Search Results

This paper presents a new methodology for analytically evaluating the natural frequencies and mode shape of a turbomachinery blade in an environment where friction phenomenon occurs. The blades analyzed in this study are unshrouded and located in the high-pressure turbine found in turbofan engines, and in the compressor turbine found in turboprop engines. The goal of this method is to correctly predict the modal parameters of the blade in order to determine whether there will be any resonance in the running range of the turbomachinery, and to more accurately predict the stresses at the blade-disc interface. This study was performed using ANSYS® contact elements. After comparison, the analytical results were found to agree with the experimental results. A convergence study was also performed, and it was found that only the friction coefficient and the surface contact stiffness had a considerable effect on the natural frequencies and mode shape convergence.

The two major factors that affect auxiliary power system design decisions are: the working fluid to be used, and vehicle mission requirements. It has been found that optimum turbine designs will be similar for the two working fluids (hydrazine or hydrogen-oxygen) considered for the shuttle orbiter system due to the constraints imposed by geometrical and mechanical design limitations. As a consequence, variations in power level and/or working fluid selection can be efficiently accommodated by relatively minor modifications to turbine nozzle design. Analytical techniques for optimization of turbine aerodynamic design parameters have been developed. These techniques can be extended to include transient-state simulation and design optimization of the other system components, including the turbine controller, in a manner similar to that used for development of control systems for multi-spool fan-jet engines.

Considerable operational experience has been acquired in South America, Africa, Europe, Southeast Asia, and in other remote areas in STOL type aircraft operating from extremely short, primitive, unimproved fields. This type operation not only makes certain special demands of the engine, but also exposes it to a rather hostile environment. The engine is subjected to all types of foreign object ingestion, as well as the fine sand and dust that is stirred up by propeller reversing. This paper describes this type of operation, emphasizing those aspects which make life difficult for the engine. Solutions to some of these special problems are described, as well as activities now in process seeking further improvement.

This technical paper discusses the evolution of turbopumps designed for U.S. rocket engines, starting with the Thor, Jupiter, and Atlas missiles, which were developed in the 1950s; the F-1 and J-2 engines, which were developed in the 1960s for the Saturn V vehicle to put man on the moon; and the Space Shuttle Main Engine (SSME), which was developed in the 1970s for the United States' first reusable space vehicle. Technology development in the 1980s that will influence the design of turbopumps for the National Launch System (NLS), the National Aero-Space Plane (NASP), and Orbital Transport Vehicles (OTV) are also discussed.

The civil aircraft market frequently employs propulsion systems originally developed and qualified for military aircraft applications. When this occurs, the civil sector benefits greatly from the lessons learned during the military engine development and qualification process. This paper presents the unique test experiences and lessons learned during development of the T406-AD-400 turboshaft engine that the GMA2100 turboprop, GMA3007 turbofan, and GMA1107 turboshaft engines will profit from for years to come. Some of these valuable T406 test experiences include: 1) development of engine attitude capabilities, 2) integration with a fly-by-wire control system, 3) incorporation of flight test experience into the engine design, and 4) utilization of unique test facilities.

The turbulent impinging jet flows associated with vertical or short take-off and landing (VTOL) aircraft hovering in ground effect can have a critical effect on aircraft performance, and they are modeled very poorly by existing models. Three flow phenomena representative of VTOL ground effects flows, the upwash fountain, the ground vortex, and the impingement zone of a round jet, are considered. Extensions to the k-ϵ model are presented which are designed to account for streamline curvature, large scale mixing, and anisotropy. The extensions significantly improve the model's ability to predict some aspects of these flows. Requirements for further model development are identified.

Enhanced turbulence in an upwash fountain and fluid/acoustic resonance of an impinging axisymmetric jet are investigated by numerical simulations of the mean flow and the largest scales of the unsteady fluid motion. In the planar upwash, the simulated shear stress and spreading rate are three times greater than in a normal jet and are in good agreement with experimental data. Reynolds-stress transport mechanisms which lead to the enhanced turbulence are discussed, and a qualitative description of the large scale turbulent motions is proposed. A model for the pressure-strain term is determined to be a major source of error in Reynolds-stress transport modeling of the upwash. In an axisymmetric impinging jet at Mj = 0.9, resonant-like behavior with elevated levels of pressure fluctuations and dominance of a single frequency of vortex generation are observed. Vortex stretching is observed to be critical to the generation of noise in the impingement zone.

The Turret Head Fastening System is an enhancement of current three position “C-frame” wing riveting machines. It was designed and built by Boeing as a fully instrumented research machine in 1991 for the 777 Airplane, and as a potential retrofit package for conventional drill, rivet, shave wing assembly machines. It was designed to automatically install rivets and bolts and perform the required hole preparation prior to fastener installation. In its current form, it will clamp a panel; and then as the fastener requires, drill, coldwork, ream, countersink the hole; inspect the hole; apply sealant when required; install threaded fasteners or rivets; torque the nut, swage the collar or upset the rivet as required; shave the rivet to ensure flushness; and finally unclamp the part - all within the current working envelope of a drill, rivet shave machine. Currently, switching from rivets to bolts requires a 5 minute tool change.

About 20 years ago, the existence of a new miniature turbojet engine inspired an imaginative designer to create a small unmanned aircraft for reconnaissance missions. This marked the beginning of a new era of turbojet development. Visionary designers predicted that miniature engines would someday perform missions comparable to those of larger unmanned aircraft. The WR2/WR24 series of engines has grown from the original 50-lb thrust to over 200-lb thrust. Unique challenges were encountered during the early period as the engine developers found themselves pioneering a specialized field. Innovative concepts were necessary to maintain simplicity, light weight and high performance.

This paper describes the second government-conducted, piloted flight simulation of the Grumman Design 698 V/STOL (vertical and short takeoff and landing) aircraft. Emphasis is on the aircraft's handling qualities as rated by various NASA, Navy, and GAC pilots with flight experience ranging from CTOL (conventional takeoff and landing) to V/STOL aircraft. The Design 698 had been modified to resolve the flight problems that were of most concern to the pilots in the first investigation (Phase I). Those problems included an adverse nonminimum phase (NMP) acceleration response in both the longitudinal and lateral axes, a large thrust-response lag, and adverse ground effects. The adverse NMP acceleration is an attribute of the vertical vanes (a Grumman patent) positioned in the fan exhaust flow.

The purpose of this paper is to review factors related to extended range operations with twin-engine transport aircraft (ETOPS) from the viewpoint of the pilot. The review relies on the years of experience of pilots from around the world for operational insight and interpretations of historic, current, and forecast events. In particular, technical issues are addressed, present-day operations are critiqued, and recommendations are made. It is hoped that this paper will provide the reader with a real-world look at bookbound rules and regulations, computer-generated statistics about rare events, and advertised equipment reliabilities.

Two approaches have been attempted to establish an icing climatology over Europe. Firstly, a climatology has been established by using the results of SIGMA (Severe Icing Geographic identification in Meteorology for Aviation). The situations calculated by SIGMA during two winters have been studied. Secondly, a climatology of the occurrence of freezing precipitations at ground level has been established. It is based on reports of freezing precipitation in SYNOP messages from the winters covering the years 1995 to 1998. The geographical domain covered is Western and Central Europe. The frequency of occurrence of freezing precipitations (freezing rain, freezing drizzle and ice pellets) and freezing fog was computed. The results of these two climatologies show that north eastern Europe is more prone to icing phenomena.

This paper describes the effectiveness and possibility of practical use about two types of visual display systems to improve the situation awareness of the pilot, when an aircraft is approaching and landing under the condition of low weather minimum. The one of these systems, when an aircraft is on the final approach course under the condition of IMC, provides a display of simulated airport lighting to the pilot, which is just like a night view of airport lighting at visual approach. By using this system, a pilot could make approach and landing in the same feeling as a visual approach by watching this image projection on the cockpit front windshield whatever any weather condition. The second one, display the runway contour on the airborne weather radar scope by radar reflectors which are installed on the ground along runway lights of the airport. By using this system, a pilot could easily find the airport on the radar scope and approach in the same feeling as a visual approach.

Hydroponics is the cultivation of plants in water containing dissolved inorganic nutrients. Over the past two decades, hydroponics has established itself as a valued component in the overall effort to achieve closed cycle environmental systems. This has a particularly significant impact on future long-duration missions such as lunar colony and exploration of the solar system where resupply is either impossible or impractical. In order to make hydroponics a truly practical solution in the microgravity conditions found in space, it is essential that techniques be developed for separating liquid from air in a simple and effective manner.

A new type of two-phase thermal control system insensitive to some “g” acceleration is suggested for space and ground application. This system is composed of a loop heat pipe (LHP), or capillary pumped loop (CPL) and a solid sorption cooler (SSC). The most essential feature of this system is that LHP and SSC are connected to the same evaporator, but are working alternatively. Such combination can be used also for the cryogenic fluid storage, when system is out of work at low pressure and room temperature, and for cryogenic thermal control system of spacecraft on the orbit (cold plate for infrared observation of the Earth, or Space), or efficient electronic components cooling device.

The Air Force Research Laboratory (AFRL), in cooperation with the University of Dayton Research Institute (UDRI) and Fairchild Controls Corporation, is building a test facility to study the use of advanced vapor cycle systems (VCS) in an expanded role in aircraft thermal management systems (TMS). It is dedicated to the study and development of VCS control and operation in support of the Integrated Vehicle ENergy Technology (INVENT) initiative. The Two Phase Thermal Energy Management System (ToTEMS1) architecture has been shown through studies to offer potential weight, cost, volume and performance advantages over traditional thermal management approaches based on Air Cycle Systems (ACS). The ToTEMS rig will be used to develop and demonstrate a control system that manages the system capacity over both large amplitude and fast transient changes in the system loads.

NASA's Exploration Mission program is planning for a return to the Moon in 2020. The Exploration Systems Mission Directorate (ESMD)'s Lunar Architecture Team (LAT) is currently refining their lunar habitat architectures. The Advanced Thermal Control Project at the Johnson Space Center, as part of the Exploration Technology Development Program (ETDP) is developing technologies in support of the future lunar missions. In support of this project, a trade study was conducted at the Jet Propulsion Laboratory on the mechanically pumped two-phase and single-phase thermal loops for lunar habitats located at the South Pole for the LAT II architecture. This paper discusses the various trades and the results for a representative architecture which shares a common external loop for the single and two-phase system cases.

We have proposed the engine featuring a new compressive combustion principle based on pulsed supermulti-jets colliding through a focusing process in which the jets are injected from the chamber walls to the chamber center. This principle has the potential for achieving relatively silent high compression around the chamber center because autoignition occurs far from the chamber walls and also for stabilizing ignition due to this plug-less approach without heat loss on mechanical plugs including compulsory plasma ignition systems. Then, burned high temperature gas is encased by nearly complete air insulation, because the compressive flow shrinking in focusing process gets over expansion flow generated by combustion.

TWO SPECIALTY APPLICATIONS for electrochemical metallizing have recently proved cost-effective and technologically sound. Aircraft engine manufacturers and maintenance facilities find nickel electrochemical metallizing an excellent way to enhance braze-ability of super alloys on turbine engines and other components. A base nickel deposit permits even brazing at lower temperatures, avoiding heat damage to adjacent honeycomb. Aluminum helicopter rotors present bonding problems, now solved by selective electrochemical anodizing. Leading edges are often covered with a hard alloy shield or a layer of synthetic rubber, bonded to the aluminum base with high-strength adhesives. Selective electrochemical anodizing leading edges of rotors guarantees adhesion vastly superior to direct bonding.