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Yeo H.,NASA | Yeo H.,U.S. Army | Yeo H.,Aviation and Missile Research | Yeo H.,Development and Engineering Center | Johnson W.,NASA
Journal of Aircraft | Year: 2015

Maximum rotor lift capability is investigated using wind-tunnel test data of McHugh (modified 1/10-scale CH-47B rotor) and a full-scale UH-60A rotor. Rotor performance calculations with the comprehensive rotorcraft analysis CAMRAD II are compared with the wind-tunnel test data. The analysis of the McHugh rotor with the Reynolds-number-corrected airfoil table shows good correlation with the measurements for μ = 0.1 to 0.5 and is able to predict the maximum rotor lift reasonably well, especially at 0.2 ≤ μ ≤ 0.4. The analysis is also able to predict the maximum lift of the full-scale UH-60A rotor within about 3.5% at μ = 0 .24 and 0.3. Calculations with dynamic stall models, in general, show only a small influence on the rotor performance and are not necessary to predict maximum lift. Airfoils have an important role in defining the maximum lift capability of the rotor. The VR-12 airfoil, which has stall characteristics superior to the baseline V23010 airfoil, substantially improves the maximum lift capability of the McHugh rotor, showing the potential to improve the behavior of a rotor by improving the airfoil's static stall characteristics. Source

Berry J.L.,Aviation and Missile Research | Hayduke D.,Materials Sciences Corporation
International SAMPE Symposium and Exhibition (Proceedings) | Year: 2010

Progressive failure analysis of carbon epoxy pressure vessels is an important tool for optimum weight and durability designs. This paper compares failure criteria implemented within a progressive failure modeling method for fiber composite materials within the ABAQUS environment. The model assessed was the fiber damage and failure model written by Materials Science Corporation (MSC) with the capability of modeling composite failure based on Max-Stress, Max-Strain, and Hashin criterion. Evaluation of these models was based on implicit, static, reduced integration, single shell element results compared to published experimental results of ultimate laminate tensile stress for multiple lay-ups and off-axis loading angles. All the criteria yielded comparable results to the experimental study. Average percent differences of 25.47, 9.22, and 8.00 were found for the Hashin, Max-Strain, and Max-Stress models, respectively. Source

Stephenson J.H.,Aviation and Missile Research | Greenwood E.,NASA
Annual Forum Proceedings - AHS International | Year: 2015

Blade-vortex interaction noise measurements are analyzed for an AS350B helicopter operated at 7000 ft elevation above sea level. Blade-vortex interaction (BVI) noise from four, 6 degree descent conditions are investigated with descents flown at 80 knot true and indicated airspeed, as well as 4400 and 391S pound take-off weights. BVI noise is extracted from the acquired acoustic signals by way of a previously developed time-frequency analysis technique. The BVI extraction technique is shown to provide a better localization of BVI noise, compared to the standard Fourier transform integration method. Using this technique, it was discovered that large changes in BVI noise amplitude occurred due to changes in vehicle gross weight. Changes in BVI noise amplitude were too large to be due solely to changes in the vortex strength caused by varying vehicle weight. Instead, it is suggested that vehicle weight modifies the tip-path-plane angle of attack, as well as induced inflow, resulting in large variations of BVI noise. It was also shown that defining flight conditions by true airspeed, rather than indicated airspeed, provides more consistent BVI noise signals. Source

News Article
Site: http://www.treehugger.com/feeds/category/solar-technology/

The U.S. military is where many new technologies get their start. So much of what we now see as standard tech was once being invented in a military lab. Continuing that tradition, a team of Army scientists has created a new solar cell that could mark a major breakthrough. The researchers have patented a new type of solar cell that is less expensive to manufacture, stronger and more robust than current solar cell technology. The main difference between this solar cell and those in existing solar panels is their size -- the new solar cell is approximately 1,000 times thinner. The thin-film cell consists of layers of silver and gold between the semiconductor layers, but the combined thickness is still only a few hundred nanometers thick, compared to a piece of paper which is 100,000 nanometers thick. The cell also overcomes some of the major problems with current solar tech like wear out or damage from high heat that comes from the absorption of great amounts of ultraviolet and infrared radiation that can't actually be turned into electricity due to a narrow band gap (the wavelength of light that can effectively be used to generate electricity). The addition of the silver and gold layers widens that bandgap meaning that the new solar cells can absorb and convert more of that UV and infrared radiation into electricity, which not only makes the technology more efficient, but also makes it much stronger and resilient. The solar cells can also be tuned to reflect the excess radiation if needed. The Army says that the geometry of the solar cells allows them to absorb the same rate of sunlight at any angle, which means that they don't need sophisticated sun tracking systems to generate the maximum amount of energy. "Low-cost, compact, flexible and efficient solar cells are destined to impact all sorts of Department of Defense applications, as lightweight solar panels will eventually power all kinds of equipment, particularly in remote, inaccessible areas," said Dr. Michael Scalora, a research physicist at the U.S. Army Aviation and Missile Research, Development and Engineering Center. The technology is just in the beginning stages, but the researchers see applications far beyond the military when it's ready.

Hansson J.,U.S. Software Engineering Institute | Wrage L.,U.S. Software Engineering Institute | Feiler P.H.,U.S. Software Engineering Institute | Morley J.,U.S. Software Engineering Institute | And 2 more authors.
IEEE Security and Privacy | Year: 2010

The modeling of system quality attributes, including security, is often done with low-fidelity software models and disjointed architectural specifications by various engineers using their own specialized notations. These models typically aren't maintained or documented throughout the life cycle and make it difficult to obtain a system view. However, a single-source architecture model annotated with analysis-specific information lets designers reflect changes in the various analysis models with little effort. This approach also lets designers conduct adequate trade-off analyses and evaluate architectural variations prior to system realization. This article describes how model-based development using the Architecture Analysis and Design Language (AADL) and compatible analysis tools provides the platform for multidimensional, multifidelity analysis and verification. © 2010 IEEE. Source

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