Technology Has Proven Itself In The Laboratory, And Now It's Time For The Crucible Of Flight Research To Separate The Real From The Imagined
Safer airplanes capable of avoiding conditions that lead to accidents and the ability to monitor the structure of buildings and bridges before trouble arises are possibilities if flight experiments on an emerging technology are successful.
Once the integration of hardware is complete on the Aeroelastic Test Wing 2, flight experiments on the F-15B flight test fixture are scheduled to be flown later this year. The flights will mark the culmination of work on a system that includes new sensors, a system that will be the first of its kind to measure unsteady aerodynamic loads, or forcing function, in real time and correlate that data with how the structure responds to those loads. The system, called the distributed aerodynamic sensing and processing, or DASP, toolbox project, was accelerated in a 2007 Innovative Partnerships Program seed fund project.
The merits of this new system may be validated when the aircraft flies a five-flight series to characterize structural dynamic and aerodynamic behavior across a range of flight conditions, from low to high angles of attack, low to high Mach numbers, and in steady and unsteady maneuvers.
Strain gages and accelerometers will be used to measure the structural response, while hot-film gages will be used to characterize the aerodynamic-flow features and to determine the aerodynamic forcing function. The flight experiment is expected to pave the way for development of advanced computational modeling, flutter prediction techniques, and adaptive closed-loop control technology required for the design and development of flight vehicles with active aeroelastic wings. NASA's Aeronautics Research Mission Directorate is cost sharing in the effort.
Marty Brenner, a Dryden principal investigator for the project, encapsulated the DASP toolbox this way: "It is a combination of hardware-sensing devices with software to analyze the critical aerodynamic parameters and, hopefully, to eventually be used for different applications - eventually, distributed sensing and processing for distributed controls."
The multi-faceted system is capable of obtaining structural and aerodynamic data concurrently. The system is comprised of circuit boards that are fed with information by the sensors and accelerometers that can process information that can be used to determine skin friction/sheer stress, which ultimately gives variations in the instantaneous (unsteady) lift generated by a wing section in the presence of gusts as well as structural oscillations. Absolute values of the lift coefficient in unsteady flow are obtained as a function of the instantaneous locations of the leading-edge stagnation point and the flow-separation point, Brenner explained.
In the experiment, flying directly on the ATW2 is one element of the DASP toolbox called a hot-film sensor. These sensors are mounted on flexible or bending areas of the ATW2 lifting surfaces.
"There are also piezoceramic patches that, when you put power through them, vibrate the wing at pre-programmed frequencies. These are also strain gages that measure strain in the structure. The hot-film sensors will measure flow angularity through the stagnation point as measured by angle of attack or sideslip. A stagnation point is a point in the flow field where the local velocity of the fluid is zero. Static pressure is at its maximum value at stagnation points (stagnation pressure), and the streamline at the stagnation point is perpendicular to the surface of the body," Brenner explained.
The measurement tool would benefit research into topics such as alleviating the aerodynamic pressures on an aircraft by gusts, flutter suppression, improvement of aerodynamic efficiency and supersonic wave reduction, he said. The information from the sensors also could be used for distributed control of lifting surfaces, or controlling a wing that could change its shape in flight to take advantage of aerodynamic efficiencies, Brenner added.
In addition, the DASP toolbox offers a less obtrusive way of gaining the data without having to add tubing or other structures to the aircraft. It conforms to the aircraft's structure and has tolerances that can be adapted to within a millimeter, he said.
"It is a real-time aerodynamic measurement tool to identify flow-verification points on an elliptic surface. It enables us to determine the forces on that surface based on a few critical points. That can be used by NASA to determine what the wing is doing in real time and do what is necessary to control it to get the best performance," said Siva M. Mangalam, president of Tao Systems, Dryden's partner on the project.
David Voracek, who is serving as the project manager, said the concept evolved through collaboration with the Air Force Research Laboratories. The AFRL sponsored the sensors that are the focus of this flight experiment in the Langley Research Center, Hampton, Va., transonic wind tunnel. The excellent results in the wind tunnel provided the foundation for the IPP agreement, Voracek said.
"Part of my role is to look at what we are going to be doing in the future with that technology in terms of integrating that with several with other, different technologies. We are building a partnership with the Air Force Research Labs in hopes of getting it [the technology] off a test article and onto an airplane. Developing the technology through the IPP was a great opportunity for us to get funding we could not get anywhere else and get it to a technology readiness level that allows us to integrate it into a larger flight vehicle," Voracek said.
The IPP created an opportunity for Brenner, Voracek and partners Tao Systems to further develop the program.
"We have been working on this with Dryden for a long time. Some of the basic ideas were already there and this was a culmination of the ideas," Mangalam said.
A series of increasingly complex Small Business Innovative Research projects are at the heart of the DASP toolbox and qualified it as an IPP project. It evolved from sensing and instrumentation to diagnostics and ultimately it is intended to lead to controls that offer better performance and safety, Mangalam explained.
DASP toolbox components also are expected to be incorporated onto the F-18 Intelligent Flight Control System aircraft when it is ready to fly, Brenner said. The aircraft is a good choice for the DASP toolbox because F-18 no. 853 was used for Active Aeroelastic Wing research, through which a wing was controlled with twisting.
"Using this technology, we are able to look at the structure of the airplane wing and use the sensors and integration with the adaptive control to re-distribute the control surfaces to obtain a more aero-efficient shape for the flight condition. Using stagnation point control will be one technology we will look at after the sensors are proven through the IPP," Voracek said.
Dryden project co-chief engineers Claudia Herrera, Christine Jutte and Brenner said Voracek has worked with Robert Medina, Dryden small business procurement officer, and Greg Poteat of the Dryden IPP office to streamline the IPP processes that resulted in an agreement that meant IPP funding of $238,000, with in-kind services, work force and use of facilities totaling about $250,000.
Fiber optic wing shape sensors, adaptive controls and distributed sensing controls could benefit from the DASP toolbox technology and potential partnerships are forming for a larger program, Voracek said.
The DASP toolbox also offers the potential to prevent accidents.
"With this technology we should be able to identify the load in real time so it does not exceed its [design] limits. The other type of accident that could be avoided is the computer mistakenly acting as if the aircraft were in a dive because pitot tube measurements were wrong and the flight controls reacted to that information instead of the actual flight conditions of the aircraft climbing following a takeoff," Voracek explained.
Mangalam's son, Arun, said the DASP toolbox could maximize wind turbine efficiency and productivity, minimize structural oscillations and fatigue and maximize energy transfer. Formula One and yacht racing could be made more efficient using the technology as well, he added. In addition, health monitoring of building or bridges could be possible.
The IPP creates a partnership with NASA, where NASA's platforms and ideas can be tapped, Arun Mangalam said. This partnership permits a small business to move technology readiness up a level so that the innovation can be ready for when it is needed.
For small business, IPP partnership projects like this one offer vast opportunities.
"This helps us in many ways. When we do SBIR we generally work on our own. Because of this partnership, we get to work with people who know the problem and who are looking for a solution and we can more effectively support that type activity. This IPP program, from that point of view, is extremely useful for getting the players together. We are able to work with all the people at NASA - that's a big plus for us. Because of that opportunity, we know what needs to be done to this instrumentation if you want to put it into an aircraft," Arun Mangalam said.
And the equipment to do the "baking-and-shaking" tests to validate it for flight is not usually found at a small business. That's another benefit of the partnership: the resources of a NASA center can be used for the flight validation process, he added.
Brenner agrees that IPP partnerships help move technology along.
"It's a good outlet for bringing in outside ideas and more efficient ones," Brenner said. "It's also a way for engineers to get small, invaluable ideas out, put together a plan and use that in the technology development. It is a way to develop big plans by showing the potential of critical applications. It is a block approach to technology that would not be advanced any other way."