05/31/2010. Remarks by Johan Visschedijk: "Designed around a proposal made by Northrop in December 1945, the Scorpion became the first USAF multi-seat jet fighter capable of all-weather operation. The AF accepted the Northrop proposal and issued a development contract on May 3, 1946, following this with a firm order for two XP-89 prototypes in December 1946. Between 1949 and 1956, 1,050 production examples of the Scorpion were built by Northrop.

The Scorpion was of conventional construction, with a shoulder-mounted wing and two 4,000 lb (1,814 kg) st Allison J35-A-9 turbojets side-by-side in the fuselage under the cockpit floor. As originally designed, the aircraft had a basic wing span of 52 ft (15.85 m) with tip-mounted fuel tanks which were removable on the first prototype but were subsequently fixed. Armament of four cannon was grouped in the nose together with A.I. radar, and the pilot and radar operator were in tandem beneath a long cockpit canopy.

The first (s/n 46-678) of the two XF-89 prototypes (redesignated from XP-89 in 1948) was flown by Fred Bretcher on August 16, 1948 from Edwards AFB, California. For the first 32 flights it had conventional wing ailerons but on February 1, 1949, a new series of trials began with Northrop 'decelerons' which were to be a standard feature of all production Scorpions. The 'deceleron' was a split surface which operated in one piece as an aileron but which could be opened out to serve also as a dive brake.

The XF-89 was lost on its 102nd flight on February 22, 1950, after making a low pass at high speed for USAF officials at Hawthorne Airport (Northrop Field). It crashed ca. 5 mls (8 km) from the Northrop factory on Rosecrans Avenue at Flournoy Road, Manhattan Beach, California. The pilot, Charles Tucker, parachuted to safety, but the flight engineer, Arthur Turton, was killed. Cause of accident was high-frequency, low amplitude aeroelastic flutter of both vertical and horizontal stabilizers.

By that time, the second prototype (s/n 46-679) was in flight test, having first flown on November 15, 1949. Modifications introduced when the airframe was about 90% complete led to a change of designation to Model N-49 XF-89A. The changes were intended to prove in flight features of the F-89A production model. External differences between the two prototypes included the silver finish of the XF-89A instead of black, and more pointed nose shape which lengthened the fuselage from 50 ft 5.5 in to 53 ft 5.5 in (15.37 m to 16.15 m). The XF-89A, which flew on June 27, 1950, had two J35-A-21 engines, rated at 5,200 lb (2,359 kg) st with afterburners (a/b).

Deliveries of the Model N-35 F-89A Scorpion, a contract for which had been approved on July 14, 1949, began in July 1950. Generally similar to the YF-89A, it had six 0.787 in (20 mm) T-31 guns in the nose and provision under the wings for two bombs of up to 1,600 lb (726 kg) each plus a maximum of sixteen rockets. The engines were subsequently changed to J35-A-21A, rated at 5,100 lb (2,313 kg) st and 6,800 lb (3,084 kg) st with a/b. The lines of the rear fuselage behind the jet pipes were altered to overcome excessive turbulence encountered on the YF-89A at high speeds.

After eight F-89As (s/n 49-2431 to 49-2438) had been delivered, production changed to the Model N-35 F-89B, distinguished by internal equipment changes including the introduction of an autopilot, an ILS system and a Zero-reader system. The armament and radar were unchanged and like the F-89As, the forty F-89Bs (s/n 49-2439 to 49-2478) were built with J35-A-21 engines which were later changed to J35-A-21As. All F-89As and F-89Bs had externally mass balanced elevators, adopted to overcome the earlier mentioned flutter problem induced by the jet exhaust, but elevators with internal mass balance were fitted retroactively after being developed for the F-89C.

Apart from the new tail plane, the Model N-35 F-89C incorporated numerous equipment changes. The first few carried a fuel system purge generator in an external fairing under the starboard engine, and another interim feature was an alcohol tank on the port wing bomb shackle, to provide for engine air inlet de-icing. To overcome a wing structural problem on this model, fins were added to the tip tanks and were then applied retroactively to the F-89A and F-89B. Production of the F-89C totaled 164; the first 34 (s/n 50-741 to 50-774) were delivered with J35-A-21 engines followed by 30 (s/n 50-775 to 50-804) with the J-35-21A engine, 45 (s/n 51-5757 to 51-5801) with the J35-33 rated at 5,400 lb (2,449 kg) st and 7,400 lb (3,357 kg) st with a/b, and 55 (51-5802 to 51-5856) with the 5,500 lb (2,495 kg) st J35-33A.

Armament and radar remained unchanged in the F-89C, but work was proceeding meanwhile on a new wing tip installation containing 52 2.75 in (70 mm) FFARs in addition to fuel. The pods were first flown during 1951 on a modified F-89B re-designated YF-89D (49-2463) and were a standard feature of the 682 production Model N-68 F-89Ds, that also had equipment changes, extra fuel in the nose and under-wing pylon tanks to increase the total capacity by 862 gal (3,263 l), and later engines. The first 47 aircraft (51-400 to 51-426) had the J35-A-33A, the next 130 (s/n 51-427 to 51-446, 51-11298 to 51-11407) had the J35-A-41 engine and the remaining 525 (s/n 51-11408 to 51-11443, 52-1829 to 52-1961, 52-2127 to 52-2165, 53-2447 to 53-2686, 54-184 to 54-260) had the J35-A-35.

Installation of two Allison YJ71-A-3 engines in an F-89C (s/n 50-752) accounted for the Model N-71 YF-89E, used as an engine test bed. A production version with these engines and 'D' armament was to have been the F-89F but was cancelled. So also was the F-89G, with revised armament and fire control. The final production version of the Scorpion therefore was the Model N-138 F-89H, in which the wing tip pods were redesigned to carry three Hughes Falcon AAMs with 21 FFARs. Up to six more FFARs could be carried under the wings. The engines were J35-A-35s.

Production totaled 156 (54-261 to 51-416), in addition to three F-89Ds (s/n 53-2449, 52-1830 and 52-1938) modified to test the new features but not redesignated. A further change of armament was made in 1956 to introduce the Douglas Genie unguided, nuclear-tipped rocket on under-wing pylons, one each side. Additional pylons could carry up to four GAR-2A AAMs, and the wing tip installation could be either FFAR pods or fuel tanks. So modified, the aircraft were designated Model N-160 F-89J; 350 were delivered by conversion from F-89Ds, with J35-A-35 or J35-A-35A engines, and Hughes MG-12 fire control system."