Hover Stabilization Research Articles

Hover Control of an UAV With Backstepping Design Including Input Saturations

This brief presents a backstepping-based controller with input saturations, applicable for the hover flight of an unmanned aerial vehicle (UAV). A dynamic model for a generic UAV is introduced that is valid for quasi-stationary conditions, with quaternion formulation of the kinematics equations. Based on this model, a backstepping design formulation is deduced for UAV hover control, and its global asymptotic stability is demonstrated. In order to cope with limitations due to reduced actuation, saturations are introduced in the control design, and the stability of the modified control solution is verified. Simulation results are presented for the hover stabilization of an airship UAV, which are demonstrative of the excellent performance of the proposed controller and illustrate its robustness in face of wind disturbances.

Airship Hover Stabilization Using a Backstepping Control Approach

The present paper introduces a novel approach for the airship hover stabilization problem. A synthetic modeling of the airship dynamics is introduced using a quaternion formulation of the kinematics equations. Based on this model, a backstepping design formulation is deduced for the aircraft hovering control. To deal with limitations caused by reduced actuation, saturations are introduced in the control design, and the global asymptotic stability of the system under saturation is demonstrated. The control objective is finally modified to cope with the strong lateral underactuation. Simulation results are presented for the hover stabilization of an unmanned robotic airship, with wind and turbulence conditions selected to demonstrate the behavior and robustness of the proposed solution.

HOVER STABILIZATION OF AN AIRSHIP USING DYNAMIC INVERSION

This paper proposes a new strategy for the hover stabilization of an airship using Dynamic Inversion. We start by introducing a synthetic model of the airship nonlinear dynamics considering forces and moments as input. This model disregards the aerodynamic forces, negligible near hover conditions. Based on the dynamic inversion approach, the model is then inverted so as to obtain the control law. In order to cope with the airship real inputs, a conversion from forces to actuators input is also made. Simulation results illustrate the good performance of the designed controller for the hover control of the Aurora airship.

An aeroelastic model for composite rotor blades with straight and swept tips. Part I: Aeroelastic stability in hover

An analytical model for predicting the aeroelastic behavior of composite rotor blades with straight and swept tips is presented. The blade is modeled by beam type finite elements along the elastic axis. A single finite element is used to model the swept tip. The non-linear equations of motion for the finite element model are derived using Hamilton's principle and based on a moderate deflection theory and accounts for: arbitrary cross-sectional shape, pretwist, generally anisotropic material behavior, transverse shears and out-of-plane warping. Numerical results illustrating the effects of tip sweep, anhedral and composite ply orientation on blade aeroelastic behavior are presented. It is shown that composite ply orientation has a substantial effect on blade stability. At low thrust conditions, certain ply orientations can cause instability in the lag mode. The flap-torsion coupling associated with tip sweep can also induce aeroelastic instability in the blade. This instability can be removed by appropriate ply orientation in the composite construction.

Machine vision-based sensing for helicopter flight control

Machine vision-based sensing enables automatic hover stabilization of helicopters. The evaluation of image data, which is produced by a camera looking straight to the ground, results in a drift free autonomous on-board position measurement system. No additional information about the appearance of the scenery seen by the camera (e.g. landmarks) is needed. The technique being applied is a combination of the 4D-approach with two dimensional template tracking of a priori unknown features.

Tracking Sensor for Autonomous Helicopter Hover Stabilization

Within a feasibility study a restricted computer vision system, which is capable of locating and tracking a square, was developed and integrated into a helicopter. Flight tests demonstrated automatic helicopter hover stabilization above the moving square, being mounted on a car. This lead to the development of a general computer-vision system, which is able to observe the helicopter flight state during hover and low speed, based on the detection and tracking of significant but arbitrary features within camera images. No additional information about the appearance of the camera view (e.g. landmarks) is needed.

Flap-lag-torsion stability in hover and forward flight with three-dimensional wake

The contributions of full-wake dynamics in trim analysis are demonstrated for finding the control inputs and periodic responses simultaneously, as well as in Floquet eigenanalysis for finding the damping levels. The equations of flap bending, lag bending, and torsion are coupled with a three-dimensional, finite state wake, and low-frequency ( 1/rev) multiblade modes are considered. Full blade-wake dynamics is used in trim analysis and Floquet eigenanalysis. A uniform cantilever blade in trimmed flight is investigated over a range of thrust levels, advance ratios, number of blades, and blade torsional frequencies. The investigation includes the convergence characteristics of control inputs, periodic responses, and damping levels with respect to the number of spatial azimuthal harmonics and radial shape functions in the wake representation. It also includes correlation with the measured lag damping of a three-bladed untrimmed rotor. The parametric study shows the dominant influence of wake dynamics on control inputs, periodic responses, and damping levels, and wake theory generally improves the correlation.

An Analytical Model for a Nonlinear Elastomeric Lag Damper and Its Effect on Aeromechanical Stability in Hover

An Analytical Model for a Nonlinear Elastomeric Lag Damper and Its Effect on Aeromechanical Stability in Hover

A Closed-Form Analysis of Rotor Blade Flap-Lag Stability in Hover and Low-Speed Forward Flight in Turbulent Flow

An approximate, closed-form analysis of the stability of coupled flap-lag motion of a helicopter rotor blade in the presence of turbulence is presented. The longitudinal, lateral, and vertical components of turbulence are modeled as uncorrelated physical white noise processes and a special case of the stochastic averaging method is applied to obtain the equations governing the first moments of the stochastic system. A closed-form first moment stochastic stability criterion is obtained using approximations based on realistic rms values of turbulence velocities. This closed form analysis is a generalization of a previous analysis by Peters for the deterministic case. Based on the stability criterion obtained, an interpretation is given for the result, previously obtained by the authors, that in hover the turbulence increases the stability of the coupled flap-lag motion. The interpretation is that the turbulence increases the damping in the least-stable, lead-lag mode by providing the same stabilizing effect as an increase in the profile drag coefficient in both hover and low-speed forward flight. Of the three turbulence components, the vertical turbulence is shown to have the dominant effect on this increase in stability. Numerical results are presented for the hover case and comparison with the more stringent case of second moment stability is made.

A Closed‐Form Analysis of Rotor Blade Flap‐Lag Stability in Hover and Low‐Speed Forward Flight in Turbulent Flow

A Closed‐Form Analysis of Rotor Blade Flap‐Lag Stability in Hover and Low‐Speed Forward Flight in Turbulent Flow

Cruising and Hovering Response of a Tail-Stabalized Submersible

Equations of motion are used as a basis for analyzing the inherent dynamic stability and limit maneuver response of a tail-stabilized submersible in cruising and hovering vertical plane motions. It is shown that this type of vessel can perform adequately in cruising but is subject to highly coupled, unstable hovering motion, especially in stern-to-bow ocean currents. The stability of a submersible with both bow and stern stabilizers, having fore-aft symmetry, also is treated. This type of design has inherent hovering stability, and its symmetry would have a salutory effect on the coupled motions of the vessel.