Performance investigations and systems architectures for the More Electric Aircraft
Implementation of all or more electric technologies has the potential of improving the performance of a given aircraft. Savings can manifest through improved engine performance, reduced equipment weight and improved secondary power and systems utilization. Despite the potential benefits and the amount of research invested the concept has not been implemented yet and its impact on the overall performance of the aircraft remains unclear. Adoption of a single form of secondary power and implementation of more or all electric technologies is claimed to offer a number of distinct advantages over the conventional secondary power systems. These claims include the following: 1. Improved engine performance through the optimization of off-takes and elimination of bleed air. These issues is said to become critical as the bypass ratio of the engine increases and the size of the core reduces. However, despite concerns over the capability of high bypass ratio to provide secondary power requirements of future aircraft the claims remain unproven and it is generally believed that off-take penalties are not dependent on the configuration of the engine and can be kept to a minimum if the engine is designed to provide them. 2. Improved system utilization and implementation of more efficient power units. Conventional secondary power systems developed during the years that fuel was relatively fuel was relatively inexpensive and have not been optimized for maximum efficiency. Bleeding air from the engine is largely inefficient and a large amount of power is wasted for no useful purpose. In addition, hydraulics are often sized for loads that are small in duration thus increasing the mass and power requirements of the system. Elimination of conventional hydraulic and bleed air systems could lead to a significant mass reduction. However, the mass and size of the electrical equipment would also increase and these changes must be accounted for. 4. Additional benefits include reduced single type maintenance, improved reliability and life cycle costs. The present study is focused on assessing the potential benefits of adopting the all or more electric aircraft concepts in the case of high capacity long-range aircraft. Previous studies concentrated on low to medium range aircraft powered by medium bypass bass ratio engines. As a result, the moderate power requirements and the more important weight considerations, for the class of aircraft reviewed, reduced the potential benefits and led to retrofitted designs with low savings. It is thought that high capacity long range aircraft as those examined by the present study are more suited to the all electric concepts and could benefit more. The study was aimed to address the first three claims made and also provide a better understanding of the issues involved. As a result the following topics have been considered. The effects of off-takes on the performance of the engine were studied. Two methods for assessing these effects were developed. The analysis concluded that engine parameters such as pressure ratio and turbine entry temperature have an important effect on the performance of an engine operating with bleed air or shaft power extraction. An aircraft performance model was developed and used to asses the impact of all or more electric technologies on aircraft in the classes of A330-200, A340-500 and A380-100. The models were validated against published payload range data. All electric derivatives were developed by incorporating changes in aircraft mass and engine off-takes. Sensitivity studies were also conducted. Conceptual designs and electric system architectures were developed and studied. Adoption of all electric technologies and elimination of the hydraulic system was estimated to reduce the OEW by 0.4% to 0.1% for the A330-200 class aircraft, 0.37% to 0.25% for the A340-500 class aircraft and 0.3% to 0.1% for the A380-100 class aircraft. The total fuel reduction with implementation of all electric technologies and elimination of hydraulics and bleed air could be as high as 2.6% for the A330-200 class aircraft, 2.75% for the A340-500 class aircraft and 3.5% for the A380-100 class aircraft. Adoption of all or more electric technologies could allow for the design of more efficient aircraft. Increasing the aspect ratio of the A80-100 class aircraft to 8.33 could improve aerodynamic efficiency leading to an overall fuel reduction of 4.4% and a MTOM reduction of 2.0010. In the case of twin engine aircraft reductions in MTOM and reduced off-take penalties could allow an increase in engine bypass ratio leading to increased overall performance. For the A330-200 class aircraft elimination of bleed air and increase in bypass ratio resulted in a fuel reduction of 4.5%.