The Early Days

Early NACA research on stalling and spinning in the 1920s quickly con­cluded that the primary factors that governed the physics of stall behav­ior, spin entry, and recovery from spins were very complicated and would require extensive commitments to new experimental facilities for stud­ies of aerodynamics and flight motions. Over the following 85 years, efforts by the NACA and NASA introduced a broad spectrum of spe­cialized tools and analysis techniques for high-angle-of-attack condi­tions, including vertical spin tunnels, pressurized wind tunnels to define the impact of Reynolds number on separated flow phenomena, special free-flight model test techniques, full-scale aircraft flight experiments, theoretical studies of aircraft motions, piloted simulator studies, and unique static and dynamic wind tunnel aerodynamic testing capability.[1275]

By the 1930s, considerable progress had been made at the NACA Langley Memorial Aeronautical Laboratory on obtaining wind tunnel aerodynamic data on the effectiveness of lateral control concepts at the stall and understanding control effects on motions.[1276] A basic understand­ing began to emerge on the effects of design variables for biplanes of the era, such as horizontal and vertical tail configurations, wing stagger,
and center-of-gravity location on spinning. Flight-testing of stall char­acteristics became a routine element of handling quality studies. In the race to conquer stall/spin problems, however, simplistic and regretta­ble conclusions were frequently drawn.[1277]

The sudden onset of World War II and its urgency for aeronauti­cal research and development overwhelmed the laboratory’s plodding research environment and culture with high-priority requests from the military services for immediate wind tunnel and flight assessments, as well as problem-solving activities for emerging military aircraft. At that time, the military perspective was that operational usage of high-angle – of-attack capability was necessary in air combat, particularly in classic "dogfight” engagements wherein tighter turns and strenuous maneu­vers meant the difference between victory and defeat. Tactical effective­ness and safety, however, demanded acceptable stalling and spinning behavior, and early NACA assessments for new designs prior to indus­try and military flight-testing and production were required for every new maneuverable aircraft.[1278] Spin demonstrations of prototype aircraft by the manufacturer were mandatory, and satisfactory stall character­istics and recoveries from developed spins required extensive testing by the NACA in its conventional wind tunnels and vertical spin tunnel.

The exhausting demands of round-the-clock, 7-day workweeks left very little time for fundamental research, but researchers at Langley’s Spin Tunnel, Free-Flight Tunnel, Stability Tunnel, and 7- by 10-Foot Tunnels initiated a series of studies that resulted in advancements in high-angle-of-attack design procedures and analysis techniques.[1279]