The Autonomous Formation Flight (AFF) project reports current risk reduction phase flights showing fuel flow reductions of up to 20 percent when the trailing aircraft flew 0.56 Mach at 25,000 feet.
At 0.86 Mach and an altitude of 36,000 feet, the altitude and speed similar to a transport aircraft cruise condition, the fuel benefit was approximately 15 percent.
These percentages exceed the project goal of a 10 percent fuel saving. The AFF project completed 22 dual-aircraft research flights as of Oct. 23.
The current flight phase is mapping the wingtip vortex effects of the lead aircraft on the trailing aircraft. Wingtip vortex is a spiraling wind flowing from the wing during flight. The vortex causes rolling, yawing and pitching moments on the trailing aircraft that must be counteracted with changes in the aircraft's control surfaces.
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Autonomous Formation Flight (AFF) Project Manager Gerard Schkolnik, from left, Dick Ewers, project pilot and engineer Brent Cobleigh talk about an upcoming AFF mission. The hangar houses both F/A-18 aircraft used in the AFF research. Working with partners at The Boeing Co. and UCLA, Dryden is developing a precise capability that could lead to dramatic fuel savings and revolutionize formation flying capabilities.
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It is a difficult task for the trailing pilot to maintain the proper position while flying in the vortex. Add to that the tasks of running data acquisition equipment, listening to radio calls from the control room for minor throttle or position changes, and reading fuel tank levels to allow later assessment of fuel consumption.
Dryden pilots Dick Ewers, Craig Bomben, Gordon Fullerton and Frank Batteas are flying this phase of the project. Bomben commented that AFF is a true test pilot project. "Lots of testing we do involves systems testing that usually does not test the flying skills of the pilots. This program is a real stick-and-rudder program that challenges our pilot skills each and every flight."
Ewers further explained the complications of flying AFF missions. "What makes the flying difficult is we are deliberately flying in the presence of the wingtip vortex off the lead aircraft. This means the aircraft is being buffeted around and influenced by the airflow of the lead aircraft. We are using radio calls from the ground to confirm our nose-to-tail separation. After 30 seconds to a minute or more in one position, we readjust five or so feet to a new precise position for the next data point. Do this for an hour and one is very relieved to head back for a landing."
Modeling the vortex is a significant part of AFF research. The most desirable scenario is for an aircraft's autopilot to control the formation. Data from these flights are being used to develop an aerodynamic model of an F/A-18 flying in the vortex field of another F/A-18. These data will be used to design and test the autonomous autopilot. The model will also be used to predict the aero-dynamic interactions between two aircraft. Testing of the formation autopilot is the goal of the next flight phase, scheduled for the summer of 2002.
Coming in November
The Active Aerolastic Wing (AAW) recently completed its loads laboratory research. See the November X-Press for an update on this project.
