Primary Trainers - The Pilot Makers
Development of the Army's WWII primary trainers
by Randy Wilson
Copyright © 1999 by the Confederate Air Force and Randy Wilson. All rights reserved.
When the First World War ended in November 1918, the airplane was less than fifteen years old. In four years of war, the airplane evolved from a fragile, marginally powered aerial vehicle into a complex military weapon. The results included multi-engine strategic bombers, high-performance air superiority fighters and interceptors, and armored ground attack aircraft. It was during this war that the need for specifically designed, simpler initial training aircraft was realized, and thus was born the military primary trainer or "PT".
The First American PTs
The first U.S. Army Air Corps (USAAC) trainer to bear the designation PT for Primary Trainer was the Consolidated Aircraft Corp. PT-1, a tandem two-seat biplane powered by a Wright E series water-cooled V-8 engine of 180 horsepower. Fewer than 500 of the series, including PT-3s and PT-11s were delivered to the USAAC between 1924 and 1932. The same design was purchased by the U.S. Navy as the Consolidated NY series, however, all but the first batch were powered by more reliable and powerful air-cooled radial engines. While some of these early PTs were still in service into the late 1930s, by 1934, both armed services were looking for newer trainer designs.
In the 1930s, military and civilian primary trainers were almost universally open-cockpit biplanes, despite the increased use of monoplanes for combat aircraft. The open-cockpit was thought to give the beginning student a better "feel" of the aircrafts reaction to the air, while the rugged biplane structure provided protection for both the student and instructor in the event of an accident.
The Continued Reign of the Biplane
In the 1920s, the Stearman Aircraft Co. was best know for its mail and sport planes, but in 1930 it designed a trainer to the U.S. Navys specifications. The Navy decided to build its own primary trainers, as described below, but four Stearman YPT-9s were ordered by the Army for evaluation. In 1934, the reorganized Stearman Aircraft Corp. revised the YPT-9 design, giving it a cleaner and more robust welded steel tube airframe and stronger wooden wing spars and ribs, capable of being stressed to 12 positive and 7 or more negative Gs without failure. It was called the Model 75. Power could be provided by any one of several radial engines produced by Continental, Lycoming or Wright, all of about 215 to 235 horsepower.
That same year, 1934, the Navys own Naval Aircraft Factory designed a new biplane primary trainer to meet specific naval needs. The design featured a bolted steel tube fuselage with large metal panels along the sides, for easy inspection and maintenance. The wings internal structure was of metal instead of wood. Designated the N3N, the design was initially fitted with a Wright J-5 engine, out of production since 1929 but still in Navy stockpiles. Later production N3N-1s, and a subsequent order for 816 N3N-3s were powered by the more modern Wright R-760 engine. The N3N-3 also featured a revised landing gear and tail assembly. However, the Navy did not take delivery of its first N3Ns until June 1936.
Thus, although the new Stearman design was first tested by the Army it was the Navy which placed the first order for 61 as NS-1 primary trainers in 1935. The USAAC followed suit the next year with an initial order for just 26 PT-13s, powered by a Lycoming R-680 engine. The Navy then requested 250 more Stearmans powered by the Continental R-670 engine, designating them N2S-1s but also ordered 125 with the Lycoming engine as N2S-2s. In 1937, the Army ordered 92 PT-13As and followed this up in 1939 with 225 PT-13Bs, all Lycoming powered.
In April 1938, Stearman was purchased by Boeing but remained a separate division and continued to produce primary trainers.
Increased Production of Planes and Pilots
By 1939, it was obvious that America would have to rapidly rearm to protect itself from the ever-widening conflicts in Europe and the Far East. Instead of hundreds of primary trainers, the U.S. military was suddenly faced with needing thousands to train the pilots needed. One bottleneck to such an increase in production was the limited supply of reliable engines. The small radials of 215 or more horsepower used by existing primary trainers were also in demand for multi-engine pilot and crew training aircraft, and even for use in light tanks.
A second shortage, that of flight instructors, was partially solved by the establishment of the Civilian Pilot Training (CPT) program in 1939, which encouraged the development of civilian pilot training schools. The CPT instructors gave many fledgling military aviators their primary flight training after Americas entry into the war.
In 1940, the Army began to take delivery of the first of 2,970 PT-17s from Stearman, powered by the Continental R-670 engine, and the Navy ordered 1,875 similar N2S-3s. To help increase production of both aircraft and engines, the two services agreed to the standardization of some models, beginning with the 1,407 PT-13Ds and 895 N2S-5s all equipped with Lycoming R-680 engines. To guard against a shortage of Continental and Lycoming engines, the Army ordered 150 Stearmans powered by Jacobs R-755 engines, giving them the designation PT-18. Three hundred PT-27s were also built with enclosed cockpits, intended for use in Canada. With more than 8,500 produced, the Stearman/Boeing Model 75 was the classic American primary trainer of the war.
One other biplane, the Waco UPF-7, saw limited use with the Army as the PT-14. Thirteen were ordered for evaluation in 1939 and one civilian version was impressed into service later. The power plant was the Continental R-670.
Enter the Monoplanes
In 1939, the U.S. Army purchased its first monoplane primary trainer, the Ryan XPT-16. Based on Ryans popular STA sport plane, the design was light and maneuverable, even with only the 125 horsepower of its four-cylinder Menaso L-365 inline engine. The external wire and strut bracing of the wings gave the design a slightly dated look, while the odd articulation of the landing gear seemed awkward with the fairings removed, as they were on later military models. Fifteen YPT-16s were ordered and used at Ryans own flying school in San Diego, Calif. as part of the CPT program.
Major complaints about the PT-16 were its small open-cockpits, which made entry and exit with a military parachute difficult and a general lack of power when fully loaded. Although the USAAC contracted for 773 improved PT-20s with enlarged cockpits in late 1939, only about 40 were built. Ryan took the militarys requirements and complaints about the PT-20 and produced a modified design, with the company designation ST-3.
Powered by a Kinner five-cylinder radial engine, the ST-3 had a longer and wider fuselage with full military seats and three-section windscreens. In addition, the wings were swept back slightly, decreasing the planes stability. The change in the wing resulted in a design that snapped and spun more readily than the civil models, as Ryan felt befitted a military trainer. The Army bought 100 PT-21s in 1941, based on the ST-3 design and powered by a 132 horsepower Kinner R-440 engine. The Navy ordered 100 as NR-1s late in 1940, fitted with locking tail wheels.
A demand for more power resulted in the final Ryan production version, the PT-22, powered by a 160 horsepower Kinner R-540 and officially name Recruit. The Army ordered 1,023 in 1941, and deliveries were completed the next year.
A second monoplane design, the Fairchild Engine & Aircraft Corp. Model 62, won an Army competition for new primary trainers in 1939. Powered by a Ranger inline air-cooled engine, also built by Fairchild, the design had a fabric-covered welded steel tube fuselage. The wooden wings and tail surfaces were laminated with a thin plywood covering for rigidity and aerodynamic smoothness. The wings airfoil had a decrease in its angle of attack from root to tip, called washout, which allowed aileron control to be maintained even into a stall.
The Army ordered 270 of the Fairchild Model 62s as PT-19s, powered by a Ranger L-440-1 engine of 175 horsepower. Deliveries began in early 1940 and were soon followed by orders for more PT-19A versions, fitted with a more powerful 200 horsepower Ranger L-440-3 engine. More than 3,700 PT-19As were produced, plus 917 similar PT-19Bs with hoods for instrument or "blind flying" training. To meet this demand, the Fairchild contracted with several existing aircraft companies, including Aeronca, St. Louis, Howard and Fleet, to build PT-19s.
Once again, concerns about engine availability, even from Fairchilds own Ranger division, resulted in the XPT-23, with a 220 horsepower Continental R-670 radial being mated to a PT-19 fuselage. The results were, at best, ungainly but the modification was deemed workable. Fairchild built two PT-23s then turned manufacture over to the sub-contractors mentioned above, who delivered 867 PT-23s and 256 PT-23As with instrument hoods.
In Canada, the Commonwealth Air Training Scheme was also in need of modern primary trainers preferably those with enclosed cockpits for use in the cold northern air. Stearman had vied for this market with its canopy-equipped PT-27, but it was a version of Fairchilds PT-19 that went north to Canada. The PT-26 Cornell was fitted with an enclosed sliding canopy, similar to that used on the original PT-19 prototype. A total of 670 PT-26s, 807 PT-26As and 250 PT-26Bs were built, many in Canada by Fleet Aircraft. Some late production P-26s were delivered to and served with the U.S. Army Air Forces.
Production of the Fairchild PT monoplane almost caught up to that of Stearmans biplane by the end of the war, with over 7,700 being delivered to all users.
While the U.S. Navy relied almost exclusively on its biplane N2S and N3Ns, it did purchase 262 Timm N2T Tutor monoplanes, which were delivered in 1943. The Timm design featured a plastic-bonded plywood structure, called Aeromold, to avoid possible shortages of aluminum and other strategic metals. The open cockpits were in tandem and the engine was a 220 horsepower Continental.
The Final Results
Total production of primary trainers in America from 1935 until the end of WWII was nearly 19,000 planes. The majority, more than two-thirds, went to train the 191,654 Army pilots who won their wings during the war, while the Navys trained tens of thousands more as naval aviators. The next time you see a PT, remember that these werent just planes they were pilot makers.
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