• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 5
  • 3
  • Tagged with
  • 83
  • 40
  • 35
  • 35
  • 28
  • 28
  • 9
  • 8
  • 8
  • 8
  • 8
  • 7
  • 5
  • 5
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

An airborne windshear detection system for general aviation aircraft

Dyne, Helen Katherine January 1995 (has links)
No description available.
42

Reconfigurable flight control systems for a generic fighter aircraft

Aslam-Mir, Shahzad January 1992 (has links)
No description available.
43

Fast-sampling direct flight-mode control systems

Garis, A. January 1981 (has links)
No description available.
44

Multivariable flight control systems for agile combat aircraft

Elramlawy, Abdelbaset Abdelgaied January 1992 (has links)
No description available.
45

Individual channel analysis and design and its application to helicopter flight control

Dudgeon, Graham John William January 1996 (has links)
No description available.
46

Active control of turbulence-induced helicopter vibration

Anderson, David January 1999 (has links)
Helicopter vibration signatures induced by severe atmospheric turbulence have been shown to differ considerably from nominal, still air vibration. The perturbations of the transmission frequency have significant implications for the design of passive and active vibration alleviation devices, which are generally tuned to the nominal vibration frequency. This thesis investigates the existence of the phenomena in several realistic atmospheric turbulence environments, generated using Computational Fluid Dynamic (CFD) engineering software and assimilated within a high-fidelity rotorcraft simulation, RASCAL. The RASCAL simulation is modified to calculate blade element sampling of the gust, enabling thorough, high frequency analyses of the rotor response. In a final modification, a numerical, integration-based inverse simulation algorithm, GENISA is incorporated and the augmented simulation is henceforth referred to as HISAT. Several implementation issues arise from the symbiosis, principally because of the modelling of variable rotorspeed and lead-lag motion. However, a novel technique for increasing the numerical stability margins is proposed and tested successfully. Two active vibration control schemes, higher harmonic control 'HHC' and individual blade control 'IBC', are then evaluated against a 'worst-case' sharp-edged gust field. The higher harmonic controller demonstrates a worrying lack of robustness, and actually begins to contribute to the vibration levels. Several intuitive modifications to the algorithm are proposed but only disturbance estimation is successful. A new simulation model of coupled blade motion is derived and implemented using MATLAB and is used to design a simple IBC compensator. Following bandwidth problems, a redesign is proposed using H theory which improves the controller performance. Disturbance prediction/estimation is attempted using artificial neural networks to limited success. Overall, the aims and objectives of the research are met.
47

Helicopter inverse simulation for workload and handling qualities estimation

Leacock, Garry R. January 2000 (has links)
Helicopter handling qualities are investigated using inverse simulation as the method of providing state and control information for the appropriate quantitative metrics. The main aim of the work was to develop a more comprehensive and versatile method of quantifying handling qualities levels using the available inverse algorithm "Helin v". Subsequently, the assessment of the helicopter model inherent in Helinv, "Helicopter Generic Simulation", (HGS) for its suitability to handling qualities studies was paramount. Since the Helinv inverse algorithm operates by initially defining a mathematical flight test manoeuvre for the vehicle to "fly", considerable time was given to modelling suitable handling qualities assessment manoeuvres. So-called "attitude quickness" values were then calculated thus providing an initial objective insight into handling qualities level of the vehicle under test. Validation of the tasks formed an integral part of successfully fulfilling the flight test manoeuvre development objective. The influence of the human is captured by the inclusion of a pilot model and the development of a novel method of parameter estimation, supplements the overall objective of modifying Helinv results to achieve potentially more realistic responses and thus correspondingly more realistic handling qualities. A comparative study of two helicopters, one based on the Westland Lynx battlefield/utility type and the other, a hypothetically superior configuration effectively demonstrates the capability of inverse simulation to deliver results adequate for initial handling qualities studies. Several examples are used to illustrate the point. Helinv has been shown to be versatile and efficient and can be used in initial handling qualities studies. The advantages of such a technique are clear when it is seen that actual flight testing, ground based or airborne is extremely costly, as the flight test manoeuvres must be representative of real life, reproducible and of course, as risk free as possible. Many inverse simulation runs and handling qualities calculations have been carried out for different helicopter configurations and manoeuvres thus illustrating the advantages of the technique and fulfilling all the aims mentioned above.
48

Cooling of advanced aircraft actuation systems

Gilson, Gareth M. January 2012 (has links)
Electrical machines for aerospace applications often operate close to the allowable thermal limits due to high power density requirements. The power density of electrical machines is generally dependent on the machine and thermal management design. At flight level, a reduced pressure exists which in turn results in more challenging thermal management. Aerospace electric machine manufacturers are often limited with respect to the implemented cooling mechanisms. That is, natural convection systems are the norm, as fan cooled and fluid cooled machines may suffer from reliability issues. The original contribution of this work, is the design, testing, and implementation of an alternative forced cooling convective system (FCCS) based on piezoelectric fans. This thesis commences by an investigation of the capabilities of MotorCAD (a sophisticated analytical lumped thermal package) and how it can be utilised in a fully integrated way to optimise (for a maximum power density and an overall minimum motor mass) both the electromagnetic and thermal aspects of a typical traditional horizontally-mounted permanent magnet synchronous machine (PMSM) operating at flight level. The resultant analytical temperature values were then compared to actual experimental temperature data. Piezoelectric fans are then investigated as a potential, fault tolerant FCCS that may enhance the overall cooling of a motor. These fans could be implemented in the aerospace industry as they do not suffer from the same reliability issues as traditional FFCS’s. Detailed thermal results indicating the effective piezoelectric fan cooling range together with the overall cooling effectiveness over a traditional vertical straight-finned heat sink (unit – cell) , operating under different operating conditions are also presented. Furthermore, the fin/fan geometry that minimises the thermal resistance whilst minimising the overall cooling mass is presented. Particle Image Velocimetry (PIV) techniques were implemented to further understand the flow fields generated by an oscillating piezoelectric fan. Common parameters governing the fluid flow (vibration amplitude, separation distance, fin spacing and fan orientation) were investigated and the results are herewith presented. Designs of a supporting structure for the proposed FCCS implementation are drawn up and analysed through FEA. A prototype structure was built and its durability tested. Furthermore, the reliability (fault tolerance) of the suggested FCCS was evaluated. The feasibility of implementing this innovative cooling technique was further investigated by performing a study on the weight saving potential of the FCCS over traditional natural convective fins, and the FCCS geometry that minimises the thermal resistance whilst minimising the overall mass is selected. Furthermore, a prototype FCCS was built and tested.
49

H∞-design and the improvement of helicopter handling qualities

Yue, Andrew January 1988 (has links)
This thesis presents the results of a study into the use of H<sup>ꝏ</sup>-optimization for the design of feedback control laws for improving the handling qualities of a Lynx helicopter. An important improvement to the H<sup>ꝏ</sup>-optimization procedure is the reduction in the number of iterative steps in the γ-iteration before convergence to the optimal γ. Some new algorithms are derived which significantly reduce the computation time for the γ-iteration. Both 2-block and 4-block cases are considered. Control laws are designed for precise control of pitch and roll attitude, yaw rate and heave velocity. Analysis of the raw helicopter showed the need for a stability augmentation system as the dynamic characteristics of the unaugmented helicopter do not comply with military helicopter handling qualities requirements. Results from current research on helicopter handling qualities were used as guidelines in order to define the required dynamic characteristics. A six-degree of freedom nonlinear simulation was used to analyse the helicopter dynamic time histories. A possible solution to the problem of incorporating helicopter handling qualities in the design of robust controllers is to use a two-degree of freedom controller structure. This is illustrated using both H<sub>2</sub> and H<sup>ꝏ</sup>-optimization. A piloted simulation study to assess the effectiveness of advanced control laws was initiated at RAE, Bedford. The trials were carried out in the single seat cockpit flight simulator, at the Flight Research Division and represent the first ever real-time piloted simulation using a H<sup>ꝏ</sup>-controller.
50

The design of a fuzzy logic system for control of an unmanned aircraft

Assuncao, Jose Manuel Ventura January 1996 (has links)
Many control problems are based on control objectives easily quantified and consequently realisable by standard control synthesis methods. When an unmanned aircraft navigates, it moves inside a complex environment due to interactions with its surrounding and time varying environmental conditions. Several causes of perturbations have been identified as for example gusts and corrupted information of position. The characteristics of possible missions carried out by the un manned aircraft leads to the desire to construct navigation control systems which when operated in perturbed environments combine the advantages of smooth control with accurate navigation. Rule based, and adaptive controllers have favourable properties for such systems. This thesis investigates the use of a rule based navigation controller for a particular unmanned aircraft, the XRAEl aircraft. To achieve this objective several different types of fuzzy logic controllers are analysed as for example conventional and direct and indirect adaptive fuzzy controllers. They are designed by employing simple control engineering knowledge and subsequently validated using a stability method. For this purpose diverse stability methods are described and a new technique presented, the fuzzy root locus method, which is also based on the introduction of a new concept for fuzzy logic controllers, the fuzzy cell. The realisation of this work has been achieved by a series of simulation tests employing different processes and a simulation model of the XRAEl aircraft. The conclusions drawn from the results of the experiments consider in general that a rule based controller can improve the quality of navigation when compared to conventional controllers.

Page generated in 0.0496 seconds