Challenger radial piston engine; about 50 built. Robin C-1 (Model 50C) An improved version of the Robin C, powered by a Curtiss Challenger radial piston engine; over 200 built. Robin C-2 (Model 50D) A long-range version fitted with an extra fuel tank, powered by a Curtiss Challenger radial piston engine; six built. Robin 4C (Model 50E) A four-seat version, powered by a Curtiss Challenger radial piston engine; one built. Robin 4C-1 A three-seat version with an enlarged forward fuselage section; three built. Robin 4C-1A (Model 50G) Another four-seat version with an enlarged forward fuselage section; 11 built. Robin 4C-2 A single un-certified version powered by a Wright J-6-7 Whirlwind engine. Robin CR A one-off experimental version, fitted with a Curtiss Crusader engine. Robin J-1 (Model 50H) Powered by a Wright J-6-5 Whirlwind radial piston engine; about 40 built. Robin J-2 (Model 50I) A long-range version, with fuel. Two were built Robin J-3 A J-1 temporarily designated J-3, which reverted to the J-1 designation after being de-modified. Robin M A Robin B aircraft, fitted with the Milwaukee Tank V-502 V-8 engine (air-cooled OX-5 conversions). Robin W (Model 50J) Powered by a Warner Scarab radial piston engine. Only a small number were built in 1930. XC-10 One Robin W was sold to the United States Army Air Corps (USAAC) and converted into an unmanned pilot-less radio-controlled test aircraft, powered by a Warner R-420-1. Operators Military operators Paraguayan Air Force United States Army Air Corps Surviving aircraft Australia 477 – J-1 airworthy with John Graeme Vevers of Patterson Lakes, Victoria. Brazil 248 – C-2 in storage at the TAM Museum in São Carlos, São Paulo. Canada 405 – C-1 on display at the Reynolds-Alberta Museum in Wetaskiwin, Alberta. Costa Rica C-1 on display at the Juan Santamaría International Airport domestic terminal in Alajuela, Costa Rica. Germany 130 – J-1 airworthy with Antique Aeroflyers in Mengen, Baden-Württemberg. United States 193 – B airworthy at the Fantasy of Flight in Polk City, Florida. 213 – B airworthy at the Western Antique Aeroplane & Automobile Museum in Hood River, Oregon. 329 – B-1 on static display at the San Diego Air & Space Museum in San Diego, California. 337 – C-1 on static display at the Evergreen Aviation & Space Museum in McMinnville, Oregon. 403 – B-2 on display at the EAA Aviation Museum in Oshkosh, Wisconsin. 469 – C-1 on display at the Yanks Air