The Berliner-Joyce XFJ was a United States prototype biplane fighter aircraft that first flew in May 1930.
Designed by Berliner-Joyce Aircraft for the United States Navy, its lower wing, placed below the fuselage and just two feet above the ground, apparently gave it a tendency to ground loop when landing, and it was never ordered for production.
Berliner-Joyce had been formed in 1929, and had won a contract with the United States Army for the Berliner-Joyce P-16 aircraft.
At the same time, they submitted a similar design to the Navy, modified to meet the differing requirements, which included a metal skinned semi monocoque fuselage, shoulder mounted upper wings and a lower wing underslung on cabane-type struts.
The prototype, XFJ-1, was sent to Anacostia for testing after its initial flights, where the ground-looping habit was noted, and eventually resulted in a landing accident, necessitating return and repair.
The company took the opportunity to add a Townsend ring engine cowling, and upgraded the engine from a 450-hp Pratt & Whitney R-1340C to a 500-hp R-1340-92 Wasp.
This and other improvements boosted speed from 177 to 193 mph, and the Navy gave the reconstructed aircraft the designation XFJ-2.
However, improved performance came at the expense of stability, and the ground loop problem persisted, and there was no interest in continuing with this design.
Nevertheless, the prototype continued to be used for other tests for several years.