Simulation study of traffic-sensor noise effects on utilization of traffic situation display for self-spacing task

The effect of traffic sensor noise on the ability of a pilot to perform an intrail spacing task was determined. The tests were conducted in a fixed base cockpit simulator configured as a current generation transport aircraft, with an electronic traffic display provided in the weather radarscope location. The true positions of the traffic were perturbed in both relative range and azimuth by random errors to simulate traffic sensor noise associated with an onboard sensor. The evaluation task involved simulated instrument approaches into a terminal area while maintaining self separation on a lead aircraft. Separation performance data and pilot subjective ratings and comments were obtained. The results of the separation data indicate that displayed traffic position errors, having standard deviation values up to 0.3-n.mi. range and 8 deg azimuth, had negligible effect on the spacing performance achieved by the pilots. Speed profiles of the lead aircraft, display of the lead aircraft groundspeed, and individual pilot techniques were found to significantly affect the mean spacing performance

Bracing Design for Torsional Bucking of Cold-Formed Steel Wall Stud Columns

A method is presented for calculating the required brace stiffness and strength to limit torsional buckling deformation in cold-formed steel wall stud columns. The bracing (bridging) design method utilizes recent insight from classical stability solutions that define twist of singly and doubly-symmetric columns with an initial twist imperfection as a function of column compressive load. A wall stud design example is provided

Bracing Design for Torsional Bucking of Cold-Formed Steel Wall Stud Columns

A method is presented for calculating the required brace stiffness and strength to limit torsional buckling deformation in cold-formed steel wall stud columns. The bracing (bridging) design method utilizes recent insight from classical stability solutions that define twist of singly and doubly-symmetric columns with an initial twist imperfection as a function of column compressive load. A wall stud design example is provided

Methane Dual Expander Aerospike Nozzle Rocket Engine

The Air Force Institute of Technology (AFIT), working to meet requirements set by the Air Force Research Laboratory\u27s Next Generation Engine (NGE) initiative, is developing upper stage rocket models. The current path of investigation focuses on combining a dual expander cycle with an aerospike nozzle, or the Dual Expander Aerospike Nozzle (DEAN) using methane fuel. The design process will rely heavily on AFIT\u27s previous work, which focused on the development of tools for and the optimization of a hydrogen/oxygen DEAN engine. The work outlined in this paper expands the existing research by substituting methane for hydrogen. The targets derived from the NGE program include a vacuum specific impulse of 383 seconds, 25,000 lbf of thrust, and a thrust to weight ratio of 108. NASA\u27s Numerical Propulsion System Simulation was used in conjunction with Phoenix Integration\u27s ModelCenter to optimize over several parameters to include O/F ratio, thrust, and engine geometry. After thousands of iterations over the design space, the selected MDEAN engine concept has 349 s of Isp and a thrust to weight ratio of 120. The MDEAN was compared to liquid hydrogen technology, existing methane technology, and the NGE goals

Structural Design Example -- Four Span Metal Building Z-Purlin Line Supporting a Standing Seam Roof

This example provides a step-by-step strength calculation of a 4-span continuous Z-purlin system supporting a standing seam roof. Design inputs are defined first, including cross-section dimensions and orientation, span lengths, roof slope, and bracing provided by the standing seam to the purlin line. The calculations consider gravity (downward) and suction (uplift) loadings

A parametric analysis of visual approaches for helicopters

A flight investigation was conducted to determine the characteristic shapes of the altitude, ground speed, and deceleration profiles of visual approaches for helicopters. Two hundred thirty-six visual approaches were flown from nine sets of initial conditions with four types of helicopters. Mathematical relationships were developed that describe the characteristic visual deceleration profiles. These mathematical relationships were expanded to develop equations which define the corresponding nominal ground speed, pitch attitude, pitch rate, and pitch acceleration profiles. Results are applicable to improved helicopter handling qualities in terminal area operations

Evaluating the LRFD Factor for Cold-formed Steel Compression Members

This paper summarizes recent work to determine if the LRFD resistance factor for cold-formed steel compression member s can be increased above its current value of φ c =0.85. An experimental database of 675 concentrically loaded columns with plain and lipped C-sections, plain and lipped Z-sections, hat sections and angle sections, including members with holes was compiled. The predicted strength of each specimen was calculated with the AISI-S100-07 Main Specification and Direct Strength Method (DSM). Test-to-predicted strength statistics were employed with the first order second moment reliability approach in AISI-S100-07 Chapter F to calculate the resistance factors. The observed trends demonstrate that DSM is a more accurate strength predictor than the current Main Specifica tion, especially for columns with partially effective cross sections. Serious consideration should be given to replacing the Main Specification with DSM, which would provide improved prediction accuracy and a viable rationale for increasing the resistance factor. The test-to-predicted strength ratios for columns with plain and lipped angle cross-sections exhibit a high coefficient of variation and b ecome increasingly conservative with increasing global slenderness. Fundamen tal research on the mechanics of angle compression members is needed to improve existing design methods

Direct Strength Design of Metal Building Wall and Roof Systems - Through-fastened Simple Span Girts and Purlins with Laterally Unbraced Compression Flanges

A Direct Strength Method (DSM) prediction approach is introduced and validated for metal building wall and roof systems constructed with steel panels through-fastened with screws to girts or purlins. The focus is capacity prediction for simple spans under wind uplift or suction, however the DSM framework is generally formulated to accommodate gravity loads, continuous spans, standing seam roofs, and insulated roof and wall systems in the future. System flexural capacity is calculated with the usual DSM approach – global buckling, local global buckling interaction, and distortional buckling strengths are determined with a finite strip eigen-buckling analysis including a rotational spring that simulates restraint provided by the through-fastened steel panel. The DSM flexural capacity is then reduced with a code-friendly equation consistent with existing Eurocode provisions to account for the additional stress at the intersection of the web and free flange that occurs as the girt or purlin rotates under a suction (uplift) load. A database of 62 simple span tests was assembled to evaluate strength prediction accuracy of the proposed DSM approach alongside existing Eurocode and American Iron and Steel Institute (AISI) provisions. The proposed DSM approach is confirmed to be viable and accurate for simple spans. Modifications to the Eurocode approach are proposed, and if they are made, the Eurocode is also an accurate and potentially general prediction method. The AISI R-factor prediction method is accurate for C-section simple spans, unconservative for Z-section simple spans, and overall lacks the generality of the DSM and Eurocode

Critical Elastic Shear Buckling Stress Hand Solution for C- and Z-sections Including Cross-section Connectivity

This paper presents an approximate solution for the critical elastic buckling stress of cold-formed steel C- and Z-section members including cross-section connectivity. The elastic buckling solution is developed to support the extension of the Direct Strength Method to the shear ultimate limit state, where the cross sectional critical elastic shear buckling stress (load) is employed to predict shear capacity. The shear buckling stress and buckled half-wavelength are calculated with a classical energy solution for a thin plate with edges rotationally restrained. Rotational stiffness expressions in the AISI S100-07 specification, originally derived for distortional buckling of C- and Z-sections, are used with the energy solution to calculate the rotational restraint provided to the web flange juncture by the flanges. The approach is validated with thin shell finite element eigen-buckling analysis