The third XP-84 aircraft, because of numerous evolutionary changes and being fitted with an Allison J-35-A-15 of 4,000 pounds thrust, was redesignated from XP-84 to XP-84A, and was the only Thunderjet so designated. Flight and wind tunnel tests on the XP-84s and models revealed several structural and instability problems. In particular, the rear fuselage skin would suffer buckling and distortion when the aircraft exceeded certain G-forces, and there was longitudinal instability. Meanwhile, delays in delivery of the engine for the XP-84A gave the Republic engineers time to resolve some of the problems encountered with the first two prototypes, and these "fixes" were incorporated into the XP-84A. Like the two prototype XP-84 aircraft, the XP-84A was not fitted with any armament. The XP-84, XP-84A, and YP-84A were primarily test vehicles.
Pitot tube on mid left wing; navigation lights centered on wingtips.
No photos of XP-84A at this time