The Northrop C-19 Alpha was a series of three aircraft purchased from Northrop by the US Army Air Corps in 1931. They were slightly modified versions of the civil Northrop Alpha Type 2.
The Letov Š-18 was a Czechoslovak single-engined, two-seat biplane trainer. It was designed by Alois Smolík at Letov Kbely. The Š-18 first flew in 1925.
The Avia BH-11 was a two-seat sport aircraft built in Czechoslovakia in 1923, a further development of the Avia BH-9. The main changes in this version involved a redesign of the forward fuselage. 15 examples were ordered by the Czechoslovakian Army as trainers and general liaison aircraft, and operated under the military designation B.11.
The Avia BH-29 was a trainer aircraft built in Czechoslovakia in 1927, in the hope of marketing it to both the Czechoslovakian Army, and to Czechoslovakian Airlines as a primary trainer. It was an conventional design, an unequal-span biplane of wooden construction and with tailskid undercarriage. The pilot and instructor sat in tandem open cockpits. A more powerful version was built, powered by a 120 hp (89 kW) Walter NZ-120 radial engine.
The Breda A.4 was a biplane trainer produced in Italy in the mid-1920s. It was of conventional configuration with a two-bay unstaggered wing cellule and seating for the pilot and instructor in tandem open cockpits. Apart from civil use, the A.4 was also adopted by the Regia Aeronautica as a trainer. At least some examples were produced in floatplane configuration as the A.4idro.
The CAMS 46 was a flying boat trainer aircraft built in France in the mid-1920s, essentially an updated version of the CAMS 30 that had flown in 1922. While retaining that aircraft's basic form, CAMS offered the French Navy two new versions with aerodynamic refinements over the earlier aircraft: the CAMS 46 E primary trainer, and the CAMS 46 ET intermediate trainer. Only the latter was selected for production and was built in quantity to supply one escadrille at the Naval training station at Hourtin.
The Hirtenberg HS.9 was an Austrian two-seat touring or training aircraft of the early 1930s.
The International F-17 Sportsman was a 1920s American three-seat open-cockpit biplane designed and manufactured by the International Aircraft Corporation in Long Beach, California and Cincinnati, Ohio. 107 aircraft were built, 77 of them at Cincinnati.
The SIAI-Marchetti SM.1019 is an Italian STOL liaison monoplane built by SIAI-Marchetti for the Italian Army, and based on the Cessna O-1 Bird Dog.
The Hopfner HS-5/28 was a utility aircraft built in Austria in the late 1920s. It was a conventional, parasol-wing monoplane with seating for two occupants in tandem, open cockpits. The landing gear was of fixed, tailskid type with divided main units. Two examples were built with Walter NZ60 engines, followed by two more with the more powerful NZ85 for Swiss aeroclub use. One of these latter machines remained in service until 1934.
The Hopfner HS-10/32 was a utility aircraft built in Austria in the early 1930s. It was a conventional, high-wing, strut-braced cabin monoplane derived from Hopfner's series of parasol-wing light aircraft that began with the HS-5/28. Three examples flew in late 1932 under the designation HS-10/32, followed by a single example of the improved HS-10/33 the following year, a generally similar aircraft with revised ailerons. The HS-10/33 was eventually purchased by the Austrian Air Force to use as a liaison machine.
The Hopfner HA-11/33 was an amphibious flying boat built in Austria in 1933 to a specification by the Dr. Oetker company. The result was a conventional, high-wing cantilever monoplane with a stepped flying boat hull and pontoons on struts under the wings at mid-span. The cabin was fully enclosed, and the twin engines were mounted tractor-fashion on struts above the wing.
The Lublin R-XI was the Polish passenger plane for 4 passengers, designed in 1930 in the Plage i Laśkiewicz factory in Lublin, that remained a prototype.
The PWS-51 was a Polish sports plane of 1930, a single-engine low-wing monoplane, constructed by the Podlaska Wytwórnia Samolotów (PWS), that remained a prototype.
The IMAM Ro.5 was a sport aircraft designed by Alessandro Tonini and produced by IMAM in Italy in the late 1920s.
The Spartan C4 was an American four-seat cabin monoplane designed and built by the Spartan Aircraft Company.
The PWS 3 was a Polish sport aircraft, developed in 1927 by PWS, which remained a prototype.
The Skandinaviska Aero BHT-1 Beauty is a 1940s Swedish single-seat light monoplane designed by E. Bratt, K.E. Hilfing and B.Törnblom and built by Skandinaviska Aero of Stockholm.
The Kalinin K-9 was a liaison/sport aircraft designed by Konstantin Alekseevič Kalinin. It had a parasol wing, only one was built in 1932. The prototype was evaluated during some test flights, but development was never carried out. The tests revealed that the K-9 was too large and too heavy in relation to the installed engine,.
The Klemm L 26, later Klemm Kl 26, was a low-wing trainer aircraft built by Klemm.
