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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Handling Qualities Influences on Civil Tiltrotor Terminal Operating Procedure Development

The potential for tiltrotor aircraft as civil transports has been well recognized. Realization of that potential requires development of operating procedures tailored to take advantage of the tiltrotor's capabilities, including thrust vectoring independent of body pitch attitude and good low-speed control. While the tiltrotor shares flight characteristics with both fixed wing airplanes and helicopters, it must convert between those flight modes, typically within the context of precise terminal operations. A series of piloted simulation experiments has been conducted on the NASA Ames Research Center Vertical Motion Simulator (VMS) to investigate the influence of tiltrotor cockpit design features on developing certification and operating criteria for civil tiltrotor transports. Handling qualities evaluations have shaped cockpit design guidelines and operating procedure development for a civil tiltrotor. In particular, four topics demonstrate the interplay of handling qualities and operations profile in the development of terminal operating procedures and cockpit or control equipment for a civil tiltrotor: conversion (airplane to helicopter mode), final approach path angle, operating profile speeds and speed changes (particularly under instrument conditions), and one engine inoperative operational considerations.

Decker, William A.↗
NASA NTRS2005

Gen 2.0 Mixer/Ejector Nozzle Test at LSAF June 1995 to July 1996

Testing of the HSCT Generation 2.0 nozzle model hardware was conducted at the Boeing Low Speed Aeroacoustic Facility, LSAF. Concurrent measurements of noise and thrust were made at critical takeoff design conditions for a variety of mixer/ejector model hardware. Design variables such as suppressor area ratio, mixer area ratio, liner type and thickness, ejector length, lobe penetration, and mixer chute shape were tested. Parallel testing was conducted at G.E.'s Cell 41 acoustic free jet facility to augment the LSAF test. The results from the Gen 2.0 testing are being used to help shape the current nozzle baseline configuration and guide the efforts in the upcoming Generation 2.5 and 3.0 nozzle tests. The Gen 2.0 results have been included in the total airplane system studies conducted at MDC and Boeing to provide updated noise and thrust performance estimates.

Arney, L. D.↗
NASA NTRS2015

Influence of Surface Properties and Impact Conditions on Insect Residue Adhesion

Airflow over airfoils used on current commercial aircraft transitions from laminar to turbulent at relatively low chord positions. As a result, drag increases, requiring more thrust to maintain flight. An airfoil with increased laminar flow would experience reduced drag and a lower fuel burn rate. One of the objectives of NASA's Environmentally Responsible Aviation project is to identify and demonstrate technologies that will enable more environmentally friendly commercial aircraft. While more aerodynamically efficient airfoil shapes can be designed, surface contamination from ice, dirt, pollen, runway debris, and insect residue can degrade performance.

Wohl, Christopher J.↗
NASA NTRS2015

NASA's Vision for Potential Energy Reduction from Future Generations of Propulsion Technology

Through a robust partnership with the aviation industry, over the past 50 years NASA programs have helped foster advances in propulsion technology that enabled substantial reductions in fuel consumption for commercial transports. Emerging global trends and continuing environmental concerns are creating challenges that will very likely transform the face of aviation over the next 20-40 years. In recognition of this development, NASA Aeronautics has established a set of Research Thrusts that will help define the future direction of the agency's research technology efforts. Two of these thrusts, Ultra-Efficient Commercial Vehicles and Transition to Low-Carbon Propulsion, serve as cornerstones for the Advanced Air Transport Technology (AATT) project. The AATT project is exploring and developing high-payoff technologies and concepts that are key to continued improvement in energy efficiency and environmental compatibility for future generations of fixed-wing, subsonic transports. The AATT project is primarily focused on the N+3 timeframe, or 3 generations from current technology levels. As should be expected, many of the propulsion system architectures technologies envisioned for N+3 vary significantly from todays engines. The use of batteries in a hybrid-electric configuration or deploying multiple fans distributed across the airframe to enable higher bypass ratios are just two examples of potential advances that could enable substantial energy reductions over current propulsion systems.

Airbreathing Propulsion↗
NASA NTRS2015

Key Performance Parameter Driven Technology Goals for Electric Machines and Power Systems

Transitioning aviation to low carbon propulsion is one of the crucial strategic research thrust and is a driver in the search for alternative propulsion system for advanced aircraft configurations. This work requires multidisciplinary skills coming from multiple entities. The feasibility of scaling up various electric drive system technologies to meet the requirements of a large commercial transport is discussed in terms of key parameters. Functional requirements are identified that impact the power system design. A breakeven analysis is presented to find the minimum allowable electric drive specific power and efficiency that can preserve the range, initial weight, operating empty weight, and payload weight of the base aircraft.

Electric Machines↗
NASA NTRS2020

Enabling Deep Space Science Missions with Nuclear Thermal Propulsion

Nuclear thermal propulsion (NTP) enables entirely new classes of deep-space science missions to yield scientific returns that, in most cases, are simply not possible with traditional architectures. NTP systems can yield dramatically reduced interplanetary travel times, deliver roughly 2- 3 times (or more) the mass that can be delivered by conventional chemical propulsion systems, or provide a combination of these advantages to further enhance scientific return. Present NASA and DoD-sponsored plans for NTP systems will mature the technology using prototype and flight demonstration engines to prove the designs. These prototype engines will have performance in the correct thrust range so as to permit use as a low-risk propulsion stage in support of high-payoff deep space science missions. Additionally, the use of low-enriched Uranium (LEU) fuels over highly-enriched Uranium (HEU) fuels reduce the costs of engine development, qualification, acceptance and launch, and lowers the risks associated with proliferation management.

Kurt A Polzin↗
NASA NTRS1989

Space data management at the NSSDC (National Space Sciences Data Center): Applications for data compression

The National Space Science Data Center (NSSDC), established in 1966, is the largest archive for processed data from NASA's space and Earth science missions. The NSSDC manages over 120,000 data tapes with over 4,000 data sets. The size of the digital archive is approximately 6,000 gigabytes with all of this data in its original uncompressed form. By 1995 the NSSDC digital archive is expected to more than quadruple in size reaching over 28,000 gigabytes. The NSSDC digital archive is expected to more than quadruple in size reaching over 28,000 gigabytes. The NSSDC is beginning several thrusts allowing it to better serve the scientific community and keep up with managing the ever increasing volumes of data. These thrusts involve managing larger and larger amounts of information and data online, employing mass storage techniques, and the use of low rate communications networks to move requested data to remote sites in the United States, Europe and Canada. The success of these thrusts, combined with the tremendous volume of data expected to be archived at the NSSDC, clearly indicates that innovative storage and data management solutions must be sought and implemented. Although not presently used, data compression techniques may be a very important tool for managing a large fraction or all of the NSSDC archive in the future. Some future applications would consist of compressing online data in order to have more data readily available, compress requested data that must be moved over low rate ground networks, and compress all the digital data in the NSSDC archive for a cost effective backup that would be used only in the event of a disaster.

Green, James L.↗
NASA NTRS1983

Aerodynamic performance of a fan stage utilizing Variable Inlet Guide Vanes (VIGVs) for thrust modulation

An experimental research program was conducted in the Lewis Research Center's 9x15-foot (2.74x4.57 m) low speed wind tunnel to evaluate the aerodynamic performance of an inlet and fan system with variable inlet guide vanes (VIGVs) for use on a subsonic V/STOL aircraft. At high VIGV blade angles (lower weight flow and thrust levels), the fan stage was stalled over a major portion of its radius. In spite of the stall, fan blade stresses only exceeded the limits at the most extreme flow conditions. It was found that inlet flow separation does not necessarily lead to poor inlet performance or adverse fan operating conditions. Generally speaking, separated inlet flow did not adversely affect the fan blade stress levels. There were some cases, however, at high VIGV angles and high inlet angles-of-attack where excessive blade stress levels were encountered. An evaluation term made up of the product of the distortion parameter, K alpha, the weight flow and the fan pressure ratio minus one, was found to correlate quite well with the observed blade stress results.

Woollett, R. R.↗
NASA NTRS2015

Low-Mass, Low-Power Hall Thruster System

NASA is developing an electric propulsion system capable of producing 20 mN thrust with input power up to 1,000 W and specific impulse ranging from 1,600 to 3,500 seconds. The key technical challenge is the target mass of 1 kg for the thruster and 2 kg for the power processing unit (PPU). In Phase I, Busek Company, Inc., developed an overall subsystem design for the thruster/cathode, PPU, and xenon feed system. This project demonstrated the feasibility of a low-mass power processing architecture that replaces four of the DC-DC converters of a typical PPU with a single multifunctional converter and a low-mass Hall thruster design employing permanent magnets. In Phase II, the team developed an engineering prototype model of its low-mass BHT-600 Hall thruster system, with the primary focus on the low-mass PPU and thruster. The goal was to develop an electric propulsion thruster with the appropriate specific impulse and propellant throughput to enable radioisotope electric propulsion (REP). This is important because REP offers the benefits of nuclear electric propulsion without the need for an excessively large spacecraft and power system.

Pote, Bruce↗
NASA NTRS2021

Adaptive Aerostructures for Revolutionary Civil Supersonic Transportation

To enable commercially viable civil supersonic transport (SST) aircraft, innovative solutions must be developed to meet noise and efficiency requirements for overland flight. This research effort consists of a multidisciplinary team of academic and industrial experts exploring for the first time the potential of small real-time geometric outer mold line (OML) reconfigurations to minimize sonic boom signatures and aircraft drag in response to changing ambient conditions, thereby enabling noise-compliant overland supersonic flight. The team utilizes recent advances in supersonic computational fluid dynamic (CFD) methods, new noise prediction tools, and new design approaches to consider embedded highly energy-dense shape memory alloy (SMA) actuators for local shape modifications to an SST aircraft leading to optimal low boom signature and low drag in different environments. This university-led program will provide strategic leadership toward technology convergence that advances NASA's Aerospace Research Mission Directorate's (ARMD) research objectives with regard to Thrust 2: “Innovation in Commercial Supersonic Aircraft” by exploring for the first time enabling low-boom operation across a range of flight conditions via structural adaptivity, and will promote education of the next generation of engineers. The overall research strategy is to pursue three critical areas: the design of configurations for reducing boom, SMA material development and modeling, and technology feasibility demonstration in a relevant environment. Initially, the team will identify potential applications where structure or geometry adaptivity provides a benefit in noise or drag across the entire flight envelope. For selected applications/structural locations, required OML geometry changes will be determined based on analysis of sonic boom ground signature and drag reduction using new design tools, trade studies, and atmospheric sensing techniques. Designs will be developed and evaluated against requirements on loading, stroke length, and operational temperature. New alloy formulations will be developed tailored for both autonomous and controlled actuation modes. As the SMA material development matures, integrated system-level factors will be investigated. Optimized designs for small-scale distributed adaptivity applications of maximum benefit will then be matured and tested, moving toward demonstration of the innovative technology approaches at a TRL 4-5 and showing that sonic booms can be reduced by reconfiguration on demand.

Koushik Datta↗
NASA NTRS2008

Operability of an Ejector Enhanced Pulse Combustor in a Gas Turbine Environment

A pressure-gain combustor comprised of a mechanically valved, liquid fueled pulsejet, an ejector, and an enclosing shroud, was coupled to a small automotive turbocharger to form a self-aspirating, thrust producing gas turbine engine. The system was constructed in order to investigate issues associated with the interaction of pulsed combustion devices and turbomachinery. Installed instrumentation allowed for sensing of distributed low frequency pressure and temperature, high frequency pressure in the shroud, fuel flow rate, rotational speed, thrust, and laboratory noise. The engine ran successfully and reliably, achieving a sustained thrust of 5 to 6 lbf, and maintaining a rotor speed of approximately 90,000 rpm, with a combustor pressure gain of approximately 4 percent. Numerical simulations of the system without pressure-gain combustion indicated that the turbocharger would not operate. Thus, the new combustor represented a substantial improvement in system performance. Acoustic measurements in the shroud and laboratory indicated turbine stage sound pressure level attenuation of 20 dB. This is consistent with published results from detonative combustion experiments. As expected, the mechanical reed valves suffered considerable damage under the higher pressure and thermal loading characteristics of this system. This result underscores the need for development of more robust valve systems for this application. The efficiency of the turbomachinery components did not appear to be significantly affected by unsteadiness associated with pulsed combustion, though the steady component efficiencies were already low, and thus not expected to be particularly sensitive.

Paxson, Daniel E.↗
NASA NTRS2003

Ultra High Bypass Ratio Low Noise Engine Study

A study was conducted to identify engine cycle and technologies needed for a regional aircraft which could be capable of achieving a 10 EPNdB reduction in community noise level relative to current FAR36 Stage 3 limits. The study was directed toward 100-passenger regional aircraft with engine configurations in the 15,000 pound thrust class. The study focused on Ultra High Bypass Ratio (UHBR) cycles due to low exhaust jet velocities and reduced fan tip speeds. The baseline engine for this study employed a gear-driven, 1000 ft/sec tip speed fan and had a cruise bypass ratio of 14:1. A revised engine configuration employing fan and turbine design improvements are predicted to be 9.2 dB below current takeoff limits and 12.8 dB below current approach limits. An economic analysis was also done by estimating Direct Operating Cost (DOC).

Dalton, W. N., III↗
NASA NTRS1983

Energetics and optimum motion of oscillating lifting surfaces

Low-frequency, unsteady, lifting-line theory is used to characterize the energetics and optimum motion of an unswept rigid wing oscillating harmonically in an inviscid, incompressible flow. The energetics calculations account for the leading edge suction force, the power absorbed in the wing oscillations, and the energy loss rate produced by vortex shedding. Optimization is achieved by minimizing the average energy loss rate in relation to a given thrust, and a unique solution is found in the three dimensional case for low, reduced frequencies. The two-dimensional solution is nonunique, a condition which is examined in terms of the normal modes of the energy loss rate matrix. An invisible mode with a hydrodynamic efficiency of 100 pct is obtained in the two-dimensional case, causing the nonuniqueness of the solution by yielding no fixed positive thrust through perfect unsteady feathering.

Ahmadi, A. R.↗
NASA NTRS1999

Piloted Simulation Study of the Effects of High-Lift Aerodynamics on the Takeoff Noise of a Representative High-Speed Civil Transport

As part of an effort between NASA and private industry to reduce airport-community noise for high-speed civil transport (HSCT) concepts, a piloted simulation study was initiated for the purpose of predicting the noise reduction benefits that could result from improved low-speed high-lift aerodynamic performance for a typical HSCT configuration during takeoff and initial climb. Flight profile and engine information from the piloted simulation were coupled with the NASA Langley Aircraft Noise Prediction Program (ANOPP) to estimate jet engine noise and to propagate the resulting source noise to ground observer stations. A baseline aircraft configuration, which also incorporated different levels of projected improvements in low-speed high-lift aerodynamic performance, was simulated to investigate effects of increased lift and lift-to-drag ratio on takeoff noise levels. Simulated takeoff flights were performed with the pilots following a specified procedure in which either a single thrust cutback was performed at selected altitudes ranging from 400 to 2000 ft, or a multiple-cutback procedure was performed where thrust was reduced by a two-step process. Results show that improved low-speed high-lift aerodynamic performance provides at least a 4 to 6 dB reduction in effective perceived noise level at the FAA downrange flyover measurement station for either cutback procedure. However, improved low-speed high-lift aerodynamic performance reduced maximum sideline noise levels only when using the multiple-cutback procedures.

Glaab, Louis J.↗
NASA NTRS1978

Supersonic transport

An aircraft of supersonic transport configuration is described, featuring thrust vectoring in conjunction with wing apex segments used as canard surfaces during takeoff, landing, and low-speed flight. The angle of incidence of the wing apex segments, when the segments were functioning as canard surfaces, was variable with respect to the aircraft angle of attack. The wing apex segments furthermore formed a portion of the main wing panel swept leading edge when not functioning as canard surfaces. The combination of thrust vectoring and deployable wing apex segments resulted in increased aircraft range and improved low speed longitudinal stability while providing acceptable takeoff length capabilities.

Coe, P. L., Jr.↗
NASA NTRS2004

Generation 1.5 High Speed Civil Transport (HSCT) Exhaust Nozzle Program

The objective of this program was to conduct an experimental and analytical evaluation of low noise exhaust nozzles suitable for future High-Speed Civil Transport (HSCT) aircraft. The experimental portion of the program involved parametric subscale performance model tests of mixer/ejector nozzles in the takeoff mode, and high-speed tests of mixer/ejectors converted to two-dimensional convergent-divergent (2-D/C-D), plug, and single expansion ramp nozzles (SERN) in the cruise mode. Mixer/ejector results show measured static thrust coefficients at secondary flow entrainment levels of 70 percent of primary flow. Results of the high-speed performance tests showed that relatively long, straight-wall, C-D nozzles could meet supersonic cruise thrust coefficient goal of 0.982; but the plug, ramp, and shorter C-D nozzles required isentropic contours to reach the same level of performance. The computational fluid dynamic (CFD) study accurately predicted mixer/ejector pressure distributions and shock locations. Heat transfer studies showed that a combination of insulation and convective cooling was more effective than film cooling for nonafterburning, low-noise nozzles. The thrust augmentation study indicated potential benefits for use of ejector nozzles in the subsonic cruise mode if the ejector inlet contains a sonic throat plane.

Thayer, E. B.↗
NASA NTRS1983

Aerodynamic performance of a fan stage utilizing variable inlet guide vanes (VIGV's) for thrust modulation

An experimental research program was conducted in the Lewis Research Center's 9 x 15-foot (2.74 x 4.57 m) low speed wind tunnel to evaluate the aerodynamic performance of an inlet and fan system with variable inlet guide vanes (VIGVs) for use on a subsonic V/STOL aircraft. At high VIGV blade angles (lower weight flow and thrust levels), the fan stage was stalled over a major portion of its radius. In spite of the stall, fan blade stresses only exceeded the limits at the most extreme flow conditions. It was found that inlet flow separation does not necessarily lead to poor inlet performance or adverse fan operating conditions. Generally speaking, separated inlet flow did not adversely affect the fan blade stress levels. There were some cases, however, at high VIGV angles and high inlet angles-of-attack where excessive blade stress levels were encountered. An evaluation term made up of the product of the distortion parameter, K alpha, the weight flow and the fan pressure ratio minus one, was found to correlate quite well with the observed blade stress results. Previously announced in STAR as N83-27957

Woollett, R. R.↗
NASA NTRS1999

Electrodynamic Thrust Performance for Space Solar Satellite Applications

The use of spinning tethers to transfer payloads from low earth orbit (LEO) to geosynchronous earth orbit (GEO) has previously been considered for payload masses up to 4000 kg (4 MT). The construction of the solar power station requires a transfer of 22,568 MT per year from LEO to GEO. This is envisioned to be carried out in payload units of 20 MT or 40 MT, which implies a frequency of 1188 or 594 flights per year, respectively. We could say from the outset that the use of spinning tethers for such large payloads at such high launch frequencies does not appear promising. This is inherent in the principles of spinning tether transfer, which we will briefly sketch below. Somewhat different scenarios are possible, but the basic physics remains the same. We consider only a single stage from LEO to GTO tether system, since the complexity involved in phasing the launches, docking, and spinups for a two-stage system for so many payloads rules out a two-stage system, in our opinion. The payload must first be launched to LEO, where it docks with the tether launch platform and is connected to the tether. The tether (tens of kilometers long) is then deployed with the payload upward. In order to give the payload the velocity necessary to launch it into a geosynchronous transfer orbit (GTO), i.e., to impart the required Av, the tethered system must be spun up about the center of mass of the tether-platform-payload system. The two end masses (platform and payload) are driven to rotate about the center of mass of the tethered system. Both the final rotational velocity and the phasing of the tether spin have to be controlled so that payload is in the vertically up position at the perigee of the LEO and with the velocity required to achieve the GTO when it is released at that point. Upon release, the payload then goes into GTO, where it again requires an acceleration to reach GEO (circularization of the orbit). The platform goes into a lower orbit, from which it must be raised in order to be at the proper LEO for docking with another payload. For this scheme to make sense at all, the platform must be envisioned as having a solar powered electrical thrust system to regain LEO and to spin up the tethered system. Similarly, solar powered electrical propulsion would be used to circularize the orbit to GEO.

Estes, Robert D.↗