The first production version of the Scorpion was the F-89A (Model N-35). Forty-eight F-89As had been ordered on July 14, 1949. Production of the F-89A got underway even while the XF-89 and YF-89 were still under test, but the crash of the XF-89 prototype on February 22, 1950 brought the whole program to a halt while the problems were being fixed.
At the time of the XF-89 accident, three F-89As were nearing completion. It was decided that these three machines, acting in conjunction with the YF-89A, would be the test force used to wring out the problems with the Scorpion. The first production F-89A was accepted by the USAF on September 28, 1950, followed by the second and third examples a few weeks later.
The F-89A could be distinguished from the YF-89A by the mounting of an armament of six 20-mm T-31 (M-24) cannon in the nose with 200 rpg. Neither the XF-89 nor the YF-89A had carried any armament. Underwing pylons were provided which could carry sixteen rockets or up to 3200 pounds of bombs. An A1-CM gunsight was fitted, and an AN/APG-33 radar was mounted in the nose.
The fix for the tail flutter problem was found to be the fitting of a series of external mass balance horns attached to the hinge area of the horizontal stabilizer/elevator. The configuration of the underfuselage exhaust deflector fairings was changed, and a number of different fairing designs were tried until a final design was adopted. The lines of the rear fuselage behind the jet pipes were altered to overcome some of the excessive turbulence that had been encountered by the YF-89A at high speeds. With these changes, the fail flutter problem was finally believed to be cured, and in January of 1951 production of the F-89A was resumed.
The engines of the F-89A were originally a pair of Allison J35-A-21s. After a rash of engine failures on early F-89As, these aircraft were reengined with Allison J35-A-21A turbojets, rated at 5100 lb.s.t.dry and 6800 lb.s.t with afterburning. These engines had an engine oil scavenging system and different kinds of afterburner eyelids, which gave smoother afterburner control.
The external mass balances on the early F-89As were eventually replaced by elevators with internal maass balance which were fittedretroactively after having been developed for the F-89C.
A total of eight F-89as were accepted between September 1950 and March 1951. This was 40 less than ordered under the contract of July 1949. The remainder were delivered as F-89B or F-89C. Because of their limited number, most of the F-89As were used primarily for operational suitability tests and did not enter active service. However, a few did enter the operational inventory of the USAF.
Several obsolete F-89As were later modified into radio-controlled target planes under the designation DF-89A.
49-2433 was used to test air-to-ground capability at Eglin AFB in Florida.
The Martin D-1 four-gun swivelling turret was tested briefly on F-89A 49-2434. The entire nose section rotated as a unit, while the guns traversed through 105 degrees from the forward facing position. The system was not adopted for production F-89s.
49-2438 was used by Allison for experimental work under the designation JF-89A.
49-2431/2438 Northrop F-89A Scorpion