Approaches to representing aircraft performance for the purpose of a CO₂ certification standard

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 79-80).Increasing concern over the potential harmful effects of green house gas emissions from various sources has motivated the consideration of an aircraft certification standard as one way to reduce aircraft C02 emissions and mitigate aviation impacts on the climate. In order to develop a commercial aircraft certification standard, a fuel efficiency performance metric and the condition at which it is evaluated must be determined. The fuel efficiency metric form of interest to this research is fuel/range, where fuel and range can either be evaluated over the course of a reference mission or at a single, instantaneous point. A mission-based metric encompasses all phases of flight and is robust to changes in technology; however, definition of the reference mission requires many assumptions and is cumbersome for both manufacturers and regulators. An instantaneous metric based on fundamental aircraft parameters measures the fuel efficiency performance of the aircraft at a single point, greatly reducing the complexity of the standard and certification process; however, a single point might not be robust to future changes in aircraft technology. In this thesis, typical aircraft operations are assessed in order to develop evaluation assumptions for a mission-based metric, Block Fuel divided by Range (BF/R), and an instantaneous metric, incremental fuel burn per incremental distance (inverse Specific Air Range (1/SAR)). Operating patterns and fuel burn maps are used to demonstrate the importance of mission range on fleet fuel burn, and thus the importance of a properly defined range evaluation condition for BF/R. An evaluation condition of 40% of the range at Maximum Structural Payload (MSP) limited by Maximum Takeoff Weight (MTOW) is determined to be representative for the mission-based metric. A potential evaluation condition for 1/SAR is determined to be optimal speed and altitude for a representative mid-cruise weight defined by half of the difference between MTOW and Maximum Zero Fuel Weight (MZFW). To demonstrate suitability as a potential surrogate for BF/R, correlation of 1/SAR with BF/R is shown for the current fleet, and a case study of potential future aircraft technologies is presented to show the correlation of improvements in the 1/SAR metric with improvements in BF/R.by Brian M. Yutko.S.M

The impact of aircraft design reference mission on fuel efficiency in the air transportation system

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, February 2014.Cataloged from PDF version of thesis. "October 2013."Includes bibliographical references (pages 153-157).Existing commercial aircraft are designed for high mission flexibility, which results in decreased fuel efficiency throughout the operational life of an aircraft. The objective of this research is to quantify the impact of this practice and other non-optimal emergent behaviors of the current global air transportation system. The analysis focuses on improvements that can be made using existing technology. Previous attempts at performing this type of analysis, especially the joint optimization of aircraft design and operations, have been hindered by problem complexity and computational time. In order to overcome these issues and perform the analysis on a global scale, a machine-learning algorithm is used to create a computationally efficient artificial neural network relating aircraft design and off-design mission performance to operational fuel burn and flight time. The data used to train the aircraft performance neural network is generated from an extensive sample of new vehicles optimized for minimum fuel burn on an extremely broad combination of Design Reference Missions (design-payload, -range, and cruise Mach). The resulting comprehensive model of aircraft performance is capable of solving large-scale air transportation network optimization problems. A set of scenarios is analyzed to both establish the limits of the major contributors to system fuel consumption and determine potential realistic benefits from introducing new aircraft with varying design reference missions. Results indicate that approximately 33% of current system fuel consumption is due to the slow retirement and replacement of aircraft in the operational fleet. Additionally, a significant pool of potential fuel burn savings can be realized by designing aircraft closer to their intended operating regime. Multiple large-scale optimization scenarios are presented, including the optimal choice of new aircraft designs for fixed cruise Mach numbers and the globally optimum aircraft choices given any cruise Mach. It is found that reducing design cruise speed can yield system fuel benefits on the order of 7%. Fuel stops are shown as a potentially promising method to operate long-haul missions closer to the maximum fuel efficiency range of an aircraft, and also as a way to mitigate the impact of designing high-efficiency, short-range aircraft that can no longer fly long haul missions directly.by Brian Yutko.Ph. D