The structure of atmospheric turbulence

Brief Reliable H∞ controller design for linear systems

Autonomous unmanned air vehicle ∞ight control systems require robust path generation to account for terrain obstructions, weather, and moving threats such as radar, jammers, and unfriendly aircraft. In this paper, we outline a feasible, hierarchal approach for real-time motion planning of small autonomous flxed-wing UAVs. The approach divides the trajectory generation into four tasks: waypoint path planning, dynamic trajectory smoothing, trajectory tracking, and low-level autopilot compensation. The waypoint path planner determines the vehicle’s route without regard for the dynamic constraints of the vehicle. This results in a signiflcant reduction in the path search space, enabling the generation of complicated paths that account for pop-up and dynamically moving threats. Kinematic constraints are satisfled using a trajectory smoother which has the same kinematic structure as the physical vehicle. The third step of the approach uses a novel tracking algorithm to generate a feasible state trajectory that can be followed by a standard autopilot. Monte-Carlo simulations were done to analyze the performance and feasibility of the approach and determine real-time computation requirements. A planar version of the algorithm has also been implemented and tested in a low-cost micro-controller. The paper describes a custom UAV built to test the algorithms.

/pdf/autonomous-vehicle-technologies-for-small-fixed-wing-uavs-1lr64kzlwl.pdf

Autonomous Vehicle Technologies for Small Fixed-Wing UAVs

SUMMARY Here we provide the first formal quantitative analysis of dynamic stability
in a flying animal By measuring the longitudinal static stability derivatives
and mass distribution of desert locusts Schistocerca gregaria , we
find that their static stability and static control responses are insufficient
to provide asymptotic longitudinal dynamic stability unless they are sensitive
to pitch attitude (measured with respect to an inertial or earth-fixed frame)
as well as aerodynamic incidence (measured relative to the direction of
flight) We find no evidence for a `constant-lift reaction9, previously
supposed to keep lift production constant over a range of body angles, and
show that such a reaction would be inconsequential because locusts can
potentially correct for pitch disturbances within a single wingbeat The
static stability derivatives identify three natural longitudinal modes of
motion: one stable subsidence mode, one unstable divergence mode, and one
stable oscillatory mode (which is present with or without pitch attitude
control) The latter is identified with the short period mode of aircraft, and
shown to consist of rapid pitch oscillations with negligible changes in
forward speed The frequency of the short period mode (approx 10 Hz) is only
half the wingbeat frequency (approx 22 Hz), so the mode would become coupled
with the flapping cycle without adequate damping Pitch rate damping is shown
to be highly effective for this purpose — especially at the small scales
associated with insect flight — and may be essential in stabilising
locust flight Although having a short period mode frequency close to the
wingbeat frequency risks coupling, it is essential for control inputs made at
the level of a single wingbeat to be effective This is identified as a
general constraint on flight control in flying animals

Dynamic flight stability in the desert locust Schistocerca gregaria.

This paper uses a team of unmanned air vehicles (UAVs) to cooperatively search, an area of interest that contains regions of opportunity and regions of potential hazard. The objective of the UAV team is to visit as many opportunities as possible, while avoiding as many hazards as possible. To enable cooperation, the UAVs are constrained to stay within communication range of one another. Collision avoidance is also required. Algorithms for team-optimal and individually-optimal/team-suboptimal solutions are developed and their computational complexity compared. Simulation results demonstrating the feasibility of the cooperative search algorithms are presented.

/pdf/multiple-uav-cooperative-search-under-collision-avoidance-1k25smcfqq.pdf

Multiple UAV cooperative search under collision avoidance and limited range communication constraints

1Introduction 2 Static Stability and Control 3 Aircraft Equations of Motion 4 Longitudinal Motion (Stick Fixed) 5 Lateral Motion (Stick Fixed) 6 Aircraft Response to Control on Atmospheric Inputs 7 Automatic Control Theory-The Classical Approach 8 Application of Classic Control Theory to Aircraft Autopilot Design 9 Modern Control Theory 10 Applications of Modern Control Theory to Aircraft Autopilot Design Appendixes A Atmospheric Tables B Geometric, Mass, and Aerodynamic Characteristics of Selected Airplanes C Mathematical Review of Laplace Transforms and Matrix Algebra D Review of Control System Analysis Techniques

Flight Stability and Automatic Control

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Flight Stability and Automatic Control