The Kreider-Reisner Challenger (later the Fairchild KR series) was an American utility biplane aircraft designed and produced by the Kreider-Reisner Aircraft Company, which was later taken over by the Fairchild Aircraft Company.
The Challenger was related to the earlier Waco 10, later renamed as the Waco GXE. A poorly documented Kreider-Reisner aircraft, the C-1, was used to modify the Waco in stages to the Challenger.
The Challenger was a conventional mixed-construction biplane with a fixed tailskid landing gear. It had two open tandem cockpits for a pilot (at the rear), and passenger (forward) and was powered by a 90 hp (67 kW) Curtiss OX-5 inline engine. A number of variants were built designated the C-3 Challenger and C-4 Challenger which had detailed differences and different engines fitted. Late in 1928 the company introduced a new and slightly smaller design designated the C-6 Challenger.
In 1929 the company was bought by the Fairchild Aircraft Company who continued the production of the C-4 as the Fairchild KR-34 and the C-6 as the Fairchild KR-21. Although not built by Fairchild the C-2 was redesignated the Fairchild KR-31.
To act as an engine testbed a KR-21 was modified to use a Fairchild 6-390 engine (later named Ranger) and changes were made to the wing and landing gear geometry. The modified aircraft was known as the Fairchild KR-125. In 1931 a similar aircraft without the geometry changes but with a Ranger engine was sold under the designation KR-135.
In 1930, the KR-34CA, a military version of the Fairchild KR-34 based on the Kreider-Reisner C-4C Challenger design, was built in Farmingdale, New York. A light attack craft, it had two .30 caliber Browning machine guns mounted on the nose, firing through the propellers. The Chinese version had bomb racks under the fuselage. Two of this military version of the Fairchild KR-34 were sold to the warlord generals Liu Wenhui and Liu Xiang in Szechwan Province.
Fairchild type numbers in brackets
Data from The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985), 1985, Orbis Publishing, Page 1674.