Jeffrey L. Freeman

Bio: Jeffrey L. Freeman is an academic researcher. The author has contributed to research in topics: Propulsion & Thrust. The author has an hindex of 4, co-authored 6 publications receiving 73 citations.

Challenges and opportunities for electric aircraft thermal management

Abstract: Purpose – The purpose of this article is to provide an outline of the challenges of thermal management for more-electric, hybrid-electric and all-electric aircraft, and to notionally discuss potential solutions. Design/methodology/approach – A code algorithm was developed to facilitate architecture-level analysis of the coupled relationship between the propulsion system, the thermal management system, and the takeoff gross weight of aircraft with advanced propulsion systems. Findings – A variety of coupled relationships between the propulsion and thermal management systems are identified, and their impact on the conceptual design choices for electric aircraft are discussed qualitatively. Research limitations/implications – This conceptual article merely illuminates some driving factors associated with thermal management. The software is still in its adolescence and is experiencing ongoing development. Practical implications – Thermal regulation in electric aircraft is shown to be a topic that should be ad...

Dynamic Flight Simulation of Spanwise Distributed Electric Propulsion for Directional Control Authority

Abstract: A linear time-invariant state-space model was developed to simulate the six-degree-of-freedom aircraft dynamics of the Aircraft for Distributed Electric Propulsion Throttle-based Flight Control (ADEPT-FC), a 34 lb remote controlled aircraft featuring eight overwing electric ducted fans (EDFs) distributed spanwise along the wing's trailing edge. This model utilized parasite drag estimates from OpenVSP's parasite drag tool, trimmed stability coefficients from VSPAERO's stability coefficient solver, and mass properties measured from the as-built aircraft to populate the traditional vehicle dynamics portion of the model's state-space matrices. A second-order state-space frequency model of propulsor dynamics was developed and tuned to the frequency response of the Schubeler EDF as measured in wind-tunnel testing. The influence of propulsor thrust on the vehicle's dynamics was derived and superimposed into the vehicle dynamics state-space model, bridging the gap between a conventional vehicle's state-space model and the propulsor dynamics frequency models for each propulsor. This updated vehicle dynamics model can be provided both aircraft control surface deflections and propulsor thrust inputs to simulate the dynamic response of the vehicle. Without consideration of anticipated propulsion airframe integration (PAI) cross-coupling effects, the simulator developed herein suggested that asymmetric throttle mixing of the EDFs should provide a similar response to that of a rudder deflection. It is anticipated that addition of the PAI effects will magnify the roll rate associated with the maneuver, caused by thrust-induced lift over the outside wing. Further development of this technology could enable a reduction or elimination of the aircraft's vertical tail.

On the Growth Rate of Turbulent Mixing Layers: A New Parametric Model

Abstract: A new parametric model for the growth rate of turbulent mixing layers is proposed. A database of experimental and numerical mixing layer studies was extracted from the literature to support this effort. The domain of the model was limited to planar, spatial, nonreacting, free shear layers that were not affected by artificial mixing enhancement techniques. The model is split into two parts which were each tuned to optimally fit the database; equations for an incompressible growth rate were derived from the error function velocity profile, and a function for a compressibility factor was generalized from existing theory on the convective Mach number. The compressible model is supported by a detailed evaluation of the currently accepted models and practices, including error analysis of the convective Mach number derivation and a critical analysis of Slessor's re-normalization technique which affected his 1998 compressibility parameter. Analysis of the database suggested that a distinction should be made between thickness definitions that are based on the velocity profile and those based on the density profile. Additionally, the accumulation of different normalization approaches throughout the literature was shown to have introduced non-physical variance in the trends. Resolution of this issue through a consistent normalization process has greatly improved the normality and scatter of the data and the goodness-of-fit of the models, resulting in R 2 = 0.9856 for the incompressible model and R 2 = 0.9004 for the compressible model.

Tail Area Reduction for Aircraft with Spanwise Distributed Electric Propulsion

Abstract: Spanwise arrays of electrically driven propulsors may enable significant reductions to the required vertical tail area of an aircraft. The relationship between traditional empennage design and the driving requirements detailed in 14 CFR Part 25 was mapped, and the opportunities in which spanwise distributed electric propulsion could influence the empennage design were identified. The design of the electric microgrid that transmits and controls the flow of power to the propulsors was found to play a critical role in evaluating the potential merits of those opportunities. Careful design of the microgrid architecture was found to relax the asymmetric thrust design condition for the vertical tail to a point of irrelevance. Furthermore, active control of differential thrust between the propulsors could provide dynamic yaw stability to the aircraft, allowing the entire vertical tail to be removed. In contrast, however, a lighter weight microgrid architecture designed with no reconfigurability could exacerbate the asymmetric thrust and require a larger-than-nominal vertical tail. This paper explores the above opportunities and their associated costs as applied to the ECO-150 vision vehicle.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Overview of NASA Electrified Aircraft Propulsion Research for Large Subsonic Transports

Abstract: NASA is investing in Electrified Aircraft Propulsion (EAP) research as part of the portfolio to improve the fuel efficiency, emissions, and noise levels in commercial transport aircraft. Turboelectric, partially turboelectric, and hybrid electric propulsion systems are the primary EAP configurations being evaluated for regional jet and larger aircraft. The goal is to show that one or more viable EAP concepts exist for narrow body aircraft and mature tall-pole technologies related to those concepts. A summary of the aircraft system studies, technology development, and facility development is provided. The leading concept for mid-term (2035) introduction of EAP for a single aisle aircraft is a tube and wing, partially turbo electric configuration (STARC-ABL), however other viable configurations exist. Investments are being made to raise the TRL level of light weight, high efficiency motors, generators, and electrical power distribution systems as well as to define the optimal turbine and boundary layer ingestion systems for a mid-term tube and wing configuration. An electric aircraft power system test facility (NEAT) is under construction at NASA Glenn and an electric aircraft control system test facility (HEIST) is under construction at NASA Armstrong. The correct building blocks are in place to have a viable, large plane EAP configuration tested by 2025 leading to entry into service in 2035 if the community chooses to pursue that goal.

A review of concepts, benefits, and challenges for future electrical propulsion-based aircraft

Abstract: Electrification of the propulsion system has opened the door to a new paradigm of propulsion system configurations and novel aircraft designs, which was never envisioned before. Despite lofty promises, the concept must overcome the design and sizing challenges to make it realizable. A suitable modeling framework is desired in order to explore the design space at the conceptual level. A greater investment in enabling technologies, and infrastructural developments, is expected to facilitate its successful application in the market. In this review paper, several scholarly articles were surveyed to get an insight into the current landscape of research endeavors and the formulated derivations related to electric aircraft developments. The barriers and the needed future technological development paths are discussed. The paper also includes detailed assessments of the implications and other needs pertaining to future technology, regulation, certification, and infrastructure developments, in order to make the next generation electric aircraft operation commercially worthy.

Preliminary Sizing Method for Hybrid-Electric Distributed-Propulsion Aircraft

Abstract: The use of hybrid-electric propulsion (HEP) entails several potential benefits such as the distribution of power along the airframe, which enables synergistic configurations with improved aerodynamic and propulsive efficiency. This paper presents a comprehensive preliminary sizing method suitable for the conceptual design process of hybridelectric aircraft, taking into account the powertrain architecture and associated propulsion–airframe integration effects. To this end, the flight-performance equations are modified to account for aeropropulsive interaction. A series of component-oriented constraint diagrams are used to provide a visual representation of the design space. A HEPcompatible mission analysis and weight estimation are then carried out to compute the wing area, powerplant size, and takeoff weight. The resulting method is applicable to a wide range of electric and hybrid-electric aircraft configurations and can be used to estimate the optimal power-control profiles. For demonstration purposes, the method is applied to a regional HEP aircraft featuring leading-edge distributed propulsion (DP). Three powertrain architectures are compared, showing how the aeropropulsive effects are included in the model. Results indicate that DP significantly increases wing loading and improves the cruise lift-to-drag ratio by 6%, although the growth in aircraft weight leads to an energy consumption increase of 3% for the considered mission.