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At least 955 records · Page 53
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NASA NTRS2008

Vibration Response Models of a Stiffened Aluminum Plate Excited by a Shaker

Numerical models of structural-acoustic interactions are of interest to aircraft designers and the space program. This paper describes a comparison between two energy finite element codes, a statistical energy analysis code, a structural finite element code, and the experimentally measured response of a stiffened aluminum plate excited by a shaker. Different methods for modeling the stiffeners and the power input from the shaker are discussed. The results show that the energy codes (energy finite element and statistical energy analysis) accurately predicted the measured mean square velocity of the plate. In addition, predictions from an energy finite element code had the best spatial correlation with measured velocities. However, predictions from a considerably simpler, single subsystem, statistical energy analysis model also correlated well with the spatial velocity distribution. The results highlight a need for further work to understand the relationship between modeling assumptions and the prediction results.

Cabell, Randolph H.↗
NASA NTRS2009

An Analytical Assessment of NASA's N+1 Subsonic Fixed Wing Project Noise Goal

The Subsonic Fixed Wing Project of NASA's Fundamental Aeronautics Program has adopted a noise reduction goal for new, subsonic, single-aisle, civil aircraft expected to replace current 737 and A320 airplanes. These so-called 'N+1' aircraft - designated in NASA vernacular as such since they will follow the current, in-service, 'N' airplanes - are hoped to achieve certification noise goal levels of 32 cumulative EPNdB under current Stage 4 noise regulations. A notional, N+1, single-aisle, twinjet transport with ultrahigh bypass ratio turbofan engines is analyzed in this study using NASA software and methods. Several advanced noise-reduction technologies are analytically applied to the propulsion system and airframe. Certification noise levels are predicted and compared with the NASA goal.

Berton, Jeffrey J.↗
NASA NTRS2009

Smoke Detection for the Orion Crew Exploration Vehicle

The Orion Crew Exploration Vehicle (CEV) requires a smoke detector for the detection of particulate smoke products as part of the Fire Detection and Suppression (FDS) system. The smoke detector described in this paper is an adaptation of a mature commercial aircraft design for manned spaceflight. Changes made to the original design include upgrading the materials and electronic to space-qualified parts, and modifying the mechanical design to withstand launch and landing loads. The results of laboratory characterization of the response of the new design to test particles are presented.

Sutin, Brian M.↗
NASA NTRS2010

An Analytical Assessment of NASA's N(+)1 Subsonic Fixed Wing Project Noise Goal

The Subsonic Fixed Wing Project of NASA s Fundamental Aeronautics Program has adopted a noise reduction goal for new, subsonic, single-aisle, civil aircraft expected to replace current 737 and A320 airplanes. These so-called "N+1" aircraft--designated in NASA vernacular as such since they will follow the current, in-service, "N" airplanes--are hoped to achieve certification noise goal levels of 32 cumulative EPNdB under current Stage 4 noise regulations. A notional, N+1, single-aisle, twinjet transport with ultrahigh bypass ratio turbofan engines is analyzed in this study using NASA software and methods. Several advanced noise-reduction technologies are empirically applied to the propulsion system and airframe. Certification noise levels are predicted and compared with the NASA goal.

Berton, Jeffrey J.↗
NASA NTRS2011

Effects of Inlet Distortion on Aeromechanical Stability of a Forward-Swept High-Speed Fan

Concerns regarding noise, propulsive efficiency, and fuel burn are inspiring aircraft designs wherein the propulsive turbomachines are partially (or fully) embedded within the airframe; such designs present serious concerns with regard to aerodynamic and aeromechanic performance of the compression system in response to inlet distortion. Separately, a forward-swept high-speed fan was developed to address noise concerns of modern podded turbofans; however this fan encounters aeroelastic instability (flutter) as it approaches stall. A three-dimensional, unsteady, Navier-Stokes computational fluid dynamics code is applied to analyze and corroborate fan performance with clean inlet flow. This code, already validated in its application to assess aerodynamic damping of vibrating blades at various flow conditions, is modified and then applied in a computational study to preliminarily assess the effects of inlet distortion on aeroelastic stability of the fan. Computational engineering application and implementation issues are discussed, followed by an investigation into the aeroelastic behavior of the fan with clean and distorted inlets.

Herrick, Gregory P.↗
NASA NTRS2011

MASCOT - MATLAB Stability and Control Toolbox

MASCOT software was created to provide the conceptual aircraft designer accurate predictions of air vehicle stability and control characteristics. The code takes as input mass property data in the form of an inertia tensor, aerodynamic loading data, and propulsion (i.e. thrust) loading data. Using fundamental non-linear equations of motion, MASCOT then calculates vehicle trim and static stability data for any desired flight condition. Common predefined flight conditions are included. The predefined flight conditions include six horizontal and six landing rotation conditions with varying options for engine out, crosswind and sideslip, plus three takeoff rotation conditions. Results are displayed through a unique graphical interface developed to provide stability and control information to the conceptual design engineers using a qualitative scale indicating whether the vehicle has acceptable, marginal, or unacceptable static stability characteristics. This software allows the user to prescribe the vehicle s CG location, mass, and inertia tensor so that any loading configuration between empty weight and maximum take-off weight can be analyzed. The required geometric and aerodynamic data as well as mass and inertia properties may be entered directly, passed through data files, or come from external programs such as Vehicle Sketch Pad (VSP). The current version of MASCOT has been tested with VSP used to compute the required data, which is then passed directly into the program. In VSP, the vehicle geometry is created and manipulated. The aerodynamic coefficients, stability and control derivatives, are calculated using VorLax, which is now available directly within VSP. MASCOT has been written exclusively using the technical computing language MATLAB . This innovation is able to bridge the gap between low-fidelity conceptual design and higher-fidelity stability and control analysis. This new tool enables the conceptual design engineer to include detailed static stability and trim constraints in the conceptual design loop. The unique graphical interface developed for this tool presents the stability data in a format that is understandable by the conceptual designer, yet also provides the detailed quantitative results if desired.

Kenny, Sean↗
NASA NTRS2006

Statistical Detection of Atypical Aircraft Flights

A computational method and software to implement the method have been developed to sift through vast quantities of digital flight data to alert human analysts to aircraft flights that are statistically atypical in ways that signify that safety may be adversely affected. On a typical day, there are tens of thousands of flights in the United States and several times that number throughout the world. Depending on the specific aircraft design, the volume of data collected by sensors and flight recorders can range from a few dozen to several thousand parameters per second during a flight. Whereas these data have long been utilized in investigating crashes, the present method is oriented toward helping to prevent crashes by enabling routine monitoring of flight operations to identify portions of flights that may be of interest with respect to safety issues.

Statler, Irving↗
NASA NTRS2011

First-Order Altitude Effects on the Cruise Efficiency of Subsonic Transport Aircraft

Aircraft fuel efficiency is a function of many different parameters, including characteristics of the engines, characteristics of the airframe, and the conditions under which the aircraft is operated. For a given vehicle, the airframe and engine characteristics are for the most part fixed quantities and efficiency is primarily a function of operational conditions. One important influence on cruise efficiency is cruise altitude. Various future scenarios have been postulated for cruise altitude, from the freedom to fly at optimum altitudes to altitude restrictions imposed for environmental reasons. This report provides background on the fundamental relationships determining aircraft cruise efficiency and examines the sensitivity of efficiency to cruise altitude. Analytical models of two current aircraft designs are used to derive quantitative results. Efficiency penalties are found to be generally less than 1% when within roughly 2000 ft of the optimum cruise altitude. Even the restrictive scenario of constant altitude cruise is found to result in a modest fuel consumption penalty if the fixed altitude is in an appropriate range.

Guynn, Mark D.↗
NASA NTRS2011

PRSEUS Development for the Hybrid Wing Body Aircraft

NASA has created the Environmentally Responsible Aviation (ERA) Project to explore and document the feasibility, benefits and technical risk of advanced vehicle configurations and enabling technologies that will reduce the impact of aviation on the environment. A critical aspect of this pursuit is the development of a lighter, more robust airframe that will enable the introduction of unconventional aircraft configurations that have higher lift to drag ratios, reduced drag, and lower community noise. The primary structural concept being developed for the Hybrid Wing Body aircraft design under the ERA project in the Airframe Technology element is the PRSEUS concept. This paper describes how researchers at NASA and Boeing are working together to develop fundamental PRSEUS technologies that could someday be implemented on a transport size HWB airplane design.

Velicki, Alex↗
NASA NTRS2011

Engine Yaw Augmentation for Hybrid-Wing-Body Aircraft via Optimal Control Allocation Techniques

Asymmetric engine thrust was implemented in a hybrid-wing-body non-linear simulation to reduce the amount of aerodynamic surface deflection required for yaw stability and control. Hybrid-wing-body aircraft are especially susceptible to yaw surface deflection due to their decreased bare airframe yaw stability resulting from the lack of a large vertical tail aft of the center of gravity. Reduced surface deflection, especially for trim during cruise flight, could reduce the fuel consumption of future aircraft. Designed as an add-on, optimal control allocation techniques were used to create a control law that tracks total thrust and yaw moment commands with an emphasis on not degrading the baseline system. Implementation of engine yaw augmentation is shown and feasibility is demonstrated in simulation with a potential drag reduction of 2 to 4 percent. Future flight tests are planned to demonstrate feasibility in a flight environment.

Taylor, Brian R.↗
NASA NTRS2011

Engine Yaw Augmentation for Hybrid-Wing-Body Aircraft via Optimal Control Allocation Techniques

Asymmetric engine thrust was implemented in a hybrid-wing-body non-linear simulation to reduce the amount of aerodynamic surface deflection required for yaw stability and control. Hybrid-wing-body aircraft are especially susceptible to yaw surface deflection due to their decreased bare airframe yaw stability resulting from the lack of a large vertical tail aft of the center of gravity. Reduced surface deflection, especially for trim during cruise flight, could reduce the fuel consumption of future aircraft. Designed as an add-on, optimal control allocation techniques were used to create a control law that tracks total thrust and yaw moment commands with an emphasis on not degrading the baseline system. Implementation of engine yaw augmentation is shown and feasibility is demonstrated in simulation with a potential drag reduction of 2 to 4 percent. Future flight tests are planned to demonstrate feasibility in a flight environment.

Taylor, Brian R.↗
NASA NTRS1997

Flutter Boundary Identification From Simulation Time Histories

While there has been much recent progress in simulating nonlinear aeroelastic systems, and in predicting many of the aeroelastic phenomena of concern in transport aircraft design (i.e. transonic flutter buckets), the utility of a simulation in generating an understanding of the flutter behavior is limited. This is due in part to the high cost of generating these simulations; and the implied limitation on the number of conditions that can be analyzed, but there are also some difficulties introduced by the very nature of a simulation. Flutter engineers have traditionally worked in the frequency domain, and are accustomed to describing the flutter behavior of an airplane in terms of its V-G and V-F (or Q-G and Q-F) plots and flutter mode shapes. While the V-G and V-F plots give information about how the dynamic response of an airplane changes as the airspeed is increased, the simulation only gives information about one isolated condition (Mach, airspeed, altitude, etc.). Therefore, where a traditional flutter analysis can let the engineer determine an airspeed at which an airplane becomes unstable, while a simulation only serves as a binary check: either the airplane is fluttering at this condition, or it is not. In this document, a new technique is described in which system identification is used to easily extract modal frequencies and damping ratios from simulation time histories, and shows how the identified parameters can be used to determine the variation in frequency and dampin,o ratio as the airspeed is changed. This technique not only provides the flutter engineer with added insight into the aeroelastic behavior of the airplane, but it allows calculation of flutter mode shapes, and allows estimation of flutter boundaries while minimizing the number of simulations required.

Baker, Myles↗
NASA NTRS2012

MATLAB Stability and Control Toolbox Trim and Static Stability Module

MATLAB Stability and Control Toolbox (MASCOT) utilizes geometric, aerodynamic, and inertial inputs to calculate air vehicle stability in a variety of critical flight conditions. The code is based on fundamental, non-linear equations of motion and is able to translate results into a qualitative, graphical scale useful to the non-expert. MASCOT was created to provide the conceptual aircraft designer accurate predictions of air vehicle stability and control characteristics. The code takes as input mass property data in the form of an inertia tensor, aerodynamic loading data, and propulsion (i.e. thrust) loading data. Using fundamental nonlinear equations of motion, MASCOT then calculates vehicle trim and static stability data for the desired flight condition(s). Available flight conditions include six horizontal and six landing rotation conditions with varying options for engine out, crosswind, and sideslip, plus three take-off rotation conditions. Results are displayed through a unique graphical interface developed to provide the non-stability and control expert conceptual design engineer a qualitative scale indicating whether the vehicle has acceptable, marginal, or unacceptable static stability characteristics. If desired, the user can also examine the detailed, quantitative results.

Kenny, Sean P.↗
NASA NTRS2011

Particle Trajectory and Icing Analysis of the E(sup 3) Turbofan Engine Using LEWICE3D Version 3

Particle trajectory and ice shape calculations were made for the Energy Efficient Engine (E(sup 3)) using the LEWICE3D Version 3 software. The particle trajectory and icing computations were performed using the new "block-to-block" collection efficiency method which has been incorporated into the LEWICE3D Version 3 software. The E(sup 3) was developed by NASA and GE in the early 1980 s as a technology demonstrator and is representative of a modern high bypass turbofan engine. The E(sup 3) flow field was calculated using the NASA Glenn ADPAC turbomachinery flow solver. Computations were performed for the low pressure compressor of the E(sup 3) for a Mach 0.8 cruise condition at 11,887 m assuming a standard warm day for three drop sizes and two drop distributions typically used in aircraft design and certification. Particle trajectory computations were made for water drop sizes of 5, 20, and 100 microns. Particle trajectory and ice shape predictions were made for a 20 micron Langmuir-D distribution and for a 92 mm Super-cooled Large Droplet (SLD) distribution with and without splashing effects for a Liquid Water Content (LWC) of 0.3 g/cu m and an icing time of 30 min. The E3 fan and spinner combination proved to be an effective ice removal mechanism as they removed greater than 36 percent of the mass entering the inlet for the icing cases. The maximum free stream catch fraction for the fan and spinner combination was 0.60 while that on the elements downstream of the fan was 0.03. The non-splashing trajectory and collection efficiency results showed that as drop size increased impingement rates increased on the spinner and fan leaving less mass to impinge on downstream components. The SLD splashing case yielded more mass downstream of the fan than the SLD non-splashing case due to mass being splashed from the upstream inlet lip, spinner and fan components. The ice shapes generated downstream of the fan were either small or nonexistent due to the small available mass and evaporation except for the 92 m SLD splashing case. Relatively large ice shapes were predicted for internal guide vane #1 and rotor #1 for the 92 m SLD splashing case due to re-impingement of splashed mass.

Bidwell, Colin S.↗
NASA NTRS2012

Advanced Jet Noise Exhaust Concepts in NASA's N+2 Supersonics Validation Study and the Environmentally Responsible Aviation Project's Upcoming Hybrid Wing Body Acoustics Test

Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts presented here utilized lobed-mixers and ejectors. A powered third-stream was implemented to improve ejector acoustic performance. One concept was found to produce stagnant flow within the ejector and the other produced discrete-frequency tones (due to flow separations within the model) that degraded the acoustic performance of the exhaust concept. NASA's Environmentally Responsible Aviation (ERA) Project has been investigating a Hybrid Wing Body (HWB) aircraft as a possible configuration for meeting N+2 system level goals for noise, emissions, and fuel burn. A recently completed NRA led by Boeing Research and Technology resulted in a full-scale aircraft design and wind tunnel model. This model will be tested acoustically in NASA Langley's 14-by 22-Foot Subsonic Tunnel and will include dual jet engine simulators and broadband engine noise simulators as part of the test campaign. The objectives of the test are to characterize the system level noise, quantify the effects of shielding, and generate a valuable database for prediction method development. Further details of the test and various component preparations are described.

Henderson, Brenda S.↗
NASA NTRS2014

Optimal Topology of Aircraft Rib and Spar Structures under Aeroelastic Loads

Several topology optimization problems are conducted within the ribs and spars of a wing box. It is desired to locate the best position of lightening holes, truss/cross-bracing, etc. A variety of aeroelastic metrics are isolated for each of these problems: elastic wing compliance under trim loads and taxi loads, stress distribution, and crushing loads. Aileron effectiveness under a constant roll rate is considered, as are dynamic metrics: natural vibration frequency and flutter. This approach helps uncover the relationship between topology and aeroelasticity in subsonic transport wings, and can therefore aid in understanding the complex aircraft design process which must eventually consider all these metrics and load cases simultaneously.

Stanford, Bret K.↗
NASA NTRS2014

Acoustic Data Processing and Transient Signal Analysis for the Hybrid Wing Body 14- by 22-Foot Subsonic Wind Tunnel Test

An advanced vehicle concept, the HWB N2A-EXTE aircraft design, was tested in NASA Langley's 14- by 22-Foot Subsonic Wind Tunnel to study its acoustic characteristics for var- ious propulsion system installation and airframe con gurations. A signi cant upgrade to existing data processing systems was implemented, with a focus on portability and a re- duction in turnaround time. These requirements were met by updating codes originally written for a cluster environment and transferring them to a local workstation while en- abling GPU computing. Post-test, additional processing of the time series was required to remove transient hydrodynamic gusts from some of the microphone time series. A novel automated procedure was developed to analyze and reject contaminated blocks of data, under the assumption that the desired acoustic signal of interest was a band-limited sta- tionary random process, and of lower variance than the hydrodynamic contamination. The procedure is shown to successfully identify and remove contaminated blocks of data and retain the desired acoustic signal. Additional corrections to the data, mainly background subtraction, shear layer refraction calculations, atmospheric attenuation and microphone directivity corrections, were all necessary for initial analysis and noise assessments. These were implemented for the post-processing of spectral data, and are shown to behave as expected.

Bahr, Christopher J.↗
NASA NTRS2014

Assessing Fan Flutter Stability in the Presence of Inlet Distortion Using One-way and Two-way Coupled Methods

Concerns regarding noise, propulsive efficiency, and fuel burn are inspiring aircraft designs wherein the propulsive turbomachines are partially (or fully) embedded within the airframe; such designs present serious concerns with regard to aerodynamic and aeromechanic performance of the compression system in response to inlet distortion. Previously, a preliminary design of a forward-swept high-speed fan exhibited flutter concerns in cleaninlet flows, and the present author then studied this fan further in the presence of off-design distorted in-flows. Continuing this research, a three-dimensional, unsteady, Navier-Stokes computational fluid dynamics code is again applied to analyze and corroborate fan performance with clean inlet flow and now with a simplified, sinusoidal distortion of total pressure at the aerodynamic interface plane. This code, already validated in its application to assess aerodynamic damping of vibrating blades at various flow conditions using a one-way coupled energy-exchange approach, is modified to include a two-way coupled time-marching aeroelastic simulation capability. The two coupling methods are compared in their evaluation of flutter stability in the presence of distorted in-flows.

aeroelasticity↗