Some vortical-flow flight experiments on slender aircraft that impacted the advancement of aeronautics

This paper highlights the three aerodynamic pillars of aeronautics; namely, theory/CFD, wind-tunnel experiments and flight tests, and notes that at any given time these three are not necessarily at the same level of maturity. After an initial history of these three pillars, the focus narrows to a brief history of some vortical-flow flight experiments on slender aircraft that have impacted the advancement of aeronautics in recent decades. They include the F-106, Concorde, SR-71, light-weight fighters (F-16, F/A-18), and F-16XL. These aircraft share in common the utilization of vortical flow and have flown at transonic speeds during a part of the flight envelope. Due to the vast amount of information from flight and CFD that has recently become available for the F-16XL, this aircraft is highlighted and its results detailed. Lastly, it is interesting to note that, though complicated, vortical flows over the F-16XL aircraft at subsonic speeds can be reliably and generally well-predicted with the current CFD flow solvers. However, these solvers still have some problems in matching flight pressure data at transonic speeds. That this problem has been highlighted is both an advancement in aeronautics and a tempting prize to those who would seek its solution.