Congress approved initial production of the F/A-18 E/F Super Hornet beginning in 1995 to allow for extensive operational testing and evaluation. Naval pilots tested the aircraft in a complex variety of tactical missions, representing all possible operational arenas.
In March 1996, during flight tests at Patuxent River, an F/A-18E/F experienced wing drop-an unacceptable, uncommanded abrupt lateral roll-off that randomly occurred and involved rapid bank angle changes of up to 60 deg. Although not a safety of flight issue, the roll-offs occur during high-speed, high-g maneuvers and prevent the pilot from performing close-in tracking maneuvers on potential adversaries. The problem was viewed as extremely serious and posed a threat to operational tests and the overall development schedule. During the first year of flight tests, the wing-drop phenomenon was only seen at high altitudes because load restrictions prevented the aircraft from reaching the relevant range of angle of attack at low altitudes. As the loads test program opened the flight envelope to 7.5g at all altitudes, the full extent of the wing-drop problem became evident. Objectionable wing-drop events occurred through-out the flight envelope at Mach numbers between 0.5 and 0.9, and this deficiency became a significant threat to the technical and political health of the F/A-18E/F Program.
Having identified wing drop as a problem in early 1996, the Boeing/Navy team performed wind tunnel tests and computational fluid dynamic (CFD) studies in an effort to identify the root cause. The joint Navy team concluded that the wing drop was caused by a sudden, abrupt loss of lift on one of the outer wing panels during maneuvering. Though the basic cause of the wing drop was determined, how to moderate the airflow separation differences between the left and right wings was not. A variety of solutions were explored.
During this period, Langley engineers suggested that the flight program apply a NASA-developed technology -- passive porosity -- to a small section of the upper surface of the wing at the point where the wing folds for aircraft carrier operations. This solution, refined by the NASA and Boeing team, resolved the wing drop problem and permitted the Department of Defense to authorize continued production of the aircraft. To contrast the airflow patterns between the F/A-18E/F and earlier F-18's, NASA Dryden flew an F-18B to visualize in-flight wing surface flow field data. The data verified that there are significant differences between airflow characteristics of the two aircraft. NASA engineers also served on a Department of Defense blue ribbon panel convened to review the approach taken by Boeing to resolve the wing drop, and participated on various Boeing/Navy "tiger teams" created to resolve issues related to the wing drop problem.
As a low impact "80-percent solution" to the F/A-18E/F wing-drop problem, a revised deflection schedule for the leading-edge flaps was evaluated in flight tests in early 1997, with very favorable results. Although the leading-edge flap schedule modification significantly reduced the magnitude of the problem, the aircraft still exhibited smaller wing drops at many test conditions. The original wing-drop problem had been viewed as a potential safety hazard and a roadblock to productive load tests. After the modification, the problem was reduced to a flying qualities issue that allowed other tests to continue.
In November 1997, a diagnostic flight test of an F/A-18E/F with the wing-fold fairing removed was conducted and the results showed that wing drop had been eliminated from most of the flight envelope. But the fairing-off configuration was not a viable approach for production aircraft. NASA Langley suggested that the flight program apply porosity, a passive technology developed at NASA, to the wing in the fold area. Langley researchers had been conducting experiments with passive porosity to control shock locations and other characteristics for several years. During the initial concept evaluation on the F/A-18E/F, the porous fairing was simply a standard wing-fold fairing with areas cut out and a screen mesh substituted. Langley provided design guidelines for the porosity and thickness of the mesh. This solution, refined by the NASA, Navy, and Boeing team, resolved the wing-drop problem and permitted continued production of the aircraft.
On 15 February 2000, the Navy determined the aircraft to be "operationally effective and operationally suitable," and recommended the aircraft's full introduction into the fleet. The Navy announced the results of the F/A-18E/F Super Hornet operational evaluation (OPEVAL). The OPEVAL report awarded the best possible grade to the Super Hornet, calling it "operationally effective and operationally suitable." In addition, the report recommended the aircraft's introduction into the fleet.
Chief of Naval Operations, Adm. Jay Johnson, stated "The F/A-18E/F Super Hornet is the cornerstone of the future of naval aviation. The superb performance demonstrated throughout its comprehensive operational evaluation was just what we expected and confirms why we can't wait to get it to the fleet!" Air Test and Evaluation Squadron Nine (VX-9) at China Lake, Calif., flew 1,233 hours in over 850 sorties and expended more than 400,000 pounds of ordnance in the Super Hornet during nearly six months of flights. The 23-member aircrew tested the aircraft in a complex variety of tactical missions representing the operational arena.
|Join the GlobalSecurity.org mailing list|