Sources disagree on the date of the first flight (and on the armament as well).
XF2G-1 first flight on 26 August 1944 according to Vought F4U Corsair by Martin W. Bowman, Crowood Press, 2002, p.121:
Almost immediately the F2G programme ran into problems, caused by production delays of the R-4360 engines to Goodyear. Donald Armstrong, Goodyear's chief engineering test pilot, carried out the first flight in XFG2-1 Bu No. 13471 on 26 August 1944. The second XFG2, Bu No. 13472, was used to complete tests on various propellers, the automatic oil cooler and automatic cowl-flap controls, and a variety of other tasks. The third XF2G-l, Bu No. 14691, was delivered to the Navy on 27 November 1944. Bu No. 14692, the fourth XF2G, was used to test new wing fuel tanks and a number of different rudder installations, and to fly the final dive tests for the Navy. Pratt & Whitney used the fifth XF2G, Bu No. 14693, to test the performance of a water-injection system. Bu No. 14694 was the sixth XF2G-l used for testing. The seventh and last model, Bu No. 14695, first flown on 4 December 1945, suffered hydraulic failure eight days later during an instrument shake-down flight, and test pilot Armstrong was forced to make a belly landing without flaps.
XF2G-1 first flight on 15 October 1944 according to Vought F4U Corsair by Barrett Tillman, Specialty Press, 1996, p.91:
The F2G contract was inked on 22 March 1944 with first flight nine weeks later, on 31 May. However, early flight tests were conducted in FG-1s modified to accept the Wasp Major engine. These aircraft were given the factory designation EXF2G-1 — a model unknown to the Navy to this day.
First flight of the prototype "real" XF2G-1 came on 15 October 1944, with Don Armstrong in the cockpit. Intimately involved with the "Super Corsair." Armstrong was an experienced test pilot who had previously worked at Curtiss and Douglas. At the end of that first F2G flight, Armstrong was asked by Goodyear vice president Karl Arnstein how the fighter performed. Impressed with the spectacular rate of climb, Armstrong enthusiastically replied, "It's a homesick angel!"