The Ryan ST as had been built in strict accordance with military requirements
With Stearman and Vultee, Ryan was one of three companies selected in 1940 to produce primary trainers for the USAAC’s great expansion of the period, and its initial type was the PT-16 modelled on the civil STA with wheel spats/leg fairings, a wire-braced low-set monoplane wing, and the 93-kW (125-hp) Menasco L-365-1 inline. The Army tested it as the XPT-16. Its performance won a 15-plane service evaluation order, these to be designated YPT-16s.
. In the redesign for the YPT-16s, the basic and familiar ST airframe underwent its first external appearance change. The cockpit openings were cut larger, down to meet the channel stiffeners. Addition of a turnover mast at the front cockpit windshield, A Bendix hand-cranked direct drive inertia engine starter, toe brakes and parking brake completed the redesign and met the immediate military specifications. This was the first low-wing trainer to convince the Army to break away from their 30-year precedent of biplanes being used for initial instruction of aviation cadets.
The 16 prototype and trials aircraft were followed by 40 improved PT-20s. Adoption of the 94-kW (132-hp) Kinner R-440-3 radial with a stronger structure led to the PT-21, of which 100 were produced ; re-engining of older aircraft with the R-440-1 produced the PT-16A and PT-20A.
Next came the PT-22 Recruit with the 119-kW (160-hp) Kinner R-540-1 radial, swept back wings, and the 1,023 army aircraft were complemented by 100 naval equivalents designated NR.
The PT-22 was first ordered by the U.S. Army in 1941, and deliveries commenced the same year. The PT-22 was somewhat different to meet military requirements for ease of accessibility to both cockpits with a parachute. The designations PT-22A and PT-22B were applied respectively to 25 aircraft taken over from a Dutch order in 1942, and to 250 PT-22s retrofitted with the R-540-3 radial. The PT-22 was known post WW2 as the civil ST-3-KR.
In the mid 'thirties, Ryan offered a single-seat armed version of its tandem two-seat STM primary trainer, which, in turn, had been derived from the S-T initially flown on 8 June 1934. Dubbed STA-Special, the single-seater was powered by a 150hp Menasco C4S air-cooled engine, and a second batch of six ordered in December 1938 for the Guatemalan Cuerpo de Aviacion Militar were each fitted with two 7.7mm wing-mounted guns and referred to as light fighters.
The first of the STM-2s were ordered to be equipped with Menasco C-4S "Pirate" supercharged 150hp engines.
The first group of STM-2s was shipped to the Pilots and Observers School (Army Primary Flying School) at the Kalidjati Air Base to the north of Bandung in Western Java. These ships replaced the Koolhoven FK-51s as basic trainers.
Although training was the main duty of the Ryans, when the war got hot in the area, they were constantly being dispersed and used in other roles. The airplanes were pressed into service as reconnaissance aircraft and to supply remote outposts or patrol ships. It was not unusual for the pilots to strap a five-gallon fuel tank in the front cockpit and go out on a long coastal patrol. When the fuel became low the pilot would land at a convenient clearing, refuel the aircraft and continue his flight. During air raids the Ryans would be hidden under palm leaves.
There are a number of reports involving the agile Ryans serving with the Dutch colonial military services. Several were caught or chased by Japanese aircraft while on training or reconnaissance flights; some managed to get back to their base safely, while others were shot down. During another attack the aviators were given orders to fly at a very high altitude in order to report Japanese airplanes approaching the airfield. At times the Ryans engaged in dogfights with the Zeros. The Ryan showed such maneuverability that it did a fair job of staying out of the firing range of the Japanese airplane. One Ryan had an aileron shot off and still the pilot was able to set the airplane down safely.
Engine: Menasco B4, 95 hp
Engine: Menasco C-4S, 150 hp
Propeller: Sensenich wooden, fixed pitch
Fuel: Aviation Gasoline 100 Octane
Wingspan: 29' 11" / 9.12 m
Length: 21' 5" / 6.54 m
Wing Area: 124.0 sq. ft / 11.52 sq. m
Height: 6' 11" / 2.11 m
Empty: 1,083 lb / 491 kg
Maximum Takeoff weight: 1,600 lb / 726 kg
Maximum Speed: 123 knots / 141 mph / 228 km/h
Cruise Speed: 111 knots / 128 mph / 206 km/h
Loading: +/- 10G
Engine: Menasco C4
Engine: Supercharged Menasco, 150 hp
Engine: Menasco C-4/D-4, 125 hp
HP range: 125-160
Height: 6.9 ft
Length: 21.5 ft
Wing span: 30 ft
Wing area: 124 sq.ft
Fuel cap: 24 USG
Weight empty: 1030 lb
Gross: 1575 lb
Speed max: 140 mph
Cruise: 120 mph
Range: 350 sm
Stall: 42 mph
ROC: 850 fpm
Take-off dist: 525 ft
Landing dist: 1000 ft
Service ceiling: 17,500 ft
Landing gear: tail wheel
ST3KR / PT-21-RY
Powerplant: l x Menasco L-365-1, 93kW (125 hp)
Span: 9.14m (30ft )
Length: 6.55m (21 ft 6in)
Max TO weight: 726 kg (1,600 lb)
Max speed: 128 mph at sea level
Operational range: 350 miles
Engine: Kinner R-540-1 5 cylinder radial, 540ci, 160 hp
Empty wt: 1316 lb
MAUW: 1860 lb
Fuel cap: 20 Imp Gal
Cruise approx: 105 mph
Loading: +/- 10G
Stall: 62-64 mph
Engine: Kinner R-440, 132 hp