NASA's F/A-18 No. 853 validated through flight in December that a streamlined adaptive system could help an aircraft that has sustained damage to its flight control surfaces remain flyable. It also proved the aircraft's capabilities for a number of potential flight research projects. (NASA Photo / Carla Thomas)
› View Larger Image A Dryden F/A-18 proved a simplified adaptive controller can compensate for simulated failures of flight control surfaces and keep the aircraft flyable until landing safely. The Model Reference Adaptive Control, or MRAC, project also showed the range of the aircraft's research capabilities during a December flight.
Mark Dickerson, deputy project manager for Dryden's aviation safety program, and Jim Lee, project chief engineer for the MRAC and F/A-18 No. 853, recently talked about the success of the MRAC and the aircraft. It has been demonstrated through flight that the aircraft can be used to validate a number of new technologies that could lead to safer aircraft and a smoother ride and enable the aircraft to communicate when it needs maintenance.
The MRAC work takes what was started on the F-15 No. 837 prior to that test bed's retirement and finished on the F/A-18 aircraft, also referred to as the Full Scale Advanced Systems Technology, or FAST aircraft. The current adaptive control is comprised of less complex systems and algorithms that could make for a smoother transition to commercial use in the future, when new technologies are fully validated and verified, Dickerson said.
"We pulled out what wasn't absolutely needed," he added.
However, the aircraft has significant capability. For example, Lee explained that the FAST aircraft has a dual computer system - a quad-redundant research flight control system, or RFCS, and a dual-redundant airborne research test system, dubbed ARTS IV - that provides a robust system for testing new concepts. In addition, about 200 strain gages remain on the flight control surfaces from the Active Aeroelastic Wing research program, which tested the concept of using lighter weight wings and wing twist for enhanced aircraft roll control.
The ARTS IV computer, a fourth-generation system developed at Dryden in collaboration with the West Virginia High Technology Consortium, enables testing of advanced control and sensor concepts. These concepts could lead to vehicles that control the shape of a fuselage while an aircraft is traveling supersonically. This could allow lighter-weight structures to be built and reduce the overall weight of the aircraft. These advanced concepts could be used to maintain a desired shape, alter the shape for performance, minimize gust loads or alter loads and shift stresses, Lee explained. Also, that technology could be used to reduce the signature of sonic booms.
Dickerson and Lee said the technology also is crosscutting because it could be used for lightweight structures intended for use in space. In addition, potential Dryden partners such as the Air Force Research Laboratory and a commercial aircraft company are looking at future technologies like MRAC that could offer significant improvements to next-generation aircraft and spacecraft.
The dual ARTS IV flight control computer allows up to eight experiments to be tested in a single flight, Lee said. Researchers believe the ARTS IV will be able to collect data from advanced sensors and send the information to the flight control system for adapting to conditions as they are happening, such as in gust alleviation, or fly-by-feel control. That is one possible experiment that could be researched thanks to the MRAC flight validation, he said.
Don Warren, right, writes a tag for the pallet removed from the bay of F/A-18 No. 853. Todd Shaw installs wiring in the aircraft. (NASA Photo / Tony Landis)
View Larger Image> The streamlined MRAC system will continue to evolve.
"This is a basic system without the features that add complexity. We are working to try to figure out if the bells and whistles are needed," Lee said.
In the meantime, the MRAC flight demonstrated aircraft capabilities that will allow for accelerated approval of a flight experiment, he added.
"ARTS enables researchers to propose a concept or experiment with NASA and get it to flight more quickly than [was] previously possible, and put the code and algorithms directly into the ARTS for verification and validation in a greatly reduced time frame. In addition, changes can be made to the experiment and those changes can be verified and validated and [made] ready to fly," Lee said.
Dickerson and Lee credited a talented and motivated team for completion of the milestone flight in the aviation safety program three to four months ahead of schedule. A combination of experience with similar, more complex systems, less complex code and anticipated funding deadlines at the end of the fiscal year allowed the team to reach the key flight, Dickerson said.
"We have quite a team. It took a lot of work - challenging work that was time-consuming and added pressure. However, our team kept focus," he said.
The MRAC work is a breakthrough that could have a big payoff. For example, there have been situations during the past two years in which commercial airliners carrying MRAC-type systems would have had an excellent chance of being saved or seeing a reduction in the number of injuries and fatalities, Dickerson said.
Such a system would allow an aircraft damaged by severe turbulence and loss of flight control surfaces to remain flyable with the damage. With the addition of a propulsion-controlled aircraft recovery, or PCAR, system also developed and validated at Dryden, even a case in which a horizontal tail was frozen in place might not have resulted in a crash, Dickerson said.
"There is strong potential that those aircraft could have been saved. There is the potential [through use of the new technology] to enable flying qualities that would allow a pilot to land," Dickerson said.
Within five years researchers hope to understand the system's full potential, he said. One idea researchers want to pursue is a ground collision-avoidance system such as that validated at Dryden during the Automatic Collision Avoidance Technology project, which could be used by a commercial airliner.
The concept of a system that predicts and characterizes structural failures also is high on the list. The addition of fiber optic shape sensors to the F/A-18 could collect and send information about what is happening to the wing as it occurs to the flight control computer, which could detect and mitigate failures before the situation becomes critical. That could ultimately limit or eliminate the need for structural inspections and reduce unnecessary down time for the aircraft, Dickerson said.
The F/A-18 is expected to continue to fly MRAC flights early this year. Regardless of what the F/A-18 will be used to research next, it now has the capability to prove concepts that will have a significant influence on future aircraft and spacecraft that could make them safer and improve their ride as well as advise maintenance staff when in need of attention.