Northrop F-89C Scorpion

Last revised September 17, 2000






The F-89C (Model N-35) was the first major production version of the Scorpion, with a total of 164 being built.

The first F-89C flew on September 18, 1951. It incorporated most of the changes that had been made to the F-89A/B small-scale production run in an attempt to make the Scorpion a fully operational and safe aircraft.

Some of the changes incorporated in the F-89C were primarily internal. A fuel purging system was added which helped alleviate the danger of fuel vapor explosions. A bulge could be seen on the starboard engine nacelle that was introduced by this system. This used engine bleade air and fuel to create an intert gas to purge the fuel system. The wingtip fuel tanks had dump valves installed which allowed them to be emptied in flight. The cockpit air conditioning and pressurization system were upgraded. A Lear vertical gyro was added to provide artificial horizon information to the autopilot. An alcohol deicer tank was added on one of the underwing racks.

Other changes incorporated in the F-89C were external and hence more obviously recognizable. The shape of the canopy was slightly altered. Some sources claim that after production of the first 40 F-89Cs, the external mass balance horns on the horizontal stabilizer/elevator were deleted and replaced by a strengthened horizontal tail with internal mass balances. However, it appears that these internal mass balances were actually fittted to the F-89C from the very beginning. This feature was retrofitted to all previous Scorpions.

During January of 1952, the 74th Fighter Interceptor Squadron based at Presque Isle AFB in Maine (already a user of the F-89B) was declared operational with the F-89C. Other units soon followed. Winterized F-89Cs were sent to Elmendorf AFB in Alaska and to Harmon AFB in Newfoundland.

Even though the Scorpion was rapidly entering squadron service all throughout 1952, the interceptor continued to be plagued by engine failures. The initial production blocks (1 through 20) of the F-89C were powered by a pair of J35-A-21 engines. In service, these engines were very unreliable and were subject to frequent failures. The problem was solved as in the case of the F-89A and B by retrofitting these early F-89Cs with the improved and more reliable J35-A-21A engine.

Beginning with the F-89C-25-NO production block, the engine was changed yet again to the Allison J35-A-33 jet rated at 5400 lb.s.t. dry and 7400 lb.s.t. with afterburner.

Finally, production blocks -35 and -40 were fitted with the Allison J35-A-33A, rated at 5600 lb.st. dry and 7400 lb.st with afterburner. The -33A engine not only had more power, it also had a redesigned inlet, deicing equipment, inlet guide vanes, and redesigned forward engine mounts. The F-89's engines, being mounted quite low on the fuselage, had a tendency to scoop up runway debris into their intakes. To cure this problem, retractable inlet screens were added to the -33A engine.

Other problems with the Scorpion turned out to be much more serious. During 1952, several F-89Cs crashed due to wing structural failures. No less than six aircraft were lost in the spring and early summer of 1952, one spectacular crash taking place in front of thousands of spectators at the International Aviation Exposition at Detroit. The Air Force was forced to ground the entire Scorpion fleet on September 22, 1952 until the cause could be found.

After an exhaustive series of flight tests, the problem was finally traced to a previously unknown effect, known as aero-elasticity. During high-G maneuvers, the wing tended to twist at the tip, exerting excessive strain on the wing attachment points and causing them eventually to fail. The large wingtip fuel tanks were found to be a significant factor in exerting this twisting moment. A total of 194 F-89A, B, and C aircraft were shipped back to Northrop where they were fitted with stronger wings with forged steel attachment points. At the same time, a small fin was added to the outboard rear of each wingtip tank, which reduced the aerodynamic forces on the tank that caused it to flex and twist during maneuvering.

Before the F-89C fleet had been fully retrofitted with the new stronger wing, a total of fourteen months had passed and it was not until 1954 that the Scorpion force reached its intended level. As fast as the F-89Cs could be modified, they were flown directly to their operational units. With the modified wing and the improved engines, the Scorpion became one of the safest and most reliable combat aircraft in the USAF inventory. The 74th Fighter Interceptor Squadron, following its transfer to Thule, Greenland in August of 1954 completed a full year of service with the type without a single accident of any kind.

The F-89C served with the 27th, 74th, and 433rd Fighter Interceptor Squadrons from 1952 onwards. The 57th FIS, based in Iceland, the 65th FIS based in Alaska, and the stateside 438th FIS took delivery of the F-89C in 1953.

The F-89C was phased out of active USAF service during 1954, when later Scorpion models became available. F-89Cs were then transferred to the Air National Guard, equipping some seven units in northern states. ANG squadrons operated the F-89C until well into the 1960s until they were finally phased out of service.

F-89C 51-5795 was modified to test a nose installation with two T110E3 rocket launchers in the nose, one on each side. Each of these rifled barrels was fed by a magazine loaded with a clip of 2.75-inch FFARs. Another F-89C was tested with a battery of four 30-mm Oerlikon 302RK cannon with 100 rounds each.

Specification of the F-89C:

Engines: Two Allison J33-A-33A, 5600 lb.s.t. dry, 7400 lb.s.t. with afterburner. Performance: Maximum speed: 650 mph at sea level, 562 mph at 40,000 feet. Initial climb rate 12,300 feet per minute. Service ceiling 50,500 feet. Maximum range 905 miles. Dimensions: wingspan 56 feet 0 inches, length 53 feet 5 inches, height 17 feet 6 inches, wing area 606 square feet. Weights:24,570 pounds empty, 33,100 pounds combat, 37,348 pounds gross. Armed with six 20-mm cannon in nose. Underwing racks could carry 16 five-inch rockets or 3200 pounds of bombs.

Serials of the F-89C:



50-741/744 	Northrop F-89C-1-NO Scorpion 
50-745/759 	Northrop F-89C-5-NO Scorpion 
50-760/774 	Northrop F-89C-10-NO Scorpion 
50-775/789 	Northrop F-89C-15-NO Scorpion 
50-790/804 	Northrop F-89C-20-NO Scorpion 
51-5757/5771 	Northrop F-89C-25-NO Scorpion 
51-5772/5801 	Northrop F-89C-30-NO Scorpion 
51-5802/5836 	Northrop F-89C-35-NO Scorpion 
51-5837/5856 	Northrop F-89C-40-NO Scorpion 

Sources:


  1. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.

  2. F-89 Scorpion in Action, Aircraft Number 104, Larry Davis and Dave Menard, Squadron/Signal Publications, 1990. Sources:

  3. Fighters of the United States Air Force, Robert F. Dorr and David Donald, Temple Press Aerospace, 1990.

  4. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

  5. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

  6. Post World War II Fighters, Marcelle Size Knaack, Office of Air Force History, 1986.

  7. E-mail from James Ensign who flew F-89Ds with the 66th FIS at Elmendorf AFB. The 66th transitioned from F-94As to F-89Ds, and did not operate the F-89C. Several publications have incorrectly identified the 66th FISs F-89s with those of the 64th and the 65th. The 66th had yellow-painted rocket/fuel tanks, the 65th used red and the 64th used green.