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Technical Paper

Tradeoff Study of High Altitude Solar Reflector Concepts

2017-09-19
2017-01-2143
A direct solution to Global Warming would be to reflect a part of sunlight back into Space. A system tradeoff study is being developed with three of the concepts that are being evaluated as long-endurance high-altitude reflectors. The first concept is a high aspect ratio solar powered flying wing towing reflector sheets. This concept is named “Flying Carpet”. Second is a centrifugally stretched high altitude solar reflector (CSHASR). The CSHASR has 4 rotors made of reflector sheets with a hub stretching to 60 percent of the radius, held together by an ultralight quad-rotor structure. Each rotor is powered by a solar-electric motor. A variation on this concept, forced by nighttime descent rate concerns, is powered by tip-mounted solar panels and propellers with some battery storage augmenting rotational inertia as well as energy storage. The third concept is an Aerostatically Balanced Reflector (ABR) sheet, held up by hydrogen balloons.
Technical Paper

Aerodynamic Loads on Arbitrary Configurations: Measurements, Computations and Geometric Modeling

2017-09-19
2017-01-2162
This paper brings together three special aspects of bluff-body aeromechanics. Experiments using our Continuous Rotation method have developed a knowledge base on the 6-degree-of-freedom aerodynamic loads on over 50 different configurations including parametric variations of canonical shapes, and several practical shapes of interest. Models are mounted on a rod attached to a stepper motor placed on a 6-DOF load cell in a low speed wind tunnel. The aerodynamic loads are ensemble-averaged as phase-resolved azimuthal variations. The load component variations are obtained as discrete Fourier series for each load component versus azimuth about each of 3 primary axes. This capability has enabled aeromechanical simulation of the dynamics of roadable vehicles slung below rotorcraft. In this paper, we explore the genesis of the loads on a CONEX model, as well as models of a short and long container, using the “ROTCFD” family of unstructured Navier-Stokes solvers.
Technical Paper

Yaw Effects on the Narrowband Spectra Above a Delta Wing in Turbulent Flow

2016-09-20
2016-01-2056
Combat aircraft maneuvering at high angles of attack or in landing approach are likely to encounter conditions where the flow over the swept wings is yawed. This paper examines the effect of yaw on the spectra of turbulence above and aft of the wing, in the region where fins and control surfaces are located. Prior work has shown the occurrence of narrowband velocity fluctuations in this region for most combat aircraft models, including those with twin fins. Fin vibration and damage has been traced to excitation by such narrowband fluctuations. The narrowband fluctuations themselves have been traced to the wing surface. The issue in this paper is the effect of yaw on these fluctuations, as well as on the aerodynamic loads on a wing, without including the perturbations due to the airframe.
Technical Paper

Coaxial Rotor Flow Phenomena in Forward Flight

2016-09-20
2016-01-2009
Coaxial rotors are finding use in advanced rotorcraft concepts. Combined with lift offset rotor technology, they offer a solution to the problems of dynamic stall and reverse flow that often limit single rotor forward flight speeds. In addition, coaxial rotorcraft systems do not need a tail rotor, a major boon during operation in confined areas. However, the operation of two counter-rotating rotors in close proximity generates many possible aerodynamic interactions between rotor blades, blades and vortices, and between vortices. With two rotors, the parameter design space is very large, and requires efficient computations as well as basic experiments to explore aerodynamics of a coaxial rotor and the effects on performance, loads, and acoustics.
Technical Paper

Slung Load Divergence Speed Predictions for Vehicle Shapes

2015-09-15
2015-01-2570
Loads slung under aircraft can go into divergent oscillations coupling multiple degrees of freedom. Predicting the highest safe flight speed for a vehicle-load combination is a critical challenge, both for military missions over hostile areas, and for evacuation/rescue operations. The primary difficulty was that of obtaining well-resolved airload maps covering the arbitrary attitudes that a slung load may take. High speed rotorcraft using tilting rotors and co-axial rotors can fly at speeds that imply high dynamic pressure, making aerodynamic loads significant even on very dense loads such as armored vehicles, artillery weapons, and ammunition. The Continuous Rotation method demonstrated in our prior work enables routine prediction of divergence speeds. We build on prior work to explore the prediction of divergence speed for practical configurations such as military vehicles, which often have complex bluff body shapes.
Technical Paper

Aerodynamic Load Maps of Vehicle Shapes at Arbitrary Attitude

2015-09-15
2015-01-2574
The interest in flying cars comes with the question of characterizing aerodynamic loads on shapes that go beyond traditional aircraft shapes. When carried as slung loads under aircraft, vehicles can encounter severe aerodynamic loads, which may also cause them to go into divergent oscillations that can threaten the vehicle and aircraft. Slung loads can encounter the wind at arbitrary attitudes. Flight test certification for every vehicle-aircraft combination is prohibitive. Characterizing the aerodynamic loads with sufficient resolution for use in dynamic simulation, has in the past been extremely arduous. Sharp changes that drive instabilities arise over small ranges of yaw and pitch. With the Continuous Rotation technique developed by our group, aerodynamic load characterization is viable and efficient. With two well-chosen attitude sweeps and appropriate transformations, the entire 6-DOF load map can be obtained, for several rates.
Technical Paper

Narrow-Band Excitation of Vortex Flows

2015-09-15
2015-01-2572
At high angles of attack, the flow over a swept wing generates counter-rotating vortical features. These features can amplify into a nearly sinusoidal fluctuation of velocity components. The result is excitation of twin-fin buffeting, driven at clearly predictable frequencies, or at nearby lock-in frequencies of the fin structure. This is distinct from the traditional model of fin buffeting as a structural resonant response to broadband, large-amplitude excitation from vortex core bursting. Hot-film anemometry was conducted ahead of the vertical fins of a 1:48 scale model of the F-35B aircraft, in the angle of attack range between 18 and 30 degrees. Auto spectral density functions from these data showed a sharp spectral peak in the flow ahead of the fins for angles of attack between 20 and 28 degrees. Small fences placed on the top surface of the wing eliminated the spectral peak, leaving only a broadband turbulent spectrum.
Technical Paper

Progress in Rotorcraft Icing Computational Tool Development

2015-06-15
2015-01-2088
The formation of ice over lifting surfaces can affect aerodynamic performance. In the case of helicopters, this loss in lift and the increase in sectional drag forces will have a dramatic effect on vehicle performance. The ability to predict ice accumulation and the resulting degradation in rotor performance is essential to determine the limitations of rotorcraft in icing encounters. The consequences of underestimating performance degradation can be serious and so it is important to produce accurate predictions, particularly for severe icing conditions. The simulation of rotorcraft ice accretion is a challenging multidisciplinary problem that until recently has lagged in development over its counterparts in the fixed wing community. But now, several approaches for the robust coupling of a computational fluid dynamics code, a rotorcraft structural dynamics code and an ice accretion code have been demonstrated.
Technical Paper

Facilitating the Energy Optimization of Aircraft Propulsion and Thermal Management Systems through Integrated Modeling and Simulation

2010-11-02
2010-01-1787
An integrated, multidisciplinary environment of a tactical aircraft platform has been created by leveraging the powerful capabilities of both MATLAB/Simulink and Numerical Propulsion System Simulation (NPSS). The overall simulation includes propulsion, power, and thermal management subsystem models, which are integrated together and linked to an air vehicle model and mission profile. The model has the capability of tracking temperatures and performance metrics and subsequently controlling characteristics of the propulsion and thermal management subsystems. The integrated model enables system-level trade studies involving the optimization of engine bleed and power extraction and thermal management requirements to be conducted. The simulation can also be used to examine future technologies and advanced thermal management architectures in order to increase mission capability and performance.
Technical Paper

A General Aviation Aircraft Retrofit with a PEM Fuel Cell

2008-11-11
2008-01-2914
As gas prices and climate change become the preeminent issues of today, more research effort is being directed towards the development of cheaper and cleaner alternative energy sources. These efforts have been further complemented with research into the applicability of these sources to air, land and sea borne vehicles. In this report a notional C-172R general aviation aircraft is retrofitted with a PEM power plant as a case-study. Lower bounds for useful load and range are set in such a way that the results can be useful in determining how much improvement in the technology would be required to power a useful general aviation vehicle. It is seen that even at the predicted 2015 fuel cell technology level (per US Department of Energy projections), PEM systems would still be infeasible for this vehicle due to low specific power. Further investigation revealed that a PEM-battery hybrid system had better chances of feasibility.
Journal Article

Superconducting Machines and Power Systems for Electric-Drive Aeropropulsion

2008-11-11
2008-01-2862
Societal demands of recent years have increasingly pressured the development of greener technologies in all sectors of the nation's transportation infrastructure, including that of civilian aviation. This study explores the concept of electric-drive aeropropulsion, aided by high-temperature superconducting technology, as an enabler for enhancing the environmental characteristics at the air-vehicle level. Potential improvements in the areas of aircraft noise, emissions, and energy efficiency are discussed in the context of supporting the latest strategic goals of leading governmental organizations.
Technical Paper

Test Results for a Fuel Cell-Powered Demonstration Aircraft

2006-11-07
2006-01-3092
A fuel cell powered airplane has been designed and constructed at the Georgia Insitute of Technology to develop an understanding of the design and implementation challenges of fuel cell-powered unmanned aerial vehicles (UAVs). A custom 448W net output proton exchange membrane fuel cell powerplant has been constructed and tested. A demonstrator aircraft was designed and built to accommodate this powerplant and the fuel cell powered aircraft has performed seven test flights to date. Test data show that the aircraft performance validates the models used for design and optimization and that the fuel cell aircraft is capable of longer endurance, higher performance test flights.
Technical Paper

Towards Electric Aircraft: Progress under the NASA URETI for Aeropropulsion and Power Technology

2006-11-07
2006-01-3097
The environmental impact of aircraft, specifically in the areas of noise and NOx emissions, has been a growing community concern. Coupled with the increasing cost and diminishing supply of traditional fossil fuels, these concerns have fueled substantial interest in the research and development of alternative power sources for aircraft. In 2003, NASA and the Department of Defense awarded a five year research cooperative agreement to a team of researchers from three different universities to address the design and analysis of revolutionary aeropropulsion technologies.
Technical Paper

Quiet, Clean, and Efficient, but Heavy - Concerns for Future Fuel Cell Powered Personal Air Vehicles

2006-08-30
2006-01-2436
Unfortunately, the promises of efficient, clean, quiet power that fuel cells offer are balanced by extremely low power densities and great infrastructure-related challenges. Studies by government and industry have investigated their feasibility for primary propulsion in light aircraft. These studies have produced mixed results but have tended to rely on integrating fuel cells into existing airframes, with respectably-performing light sport planes being turned into underpowered show planes with horribly compromised range and payload capabilities. Fuel cells today are in the earliest phases of technological development. As an aircraft propulsion system, they are as advanced as the Wright's reciprocating engine was a hundred years ago.
Technical Paper

A Comparative Study of a Multi-Gas Generator Fan to a Turbofan Engine on a Vertical Takeoff and Landing Personal Air Vehicle

2006-08-30
2006-01-2435
This paper attempts to assess the benefits of a unique distributed propulsion concept, known as the Multi-Gas Generator Fan (MGGF) system, over conventional turbofan engines on civilian vertical takeoff and landing (VTOL) applications. The MGGF-based system has shown the potential to address the fundamental technical challenge in designing a VTOL aircraft: the significant mismatch between the power requirements at lift-off/hover and cruise. Vehicle-level performance and sizing studies were implemented using the Grumman Design 698 tilt-nacelle V/STOL aircraft as a notional personal air vehicle (PAV), subjected to hypothetical single engine failure (SEF) emergency landing requirements and PAV mission requirements.
Technical Paper

A System Dynamics Approach for Dynamic Uncertainty Assessment in a PAV Design Environment

2006-08-30
2006-01-2434
One the most critical barriers to the advancement of Personal Air Vehicles in today's market environment is that the technological capabilities can never seem to outweigh the risks associated with financing such an endeavor. To address such a need, a system dynamics approach with the capability to model the uncertainties in the supply chain is presented in this paper. The overall modeling framework is first presented and the modeling process of the various relevant elements, such as demand prediction and manufacturer analysis, is then described. The aim of this research is ultimately to assess the viability of a next-generation aircraft program beyond the static confines of a net present value approach, through the inclusion of dynamic events and uncertainties that can occur throughout the life-cycle of the aircraft.
Technical Paper

Conceptual Design of Current Technology and Advanced Concepts for an Efficient Multi-Mach Aircraft

2005-10-03
2005-01-3399
A design process is formulated and implemented for the taxonomy selection and system-level optimization of an Efficient Multi-Mach Aircraft Current Technology Concept and an Advanced Concept. Concept space exploration of taxonomy alternatives is performed with multi-objective genetic algorithms and a Powell’s method scheme for vehicle optimization in a multidisciplinary modeling and simulation environment. A dynamic sensitivity visualization analysis tool is generated for the Advanced Concept with response surface equations.
Technical Paper

Technology Assessment of a Supersonic Business Jet

2005-10-03
2005-01-3393
This paper presents a quantitative process to track the progress of technology developments within NASA’s Vehicle Systems Program (VSP) as implemented on a Supersonic Business Jet (SBJ). The process, called the Technology Metric Assessment and Tracking (TMAT) process, accounts for the temporal aspects of technology development programs such that technology portfolio assessments, in the form of technological progress towards VSP sector goals, may be tracked and assessed. Progress tracking of internal research and development programs is an essential element to successful strategic endeavors and justification of the pursuit of capital projects [1].
Technical Paper

A Parametric Design Environment for Including Signatures Analysis in Conceptual Design

2000-10-10
2000-01-5564
System effectiveness has become the prime metric for the evaluation of military aircraft. As such, it is the designer's goal to maximize system effectiveness. Industry documents indicate that all future military aircraft will incorporate signature reduction as an attempt to improve system effectiveness. Today's operating environments demand low observable aircraft which are able to reliably eliminate valuable, time critical targets. Thus, it is desirable to be able to evaluate the signatures of a vehicle, as well as the influence of signatures on the systems effectiveness of a vehicle. Previous studies have shown that shaping of the vehicle is one of the most important contributors to radar cross section and must be considered from the very beginning of the design process. This research strives to meet these needs by developing a parametric geometry radar cross section prediction tool.
Technical Paper

Analysis of Aerobatic Flight Safety Using Autonomous Modeling and Simulation

2000-04-11
2000-01-2100
An affordable technique is proposed for fast quantitative analysis of aerobatics and other complex flight domains of highly maneuverable aircraft. A generalized autonomous situational model of the “pilot (automaton) – vehicle – operational environment” system is employed as a “virtual test article”. Using this technique, a systematic knowledge of the system behavior in aerobatic flight can be generated on a computer, much faster than real time. This information can be analyzed via a set of knowledge mapping formats using a 3-D graphics visualization tool. Piloting and programming skills are not required in this process. Possible applications include: aircraft design and education, applied aerodynamics, flight control systems design, planning and rehearsal of flight test and display programs, investigation of aerobatics-related flight accidents and incidents, physics-based pilot training, research into new maneuvers, autonomous flight, and onboard AI.
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