31 research outputs found
DelftaCopter Propulsion Optimization from Hover to Fast Forward Flight usingWindtunnel Measurements
No full textEnlarging the flight envelope of aircraft has been a goal since the beginning of aviation. But requirements to fly very fast and to hover are conflicting. During the design of the DelftaCopter, a tail-sitter hybrid UAV with a single large rotor for lift in hover and propulsion in forward flight, the design of the rotor needs to properly balance hovering requirements and fast forward flight requirements. The initial design with a one meter rotor placed too much emphasis on efficiency in hover, while most flights consist of very short periods of hover and very long phases of forward flight. Two new rotor designs and corresponding motors were tested an open jet wind tunnel. The propulsion system was tested from hover conditions to very fast forward flight in search of the most optimal operating point for each condition. The resulting system requires merely more power than the initial rotor in hover while it is capable of much faster forward speeds. The power requirements are shown to be compatible with modern power sources like Lithium-Ion batteries, which form the next step in improving the efficiency of hover-capable fast UAV.Control & Simulatio
Virtual testing of thermoplastic composites: Towards a hybrid simulation-physical testing pyramid
No full textThis paper summarizes the implementation of a Virtual Testing methodology in an industrial environment to predict the mechanical behaviour of composite material through the different scales of the conventional physical testing pyramid. A robust Virtual Test Lab allows for the generation of virtual allowables, while advanced interface models ensure accurate simulation of critical interfaces up to structural level. Hybrid simulation-physical testing approaches, that can support both conventional rapid sizing and high-fidelity analysis methods, have been applied during the development of a thermoplastic orthogrid fuselage shell and will be coupled with the manufacturing process though a virtual process chain for the development of a thermoplastic fuselage for the next generation aircraft.Aerospace Structures & Computational Mechanic
Carbon fiber-reinforced polymer pultrusions adhesively bonded inside aluminum joints: experimental and numerical study
No full textIn the context of lightweight structure design for the transportation and robotics industries, new types of composite structures are being developed, in the form of trusses made of fiber-reinforced polymer composite members of small diameter. The main objective of this work is to study adhesive joints, bonding pultruded composite tubes inside aluminum pieces, numerically and experimentally. More specifically, the objective is to determine which numerical model is able to predict the joint strength the most accurately, and to examine the influence of several design parameters on the strength and weight of the joints. With this purpose, samples are manufactured with varying dimensions, and tested in tension until failure. Next to the manufacturing numerical models using either a continuum mechanics or a damage mechanics (CZM) approach are built. The comparison of the numerical results with the experimental results show that the damage mechanics approach results in the most accurate joint strength predictions. It is also found that increasing the adhesive overlap length has the highest impact on increasing the joint strength, and that reducing the adherend thickness has the highest impact on reducing the structural weight, while preserving the joint strength.Structural Integrity & CompositesAerospace Structures & Material
Wing Sweeping Mechanism for Active Control and Stabilisation of a Flapping Wing MAV
No full textDuring flight, natural fliers flap, twist and bend their wings to enhance flight performance. Lift and thrust benefit from flexibility as well as from both passive and active wing deformation. At the same time, the active deformations are used for flight control. In this study, we investigate strategies of control moments generation in a bio-inspired flapping-wing micro air vehicle (FWMAV). In particular, we propose a method for active control and attitude stabilization by introducing a wing deformation through adjustable wing sweep. The control method is demonstrated on a tailless FWMAV with independent wing sweep modulation on each of its four wings. The actuation mechanism consists of an arm joint at the leading edge, about which the wings are swept. Forces from the servo actuation are transferred to the leading edge of the robot through strings. The actuated strings alter the wing sweep, which affects the roll and pitch movement via different combinations of string pulls. The effectiveness of the designed mechanism is being evaluated on the basis of tethered force balance tests and free flight tests. An advantage of the proposed mechanism is its lightweight design, which is crucial for small FWMAVs with stringent weight restrictions.Control & Simulatio
Modeling DelftaCopter from Flight Test Data
No full textThe DelftaCopter, a tilt-body tailsitter UAV, endures large gyroscopic moments due to the single helicopter rotor providing its thrust. In previous research by de Wagter et al.[1] the DelftaCopter’s attitude dynamics were modeled using a rigid rotor, as is customary for small helicopter modeling. A controller based on this model was unable to compensate coupling between pitch and roll rate caused by gyroscopic moments. In this paper, two models are compared for reproducing the attitude dynamics of the Delfta- Copter in hover. The Cylinder Dynamics (CD) model, used in the previous research, assumes a rigid rotor. The Tip-Path Plane (TPP) model incorporates flapping motion of the blades and was developed by Mettler[2]. The two models are compared by fitting each model’s parameters on flight data using chirps, sine waves with increasing frequency, as system identification maneuvers. The TPP model is shown to be much more accurate in reproducing the high-frequency attitude dynamics. An LQR controller directly based on the TPP model is shown to yield adequate tracking performance. This validates the applicability of this model to the DelftaCopter. For forward flight, an extension to the TPP hover model is proposed incorporating the aerodynamics of the wings and elevons. It is shown that with the extension, chirps in forward flight can be simulated with reasonable accuracy. This paves the way for a model-based controller in this flight state.Control & Simulatio
Cubegrades: Generalizing Association Rules
No full textCubegrades are a generalization of association rules which represent how a set of measures (aggregates) is affected by modifying a cube through specialization (roll down), generalization (rollup) and mutation (which is a change in one of the cube’s dimensions). Cubegrades are significantly more expressive than association rules in capturing trends and patterns in data because they use arbitrary aggregate measures, not just COUNT, as association rules do. Cubegrades are atoms which can support sophisticated “what if” analysis tasks dealing with the behavior of arbitrary aggregates over different database segments. As such, cubegrades can be useful in marketing, sales analysis, and other typical data mining applications in business. We formally define cubegrades, show methods to generate them by using efficient pruning algorithms and finally define two query languages to generate and retrieve sets of cubegrades which satisfy user-defined conditions. We also demonstrate how to evaluate simple cubegrade queries and conclude with a number of open questions and possible extensions of the work.Technical report DCS-TR-39
Optimal cure cycles for manufacturing of thick composite parts using multi-objective genetic algorithms
No full textThe paper addresses the multi-objective optimization of the cure process of a Vacuum Assisted Resin Transfer Molding for components ranging from 40 to 100 mm thickness and aims to investigate the effect of thickness on the identification and quantification of a set of optimal cure profiles that minimize temperature overshoot and process time. Optimal cure solutions are sought among three dwells temperature profiles and are compared to the manufacturer’s recommended cure cycle (MRCC). The methodology successfully approximates the efficient fronts for the three different cases under study (40, 70 and 100mm) and points out the efficiency opportunity available compared to MRCC. In the case of 70 and 100 mm thick component temperature overshoot reductions of about 75% are achievable and 67% reduction in process time. The results also suggest a change in the objectives’ landscape for the higher thicknesses in the vertical region of the Pareto.Aerospace Manufacturing TechnologiesStructural Integrity & Composite
Autonomous landing algorithm using a sun position predicting model for extended use of solar powered UAVs
No full textIn the field of robotics, a major challenge is extending the flight range of micro aerial vehicles. One way to extend the range is by charging batteries with solar arrays on the ground, while resting on intermediate landing positions. The solution we propose in this study differentiates itself from other solutions as it does not focus on improving UAV efficiency but rather on finding the most efficient landing position. In particular, an algorithm is developed to show the usefulness of the approach. This algorithm makes uses of the sonar sensor on board of the Parrot Bebop 1 drone in combination with an OptiTrack system to scan the environment for potential landing opportunities. After these measurements are discretized on a 2D grid, analysis is carried out with a sun position predicting model. Finally, a landing position is chosen within the scanned area and the drone will land accordingly. Little is known on whether a solar powered charge on the ground could be effective in a limited period of time. We present a coarse analysis, showing that the DelftaCopter with solar arrays on its wings charges its batteries in 1.3 days with relatively cheap solar cells in Africa or Australia. Future work includes the use of computer vision instead of sonar as well as the ensurance of a safe landing position using vision.Control & Simulatio
Optical-flow-based Stabilization of Micro Air Vehicles Without Scaling Sensors
No full textThis article presents an adaptive control strategy to stabilize a micro quadrotor in all three axes using only an Inertial Measurement Unit (IMU) for the attitude control and a monocular camera for canceling position drift. The proposed control scheme automatically determines the appropriate optical flow control gains. This is achieved by extending the stability-based approach to distance estimation developed in [1] to allow for the control of all three axes of a quadrotor. An analysis is done in simulation to present a proof of concept of the stabilization method and to determine the effects of scaling. Furthermore we verify the effects of varying effective camera frame rates and investigate how this control approach generalizes to smaller drone sizes. Actual flight tests are then performed on a Parrot ARDrone 2.0 and on a Parrot Bebop to show that both quadrotors achieve stable hover without position drift using only their IMU and bottom camera.Wind EnergyControl & SimulationLearning & Autonomous Contro
Skin-to-skin contact definitions in included studies where defined (alphabetical) by author/s name.
No full textSkin-to-skin contact definitions in included studies where defined (alphabetical) by author/s name.</p
