Circular formation control of fixed-wing UAVs with constant speeds

In this paper we propose an algorithm for stabilizing circular formations of fixed-wing UAVs with constant speeds. The algorithm is based on the idea of tracking circles with different radii in order to control the inter-vehicle phases with respect to a target circumference. We prove that the desired equilibrium is exponentially stable and thanks to the guidance vector field that guides the vehicles, the algorithm can be extended to other closed trajectories. One of the main advantages of this approach is that the algorithm guarantees the confinement of the team in a specific area, even when communications or sensing among vehicles are lost. We show the effectiveness of the algorithm with an actual formation flight of three aircraft. The algorithm is ready to use for the general public in the open-source Paparazzi autopilot.Comment: 6 pages, submitted to IROS 201

Development of a Long Endurance Mini-UAV: ETERNITY

This study presents the effort given for the first prototype of a Long Endurance Mini UAV concept called Eternity. A multi-disciplinary conceptual aircraft design program called CDSGN is developed and used for the design of the Eternity. Unlike the traditional design methods that uses statistical data from the previous well-flown aircrafts, CDSGN analyses numerous aircraft candidates and simulates each candidate for the given mission definition and outputs the corresponding performance. The unique property of the presented design methodology comes from a computationally fast and physically accurate modelling of the aerodynamic characteristics of each candidate by using a modified version of a vortex lattice program called AVL from Mark Drela. Two types of configurations have been analysed for the Eternity design, conventional and flying-wing. A wide envelope of variable design parameters used for both configurations such as wing surface area, cruise speed, battery capacity, different airfoils, etc... Integration of solar cells, and the management of solar energy is also considered for every candidate. Only the wing span size has been limited to one meter. Additionally, the on-board avionics and payload weights and sizes are fixed for every candidate as they are independent of the design. Analyses by CDSGN concluded the dominance of the conventional configuration for the given long endurance mission performance both on solar and nonsolar conditions. Optimum wing surface area and the on-board battery energy found interactively by a post-filtering program developed in-house. A custom airfoil family, transitioning along the span, have been designed specifically for the corresponding local Reynolds number for specific spanwise locations. A wind-tunnel campaign is performed with a full-scale model and first flight tests have been performed in order to show the feasibility of long endurance flights

Bioinspired Energy Harvesting from Atmospheric Phenomena for Small Unmanned Aerial Vehicles

This Paper discusses energy harvesting from atmospheric phenomena for small unmanned aerial vehicles, theoretically through simulations and practically through experimental flights. A comparison between different scenarios for flight within the sinusoidal wind profile is presented. A significant improvement in performance with active control of command surfaces has been found for an energy-harvesting mode when compared to autostabilization or fixed-stick flight. Moreover, a detailed decomposition of the stochastic wind profile generated from the Kaimal spectrum has shown which frequencies and magnitudes of wind time series have the highest contribution to the energy-transfer process. It is found that wind profiles with higher turbulence intensity potentially provide more energy for transfer to the aircraft. Furthermore, the Paper reveals a biologically inspired sensory system for wind field estimation. It describes the necessary equipment and control algorithms for the exploitation of atmospheric energy. Initial flight tests were performed to determine the average power consumption of the motor for altitude hold tasks and to evaluate the performance of sensors. Moreover, additional flights for autonomous exploitation of several atmospheric phenomena are presented and analyzed

Design of a high performance MAV for atmospheric research

International audienceThis article presents the design of a mini UAV dedicated to atmospheric research with tight operational constraints coming from the end-users, which are the meteorologists associated to the project. Several aspects are covered in addition to the conceptual design of the frame itself and its manufacturing process. This includes the innovative launching system based on water rocket, the design of a 5-hole probe for wind and turbulence measurements, the new version of the on-board autopilot and finally the evaluation of a long range communication system. Preliminary results are presented to conclude the paper

An analytical model for propeller aerodynamic efforts at high incidence

In the advent of electrical vertical take-off and landing aircraft development, a fast approach to predict variation of propeller axial and off-axis aerodynamic loads at large incidence angle has been desired. This paper presented an analytical approach obtained by a simplified blade element method considering local blade section conditions. The theory has been further validated against available experiments for propeller at high incidence conditions, and was found applicable to a wide range of geometries and operating conditions

Comparisons of Different Propeller Wake Models for a Propeller-Wing Combination

A detailed experimental study of propeller-wing interaction was presented. Five-hole probe was used to obtain velocity distribution at a survey plane behind trailing edge of a high-aspect-ratio wing with tractor propeller. Significant deformation of propeller slipstream was observed compared to a free propeller. The deformation was more prominent at low advance ratio, where transition flight of vertical take-off / landing aircraft were concerned. Comparison with two recent reduced-order slipstream models revealed large discrepancies between theoretical predictions and wake survey results. An analytical model of slipstream transverse deformation was proposed at the end that might be incorporated into improve such models

Analytic Model of Proprotor Forces and Moments at High Incidence

The paper presents an analytical model for estimation of proprotor aerodynamic loads at elevated incidence angles. Previous theories have concentrated on either small incidence angle for aircraft stability analysis, or edge-wise flow for helicopter forward flight. This development attempted an engineering method that covers full incidence angle range from $0$ to $\pi / 2$. Blade element theory was applied to known proprotor geometry, and off-axis loads including normal force and in-plane moment were obtained in closed form based on thrust and torque in axial condition. The model was found to be sufficiently accurate over a broader flight conditions compared to classical models, and computationally more efficient than numerical methods. Hence it could be easily used as a preliminary design and analysis tool for future convertible aircraft proprotors. The paper further discusses a dedicated wind tunnel campaign on proprotor off-axis load measurement. Experimental data from the test campaign was considered in model validation. The results suggested that the model was capable to accurately estimate proprotor performance in nominal flight regimes

Bioinspired wind field estimation—part 1: Angle of attack measurements through surface pressure distribution

One of the major challenges of Mini-Unmanned Aerial Vehicle flight is the unsteady interaction with turbulent environment while flying in lower levels of atmospheric boundary layer. Following inspiration from nature we expose a new system for angle of attack estimation based on pressure measurements on the wing. Such an equipment can be used for real-time estimation of the angle of attack during flight or even further building of wind velocity vector with additional equipment. Those information can find purpose in control and stabilization of the aircraft due to inequalities seen by the wing or even for various soaring strategies that rely on active control for energy extraction. In that purpose, flying wing aircraft has been used with totally four span-wise locations for local angle of attack estimation. In-flight angle of attack estimation from differential pressure measurements on the wing has been compared with magnetic sensor with wind vane. The results have shown that pressure ports give more reliable estimation of angle of attack when compared to values given by wind vane attached to a specially designed air-boom. Difference in local angle of attack at four spanwise locations has confirmed spatial variation of turbulence in low altitude flight. Moreover, theoretical law of energy dissipation for wind components described by Kaimal spectrum has shown acceptable match with estimated ones

Slipstream Deformation of a Propeller-Wing Combination Applied for Convertible UAVs in Hover Condition

Convertible unmanned aerial vehicle (UAV) promises a good balance between convenient autonomous launch/recovery and efficient long range cruise performance. Successful design of this new type of aircraft relies heavily on good understanding of powered lift generated through propeller-wing interactions, where the velocity distribution within propeller slipstream is critical to estimate aerodynamic forces during hover condition. Current study analysed a propeller-wing combination with a plain flap. A 5-hole probe measurement system was built to construct 3 dimensional velocity field at a survey plane after trailing edge. The study has found that significant deformation of propeller slipstream was present in the form of opposite transverse displacement on extrados and intrados. The deformation could be enhanced by flap deflections. Velocity differences caused by the slipstream deformation could imply local variation of lift distribution compared to predictions from conventional assumptions of cylindrical slipstream. The research underlined that the mutual aspect of propeller-wing interaction could be critical for low-speed aerodynamic design