The F-89 was developed as a modern successor to the radar-equipped P-61 Black Widow which had been manufactured during WWII. Shortly after the end of the World War U.S. planners stablished the requirement for an all-weather interceptor capable of guarding the United States, and particularly what was then the Territory of Alaska, against the possibility of bomber attack. The fighter would have to operate in harsh climatic conditions, during periods of low visibility, and at night.
Leaning heavily on its experience with the P-61 and related electronic detection systems, the Jack Northrop team proposed a large twin-jet fighter. The fighter would carry a two-man crew consisting of pilot and radar operator, and pack six 20mm cannons in its radar-equipped nose. An extensive array of electronic navigation equipment made flight possible in any kind of weather.
Externally, all models of the F-89 were essentially the same, with the exception of the wingtip pods and radar gun-nose shapes. After the black painted XF-89, all productions models were delivered in their natural aluminium finish. Internally the prime changes were the installations of successively more powerful turbojet engines.
The F-89 was of conventional riveted alluminium alloy, semimonocoque construction with stressed skin. The cabin was pressurized, and a large bubble-type sliding canopy installed. Two Allison turbojet engines with afterburners were mounted side-by-side in the lower centre fuselage separated by the main fuselage structural keel. Engines were "swing-out" mounts, a feature that greatly simplified field service. An unusually thin straight wing was designed for the F-89. Low-speed stability was particularly important for inclement weather missions which demanded slow, instrument-approach speeds. This layout also provided optimum flight characteristics at high altitude and permitted mounting heavy stores on the wingtips. Multiple spars and thick wing skins made up for the lack of wing spar depth, and provided ripple-free aerodynamic surfaces for low drag.
Another singular feature of the F-89 was the split of clamshell ailerons known as "decelerons". When they were opened both top and bottom, a drag was created to slow the airplane down. This was especially useful in combat situations where the pilot wanted to close rapidly on target, then decelerate while firing guns and rockets. The decelerons were also critical for braking the aircraft when it was occassionally put into a dive and achieved supersonic speed.
All F-89 models mounted nonejectable fuel pods at the wing tips. Internal fuel was carried in multiple wing cells, in combination with self-sealing fuselage tanks. The landing gear was of the trycycle type and could be retracted in just four seconds by means of a high-pressure hydraulic system. The single main wheels had thin high-pressure tyres so that they could fit within the wing panels.
In May 1946, the Air Force awarded Northrop a contract for two prototypes designated XP-89. These prototypes would enter into competition with the Curtiss-Wright XP-87 Nighthawk for a future production order. The first prototype was finished by mid-1948 and redesignated, according to the Air Force changes in system designations at that time, as XF-89. This aircraft first flew on 15 May 1948 from Muroc AFB. The results of the test program marked the F-89 as a high-performance machine with unusual easy-to-fly characteristics. In consequence, the Air Force awarded the company a production contract for 48 F-89A models in January 1949.
The second protype, finished in early 1950, was redesignated YF-89A to identify its function as "service evaluation" airplane. Programme test flying was halted when the original XF-89 crashed in February 1950 and one of his test pilots died. Investigations revealed that the horizontal stabilizer/elevator flutter had caused the accident and changes were carried out to correct the problem in all F-89As. Those still in fabrication also received internal equipment changes, including the introduction of the Lear F-5 autopilot, converting them into F-89Bs.
The F-89A/B had provisions for two bomb pedestal on the wings for the carriage of 1,600 pound bombs. In addition each wing had provisions for four rocket-launchers, each capable of carrying two 5-inch HVAR rockets (16 total). The B model retained the A model nose configuration with a radar fire-control system and six 20mm cannons.
The F-89C incorporated uprated Allison J-35 turbojet engines and new elevators. All F-89As and Bs were retrofitted with the new elevators while armament and fuel feed remained the same as on the B model. In May 1950 the Air Force ordered the improved F-89C into production with an initial order for 63 airplanes. As tension mounted in Korea, Washington ordered an acceleration in aircraft production. In September 1950 Northrop was authorised to build and operate a new installation and flight center in California and a second contract for 100 additional F-89Cs was also awarded. However, the early C model suffered a series of unexplained crashes soon after entering service with Air Defense squadrons. Consequently, all F-89 were grounded and an intensive investigation was launched by Northrop. The tests disclosed that wing attach fittings cracked and failed in certain flight regimes. Within a short time, Northrop engineers developed key structural changes and a large scale modification program affecting close to 200 aircrafts that had been in flight status. These changes made the F-89 the safest airplanes in the Air Force inventory. By the time it was retired in 1969, the Scorpion had stablished new standrds for low accident rates for operational fighters.
A major model change came with the F-89D. The most significant features were the addition of rocket/fuel pods to the wingtips, a new Hughes fire-control system, and the removal of the cannons from the nose. Each rocket pod carried 52 2.75-inch FFARs fired selectively or in salvo mode that could blanket an area as large as a football field. The aft bays of each pod contained 300 gallons of fuel. The aircraft also featured more powerful Allison engines. This model seemed to satisfy the Air Force needs during and after the outbreak the Korean war. Orders for 194, 172, 240, and finally 77 were placed with rapid succession of one another.
The single YF-89E prototype was a F-89C converted to incorporate two new Allison YJ-71 engines. Only the one prototype E was manufactured as a test bed for these new engines. The last model to be produced in quantity was the H. It was the same as the F-89D except for revised rocket/fuel pods on the wingtips, and the new Allison engines. The tip pods were redesigned to add three Hughes Falcon GAR-1 missiles (guided air-to-air) to each pod. The Falcons were mounted internally in each bay and swung out automatically on launchers in preparation for firing. The inclusion of the Falcons reduced the number of FFAR rockets to 21 in each pod. In March 1954 the Air Force ordered 156 fighters of this model. The first aircrafts to be produced came off the assembly line by 1956.
In a test at tha Atomic Energy Commission's test site in Nevada on July, 19 1957, a modified F-89D fired an MB-1 nuclear-armed Genie rocket. After this successful test, Northrop proposed an F-89J configuration to the Air Force. The new model would not require production of new airframes, but would result from the conversion of existing F-89Ds. The final F-89J configuration, after a few of them were considered, carried two Genie MB-1 nuclear rockets and four underwing Falcon GAR-2 guided missiles. Six hundred-gallons fuel tips replaced the D model rocket pods. Ultimately, 350 F-89J were delivered to the Air Force.
After serving with the regular Air Force from Thule (Greenland) and Fairbanks and Anchorage (Alaska) to continental U.S. air defense bases, the Scorpion was assigned to domestic Air National Guard units. Phase-out came in 1969, when the last two squadrons were retired at Des Moines (Iowa) and Bangor (Maine). |