Opportunities

After the results of the NASA HATP project in 1996 and the F/A-18E/F wing-drop and AWS programs were disseminated, it was widely recog­nized that computational fluid dynamics had tremendous potential as an additional tool in the designer’s toolkit for high-angle-of-attack flight conditions. However, it was also appreciated that the complexity of the physics of flow separation, the enormous computational resources required for accurate predictions, and the fundamental issues regarding representation of key characteristics such as turbulence would be for­midable barriers to progress. Even more important, the lack of commu­nication between the experimental test and evaluation community and the CFD community was apparent. More specifically, the T&E commu­nity placed its trust in design methods it routinely used for high-angle – of-attack analysis—namely, the wind tunnel and experimental methods. Furthermore, a majority of the T&E engineers were not willing to accept what they regarded as an aggressive "oversell” of CFD capabilities with­out many examples that the computer could reliably predict aircraft stability and control parameters at high angles of attack. Meanwhile, the CFD community had continued its focus on applications related to aircraft performance, with little or no awareness of the aerodynamic
problems faced by the T&E community for high-angle-of-attack pre­dictions. One example of the different cultures of the communities was that a typical CFD expert was used to striving for accuracies within a few percent for performance-related estimates, whereas the T&E ana­lyst was, in many cases, elated to know simply whether parameters at high angles of attack were positive or negative.

Stimulated to bring these two groups together for discussions, Langley conceived a plan for a project known as Computational Methods for Stability and Control (COMSAC), which could poten­tially spin off focused joint programs to assess, modify, and calibrate computational codes for the prediction of critical aircraft stability and control parameters for high-angle-of-attack conditions.[1328] Many envi­sioned the start of another HATP-like effort, with similar outlooks for success. In 2004, Langley hosted a COMSAC Workshop, which was well – attended by representatives of the military and civil aviation industries, DOD, and academia. As expected, controversy was widespread regard­ing the probability of success in applying CFD to high-angle-of-attack stability and control predictions. Stability and control attendees expressed their "show me that it works” philosophy regarding CFD, while the CFD experts were alarmed by the complexity of typical exper­imental aerodynamic data for high-angle-of-attack flight conditions. Nonetheless, the main objective of establishing communications between the two scientific communities was accomplished, and NASA’s follow-on plans for establishing research efforts in this area were eagerly awaited.

Unfortunately, changes in NASA priorities and funding distribu­tions terminated the COMSAC planning activity after the workshop. However, several attendees returned to their organizations to initiate CFD studies to evaluate the ability of existing computer codes to pre­dict stability and control at high angles of attack. Experts at the Naval Air Systems Command have had notable success using the F/A-18E as a test configuration.[1329]

Despite the inability to generate a sustainable NASA research effort to advance the powerful CFD methods for stability and control, the COMSAC experience did inspire other organizations to venture into the area. It appears that such an effort is urgently needed, especially in view of the shortcomings in the design process.