Impacts of broadened-specification fuels on aircraft turbine engine combustors
(Previously cited in issue 12, p. 1972, Accession no. A81-29927)
Bahr, D. W.↗
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General Aviation Aircraft Reliability Study
This reliability study was performed in order to provide the aviation community with an estimate of Complex General Aviation (GA) Aircraft System reliability. To successfully improve the safety and reliability for the next generation of GA aircraft, a study of current GA aircraft attributes was prudent. This was accomplished by benchmarking the reliability of operational Complex GA Aircraft Systems. Specifically, Complex GA Aircraft System reliability was estimated using data obtained from the logbooks of a random sample of the Complex GA Aircraft population.
Pettit, Duane↗
Historical Review of Uncommanded Lateral-Directional Motions at Transonic Conditions
This paper presents the results of a survey of past experiences with uncommanded lateral-directional motions at transonic speeds during specific military aircraft programs. The effort was undertaken to provide qualitative and quantitative information on past airplane programs that might be of use to the participants in the joint NASA/Navy/Air Force Abrupt Wing Stall (AWS) Program. The AWS Program was initiated because of the experiences of the F/A-l8E/F development program, during which unexpected, severe wing-drop motions were encountered by preproduction aircraft at transonic conditions. These motions were judged to be significantly degrading to the primary mission requirements of the aircraft. Although the problem was subsequently solved for the production version of the F/A-l8E/F, a high-level review panel emphasized the poor understanding of such phenomena and issued a strong recommendation to: "Initiate a national research effort to thoroughly and systematically study the wing drop phenomena." A comprehensive, cooperative NASA/Navy/Air Force AWS Program was designed to respond to provide the required technology requirements. As part of the AWS Program, a work element was directed at a historical review of wing-drop experiences in past aircraft development programs at high subsonic and transonic speeds. In particular, information was requested regarding: specific aircraft configurations that exhibited uncommanded motions and the nature of the motions; geometric characteristics of the air- planes; flight conditions involved in occurrences; relevant data, including wind-tunnel, computational, and flight sources; figures of merit used for analyses; and approaches used to alleviate the problem. An attempt was also made to summarize some of the more important lessons learned from past experiences, and to recommend specific research efforts. In addition to providing technical information to assist the AWS research objectives, the study produced fundamental information regarding the historical challenge of uncommanded lateral-directional motions at transonic conditions and the associated aerodynamic phenomena.
Chambers, Joseph R.↗
Historical Review of Uncommanded Lateral-Directional Motions At Transonic Conditions (Invited)
This paper presents the results of a survey of past experiences with uncommanded lateral-directional motions at transonic speeds during specific military aircraft programs. The effort was undertaken to provide qualitative and quantitative information on past airplane programs that might be of use to the participants in the joint NASA/Navy/Air Force Abrupt Wing Stall (AWS) Program. The AWS Program was initiated because of the experiences of the F/A-18E/F development program, during which unexpected, severe wing-drop motions were encountered by preproduction aircraft at transonic conditions. These motions were judged to be significantly degrading to the primary mission requirements of the aircraft. Although the problem was subsequently solved for the production version of the F/A-l8E/F, a high-level review panel emphasized the poor understanding of such phenomena and issued a strong recommendation to: Initiate a national research effort to thoroughly and systematically study the wing drop phenomena. A comprehensive, cooperative NASA/Navy/Air Force AWS Program was designed to respond to provide the required technology requirements. As part of the AWS Program, a work element was directed at a historical review of wing-drop experiences in past aircraft development programs at high subsonic and transonic speeds. In particular, information was requested regarding: specific aircraft configurations that exhibited uncommanded motions and the nature of the motions; geometric characteristics of the air- planes; flight conditions involved in occurrences; relevant data, including wind-tunnel, computational, and flight sources; figures of merit used for analyses; and approaches used to alleviate the problem. An attempt was also made to summarize some of the more important lessons learned from past experiences, and to recommend specific research efforts. In addition to providing technical information to assist the AWS research objectives, the study produced fundamental information regarding the historical challenge of uncommanded lateral-directional motions at transonic conditions and the associated aerodynamic phenomena.
Chambers, Joseph R.↗
Impact of NASA-sponsored research on aircraft turbine engine bearing specifications
The advancement of the state-of-the-art in aircraft bearing materials technology is reviewed. Current specifications and design practices resulting from NASA-sponsored programs are included.
Nahm, A. H.↗
Impact of broad-specification fuels on future jet aircraft
The effects that broad specification fuels have on airframe and engine components were discussed along with the improvements in component technology required to use broad specification fuels without sacrificing performance, reliability, maintainability, or safety.
Grobman, J. S.↗
Recommendations for field measurements of aircraft noise
Specific recommendations for environmental test criteria, data acquisition procedures, and instrument performance requirements for measurement of noise levels produced by aircraft in flight are provided. Recommendations are also given for measurement of associated airplane and engine parameters and atmospheric conditions. Recommendations are based on capabilities which were available commercially in 1981; they are applicable to field tests of aircraft flying subsonically past microphones located near the surface of the ground either directly under or to the side of a flight path. Aircraft types covered by the recommendations include fixed-wing airplanes powered by turbojet or turbofan engines or by propellers. The recommended field-measurement procedures are consistent with assumed requirements for data processing and analysis.
Marsh, A. H.↗
Model Specification for Rework of Aircraft Engine, Power Transmission, and Accessory/Auxiliary Ball and Roller Bearings
This document provides a model specification for the rework and/or repair of bearings used in aircraft engines, helicopter main power train transmissions, and auxiliary bearings determined to be critical by virtue of performance, function, or availability. The rolling-element bearings to be processed under the provisions of this model specification may be used bearings removed after service, unused bearings returned from the field, or certain rejected bearings returned for reinspection and salvage. In commercial and military aircraft application, it has been a practice that rolling-element bearings removed at maintenance or overhaul be reworked and returned to service. Depending on the extent of rework and based upon theoretical analysis, representative life factors (LF) for bearings subject to rework ranged from 0.87 to 0.99 the lives of new bearings. Based on bearing endurance data, 92 percent of the bearing sets that would be subject to rework would result in L(sub 10) lives equaling and/or exceeding that predicted for new bearings. The remaining 8 percent of the bearings have the potential to achieve the analytically predicted life of new bearings when one of the rings is replaced at rework. The potential savings from bearing rework varies from 53 to 82 percent of that of new bearings depending on the cost, size, and complexity of the bearing
Zaretsky, Erwin V.↗
Authoring, Analyzing, and Monitoring Requirements for a Lift-Plus-Cruise Aircraft
Requirements specification and analysis is widely applied to ensure the correctness of industrial systems in safety critical domains. Requirements are often initially written in natural language, which is highly ambiguous, and as a second step transformed into a language with rigorous semantics for formal analysis. In this paper, we report on our experience in requirements creation and analysis, as well as run-time monitor generation using the Formal Requirement Elicitation Tool (FRET), on an industrial case study for a Lift-Plus-Cruise concept aircraft. We study the creation of requirements directly in the structured language of FRET without a prior definition of the same requirements in natural language. We focus on requirements describing state machines and discuss the challenges that we faced, in terms of creating requirements and generating monitors. We demonstrate how realizability, i.e., checking whether a requirements specification can be implemented, is crucial for understanding temporal interdependencies among requirements. Our study is the first complete attempt at using FRET to create industrial, realizable requirements and generate run-time monitors. Insight from lessons learned was materialized into new features in the FRET and JKind analysis frameworks.
Requirements engineering↗
Authoring, Analyzing, and Monitoring Requirements for a Lift-Plus-Cruise Aircraft
Requirements specification and analysis is widely applied to ensure the correctness of industrial systems in safety critical domains. Requirements are often initially written in natural language, which is highly ambiguous, and as a second step transformed into a language with rigorous semantics for formal analysis. [Question/problem] In this paper, we report on our experience in requirements creation and analysis, as well as run-time monitor generation using the Formal Requirement Elicitation Tool (FRET), on an industrial case study for a Lift-Plus-Cruise concept aircraft. [Principal ideas/results] We study the creation of requirements directly in the structured language of FRET without a prior definition of the same requirements in natural language. We focus on requirements describing state machines and discuss the challenges that we faced, in terms of creating requirements and generating monitors. We demonstrate how realizability, i.e., checking whether a requirements specification can be implemented, is crucial for understanding temporal interdependencies among requirements. [Contribution] Our study is the first complete attempt at using FRET to create industrial, realizable requirements and generate run-time monitors. Insight from lessons learned was materialized into new features in the FRET and JKind analysis frameworks.
Requirements engineering↗
Supporting the Use of Unmanned Aircraft Systems(UAS) for Global Science Observations in Civil and Segregated Airspace
Unmanned Aircraft Systems (UAS) are growing more popular within the earth science community as a way to augment measurements currently made with manned aircraft. UAS arc uniquely suited for applications that require long dwell times and/or in locations that are generally too dangerous for manned aircraft. Environmental monitoring in areas like the Arctic or obtaining data within a hurricane are just a couple of examples of many applications to which UAS are ideally suited. However, UAS are not without their challenges. Most unmanned aircraft are unable to meet current airspace regulations that are in place for manned aircraft, and specific airspace standards and regulations for unmanned aircraft do not exist. As a result, gaining access to civil airspace for flights is very difficult around the world. Under Term of Reference 48 within the ISPRS Commission 1, WGI/I: Standardization of Aircraft Interfaces, efforts have been made to understand and quantify the current state of UAS airspace access on a global scale. The results of these efforts will be presented along with examples of successful science missions that have been conducted internationally during the past year.
Mulac, B. L.↗
An Intrinsic Fiber-Optic Sensor for Structure Lightning Current Measurement
An intrinsic optical-fiber sensor based on Faraday Effect is developed that is highly suitable for measuring lightning current on aircraft, towers and complex structures. Originally developed specifically for aircraft installations, it is light-weight, non-conducting, structure conforming, and is immune to electromagnetic interference, hysteresis and saturation. It can measure total current down to DC. When used on lightning towers, the sensor can help validate other sensors and lightning detection network measurements. Faraday Effect causes light polarization to rotate when the fiber is exposed to a magnetic field in the direction of light propagation. Thus, the magnetic field strength can be determined from the light polarization change. By forming closed fiber loops and applying Ampere's law, measuring the total light rotation yields the total current enclosed. A broadband, dual-detector, reflective polarimetric scheme allows measurement of both DC component and AC waveforms with a 60 dB dynamic range. Two systems were built that are similar in design but with slightly different sensitivities. The 1310nm laser system can measure 300 A - 300 kA, and has a 15m long sensing fiber. It was used in laboratory testing, including measuring current on an aluminum structure simulating an aircraft fuselage or a lightning tower. High current capabilities were demonstrated up to 200 kA at a lightning test facility. The 1550nm laser system can measure 400 A - 400 kA and has a 25m fiber length. Used in field measurements, excellent results were achieved in the summer of 2012 measuring rocket-triggered lightning at the International Center for Lightning Research and Testing (ICLRT), Camp Blanding, Florida. In both systems increased sensitivity can be achieved with multiple fiber loops. The fiber optic sensor provides many unique capabilities not currently possible with traditional sensors. It represents an important new tool for lightning current measurement where low weight, complex shapes, large structure dimension, large current, and low frequency capabilities are important considerations.
Nguyen, Truong X.↗
Initial specifications for van and aircraft
Proposed testing program for strapdown inertial system containing platform gyros and pendulous gyros
Benson, D. O., Jr.↗
NASA Collaborative Research on the Ultra High Bypass Engine Cycle and Potential Benefits for Noise, Performance, and Emissions
The National Aeronautics and Space Administration has taken an active role in collaborative research with the U.S. aerospace industry to investigate technologies to minimize the impact of aviation on the environment. In December 2006, a new program, called the Fundamental Aeronautics Program, was established to enhance U.S. aeronautics technology and conduct research on energy, efficiency and the environment. A project within the overall program, the Subsonic Fixed Wing Project, was formed to focus on research related to subsonic aircraft with specific goals and time based milestones to reduce aircraft noise, emissions and fuel burn. This paper will present an overview of the Subsonic Fixed Wing Project environmental goals and describe a segment of the current research within NASA and also were worked collaboratively with partners from the U.S. aerospace industry related to the next generation of aircraft that will have lower noise, emissions and fuel burn.
Hughes, Christopher E.↗
Multi-Agent Flight Simulation with Robust Situation Generation
A robust situation generation architecture has been developed that generates multi-agent situations for human subjects. An implementation of this architecture was developed to support flight simulation tests of air transport cockpit systems. This system maneuvers pseudo-aircraft relative to the human subject's aircraft, generating specific situations for the subject to respond to. These pseudo-aircraft maneuver within reasonable performance constraints, interact in a realistic manner, and make pre-recorded voice radio communications. Use of this system minimizes the need for human experimenters to control the pseudo-agents and provides consistent interactions between the subject and the pseudo-agents. The achieved robustness of this system to typical variations in the subject's flight path was explored. It was found to successfully generate specific situations within the performance limitations of the subject-aircraft, pseudo-aircraft, and the script used.
Johnson, Eric N.↗
Comparison of predicted engine core noise with current and proposed aircraft noise certification requirements
Predicted engine core noise levels are compared with measured total aircraft noise levels and with current and proposed federal noise certification requirements. Comparisons are made at the FAR-36 measuring stations and include consideration of both full- and cutback-power operation at takeoff. In general, core noise provides a barrier to achieving proposed EPA stage 5 noise levels for all types of aircraft. More specifically, core noise levels will limit further reductions in aircraft noise levels for current widebody commercial aircraft.
Vonglahn, U. H.↗
Ozone contamination in aircraft cabins - Results from GASP data and analyses
The paper reviews results from the NASA Global Atmospheric Sampling Program (GASP) pertaining to the problem of ozone contamination in commercial aircraft cabins. Specifically, analyses of GASP data have (1) confirmed the high ozone levels in aircraft cabins and documented the ratio of ozone inside and outside the cabins of two B747 airliners, including the effects of air conditioning modifications on that ratio; (2) defined ambient ozone climatology at commercial aircraft cruise altitudes, including tabulation of encounter frequency data; and (3) outlined procedures for estimating the frequency of flights encountering high cabin ozone levels using climatological ambient ozone data and verified these procedures against cabin measurements.
Holdeman, J. D.↗
Passive Microwave Spectral Imaging of Amospheric Structure
The primary objective of this research was to improve the scientific foundation necessary to full realization of the meteorological potential of the NOAA Advanced Microwave Sounding Unit (AMSU) recently first launched on the NOAA-15 satellite in May, 1998. These advances were made in four main areas: (1) improvements, based on aircraft observations, in the atmospheric transmittance expressions used for interpreting AMSU and similar data; (2) development of neural network retrieval methods for cloud top altitude estimates of approximately 1-km accuracy under cirrus shields--the altitude is that of the larger ice particles aloft, which is related to precipitation rate; (3) analysis of early AMSU flight data with respect to its precipitation sensitivity and fine-scale thermal structure; and (4) improvements to the 54-GHz and 118-GHz MTS aircraft imaging spectrometer now operating on the NASA ER-2 aircraft. More specifically, the oxygen transmittance expressions near 118 GHz were in better agreement with aircraft data when the temperature dependence exponent of the 118.75-GHz linewidth was increased from the MPM92 value (Liebe et al., 1992) of 0.8 to 0.97+/-0.03. In contrast, the observations 52.5-55.8 GHz were consistent with the MPM92 model. Neural networks trained on comparisons of 118-GHz spectral data and coincident stereoscopic video images of convective cells observed from 20-km altitude yielded agreement in their peak altitudes within as little as 1.36 km rms, much of which is stereoscopic error. Imagery using these methods produced useful characterizations for Cyclone Oliver in 1993 and other storms (Schwartz et al., 1996; Spina et al., 1998). Similar neural network techniques yielded simulated rms errors in relative humidity retrievals of 6-14 percent over ocean and 6-15 percent over land at pressure levels from 1013 to 131 mbar (Cabrera-Mercader and Staelin, 1995).
Staelin, David H.↗