Between 1939 and 1945 the United States expanded its pilot training system from a few hundred graduates a year to tens of thousands. Primary training, the first stage, was largely contracted to civilian flying schools under military supervision, and the Stearman, alongside Fairchild and Ryan monoplanes, was the aircraft they used. A cadet typically arrived at a primary field with no flying experience and spent about two months learning to take off, land, stall, spin and fly basic aerobatics before moving on to basic and advanced trainers.

The Stearman suited this conveyor belt. Its steel-tube fuselage and fabric-covered wooden wings could be patched in a hangar overnight, its seven-cylinder radial was simple to maintain, and its wide undercarriage tolerated heavy landings. It was no pushover. Its tailwheel layout and the long nose that blocked the view ahead punished a lazy student with a ground loop, and instructors used it to separate natural pilots from those who would not make it.

The Navy’s N2S flew from fields across the Midwest and South, including Naval Air Station Ottumwa in Iowa and Wold-Chamberlain in Minneapolis, where cadets trained through winters in open cockpits. Boeing’s Wichita Division turned out the aircraft at a remarkable rate until production ended in 1945, by which time the Stearman had become, as the National Museum of the US Air Force puts it, the primary trainer from the late 1930s to the end of the Second World War.

When the war ended, the military had thousands of trainers it no longer needed. Surplus Stearmans were sold off cheaply, and their strong airframes and slow, stable handling made them ideal agricultural aircraft. Operators fitted hoppers in the front cockpit and often replaced the 220 hp engine with a 450 hp Pratt & Whitney Wasp Junior. For two decades a Stearman spraying fields at treetop height was a familiar sight across rural America.

As purpose-built agricultural aircraft took over, restored Stearmans moved into sport flying and airshows. The extra power that suited crop dusting also suited display flying: AeroSuperBatics, the British wingwalking team, flies Stearmans with 450 hp Pratt & Whitney radials and extra ailerons, so that the pilot can fly a full display without constantly diving for speed.

In 1972 Tom Lowe and Jim Leahy organised a one-off gathering of Stearman owners at Galesburg, Illinois. Twenty-seven aircraft came. The experiment became the annual National Stearman Fly-In, the largest gathering of the type anywhere, and it was still drawing more than 60 Stearmans nearly half a century later.

The Kaydet seats student and instructor in tandem open cockpits. In most military training the student flew from the rear seat, with the instructor in front, and both had a full set of controls. Instruments were minimal: airspeed, altimeter, compass, engine gauges and little else, because primary training was about flying by feel and by looking outside. Communication was through a Gosport tube, a speaking tube that carried the instructor’s voice to the student’s helmet.

Open cockpits made winter training at northern fields an ordeal; cadets at Minneapolis trained in February in heavy flying suits. Canada’s 300 PT-27s addressed the problem with a sliding canopy and cold-weather equipment.

Many restored Stearmans have since been modified with electrical systems, radios, starters and higher-powered engines, but the essential layout remains the one that confronted wartime cadets: a long nose, a big radial and a lot of wind.

• Model 70: the prototype, first flown on 1 January 1934.
• PT-13 / PT-13A / PT-13B / PT-13D: US Army versions with Lycoming R-680 radials; the NMUSAF gives over 2,100 PT-13s for the USAAF.
• PT-17: the most numerous Army version, with the 220 hp Continental R-670.
• PT-18: a small batch with the Jacobs R-755.
• PT-27: 300 winterised aircraft with cockpit canopies for the Royal Canadian Air Force; the Canadian name Kaydet spread to the whole family.
• N2S-1 to N2S-5: US Navy versions, with engines matching the Army variants; the N2S-5 was identical to the PT-13D.

The Stearman is one of the least expensive ways to own and fly a genuine Second World War military aircraft. Its seven-cylinder radial typically burns around 10 to 12 US gallons of avgas an hour, and the airframe is simple enough for many owners to maintain with an experienced mechanic. Adding oil consumption, an engine overhaul reserve, hangarage and insurance, a reasonable estimate for a private owner is in the order of US$250 to US$450 per flying hour. That is an estimate based on typical fuel burn and general-aviation operating costs, not a published figure.

Re-engined aircraft with 450 hp Pratt & Whitney radials, such as display and ex-agricultural Stearmans, burn considerably more and cost more to run.