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At least 163 records · Page 9

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NASA NTRS2008

A Performance Assessment of an Airborne Separation Assistance System Using Realistic Complex Traffic Flows

This paper presents the results from a study that investigates the performance of a tactical Airborne Separation Assistance System (ASAS) in en route airspace, under varying demand levels, with realistic traffic flows. The ASAS concept studied here allows flight crews of equipped aircraft to perform separation from other air traffic autonomously. This study addresses the tactical aspects of an ASAS using aircraft state data (i.e. position and velocity) to detect and resolve projected conflicts. In addition, use of a conflict prevention system helps ASAS-equipped aircraft avoid maneuvers that may cause new conflicts. ASAS-capable aircraft are equipped with satellite-based navigation and Automatic Dependent Surveillance Broadcast (ADS-B) for transmission and receipt of aircraft state data. In addition to tactical conflict detection and resolution (CD&R), a complete, integrated ASAS is likely to incorporate a strategic CD&R component with a longer look-ahead time, using trajectory intent information. A system-wide traffic flow management (TFM) component, located at the FAA command center helps aircraft to avoid regions of excessive traffic density and complexity. A Traffic Alert and Collision Avoidance System (TCAS), as used today is the system of last resort. This integrated approach avoids sole reliance on the use of the tactical CD&R studied here, but the tactical component remains a critical element of the complete ASAS. The focus of this paper is to determine to what extent the proposed tactical component of ASAS alone can maintain aircraft separation at demand levels up to three times that of current traffic. The study also investigates the effect of mixing ASAS-equipped aircraft with unequipped aircraft (i.e. current day) that do not have the capability to self-separate. Position and velocity data for unequipped aircraft needs to be available to ASASequipped. Most likely, for this future concept, state data would be available from instrument flight rules (IFR) aircraft, equipped with at least ADS-B transmission capability. The objective is to reduce the number of losses of separation to a minimum and investigate the limits of tactical-only CD&R. Thus, the objective is not, expressly, to achieve zero losses of separation with tactical ASAS because this is one component of an integrated ASAS.

Smith, Jeremy C.↗

NASA NTRS2005

Airborne Management of Traffic Conflicts in Descent With Arrival Constraints

NASA is studying far-term air traffic management concepts that may increase operational efficiency through a redistribution of decisionmaking authority among airborne and ground-based elements of the air transportation system. One component of this research, En Route Free Maneuvering, allows trained pilots of equipped autonomous aircraft to assume responsibility for traffic separation. Ground-based air traffic controllers would continue to separate traffic unequipped for autonomous operations and would issue flow management constraints to all aircraft. To evaluate En Route Free Maneuvering operations, a human-in-the-loop experiment was jointly conducted by the NASA Ames and Langley Research Centers. In this experiment, test subject pilots used desktop flight simulators to resolve conflicts in cruise and descent, and to adhere to air traffic flow constraints issued by test subject controllers. Simulators at NASA Langley were equipped with a prototype Autonomous Operations Planner (AOP) flight deck toolset to assist pilots with conflict management and constraint compliance tasks. Results from the experiment are presented, focusing specifically on operations during the initial descent into the terminal area. Airborne conflict resolution performance in descent, conformance to traffic flow management constraints, and the effects of conflicting traffic on constraint conformance are all presented. Subjective data from subject pilots are also presented, showing perceived levels of workload, safety, and acceptability of autonomous arrival operations. Finally, potential AOP functionality enhancements are discussed along with suggestions to improve arrival procedures.

Doble, Nathan A.↗

NASA NTRSDate not supplied

Analysis of Conflicts among Urban Air Mobility Aircraft and with Traditional Aircraft

This paper provides an initial analysis of conflicts among Urban Air Mobility aircraft and with traditional aircraft based on fast-time simulations of 20 full-day scenarios. Several sets of separation minima with added performance-based separation are applied, and the resulting separation conflicts are classified. Safety metrics relevant to separation standards are evaluated. The results shed light on future performance-based separation standards and safety metrics for separation standards involving Urban Air Mobility aircraft.

urban air mobility↗

NASA NTRSDate not supplied

Analysis of Conflicts among Urban Air Mobility Aircraft and with Traditional Aircraft

urban air mobility↗

NASA NTRS1972

Evaluation of a self-aspirating local total enthalpy probe in a low-density arc-heated hypersonic wind tunnel

A shock-swallowing, self-aspirating, local total enthalpy probe has been evaluated in a low density nonequilibrium, hypervelocity airstream. The probe, which incorporated an air gap to separate the internal and external cooling passages, was tested in an electric archeated wind tunnel at an average Mach number of 11.7 and an average Reynolds number per meter of 57,000. The free stream enthalpy probe data are compared with bulk calorimeter measurements of total enthalpy at the beginning of the gas expansion and with local total enthalpy inferred from a theoretical nonequilibrium gas expansion model by using free stream velocity measurements obtained from a mass flow probe. The three techniques are in relative agreement at the lower enthalpies. However, at the higher enthalpies, the enthalpy probe data lie considerably below the other data. This low data may be caused by the chemical and vibrational energy frozen in the flow not being sensed by the probe. Other problems associated with the shock-swallowing total enthalpy probe are discussed, and recommendations for improving the probe performance are presented.

Guy, R. W.↗

NASA NTRS1974

Variable CO2 laser attenuator

An infrared wavelength variable attenuator based on contra-rotating germanium wedges is examined theoretically. The device redirects the paths of internal reflections associated with an optical flat to avoid closely spaced parallel beams at the output. Complementary wedges separated by an air gap compose an optical flat which, when combined with a masking arrangement, restricts unwanted reflections. A model of the device was built and experimentally evaluated. The results compare favorably with the dynamic range of attenuation of 2 to 50 db from theoretical calculations, and show a substantial reduction in the etalon effect associated with pairs of optical flats.

Klein, B. J.↗

NASA NTRS1975

Models for estimating runway landing capacity with Microwave Landing System (MLS)

A model is developed which is capable of computing the ultimate landing runway capacity, under ILS and MLS conditions, when aircraft population characteristics and air traffic control separation rules are given. This model can be applied in situations when only a horizontal separation between aircraft approaching a runway is allowed, as well as when both vertical and horizontal separations are possible. It is assumed that the system is free of errors, that is that aircraft arrive at specified points along the prescribed flight path precisely when the controllers intend for them to arrive at these points. Although in the real world there is no such thing as an error-free system, the assumption is adequate for a qualitative comparison of MLS with ILS. Results suggest that an increase in runway landing capacity, caused by introducing the MLS multiple approach paths, is to be expected only when an aircraft population consists of aircraft with significantly differing approach speeds and particularly in situations when vertical separation can be applied. Vertical separation can only be applied if one of the types of aircraft in the mix has a very steep descent angle.

Tosic, V.↗

NASA NTRS1976

Effect of multiple path approach procedures on runway landing capacity

When using the Instrument Landing System (ILS) all aircraft must follow a straight line approach path before landing. The Microwave Landing System (MLS) will allow use of differing curved approach paths. The objective of this research is to find out whether the introduction of MLS and consequently multiple approach paths can bring an increase in runway landing capacity. A model is developed which is capable of computing the expected ultimate landing runway capacity, under ILS and MLS conditions, when aircraft population characteristics and Air Traffic Control separation rules are given. This model can be applied in situations when only a horizontal separation between aircraft approaching a runway is allowed, as well as when both vertical and horizontal separations are possible. Results suggest that an increase in runway landing capacity, caused by introducing the MLS-described multiple approach paths, is to be expected only when an aircraft population consists of aircraft with significantly differing approach velocities and particularly in situations when a vertical separation can be applied.

Tosic, V.↗

NASA NTRS1981

Solar heating and hot water system installed at Arlington Raquetball Club, Arlington, Virginia

A solar space and water heating system is described. The solar energy system consists of 2,520 sq. ft. of flat plate solar collectors and a 4,000 gallon solar storage tank. The transfer medium in the forced closed loop is a nontoxic antifreeze solution (50 percent water, 50 percent propylene glycol). The service hot water system consists of a preheat coil (60 ft. of 1 1/4 in copper tubing) located in the upper third of the solar storage tank and a recirculation loop between the preheat coil and the existing electric water heaters. The space heating system consists of two separate water to air heat exchangers located in the ducts of the existing space heating/cooling systems. The heating water is supplied from the solar storage tank. Extracts from site files, specification references for solar modifications to existing building heating and hot water systems, and installation, operation and maintenance instructions are included.

Source record↗

NASA NTRS1983

Numerical study of a ramjet dump combustor flow field

Increased interest in ramjet propulsion systems with higher performance requirements and tighter constraints on system size and weight has lead to the need for improved techniques for analyzing and designing such systems. A computer program has been developed to analyze the turbulent reacting flow field in a ramjet dump combustor configuration. The program solves the axisymmetric Navier-Stokes and species equations throughout the engine diffuser and combustor providing a unified analysis of the complete engine flow field, including flow separation, fuel-air mixing, and preliminary results with chemical reaction. Details of the program development are given, along with a comparison of program results with data from a dump combustor simulation experiment, to allow assessment of the flow field modeling that is employed.

Drummond, J. P.↗

NASA NTRS1984

Study of double wall panels for use in propeller driven aircraft

Propeller driven aircraft have exhibited high levels of interior noise. Most absorption materials are not effective at low frequencies where maximum noise levels occur. Two panels separated by an air gap are suggested as an alternative means of noise attenuation. This design produces an impedance mismatch where a sound wave travels backwards to the source. The higher the impedance, the higher the reflected soundwave intensity. Two aluminum panels with helium in between and two panels with one being perforated were investigated. Helium increases the transmission loss because of a greater impedance mismatch than air. The transmission loss of the unperforated panel is higher throughout the frequency range tested.

Atwal, M.↗

NASA NTRS1985

Improved Exhaust Diffuser for Jet-Engine Testing

High-altitude simulator reduced power requirements. Test cell uses its exhaust-capture duct only to remove gases from engine; cooling air evacuated through separate path by auxiliary suction system. This way, capture duct cross-sectional area kept close to exhaust jet area, leading to greatly improved recovery performance.

Parikh, P. G.↗

NASA NTRS1989

Model system studies with a phase separated membrane bioreactor

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestial simulation.

Petersen, G. R.↗

NASA NTRS1989

Phase separated membrane bioreactor - Results from model system studies

Petersen, G. R.↗

NASA NTRS1933

The D.V.L. Gliding-angle Control : W. Hubner Design

This report describes a device for arbitrary enlargement of the gliding angle of airplanes, especially of such with flat gliding angle and difficult landing characteristics. The D.V.L. gliding angle control (design, Hubner) permits a local interruption of the lift distribution along the span and consequently an increased induced drag. The mechanism comprises two wing rudders operated by lever from the pilot's cockpit. Said rudders are fitted on the top side of the wing near the leading edge. The displacement of these rudders results in a separation of the air flow on the top side of the wing.

Hubner, Walter↗

NASA NTRS1994

Chemical composition of the atmospheric aerosol in the troposphere over the Hudson Bay lowlands and Quebec-Labrador regions of Canada

Atmospheric aerosols were collected in the boundary layer and free troposphere over continental and coastal subarctic regions of Canada during the July - August 1990 joint U.S.-Canadian Arctic Boundary Layer Expedition (ABLE) 3B/Northern Wetlands Study (NOWES). The samples were analyzed for the following water soluble species: sulfate, nitrate, ammonium, potassium, sodium, chloride, oxalate, methylsulfonate, and total amine nitrogen. Ammonium and sulfate were the major water soluble components of these aerosols. The nearly neutral (overall) chemical composition of summertime aerosol particles contrasts their strongly acidic wintertime composition. Aerosol samples were separated into several air mass categories and characterized in terms of chemical composition, associated mixing ratios of gaseous compounds, and meteorological parameters. The fundamental category represented particles associated with 'background' air masses. The summertime atmospheric aerosols in background air over the North American subarctic and Arctic regions were characterized by relatively small and spatially uniform mixing ratios of the measured species. These aerosol particles were aged to the extent that they had lost their primary source signature. The chemical profile of the background air aerosols was frequently modified by additions from biomass fire plumes, aged tropical marine air, and intrusions of upper tropospheric/lower stratospheric air. Aerosols in boundary layer background air over the boreal forest region of Quebec-Labrador had significantly larger mixing ratios of ammonium and sulfate relative to the Hudson Bay region. This may reflect infiltration of anthropogenic pollution or be due to natural emissions from this region.

Gorzelska, K.↗

NASA NTRS1996

Results of a Parametric Study on 10,000 lb. and 50,000 lb. Permanent Magnetic Actuators

The purpose of this study was to generate design data and complete dynamic performance estimates for a high performance permanent magnet actuator. The basic configuration selected for analysis is an axisymmetric Nd-B-Fe permanent magnet actuator capable of providing force in one direction along its major axis. The actuator consisted of two main axisymmetric components separated by an air gap. The design was optimized for each value of force, gap and magnetic field to yield minimum weight and maximum lift to weight ratio. The basic conclusion is that, within parameters considered, the 10,000 lb. and 50,000 lb. actuators are lightweight and compact. As expected for most permanent magnet devices, the smaller ones have higher lift to eight ratios.

Stekly, Z. J. J.↗

NASA NTRS1997

Micro-Mechanical Voltage Tunable Fabry-Perot Filters Formed in (111) Silicon

The MEMS (Micro-Electro-Mechanical-Systems) technology is quickly evolving as a viable means to combine micro-mechanical and micro-optical elements on the same chip. One MEMS technology that has recently gained attention by the research community is the micro-mechanical Fabry-Perot optical filter. A MEMS based Fabry-Perot consists of a vertically integrated structure composed of two mirrors separated by an air gap. Wavelength tuning is achieved by applying a bias between the two mirrors resulting in an attractive electrostatic force which pulls the mirrors closer. In this work, we present a new micro-mechanical Fabry-Perot structure which is simple to fabricate and is integratable with low cost silicon photodetectors and transistors. The structure consists of a movable gold coated oxide cantilever for the top mirror and a stationary Au/Ni plated silicon bottom mirror. The fabrication process is single mask level, self aligned, and requires only one grown or deposited layer. Undercutting of the oxide cantilever is carried out by a combination of RIE and anisotropic KOH etching of the (111) silicon substrate. Metallization of the mirrors is provided by thermal evaporation and electroplating. The optical and electrical characteristics of the fabricated devices were studied and show promissing results. A wavelength shift of 120nm with 53V applied bias was demonstrated by one device geometry using 6.27 micrometer air gap. The finesse of the structure was 2.4. Modulation bandwidths ranging from 91KHz to greater than 920KHz were also observed. Theoretical calculations show that if mirror reflectivity, smoothness, and parallelism are improved, a finesse of 30 is attainable. The predictions also suggest that a reduction of the air gap to 1 micrometer results in an increased wavelength tuning range of 175 nm with a CMOS compatible 4.75V.

Patterson, James D.↗