I repeated each spin twice to confirm my findings. Also, to satisfy my curiosity, I climbed to 12,000 feet and did a ten-turn spin to the right holding the ailerons with the spin. The spin was steady, and the characteristics remained the same throughout the extra five turns. Level flight was resumed at 6,500 feet.
The AT-6 demonstrated no dangerous spin characteristics, recovery was positive in every instance, and it would be safe to spin any number of turns provided the entry altitude was high enough.
The spin tests were the final flying phase of the AT-6 test program, and only the most difficult part remained — writing the final report. The report included tables of the pertinent performance figures along with the graphs plotted from the in-flight data, a detailed evaluation of the aircraft's flight characteristics and cockpit layout, a separate report on the spin tests, a completed twenty-page Pilot's Observations questionnaire, and conclusions and recommendations for changes. I concluded that the AT-6 was suitable for use as an advanced single-engine trainer. I'm sure that conclusion was reassuring to the hundreds of thousands of pilots who had trained in it.
Following the tests on the AT-6, we ran similar but not identical tests on the North American P-51D Mustang, the Beechcraft C-45F Expediter, and the Lockheed P-80A Shooting Star. I won't cover them all in detail, but I will point out the main differences between them and the AT-6 tests.
The Mustang was equipped with a second instrument panel in the radio compartment, which contained the relevant test instruments and could be photographed with a movie camera operated by the gun trigger on the control stick. The camera was actuated whenever a reading was entered on the knee board.
The airspeed indicator was calibrated by the pacer aircraft method: the test plane was flown in close formation with a previously calibrated Mustang, and ASI readings were made (both pilot's panel and photo panel) simultaneously in both planes at 30-mph increments from 130 mph to 340 mph.
Since the Mustang's Merlin engine is supercharged with a two-stage, two-speed blower, the aircraft has two critical altitudes, one in low blower and one in high blower. Therefore, we flew a low and a high sawtooth climb in each blower stage, one below and one above the respective critical altitude. We also made a series of sawtooth climbs at the same airspeed with different settings of the coolant and oil shutters to determine the effect of their drag on the climb performance. Power-required runs and speed points also were flown in low and high blower and with varying coolant and oil shutter settings. Six low-blower speed points were flown at altitudes from 2,000 to 21,000 feet, and six were flown in high blower at altitudes from 12,000 to 31,000 feet.
Check climbs were made from 2,000 to 34,000 feet at the best climbing speeds. The climb from 2,000 to 18,000 feet was made in low blower, and then a climb from 9,000 to 34,000 feet was made in high blower. The power settings on all the performance flights in the Mustang were 2,500 rpm and either 42 inches of mercury or wide-open throttle.
As in the AT-6 test, we noted the handling and stability characteristics, stalling speeds, and takeoff and landing distances and evaluated the cockpit layout.
In the C-45 we flew in pairs; I was teamed with Lt. Claire Whitney on most of the flights. He was an excellent pilot and a pleasure to work with. We alternated as pilot and copilot, with the copilot being responsible for recording the data. The test C-45 had a photo panel and a special temperature gage that registered the temperature of each of the nine cylinders individually.
Most of the test flights were made to determine the effect of various settings for the cowl flaps and oil cooler shutter on the cylinder-head temperature and oil temperature. We found that the right engine exceeded the maximum allowable temperature in a climb with full open cowl flaps on an Army Hot Day (120 degrees Fahrenheit). In testing the handling characteristics, we determined that the minimum safe single-engine speed was 105 mph. This test was flown at 1,000 feet above the ground; one engine was shut down and the speed reduced until we could no longer maintain level flight. I was glad to finish the C-45 phase of the program, since it was and still is my least favorite of any of the aircraft I've flown. It wasn't difficult to fly, but the small control wheel combined with the small separation between the rudder pedals always made me feel as though I were flying a toy. Quite a few other pilots felt the same way. One weekend at Eglin seven pilots from the fighter squadron were going to fly to Maxwell Field in Alabama to visit a former squadron member. We rushed out to the C-45, and the last one in found that the only empty seat was the pilot's. In other aircraft the first one in would have grabbed the pilot's seat.
The P-80A was the last aircraft to be tested. Its program was abbreviated, because only four of the students had enough hours in the P-80 to participate: Majors Weldon, Bray, and Brown and I. Also, we were all ordered to other assignments before the tests were completed. Accordingly, Doc Nelson, the instructor, decided that we would make one consolidated report using the data the group had accumulated. Since this was the first class at the school to include jets in the curriculum, we were feeling our way.
The speed, rate of climb, and ceiling of the P-80 were much higher than those of the other test aircraft, and flying without external fuel tanks limited our flights to less than one hour on most missions. The high rate of climb, especially at the lower altitudes, required significant changes in the sawtooth-climb procedure. Instead of measuring the time to climb 1,000 feet, we had to use 4,000 feet, with a lead of about 2,000 feet into the climb and a 500-foot follow-through, because a small timing mistake in the short time to climb 1,000 feet would have caused a large error in computing the rate of climb. The same timing mistake on a 4,000-foot climb would produce an error 75 percent smaller. At high altitude, the rate of climb was considerably lower, and no modification was required.
We were able to complete the airspeed, altimeter, and free air temperature calibrations; a series of sawtooth climbs at intervals from 6,000 feet up to 40,000 feet; power-required runs at 5,000-foot intervals up to 40,000 feet; and timed climbs to 40,000 feet. When we had reduced and plotted the data, our figures were close to those determined by the Lockheed test pilots, which was gratifying but not surprising.
Jet aircraft do not have critical altitudes, since jet thrust decreases steadily with the reduction in air pressure at increasing altitude. Concurrent with the decrease in thrust is a decrease in fuel consumption as well as a decrease in aerodynamic drag on the airplane. Consequently, the most efficient cruise altitudes are quite high, usually in excess of 30,000 feet. The first P-80 cockpits were not pressurized, but later models had a 10,000-foot pressure differential.
Although we worked hard at the school, both in the air and on the ground, camaraderie was strong among the students and the instructors, all of whom were Air Force officers except Doc Nelson. We generally ate lunch together, and when the weather precluded flying, we often watched flight testing, combat, or training films together and exchanged exaggerated stories that illustrated our superior flying skills.
We also played Ping-Pong on lunch breaks and during bad weather. The stability class must have noticed that our performance class had only a few pingers and no pongers, because they challenged us to a series of matches. To no one's surprise, they wiped us out by 6 to 1. We could stand that, but then they issued this gloating pamphlet:
2 Feb (SP) The barely willing forces (?) of the Flight Performance Course were overwhelmed 61 by the magnificent Stability and Control table tennis squad last Friday afternoon on the table of the ASTS pilot's lounge. This lopsided score clearly shows the superiority of the Stability team in this contest (?), and fully indicates results to be anticipated as the two organizations meet in other athletic jousts. The results of the massacre were: