-wing VTOL model at zero and low forward speeds has been conducted in the 17-foot test section of the Langley 300-MPH 7-by 10-foot tunnel. The model consisted of two interchangeable semispan clipped delta wings, a simplified fuselage, and a high-pressure jet for simulation of a jet exhaust. Attached to the wing behind the jet were various sets of vanes for deflecting the jet stream to different turning angles. The effect of ground proximity gave the normally expected losses in lift at zero and very low forward speeds (up to about 60 or 80 knots for the assumed wing loading of 100 lb/sq ft); at higher forward speeds ground effects were favorable. At low forward speeds, out of ground effect, the model encountered large losses in lift and large nose-up pitching moments with the model at low angles of attack and the jet deflected 90 deg or 75 deg (the angles required for VTOL performance and very low forward speeds). Rotating the model to higher angles of attack and deflecting the jet back to lower angles eliminated these losses in lift. Moving the jet rearward with respect to the wing reduced the losses in lift and the nose-up moments at all speeds within the range of this investigation.

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Investigation of Interference of a Deflected Jet with Free Stream and Ground on Aerodynamic Characteristics of a Semispan Delta-Wing VTOL Model

Publisher Summary
This chapter discusses about the rapidly increasing interest in the United States in VTOL and STOL aircraft, that is aircraft capable of performing either vertical or short take-off and landing. The chapter presents all those VTOL aircraft, falling in between that are propelled by rotors, propellers, ducted fans, or turbojets. STOL aircraft include only those in which all or most of the power available is used for producing high lift. For example, the jet flap but will not cover boundary-layer control applications that make use of only a small portion of the power available. A significant feature of VTOL–STOL research programs undertaken recently in the United States has been the use of flying test-bed aircraft that are simple and relatively inexpensive research machines.

John P. Campbell

Papers

Research on vtol and stol aircraft in the united states