[9] Interest in the transonic flight regime increased markedly after the Second World War, reflecting further attempts to increase aircraft performance. However, wind tunnels of the time were inadequate for carrying out this kind of research. For a time, tests were conducted in flight with small airfoil and aircraft models.² These models were attached to the wings of conventional fighter aircraft, in some cases on a raised surface known as a "transonic bump," where the airflow would be compressed and accelerated to transonic speeds during dives (hence the term "wing-flow" testing). Transonic model test aircraft are noted in table 2. One P-51B (figs. 9 and 10), one P-51D (fig. 11), and two P-51H Mustangs were the primary aircraft used at Ames in wing-flow test flights. Larry Clousing performed the first of these tests in the P-51B. In experiments with a thin, straight wing with a symmetrical double-wedge profile, lift data matched theoretical and wind tunnel predictions up to Mach 0.82. For Mach numbers through the transonic range up to 1.2, trends in lift disagreed with theory. Pitching moment data indicated aerodynamic center movement approached the theoretical predictions for subsonic and supersonic flow (ref. 7). In another series of tests, the control effectiveness for several flat-plate delta-wing planforms with trailing-edge flaps was explored. Pitching moments were measured for various flap angles over a speed range up to Mach 1.1. Data showed a reasonable trend through the transonic range (ref. 8).

In another approach to acquiring transonic aerodynamic data, heavily weighted models of the configuration of interest were dropped from high altitudes. In those tests, which were conducted at Edwards Air Force Base, aerodynamic bodies that were to be evaluated in the transonic flight regime were released from an aircraft at altitudes up to 43,000 feet. The instrumented bodies would pass through the transonic speed range in free fall, during which they were oscillated through a range of angles of attack and were then decelerated and recovered by means of air brakes and parachutes. Testing at these altitudes was arduous and, although the pilots wore heavy flight suits, the model drops were made on the first run to reduce the pilots' exposure to the extreme cold. ³ The F-15A-1-NO aircraft (fig. 12), a reconnaissance model of the P-61 night fighter, was used for these tests. The high-altitude capability of the F-15A made it the ideal "mother ship" for this work. An aircraft similar to this one, an ERF-61C (fig. 13), owned by the Smithsonian Institution, was lent to Ames to be....

[10] ....used in this program as well. Pilots who participated in this work were George Cooper, Rudolph (Rudy) Van Dyke, Don Heinle, and Fred Drinkwater. As with the wing-flow tests, qualitative results were obtained; nevertheless, the advent of the new transonic tunnels supplanted flight testing as a means of documenting the aerodynamics of this flight regime. The air-brake and parachute systems developed for these tests were subsequently used by many agencies for rocket and satellite payload recovery. The NACA test pilots who were at Ames in 1949 are shown in figure 14.

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2 Harry Goett and Bill Harper 1998: personal communication.

3 George Cooper 1998: personal communication.

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