Physical Problems, Challenges, and[ Pragmatic Solutions

Robert G. Hoey

The advent of the supersonic and hypersonic era introduced a wide range of operational challenges that required creative insight by the flight research community. Among these were phenomena such as inertial (roll) coupling, transonic pitch-up, panel flutter, structural resonances, pilot – induced oscillations, and aerothermodynamic heating. Researchers had to incorporate a variety of solutions and refine simulation techniques to better predict the realities of flight. The efforts of the NACA and NASA, in partnership with other organizations, including the military, enabled development and refinement of reliable aerospace vehicle systems.

HE HISTORY OF AVIATION is replete with challenges and difficul­ties overcome by creative scientists and engineers whose insight, coupled with often-pragmatic solutions, broke through what had appeared to be barriers to future flight. At the dawn of aviation, the problems were largely evident to all: for example, simply developing a winged vehicle that could take off, sustain itself in the air, fly in a con­trolled fashion, and then land. As aviation progressed, the problems and challenges became more subtle but no less demanding. The National Advisory Committee on Aeronautics (NACA) had been created in 1915 to pursue the "scientific study of the problems of flight, with a view to their practical solution,” and that spirit carried over into the aero­nautics programs of the National Aeronautics and Space Administration (NASA), which succeeded the NACA on October 1, 1958, not quite a year after Sputnik had electrified the world. The role of the NACA, and later NASA, is mentioned often in the following discussion. Both have been instrumental in the discovery and solution to many of these problems.

As aircraft flight speeds moved from the firmly subsonic through the transonic and into the supersonic and even hypersonic regimes, the con­tinuing challenge of addressing unexpected interactions and problems

followed right along. Since an airplane is an integrated system, many of these problems crossed multiple discipline areas and affected multiple aspects of an aircraft’s performance, or flight safety. Numerous examples could be selected, but the author has chosen to examine a representative sampling from several areas: experience with flight control systems and their design, structures, and their aeroelastic manifestations; flight sim­ulation; flight dynamics (the motions and experience of the airplane in flight); and aerothermodynamics, the demanding environment of aerody­namic heating that affects a vehicle and its structure at higher velocities.