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The Refill Friction Spot Joining (RFSJ) is an emerging solid-state spot welding technology that thermo-mechanically creates a molecular-level bond between the work-pieces. RFSJ does not consume any filler or foreign materials so that no additional weight is introduced to the assembly. As the solid-to-liquid phase transition is not involved in RFSJ in general, there is no lack of fusion or material deterioration caused by liquefaction and solidification. Unlike the conventional friction stir spot welding, RFSJ produces a spot joint with a perfectly flush surface finish without a key or exit hole. Currently, the aerospace industry employs solid rivets for fastening the primary structures as they meet the baseline requirements and have well-established standards and specifications.

In-service data from two Bombardier business jets, a Global 5000 and a Global Express XRS, have been compared. Flight data has been analyzed from both airframes with comparable number of ground-air-ground cycles. Individual flight phase have been examined and compared between the two airframes. Primary emphasis has been placed on airframe usage. The influence of primary mission on ground-air-ground cycles has been highlighted in the form of ground and flight loads, as well as dynamics of the flights. It is demonstrated that safe-life maintenance approach may have to be adjusted to account for the airframe usage.

Data obtained from digital flight data recorders are used to assess the actual operational environment of propellers on a fleet of Beech 1900D aircraft in commuter role. Information is given on various aerodynamic parameters as well as those pertaining to engine and propeller usage. The takeoff rotation has been identified as the most demanding phase of flight in terms of unsteady loads exerted on the propeller blades. Special attention is paid to ground operations.

The fatigue behavior of Hilok fastener joints under constant amplitude loading has been investigated experimentally. The effects of load transfer in an unbalanced joint configuration was characterized in terms of a stress severity factor relative to the open-hole configuration. The experimental data indicates that the clamp-up forces dominate the performance of fastener joints with the open-hole fatigue life being the lower bound at the stress levels investigated. The failure modes were observed to transition from a net-section type failure across the minimum section to a fretting induced failure at some distance from the hole. The experimental data has been used to develop stress severity factors to be used as a measure of the fatigue quality of the fastener joints.

The work presented in this paper is part of a long-term research program to explore methods for improving bleed air system performance. Another objective of this research is to provide detailed experimental data for the development and validation of simulation tools used in the design and analysis of bleed air systems. A business jet wing was equipped with an inner-liner hot air ice protection system and was extensively instrumented for documenting system thermal performance. The wing was tested at the NASA Glenn Icing Research Tunnel (IRT) for representative in-flight icing conditions. Data obtained include bleed air supply and exhaust flow properties, wing leading edge skin temperatures, temperatures and pressures in the interior passages of the bleed air system, flow properties inside the piccolo tube, photos of run back ice shapes and ice shape traces. Selected experimental results for a warm hold icing condition are presented in this paper.

An experimental study was performed to investigate large droplet dynamics in the vicinity of an airfoil. The investigation was conducted using the NASA Glenn Droplet Imaging Flow Tunnel (DrIFT). Mono-dispersed large droplets were released at the tunnel inlet and accelerated toward an airfoil that was mounted in the test section. The dynamic behavior of a droplet's encounter with the airfoil, which may involve droplet distortion, break-up, impingement and splashing, was recorded using a high-speed imaging system. The effects of the droplet size, tunnel velocity and airfoil configuration on the droplet dynamics were investigated in a parametric study. The droplet sizes used in the experimental study were 96 and 375 μm whereas tunnel velocities were varied from 80 to 130 mph. Three different airfoil geometries were used in the experimental study; a ‘clean’ and ‘iced’ airfoil, and a ‘clean’ three-element high-lift airfoil. The incidence angle of these airfoils was set to zero degrees.

Vehicle electronics and sensor systems have become indispensable parts in providing safety, comfort, personal communication mobility and many other advanced functions in today's vehicles. As a result, reliability requirements for these critical parts have become extremely important. To meet these requirements, more advanced technologies and tools for degradation monitoring and failure prevention are needed. Currently, the development of diagnostics and prognostics techniques, which employ accurate degradation quantification by appropriate sensor selection, location decision, and feature selection and feature fusion, still remains a vital and unsolved issue. This paper addresses several realistic concerns of failure prevention in vehicle electronics and sensor systems. A unified monitoring and prognostics approach that prevents failures by analyzing degradation features, driven by physics-of-failure, is suggested as a general framework to overcome the unsolved challenge.

This paper presents experimental methods for investigating large droplet impingement dynamics and for obtaining small and large water droplet impingement data. Droplet impingement visualization experiments conducted in the Goodrich Icing Wind Tunnel with a 21-in chord NACA 0012 airfoil demonstrated considerable droplet splashing during impingement. The tests were performed for speeds in the range 50 to 175 mph and with cloud median volumetric diameters in the range of 11 to 270 microns. Extensive large droplet impingement tests were conducted at the NASA Glenn Icing Research Tunnel (IRT). Impingement data were obtained for a range of airfoil sections including three 36-inch chord airfoils (MS(1)-0317, GLC-305, and NACA 652-415), a 57-inch chord Twin Otter horizontal tail section and 22.5-minute and 45-minute LEWICE glaze ice shapes for the Twin Otter tail section. Small droplet impingement tests were also conducted for selected test models.

Metal cutting is a substantial constituent of airframe manufacturing. During the past several decades, it has evolved significantly. However, most of the changes and improvement were initiated by the machine tool industry and cutting tool industry, thus these new technologies is generally applicable to all industries. Among them, few are developed especially for the airframe manufacture. Therefore, the potential of high efficiency could not be fully explored. In order to deal with severe competition, the aerospace industry needs improvement with a focus on achieving low cost through high efficiency. The direction of research and development in parts machining must comply with lean manufacturing principles and must enhance competitiveness. This article is being forwarded to discuss the trend of new developments in the metal cutting of airframe parts. Primary driving forces of this movement, such as managers, scientists, and engineers, have provided significant influence to this trend.

An experimental investigation was conducted to identify the aerodynamic effects of oversized low-pressure (Tundra) tires and tall landing gear on a Piper Super Cub airplane. Water tunnel and wind tunnel tests were performed using, respectively, a 1/20 scale model and full-scale landing gear and tire components. Force and moment data suggest that larger tires and taller gear most affect the drag and side force. Small trim changes are apparent, but the basic static stability behavior appears unchanged.

Aerospace manufactures purchase millions of drill bits each year for the manufacture of large aircraft structures. This paper describes an ongoing research project for the development of an automated system to detect poor quality drill bits before they are put to use.

The current emphasis on environment protection by reducing noise pollution has led to stricter noise standards for general aviation aircraft. As a result, there is a growing demand for a computational tool to predict the noise during the design process. A computer program, called ProRAPP, has been developed for the prediction of noise generated by propeller/rotor blades. The acoustic pressure is calculated using a form of Ffowcs Williams-Hawkings equation which is suitable for numerical implementation. For noise predictions, the observer can either move with the propeller/rotor hub or it can be fixed to the ground. Experimental data from both wind tunnel and flight tests are used to validate the numerical results.

Flight test experiments were conducted to measure the extent and nature of natural laminar flow on a smoothed test region of a swept-wing business jet wing. Surface hot film aneraometry and sublimating chemicals were used for transition detection. Surface pressure distributions were measured using pressure belts. Engine noise was monitored by a microphone attached to the wing surface to study possible acoustic effects on stability of the laminar boundary layer, Side-slip conditions were flown to simulate changes in effective wing sweep. Flight instrumentation and ground data analysis techniques and a method for measuring intermittency of turbulence are described, Correlation was obtained between the hot film gage signals and chemicals for transition detection. Cross-flow vortices were observed for some flight conditions. Results of spectral and statistical analysis of the hot film signals for various flight test conditions are presented.

The results of an analytical study of aerodynamic interference effects for a light twin aircraft are presented. The data presented concentrates on the influence of a wing on a body (the fuselage). Wind tunnel comparisons of three fillets are included, with corresponding computational analysis. Results indicate that potential flow analysis is useful to guide the design of intersection fairings, but experimental tuning is still required. While the study specifically addresses a light twin aircraft, the methods are applicable to a wide variety of aircraft.

Research has been conducted on the nature of airfoil behavior at pre- and post-separated angles of attack. Detailed wind tunnel studies have been made of boundary layer and wake fields for the GA(W)-1 airfoil, and the airfoil with a 0.3 chord Fowler flap. Experimental data are compared with theoretical predictions from a multi-element viscous flow computer program. Theoretical predictions are reasonably accurate for unseparated flows, but have serious errors when separation is present. Some recent techniques for modeling post-separated flow behavior are discussed in light of the present experiments.

As part of a general aviation airfoil development program being carried out under the direction of the NASA Langley Research Center, a 30% chord Fowler flap has been developed for the GA(W)-1 airfoil.. Wind tunnel tests at Wichita State University have demonstrated a c1max value of 3.80 for 40 deg flap deflection at a Reynolds number of 2.2 × 106. Effects of flap slot geometry have been systematically tested and optimum flap settings for any flight c1 have been obtained. Modification of the reflexed lower surface contour resulted in a reduced c1max with flap nested. Vortex generators provided an increase in c1max of 0.2 for flap nested and 40 deg flap along with a drag penalty at low c1 values. Flow visualization studies show that the stalling patterns for the new airfoil are characterized by an absence of leading edge separation for both the flap-nested and the 40 deg flap cases.