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No description available.

The project sponsors design and manufacture skewed roller brake devices for use in aircraft flight control actuation systems. Design tools have previously been developed to predict the torque characteristics ofthese devices. A fundamental deficiency ofthese tools is the use ofempirical friction coefficient data gathered from a limited test sample. A need was identified to develop a friction coefficient model based on the operational parameters ofthe design, namely load, speed and lubricant viscosity. The development and validation ofthis model formed the basis ofthe technical research objective. A cost benefit analysis indicated that the sponsors could reasonably expect to gain a significant technical competitive advantage over their competitors ifthe technical research objective could be achieved. This advantage should provide opportunities for premium pricing ofthe product and enhanced opportunities to enter new markets. Additionally, the sponsors could expect lead time reductions and cost savings of £69000 from the removal ofthe need to conduct prototype tests to assess the effective friction coefficient. A friction coefficient model and skewed roller torque equation design tool have been successfully developed, satisfying the technical research objective. The friction coefficient model is defined in terms of lubrication number. The lubrication number parameter incorporates lubricant viscosity, roller speed, roller load and contact surface roughness terms, fully describing the operational parameters ofa design. Experimental evidence has validated the model using two lubricants, a hydraulic fluid, Brayco 795 and a mineral oil, Catenex 79. The tests cover a lubrication number range from 2 x 10-5 to 6 X 10-2 with a mean Hertzian stress from 0.27 to 0.61 Gpa. The success ofthis project has ensured that the sponsors will reap the cost and design lead time savings predicted in the cost benefit analysis and have the tools necessary to develop new markets and premium pricing business opportunities.

Fast jet aircraft go through continuous upgrades throughout their life cycle to keep them operationally relevant until the next replacement fast jet is available. Such lifecycles can stretch over timescales of a few decades for the same fast jet aircraft (e.g. the Panavia Tornado iterations). Overall, these upgrades for typical legacy fast jet aircraft are likely to be “electronic” in nature where specific upgrades examples include additional or replacement (more powerful) sensors, mission computing, electronic warfare, communication and pilot interface equipment to increase mission effectiveness. Apart from some self-powering pod based equipment, the end result of through life upgrades is a continuously increasing power demand. This becomes problematic when the increase is against an unchanged main electrical system within a spatially unchanging compact and limited weight allowance environment within the airframe. Under normal conditions, the generic fast jet system is powered by a centralised source of power generation: being the engine mechanical off-take driven generator/s. The generator and off-take are installed at the manufacturing stage of the aircraft and at the start of the fast jet service life where the capacity of the generator is greater than the initial loading. However with the through life upgrades, past trends have shown that such built in growth is not enough. Hence to cope with such power increases one can change the main generators during the operational life of the fast jet. However, this requires cumbersome and expensive rework of the associated mechanical off take and the more powerful replacement generator will still need to fit into the same space as the original generator with the same space constraints. Hence the replacement generator needs to be more power dense. Load shedding can also be considered but due to the lack of hotel or non-critical loads on a fast jet aircraft minimises the scope to load shed (when compared to civil aircraft such as in-flight entertainment). As such, the aim of the thesis seeks to explore the novel and alternative move towards a decentralised electrical system whereby supplementary generation sources are inserted around the aircraft. In essence, this is additional generation sources distributed around the aircraft to conform to remaining space for the compact airframe i.e. “filling the gaps”. The reasoning of this work is that such distributed generation can work in parallel to the existing main generation leaving it intact with limited rework. The upgrades themselves can be added in conjunction with the equipment upgrades to minimise the downtime of the aircraft. Such an approach has not been widely seen on contemporary fast jet to date which the novelty of such is presented in this thesis. Such distributed integration of supplementary generation also requires loose coupling for retrofit/modification purposes. Hence the thesis looks at the novel application of paralleling techniques taken from other domains with similar paralleling needs: such as Electric Vehicles (EVs), microgrids, distributed generation and renewables research for the fast jet domain. In line with this, the thesis firstly reviews different types of sources that are potentially suitable for such application and provides “weight” to the argument of having distributed generation for fast jet. From the literature review of the paralleling techniques from other domains, the thesis then presents the down selected and novel adaption of three possible integration methods to integrate supplementary power generation into the fast jet network in a distributed manner. These include 1. Using passive links of existing rectifiers around the fast jet electrical system as distributed DC integration points. 2. Use of Shunt Active Filtering to inject power into the fast jet system in parallel to the main generation (additional to the base power quality improvement functionality). This is achieved by placing additional sources onto the DC link of the Shunt Active Filter. 3. Converting passive rectifiers around the fast jet electrical system into active rectifiers/inverters to feed power back into the system. Underpinning these techniques is the proposed use of a common voltage master current slave scheme at the separate DC links which is used to control power flow into the fast jet electrical system. Illustration of the operation and benefits of these are presented against generic fast jet electrical system simulations. In summary the novelty of the work comes from firstly, the proposal to move towards a more decentralised system for coping with the unique upgrade problem on fast jet where there is limited space to accommodate additional bulk generation upgrades. Addition to this, additional novelty of the work comes from the exploration of the three integration methods stated above which represents a “first pass” attempt to increase the penetration of such distributed generation.

No description available.

No description available.

This thesis is concerned with the electrical, thermal and mechanical modelling of electrical machines for the 'more-electric' aircraft. Two specific applications are considered viz. a permanent magnet brush less DC (BLDC) machine for an electrohydraulic actuator for a primary flight control surface, and a switched reluctance (SR) starter/generator for the HP spool of a large civil aero-engine. As a consequence of the highly variable and often hostile ambient environment and constrained available space envelope, these electrical machines can rarely be designed in isolation, with thermal and mechanical constraints often having a significant influence on the design. In view of these considerations, a transient lumped parameter thermal model has been developed for the BLDC machine, and validated by experimental measurements on a prototype machine at various stages of manufacture. Since the rotor cavity of the BLDC machine is flooded with hydraulic fluid leaking from the pump, fluid friction losses have been modelled, and validated by tests on a prototype machine. Optimisation of the BLDC machine airgap has also been investigated using analytical electromagneticlfluiddynamic modelling. Detailed investigation of the mechanical stresses in the rotor of the HP spool machine have led to the development of a novel rotor structure for SR machines which is shown to have comparable electromagnetic performance with a conventional SR machine. A specific design of SR machine is analysed in detail in terms of dynamic current waveforms and the subsequent iron losses, and its thermal performance is modelled in a representative aero-engine environment.

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The interaction between an aircraft's structural dynamics, unsteady aerodynamics and flight control system is known as aeroservoelasticity. The problem can occur because the control system sensors are of sufficient bandwidth to sense the structural vibrations as well as the rigid-body motion of the aircraft. This sensed structural vibration can result in further excitation of the structure through both aerodynamic and inertial excitation, leading to a potential closed-loop instability. At present, such an unstable interaction is prevented by the inclusion of notch filters within the feedback path which have a detrimental effect on the aircraft's rigid-body performance. The current clearance procedure is restricted by a poor understanding of the array of complex issues involved. The aim of the project was to develop a clearer understanding of the interactions between system components leading to a reduction in the clearance requirements. Work has concentrated on the effects of system nonlinearities and on the digital nature of modem control systems. A major source of nonlinearities within the control system are the servo-hydraulic actuators. Through detailed actuator modelling confirmed by rig testing of actual hardware, these nonlinearities are analysed and a method for predicting the response of the actuators in the presence of two input signals proposed. As a result, it is demonstrated that an unstable structural oscillation would cause a limit-cycle oscillation as opposed to an unbounded response. Through nonlinear system theory the criteria for the existence of such limit-cycles are obtained, enabling them to be predicted and therefore prevented. Consideration of the true nonlinear nature of the aeroservoelastic system has enabled an alternative design and clearance procedure to be proposed which reduces the attenuation requirements of the structural-mode filters whilst ensuring satisfactory aircraft performance even in the presence of modelling errors. This design procedure is demonstrated on both a model of the aircraft system and a simple test system enabling verification of the nonlinear analysis and comparison between the current and proposed alternative procedures. As a result, it is demonstrated that consideration of the true nonlinear nature of the aeroservoelastic interaction has the potential for allowing a significant reduction in structural filter attenuation requirements. Consequently, a reduction in the phase lag due to the filters is possible resulting in an improvement in closed-loop system performance whilst ensuring the safe operation of the aircraft.

Turbo-prop trainer aircraft are designed to offer a cost effective alternative to military jet training aircraft. As a design objective of such aircraft, the Military Specifications of handling qualities applicable to jet trainer aircraft should be satisfied. However, in line with the philosophy of low purchase and maintenance costs, the added complexity of a hydraulic power boost system for the control surfaces cannot be accepted. The objective of this work was to optimise the roll control system so as to achieve an optimum of ergonomic design combined with the performance goals of the military specifications, using purely aerodynamic means of balance. Relevant British and American civilian and military specifications and simulator studies have been reviewed to select the detailed design objectives of the study. The American Mil. Specs. were selected as a baseline, with modifications derived from the results of simulator experiments. A Baseline Aircraft was selected on which to apply the optimisation. The highest performance turbo-prop trainer of the time was selected. A mathematical model of the roll response was derived for the extrapolation of flight test data and to allow an evaluation and optimisation of the critical aileron parameters. A description of the model and comparison to flight test results is given in the text. Literature was searched to examine the availability of information for the aerodynamicist to conduct such an optimisation. The results were disappointing, showing that very little work had been conducted on aileron design since the late 1940's and that the work of that time was not entirely relevant to today's requirements. Because the literature search was not conclusive, further flight tests had to be conducted on the Baseline Aircraft to investigate different forms of aerodynamic balance. The performance of the ailerons and some of the problems encountered in their usage are reported in this thesis and forms a data bank from which to conduct the optimisation. Finally, a selection process is conducted to size the aileron to satisfy the performance goals and to select the best aerodynamic balance to achieve the ergonomic goals. The achieved performance is summarised and compared with the original design goals. It is concluded that the optimised aileron is capable of achieving the design goals over the major portion of the design envelope. The design optimisation process is not limited to turbo-prop aircraft but can be applied to any high performance aircraft with reversible controls.