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Nuts and Bolts
November 19, 2009

nuts and bolts graphic New IPP Awards Aim To Validate The Basics Ideas That Could Mean A Lot To The Readiness Level Of Technology.

DWT May Remove The Guesswork

Rather than calculate a best guess about where flutter of an aircraft will occur in flight, a new tool called the Dry Wind Tunnel developed through a recently awarded Small Business Technology Transfer, or STTR, Program Phase II agreement might pinpoint the exact location flutter will occur.

Knowing where flutter - uncontrolled vibration of an aircraft's structure - is occurring could result in a tool that saves time and money, increases safety and makes aerospace vehicle design work easier to validate, said Starr Ginn. Ginn is a Dryden contracting officer technical representative and Dryden aerostructures deputy branch chief.

"Today's flutter prediction methods have come a long way," Ginn explained. "But our main focus of flight-test validation is to determine there are no aeroelastic instabilities due to structural non-linear effects, which are not modeled. This new tool will demonstrate the flight condition in which an aeroelastic instability will or will not occur, on the ground and, as a result, increase safety and reduce the time it takes to validate the flight envelope. For example, only a few flights might be necessary to prove the absence of flutter, rather than having to build up the flight series over a number of tests."

The work completed on Phase I of the Dry Wind Tunnel STTR developed a ground-flutter testing system that verified it is possible to physically simulate flutter of very simple structures on the ground. This DWT could one day augment wind tunnels as a means for flutter and aeroservoelastic instability testing, she said.

Developed through an agreement among Dryden, Zona Technology Inc. of Scottsdale, Ariz., and Arizona State University, Tempe, the DWT system consists of a ground-vibration test hardware system and a real-time unsteady-aerodynamic-force-generation software system, Ginn said.

The DWT tests simulate in real time the unsteady aerodynamic forces through ground-vibration test hardware, namely shakers and sensors.

"What will make the DWT even more successful is to conduct the test on Dryden's soft support system, which makes the analyst's life easier and allows and apples-to-apples comparison," Ginn said.

Ginn previously developed the Starr Soft Support system, which is an aircraft jacking system that integrated an existing isolation system.

Dryden aerospace engineer Leonard Voelker resurrected the idea of a ground flutter test and brainstormed the idea with Dryden Structural Dynamics group lead Chan-gi Pak. The concept came up again during a meeting between Dryden and Zona representatives. Dryden uses Zona's Zaero code for flutter analysis.

Zona representatives decided to pursue the idea, but needed ASU to join them. ASU had testing hardware required to incorporate vital information to tell the shakers how to interpret and react to information fed into them, which was validated in Phase I work.

Phase I proved that the feedback controller was fast enough to communicate between the shakers and accelerometers to induce flutter, Ginn said.

The flutter predictions were close, but Phase II will raise the stakes with more complex test structures. A small wing used extensively at Langley Research Center, Hampton, Va., for wind-tunnel tests will be compared to tests with the Dry Wind Tunnel to see how the numbers match up.

If the research works as expected on a couple of small-scale test articles, within two years it will be applied to an F-15 or F-18 research aircraft, Ginn added.

Merits of a DWT could be many, Ginn said. It can accommodate full-size aircraft or wing structures, including inherent structural nonlinearity and flight-controller-in-the loop, or in essence tell the computer to configure itself a certain way then tell researchers how it would react to those changes, she said.

Potential NASA applications for the Dry Wind Tunnel include use as a pre-flight testing effort to identify any aeroelastic or aeroservoelastic instability that is not predicted by analysis. For example, inherent structural nonlinearities such as friction and freeplay, or areas where stiffness characteristics vary, are difficult to model in linearized analyses but would be present in the DWT testing on the actual structure.

DWT testing also could be used for a post-flight testing procedure to resolve discrepancies between the analysis and flight-test results. The DWT test concept is applicable to a broad range of test structures, from components to wing to full aircraft.

Commercial applications for the Dry Wind Tunnel system include flutter-envelope expansion and flying-quality programs for military, civil transport and general aviation aircraft.

Potential customers include the Air Force, Navy, Defense Advanced Research Projects Agency, and the aerospace industry.

Tool Could Mean Revolution In Radio Communications

Radio communications could be revolutionized if a new Innovative Partnerships Program Innovation Fund project succeeds.

The new concept, called Direct Spatial Antenna Modulation, may offer an approach for reducing the size, weight, power and complexity of radio subsystems that enable data communications, said project lead Larry Freudinger.

These advances could benefit all aircraft and spacecraft seeking to improve communication system performance or implement solutions that are constrained by volume and available power, he said.

The conventional approach for sending data is to modulate, or encode the data onto the signal to be transmitted prior to sending it to the signal amplifier. If the antenna is a phased array, a separate set of phase shifter electronics is used to steer the modulated signal in the desired direction, Freudinger explained.

The Direct Spatial Antenna Modulation, or DSAM, approach implements the modulation as a function of the antenna in a manner that simplifies directional control of the antenna's sensitivity, he added.

"DSAM might offer a path to closing capability gaps we see in the evolution of network-enhanced telemetry," Freudinger said. "For multiple vehicles and ground systems to communicate with each other as they move around, we need an affordable approach for focusing antennas in multiple directions at the same time. We will have to do this on vehicles that can't support the size, weight and power of existing approaches."

The project is a collaborative effort between Dryden and the Invertix Corporation of McClean, Va. Invertix is a communications company focused on the needs of federal agencies. Dryden team members include the Research Instrumentation, Range Operations and Range Engineering branches.

"Power efficiency, spectral efficiency, resistance to jamming, and joint modulation-beam steering are the key advantages for test applications. The ability to use less-expensive nonlinear power amplifiers in a manner that improves power efficiency by orders of magnitude is just the tip of the iceberg," said Brecken Uhl, technical lead for the project at Invertix and developer of the DSAM concept.

The recent IPP award made to the company will fund development of a prototype array element suitable for laboratory demonstration within a few months, Freudinger said. The demonstration is expected to confirm whether the technical approach will work as promoted. The Dryden team will evaluate the results of the test and recommend a technology-maturation strategy if one is warranted.

If successful, this research may enable for the first time small, low-complexity, low-cost steerable antennas that can reduce system cost. In addition, the technology could replace omni-directional antennas used not only in aircraft but also in products such as cell phones and Wi-Fi access points.

Design Tool May Support Hypersonic Vehicles

A recently awarded Small Business Technology Transfer Program contract will be used to continue work on a design tool for aero-thermo-elastic-propulsion simulation of air-breathing hypersonic flight vehicles.

In addition, the award will permit the team that includes Dryden, Advanced Engineering Solutions, Inc. of Ormond Beach, Fla., and Oklahoma State University, Stillwater, to further extend modeling from a previous Phase I STTR to include acoustics, said Kajal Gupta, Dryden's contracting officer and technical representative on the project.

"The resulting code can be used for simulation of novel Dryden flight vehicles. We can use this simulation to ensure flight safety for any new project that comes to Dryden," he explained.

Using an STTR agreement to complete the work has a number of advantages, Gupta said.

"The agreement is unique in the sense it partners Dryden with industry and academia. We are exposed to what is going on in this field and this is a good research program that will train students for the types of work NASA will need when they graduate," he said.

The team will complete development of the Multidisciplinary Design and Analysis, or MDA, tool, primarily using its respective numerical, finite element codes integrating disciplines such as structures, aerodynamics, thermal, acoustics, controls and propulsion.

The resulting MDA code, designed in modular form, could be effortlessly used with existing commercial or user-provided codes. Once completed, the code is expected to have extensive applications in the design and analysis of flight vehicles. In its request for proposals, the Aeronautics Research Mission Directorate Fundamental Aeronautics program highlighted MDA as a need, Gupta explained.

An earlier STTR Phase I permitted the team to evaluate simulation capabilities, develop an aero-thermo-elastic-propulsion simulation of air-breathing hypersonic flight vehicles and other flight vehicles, and generate recommendations for multidisciplinary simulation capability.

NASA could potentially use the MDA for research aimed at enabling advanced future flight vehicle design and analysis capabilities. One thrust of this research is hypersonics, including air-breathing vehicles that will enable safe, affordable and routine travel to low-Earth orbit in support of space science, exploration and commerce and planetary entry vehicles to enable manned and unmanned explorations, he said.

Proposed Highly Reliable Reusable Launch Systems of the future will be conceived, designed and developed to fulfill the nation's space exploration aspirations and NASA's mission, and maintain the country's aerospace edge, Gupta said. Airbreathing hypersonic flight vehicles present a promising alternative for affordable and reliable access to space.

For that reason, development of predictive capabilities and simulation tools for design of a future advanced class of flight vehicles is necessary. Also, additional capabilities in the area of aero-acoustics will have imminent applications in a number of ongoing NASA projects.

Commercially, the technology could enable industrial companies and academia to use the MDA code for analysis in individual disciplines and, more important, in the design of complete aerospace vehicles as well as other classes of vehicles in a coupled mode.

Aeroelastic, aero-thermo-elastic, aero-propulsion, and aero-acoustic analyses can be performed routinely for accurate and reliable design of complex, advanced flight vehicles, using standard personal computers, Gupta said. The optimization capability will help in achieving an economical configuration.

Potential use of MDA code for aerospace is vast. As NASA looks for in its technology development efforts, the MDA code could also have applications to fields such as mechanical, marine and civil engineering.

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