FUNDAMENTAL UNDERSTANDING OF THE CYCLOIDAL-ROTOR CONCEPT FOR MICRO AIR VEHICLE APPLICATIONS

The cycloidal-rotor (cyclorotor) is a revolutionary flying concept which has not been systematically studied in the past. Therefore, in the current research, the viability of the cyclorotor concept for powering a hover-capable micro-air-vehicle (MAV) was examined through both experiments and analysis. Experimental study included both performance and flow field measurements on a cyclorotor of span and diameter equal to 6 inches. The analysis developed was an unsteady large deformation aeroelastic analysis to predict the blade loads and average aerodynamic performance of the cyclorotor. The flightworthiness of the cyclorotor concept was also demonstrated through two cyclocopters capable of tethered hover. Systematic performance measurements have been conducted to understand the effect of the rotational speed, blade airfoil profile, blade flexibility, blade pitching amplitude (symmetric and asymmetric blade pitching), pitching axis location, number of blades with constant chord (varying solidity), and number of blades at same rotor solidity (varying blade chord) on the aerodynamic performance of the cyclorotor. Force measurements showed the presence of a significant sideward force on the cyclorotor (along with the vertical force), analogous to that found on a spinning circular cylinder. Particle image velocimetry (PIV) measurements made in the wake of the cyclorotor provided evidence of a significant wake skewness, which was produced by the sideward force. PIV measurements also captured the blade tip vortices and a large region of rotational flow inside the rotor. The thrust produced by the cyclorotor was found to increase until a blade pitch amplitude of 45 was reached without showing any signs of blade stall. This behavior was also explained using the PIV measurements, which indicated evidence of a stall delay as well as possible increase in lift on the blades from the presence of a leading edge vortex. Higher blade pitch amplitudes also improved the power loading (thrust/power) of the cyclorotor. When compared to the flat-plate blades, the NACA 0010 blades produced the highest values of thrust at all blade pitching amplitudes. The NACA blades also produced higher power loading than the flat plate blades. However, the reverse NACA 0010 blades produced better power loadings at lower pitching amplitudes, even though at high pitch amplitudes, regular NACA blades performed better. Among the three NACA sections (NACA 0006, NACA 0010 and NACA 0015) tested on the cyclorotor, NACA 0015 had the highest power loading followed by NACA 0010 and then NACA 0006. The power loading also increased when using more blades with constant chord (increasing solidity); this observation was found over a wide range of blade pitching amplitudes. Asymmetric pitching with higher pitch angle at the top of the blade trajectory than at the bottom produced better power loading. The chordwise optimum pitching axis location was approximately 25-35% of the blade chord. For a constant solidity, the rotor with fewer number of blades produced higher thrust and the 2-bladed rotor had the best power loading. Any significant bending and torsional flexibility of the blades had a deleterious effect on performance. The optimized cyclorotor had slightly higher power loading when compared to a conventional micro-rotor when operated at the same disk loading. The optimum configuration based on all the tests was a 4-bladed rotor using 1.3 inch chord NACA 0015 blade section with an asymmetric pitching of 45 at top and 25 at bottom with the pitching axis at 25% chord. The aeroelastic analysis was performed using two approaches, one using a second-order non-linear beam FEM analysis for moderately flexible blades and second using a multibody based large-deformation analysis (especially applicable for extremely flexible blades) incorporating a geometrically exact beam model. An unsteady aerodynamic model is included in the analysis with two different inflow models, single streamtube and a double-multiple streamtube inflow model. For the cycloidal rotors using moderately flexible blades, the aeroelastic analysis was able to predict the average thrust with sufficient accuracy over a wide range of rotational speeds, pitching amplitudes and number of blades. However, for the extremely flexible blades, the thrust was underpredicted at higher rotational speeds and this may be because of the overprediction of blade deformations. The inclusion of the actual blade pitch kinematics and unsteady aerodynamics was found crucial in the accurate sideward force prediction

Intelligent Vision-based Autonomous Ship Landing of VTOL UAVs

The paper discusses an intelligent vision-based control solution for autonomous tracking and landing of Vertical Take-Off and Landing (VTOL) capable Unmanned Aerial Vehicles (UAVs) on ships without utilizing GPS signal. The central idea involves automating the Navy helicopter ship landing procedure where the pilot utilizes the ship as the visual reference for long-range tracking; however, refers to a standardized visual cue installed on most Navy ships called the "horizon bar" for the final approach and landing phases. This idea is implemented using a uniquely designed nonlinear controller integrated with machine vision. The vision system utilizes machine learning-based object detection for long-range ship tracking and classical computer vision for the estimation of aircraft relative position and orientation utilizing the horizon bar during the final approach and landing phases. The nonlinear controller operates based on the information estimated by the vision system and has demonstrated robust tracking performance even in the presence of uncertainties. The developed autonomous ship landing system was implemented on a quad-rotor UAV equipped with an onboard camera, and approach and landing were successfully demonstrated on a moving deck, which imitates realistic ship deck motions. Extensive simulations and flight tests were conducted to demonstrate vertical landing safety, tracking capability, and landing accuracy

Robust Reinforcement Learning Algorithm for Vision-based Ship Landing of UAVs

This paper addresses the problem of developing an algorithm for autonomous ship landing of vertical take-off and landing (VTOL) capable unmanned aerial vehicles (UAVs), using only a monocular camera in the UAV for tracking and localization. Ship landing is a challenging task due to the small landing space, six degrees of freedom ship deck motion, limited visual references for localization, and adversarial environmental conditions such as wind gusts. We first develop a computer vision algorithm which estimates the relative position of the UAV with respect to a horizon reference bar on the landing platform using the image stream from a monocular vision camera on the UAV. Our approach is motivated by the actual ship landing procedure followed by the Navy helicopter pilots in tracking the horizon reference bar as a visual cue. We then develop a robust reinforcement learning (RL) algorithm for controlling the UAV towards the landing platform even in the presence of adversarial environmental conditions such as wind gusts. We demonstrate the superior performance of our algorithm compared to a benchmark nonlinear PID control approach, both in the simulation experiments using the Gazebo environment and in the real-world setting using a Parrot ANAFI quad-rotor and sub-scale ship platform undergoing 6 degrees of freedom (DOF) deck motion

Hover-capable Flapping-wing Aircraft

A flapping-wing aircraft includes a support frame, a motor coupled to the support frame, a pair of wings coupled to the support frame, and a linkage assembly coupled to the support frame and configured to translate an output torque of the motor into flapping motion of the wings, wherein the linkage assembly includes a first link coupled to a rotational output of the motor, a second link pivotably coupled to the first link at a first pivot joint, a third link pivotably coupled to the second link at a second pivot joint, and a fourth link pivotably coupled to the support frame and slidably coupled to the third link, and wherein the fourth link is coupled to a first wing of the pair of wings.U

Fluid bearing systems and methods

A fluid bearing includes a housing including an internal plenum disposed in the housing and an inlet in fluid communication with the plenum, wherein the inlet is configured to provide fluid to the plenum from an external source, a cushion surface facing away from the housing and the plenum, one or more nozzles positioned between the cushion surface and the housing, wherein the one or more nozzles extend from the plenum to the surrounding environment, wherein the one or more nozzles are configured to produce an annular curtain of fluid flowing at a velocity of at least Mach 1 and disposed about the cushion surface in response to a fluid flow entering the plenum from the inlet.U