David Trawick

Electric Control Surface Actuator Design Optimization and Allocation for the More Electric Aircraft

This work pertains to the optimization of electric actuators for the primary and secondary flight control surfaces of a More Electric Aircraft. Electrohydrostatic and electromechanical actuators are considered and optimized in accordance with the flight loads and actuator requirements identified in a separate work by the same authors. For the purposes of this work, the Boeing 737-800 aircraft is chosen as a test case. However the methodology is general and can be applied to any existing design or proposed design concept. Once the optimized actuator designs are obtained, the possibility of using both actuator types by allocating them to control surfaces on the basis of reliability requirements is considered.

Development of a Suite of Hybrid Electric Propulsion Modeling Elements Using NPSS

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by Boeing, General Electric, Virginia Tech, and Georgia Tech under the Subsonic Ultra Green Aircraft Research (SUGAR) project [1]. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid electric propulsion. Hybrid electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell, which can be used to provide additional propulsive energy to a conventional Brayton cycle powered turbofan engine. Employing additional power sources for thrust production increases the number of degrees of freedom both from a design and configuration standpoint and from an operational one. In order to assess and understand the myriad number of potential new configurations a modeling and simulation tool is needed; however, current state of the art propulsion modeling tools such as the Numerical Propulsion System Simulation (NPSS) are not natively capable of assessing novel hybrid electric configurations.This research addresses the gap between hybrid electric propulsion and conventional cycle analysis tools by developing a suite of native NPSS elements suitable for hybrid electric engine cycle design and analysis. Elements have been developed for a fuel cell, battery, motor, generator, and electrical distribution system. Both room temperature and cryogenically cooled superconducting variants are developed. The elements are designed such that they can be seamlessly integrated into existing NPSS cycle models to assess any system configuration or architecture the designer can envision.© 2014 ASME

Development of a Sizing and Analysis Tool for Electrohydrostatic and Electromechanical Actuators for the More Electric Aircraft

This work documents the development of a MATLAB/Simulink based methodology for the sizing, simulation, analysis, and optimization of electric actuators for the primary and secondary control surfaces of a More Electric Aircraft. For a given aircraft and control surface configuration, the control surface flight loads are first evaluated taking into account their aerodynamic characteristics and the critical flight conditions relevant to each. With this information, the performance of a given actuator design can be analyzed via a simulation of the actuator and thermal dynamics. Conversely, for a given objective function and constraint set, the actuator design can be optimized through the solution of a constrained optimization problem. This work focuses on the development of the flight load estimation capability, the modeling and simulation environment, and the weight estimation method, while a separate work describes the actuator optimization problem and a study of actuator-to-surface allocation. While applicable to a wide variety of aircraft, the current work analyzes electrohydrostatic and electromechanical actuators using the Boeing 737-800 aircraft as a test case.

Assessment of Electrically Actuated Redundant Control Surface Layouts for a Hybrid Wing Body Concept

Hybrid Wing Body configurations are currently an active field of research as potential candidates to meet NASA ERA N+2 goals. One characteristic of these configurations is the presence of a large number of redundant flight control surfaces. However, the design process and decision rationale for a given control surface layout is rarely discussed in the open literature. This paper investigates tradeoffs between drag, control authority, actuator weight, and actuation power requirements as a function of the number and spacing of elevons. The actuators will be sized based on hinge moments measured during nominal and failed control trim analyses. These effects are propagated upwards to estimate changes to fuel burn, a system level metric important to the ERA program, via the Breguet range equation. A model of the N2A-EXTE will be used to demonstrate these tradeoffs.

A Requirements-driven Methodology for Integrating Subsystem Architecture Sizing and Analysis into the Conceptual Aircraft Design Phase

Historically, during aircraft conceptual design, only limited consideration has been given to the aircraft subsystems, which have traditionally been addressed in the subsequent design phases. However, the design of future All Electric Aircraft or More Electric Aircraft will require a paradigm shift due to the lack of historical data and the presence of significant interactions among subsystems. As a result, the conceptual phase designer of such aircraft will seek the capability to perform subsystem sizing and analysis in parallel with traditional aircraft and propulsion system sizing and analysis. However, a significant challenge arises from the fact that the conceptual phase designer has limited and incomplete information regarding the design. This work presents a methodology to integrate subsystem sizing with conceptual design phase aircraft and propulsor sizing, while utilizing only the limited information that is available during this phase. The sizing of subsystem components is driven by requirements definition and the identification of critical or constraining operating scenarios. The subsystems considered include the environmental control system and ice protection system, actuation subsystems for flight control surfaces, landing gear, braking, and nose-wheel steering, and an innovative electric taxiing concept. Using a single-aisle narrowbody aircraft as a test case, the proposed methodology is demonstrated by comparing a conventional subsystem architecture to an electric one at the vehicle and mission level, and feeding back subsystem characteristics to the vehicle and propulsor sizing process.

A Surrogate Model based Constrained Optimization Architecture for the Optimal Design of Electrohydrostatic Actuators for Aircraft Flight Control Surfaces

This work pertains to the development of an optimization architecture for the optimal design of electrohydrostatic actuators for aircraft flight control surfaces in the presence of subsystem and aircraft level design constraints. A Modeling and Simulation (M&S) environment, described in detail in a separate work, is used to simulate an aircraft mission and capture relevant and constraining flight conditions and load cases. The system behavior is represented by a surrogate model that allows for rapid and computationally inexpensive evaluation of the responses of interest. The surrogate model is used to perform constrained optimization, followed by a validation of the optimal result using the M&S environment. The optimal designs obtained for two United States Air Force combat aircraft are presented and discussed, but the methodology is equally valid for other aircraft and control surface configurations. An additional capability arising from this architecture is the ability to analyze the sensitivity of the design to each of the design parameters influencing it.

Assessment of Engine and Vehicle Performance Using Integrated Hybrid-Electric Propulsion Models

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by The Boeing Company, the General Electric Company, Virginia Polytechnic Institute and State University, and the Georgia Institute of Technology under the Subsonic Ultra Green Aircraft Research Project. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid-electric propulsion. Hybrid-electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell that can be used to provide additional propulsive energy to a conventional Brayton-cycle-powered turbofan engine. This research constructs an integrated Numerical Propulsion System Simulation hybrid-electric propulsion model capable of predicting hybrid-electric engine performance throughout the operational envelope. The syste...

A Methodology for Assessing Enabling Technology Uncertainty on Advanced Aircraft Configurations

Designing advanced aircraft concepts has always involved risk caused by the challenge of predicting the level of technology maturity that will be available when the concept enters production. As the benefits from the technologies cannot be guaranteed, there is significant uncertainty during the development of the vehicle in the early stages design; leading to major design changes in the later stages of development which can lead to a sub-optimal vehicle. Evaluating the impact of the technology uncertainty on the vehicle’s design can help identify the most important technology areas, allowing more efficient allocation of limited engineering resources. In the following report, a methodology to evaluate the uncertainty in the vehicle performance due to various aircraft technologies and design metrics is presented. This is demonstrated using the NASA N3-X vehicle concept as an example. The vehicle is modeled with the Environment Design Space (EDS) by adding physics-based modules to model when necessary. Surrogate models of this environment are then used to evaluate the uncertainty in the performance metrics due to the technology benefit uncertainty on the optimal configuration of the aircraft. The uncertainty is evaluated based on overall impact of technologies and the impact of individual technology combinations of interest.

Examining Non-Uniform Generator and Propulsor Control Schemes for a Hybrid Electric Propulsion Concept

In order to meet the NASA N+3 goals, several advanced concept aircraft have been proposed, including a Hybrid Wing Body vehicle with a distributed hybrid electric propulsion system. This consists of two turboshaft generators which power motors driving a distributed set of fans mounted on the upper trailing edge of the blended fuselage. The power transmitted through the system is great enough to justify the use of High Temperature Superconducting (HTS) electric motors, generators, and power distribution systems, which must be cooled to 70 K to maintain their superconductivity. Previous studies have evaluated the performance benefit of distributed propulsion systems in detail, but have yet to explore the entire design space in detail. Leveraging heavily upon previous modeling efforts at NASA, a superconducting, distributed, turboelectric propulsions system has been modeled in Georgia Tech’s Environmental Design Space (EDS). EDS serves to capture interdependencies of fuel burn, emissions, and noise at the conceptual design level for conventional and advanced engine and airframe architectures. Previous modeling methodologies for superconducting motors, generators, distribution systems, and other supporting systems have been implemented into EDS, of which the Numerical Propulsion System Simulation (NPSS) is the primary engine modeling tool. Trade studies have been performed take assess the potential benefit of the mechanical decoupling of the fans and turbines due to the electric power systems. This was done through the investigation of different power management techniques on a sized system. These include running the two generators at different speeds and splitting the fans into banks running at different speeds. Running the two generators at different speeds was found to improve efficiency at low altitude and low throttle settings.