Nomenclature Ar = rotor disk area CD = sectional drag coefficient CD0 = zero-lift drag coefficient Clα = lift-curve slope CP = power coefficient CPi = induced power coefficient CP0 = profile power coefficient CT = thrust coefficient c = chord length D = drag force D.L . = disk loading L = lift force m = mass P.L . = power loading SF = separated flow T = rotor thrust V = local wind velocity perceived by flap W = weight W f = final weight Wo = gross takeoff weight α = blade section angle of attack η = efficiency μ = dynamic viscosity ρ = air density σ = rotor solidity = flapping amplitude (peak to peak)

Challenges Facing Future Micro-Air-Vehicle Development

This thesis is about modelling, design and control of Miniature Flying Robots (MFR) with a focus on Vertical Take-Off and Landing (VTOL) systems and specifically, micro quadrotors. It introduces a mathematical model for simulation and control of such systems. It then describes a design methodology for a miniature rotorcraft. The methodology is subsequently applied to design an autonomous quadrotor named OS4. Based on the mathematical model, linear and nonlinear control techniques are used to design and simulate various controllers along this work. The dynamic model and the simulator evolved from a simple set of equations, valid only for hovering, to a complex mathematical model with more realistic aerodynamic coefficients and sensor and actuator models. Two platforms were developed during this thesis. The first one is a quadrotorlike test-bench with off-board data processing and power supply. It was used to safely and easily test control strategies. The second one, OS4, is a highly integrated quadrotor with on-board data processing and power supply. It has all the necessary sensors for autonomous operation. Five different controllers were developed. The first one, based on Lyapunov theory, was applied for attitude control. The second and the third controllers are based on PID and LQ techniques. These were compared for attitude control. The fourth and the fifth approaches use backstepping and sliding-mode concepts. They are applied to control attitude. Finally, backstepping is augmented with integral action and proposed as a single tool to design attitude, altitude and position controllers. This approach is validated through various flight experiments conducted on the OS4.

design and control of quadrotors with application to autonomous flying

H YPERSONIC flight began in February 1949 when a WAC Corporal rocket was ignited from a U.S.-captured V-2 rocket [1]. In the six decades since this milestone, there have been significant investments in the development of hypersonic vehicle technologies. The NASA X-15 rocket plane in the early 1960s represents early research toward this goal [2,3]. After a lull in activity, the modern era of hypersonic research started in the mid-1980s with the National Aerospace Plane (NASP) program [4], aimed at developing a single-stage-to-orbit reusable launch vehicle (RLV) that used conventional runways. However, it was canceled due mainly to design requirements that exceeded the state of the art [1,5]. A more recent RLV project, the VentureStar program, failed during structural tests, again for lack of the required technology [5]. Despite these unsuccessful programs, the continued need for a low-cost RLV, as well as the desire of the U.S. Air Force (USAF) for unmanned hypersonic vehicles, has reinvigorated hypersonic flight research. An emergence of recent and current research programs [6] demonstrate this renewed interest. Consider, for example, the NASA Hyper-X experimental vehicle program [7], the University of Queensland HyShot program [8], the NASA Fundamental Aeronautics Hypersonics Project [9], the joint U.S. Defense Advanced Research Projects Administration (DARPA)/USAF Force Application andLaunch fromContinentalUnited States (FALCON) program [10], the X-51 Single Engine Demonstrator [11,12], the joint USAF Research Laboratory (AFRL)/Australian Defence Science and Technology Organisation Hypersonic International Flight Research Experimentation project [13], and ongoing basic hypersonic research at the AFRL (e.g., [14–20]). The conditions encountered in hypersonic flows, combined with the need to design hypersonic vehicles, have motivated research in the areas of hypersonic aeroelasticity and aerothermoelasticity. It is evident from Fig. 1 that hypersonic vehicle configurations will consist of long, slender lifting body designs. In general, the body, surface panels, and aerodynamic control surfaces are flexible due to minimum-weight restrictions. Furthermore, as shown in Fig. 2, these

/pdf/aeroelastic-and-aerothermoelastic-analysis-in-hypersonic-4ycxg0c3dg.pdf

Aeroelastic and Aerothermoelastic Analysis in Hypersonic Flow: Past, Present, and Future

An overview of monolithic titanium aluminides based on Ti3Al and TiAl

Flapping wings often feature a leading-edge vortex (LEV) that is thought to enhance the lift generated by the wing. Here the lift on a wing featuring a leading-edge vortex is considered by performing experiments on a translating flat-plate aerofoil that is accelerated from rest in a water towing tank at a fixed angle of attack of 15°. The unsteady flow is investigated with dye flow visualization, particle image velocimetry (PIV) and force measurements. Leading- and trailing-edge vortex circulation and position are calculated directly from the velocity vectors obtained using PIV. In order to determine the most appropriate value of bound circulation, a two-dimensional potential flow model is employed and flow fields are calculated for a range of values of bound circulation. In this way, the value of bound circulation is selected to give the best fit between the experimental velocity field and the potential flow field. Early in the trajectory, the value of bound circulation calculated using this potential flow method is in accordance with Kelvin’s circulation theorem, but differs from the values predicted by Wagner’s growth of bound circulation and the Kutta condition. Later the Kutta condition is established but the bound circulation remains small; most of the circulation is contained instead in the LEVs. The growth of wake circulation can be approximated by Wagner’s circulation curve. Superimposing the non-circulatory lift, approximated from the potential flow model, and Wagner’s lift curve gives a first-order approximation of the measured lift. Lift is generated by inertial effects and the slow buildup of circulation, which is contained in shed vortices rather than bound circulation.

Lift and the leading-edge vortex

An initial design concept for a micro-coaxial rotorcraft using custom manufacturing techniques and commercial off-the-shelf components is discussed in this paper. Issues associated with the feasibility of achieving hover and fully functional flight control at small scale for a coaxial rotor configuration are addressed. Results from this initial feasibility study suggest that it is possible to develop a small scale coaxial micro rotorcraft weighing approximately 100 grams, and that available moments are appropriate for roll, yaw and lateral control. A prototype vehicle was built and its rotors were tested in a custom hover stand used to measure Thrust and power. The radio controlled vehicle was flown untethered with its own power source and exhibited good flight stability and control dynamics. The best achievable rotor performance was measured to be 42%.

Design, Analysis and Hover Performance of a Rotary Wing Micro Air Vehicle

This paper develops the analytical framework to compare the approximate performance of periodic hypersonic cruise trajectories with previously proposed hypersonic trajectory profiles for global reach. Specifically, range, ΔV, and payload-carrying capacity are evaluated for various trajectory types to illustrate the enhanced performance achieved by flying periodic hypersonic cruise trajectories with existing hypersonic vehicle aerodynamic, propulsion, and structures technology. Analytical results reveal that periodic hypersonic cruise trajectories achieve better fuel-consumption savings and deliver more payload over long distances (≅20,000 km) than other trajectory types proposed for high-speed flight. Over 20% improvement in fuel consumption savings is possible for a Mach 10 vehicle with a modest L/D of 4, and a curve-fitted rocket-based combined cycle engine model.

Approximate performance of periodic hypersonic cruise trajectories for global reach

Recently, a class of adaptive control schemes called L1 Adaptive Control (L1-AC) has been proposed and widely advertised in aerospace control for achieving fast and robust adaptation and better performance than the existing Model Reference Adaptive Control (MRAC) Schemes. The L1-AC scheme is designed mainly for plants with full state measurement even though the name L1-AC has been used as an umbrella name for more general classes of plants. In this paper, we show that the L1-AC for plants with measured states is simply a standard MRAC with a low pass filter inserted in front of the control input. The analysis of the scheme is almost identical to that of MRAC as the same Lyapunov function is used to establish stability. The motivation for using the filter is the fact that for this class of adaptive schemes i.e. MRAC for plants with full state measurement the tracking error can be made arbitrarily small during transient by increasing the adaptive gain. A high adaptive gain however makes the differential equation of the adaptive law or estimator very stiff and leads to numerical problems that cause high oscillations in the estimated parameters leading to loss of adaptivity and deviations from what the theoretical properties dictate. The L1-AC approach mistook these numerical oscillations as properties of the adaptive scheme and inserted an input low pass filter in order to filter them out. While the filter helps reduce the frequency of these oscillations in the control law the price paid is high. First the numerical instability does not go away and the estimated parameters continue to oscillate without converging to the true parameters even in the presence of sufficiently rich signals. Second, due to the filter the tracking error is no longer guaranteed to converge to zero and the transient bounds for the tracking error also depend on the filter. As a result, the tracking properties of the L1-AC scheme are worse than what a simple MRAC scheme can generate with adaptive gains that could be high but away from the region of numerical instability. In addition, the presence of the filter reduces the robust stability margins in the presence of unmodeled dynamics and provides literally no advantage as simple robust MRAC techniques can solve the same problem achieving much better properties. The authors of L1-AC often compare the properties of a numerically unstable MRAC due to extremely high adaptive gains something that is prohibited by robust adaptive control with those of the filtered MRAC aka L1-AC to show that L1-AC performs better. Such comparisons are not only misleading but do not reveal what causes what giving the reader a false impression of a new theory that results to new performance and robustness improvements. The use of filters in adaptive control is not new and they are used to improve the performance and robustness of certain adaptive control schemes without destroying their ideal tracking properties. In this paper we present such a scheme that guarantees good transient performance and robustness and reveals the trade off between transient performance and robust stability.

What is L1 Adaptive Control

A spacecraft attitude controller balances external torques, including those resulting from gravity gradient and those resulting from other orbital disturbances, to achieve a comparatively stable, neutral attitude or orientation. Torque is balanced by selecting spacecraft attitude Euler angles and angular rates such that orbital disturbances and cross-coupling inertial effects are cancelled by the external forces, based on Euler's equation. A spacecraft attitude torque-balancing controller and related method compares spacecraft attitude angles and angular rates with an orbit reference frame, and provides instructions to conventional momentum management and propulsion controls to responsively adjust the spacecraft attitude and angular rates. This feedback loop drives to zero (or an acceptably small quantity) the rate of change of the difference between spacecraft and reference attitude and angular rates, thus minimizing the net accelerations on the vehicle. A further method is provided to determine a desired physical structure and mass distribution of the spacecraft, needed to achieve torque balancing in a spacecraft attitude such that appliances, such as antennas, solar panels, and instruments, will have the required orientation once in their final on-orbit deployed position.

System and methods for space vehicle torque balancing

An initial study of damped periodic flight trajectories that achieve optimal fuel savings for hypersonic flight is investigated. The aerodynamic characteristics of hypersonic lifting bodies including scramjet propulsion are used to achieve enhanced fuel savings compared with steady-state cruise. A parameterized form of the damped periodic altitude profile is assumed along with the constraint that the ratio of kinetic to potential energy remain the same at the endpoints of a period. Previous studies of periodic cruise neglected to impose this constraint, nor was a damped parameterized form of the altitude profile assumed. This resulted in suboptimal solutions of the two-point boundary-value problem for periodic hypersonic flight. This new parameterization along with the energy ratio constraint results in fuel savings of approximately 45 % over the initial period for a modified model of the HL-20 spaceplane vehicle.

Lael Rudd

Papers

Design, Analysis and Hover Performance of a Rotary Wing Micro Air Vehicle

Approximate performance of periodic hypersonic cruise trajectories for global reach

What is L1 Adaptive Control

System and methods for space vehicle torque balancing

Suboptimal Damped Periodic Cruise Trajectories for Hypersonic Flight