Northrop XP-89 Scorpion

Last revised November 6, 1999






The Northrop F-89 Scorpion was one of the primary defenders of North American airspace during the Cold War. A total of 1052 Scorpions were built. During its career, the F-89 equipped 36 active Air Force Units and 17 Air National Guard squadrons. The Scorpion was difficult to fly, costly to maintain, and was subject to mishaps. It had an accident rate of 383 per 100,000 hours, which was astronomically high compared to today's F-15, which has an accident rate of only 0.5 per 100,000.

On March 23, 1945, the USAAF announced a competition for the successor to the Northrop P-61 Black Widow night fighter. It was to be an all-weather fighter-bomber. Initially, a piston-engined design was specified, and on August 28, 1945, the USAAF issued a set of proposed requirements. These included a maximum speed of 525 mph at 35,000 feet, 550 mph at sea level, a climb to 35,000 feet in 12 minutes, and a combat radius of 600 miles.

It was recognized at this time that the wave of the future was jet propulsion, and in December 1945 the Army changed the requirement to stipulate that jet-powered aircraft would also be acceptable.

Six aircraft manufactures (Bell, Convair, Douglas, Goodyear, Curtiss-Wright, and Northrop) submitted proposals for the competition. The Convair entry was a radical, delta-winged design which was eventually to emerge several years later as the F-102. The Douglas entry was a denavalized adaptation of the XF3D-1 Skyknight carrier-based all-weather fighter. The Curtiss XP-87 Blackhawk was a large, four-jet aircraft carrying a pilot and radar operator seated side-by-side. Initially, the USAAF seemed to favor the Curtiss design, if for no other reason than the fact that the Curtiss-Wright company would probably be forced to close down if it did not land the contract. Two prototypes of the Curtiss design were ordered under the designation XP-87.

However, the USAAF also thought highly of the Northrop proposal, which was given the designation N-24 by the company. The N-24 project called for a cantilever, mid-wing monoplane with a long, slim fuselage. An unswept laminar-flow wing was adopted to ensure good low-speed stability, important for an aircraft called upon to make frequent landings in bad visibility. Traditional ailerons and flaps were fitted to the wing trailing edge, and provisions were made for wingtip-mounted drop tanks. The aircraft was to be powered by a pair of Allison J35 afterburning turbojets, mounted one on either side of the belly of the fuselage just underneath the wings. The twin air intakes were mounted flush in front, each intake exactly in line with its engine nacelle. The pressurized cockpit seated the pilot and radar operator in tandem ejector seats underneath a large rearward-sliding bubble canopy. The horizontal tailplane was mounted halfway up on the vertical tail, well out of the way of the turbulent engine exhaust. The nosegear was of a very short, twin-wheel design. The main retractable undercarriage had larger than usual wheels, giving the prototype a rather unusual appearance when sitting on the ground

Since the Northrop aircraft was to be an all-weather fighter, an airborne interception radar was to be installed in the nose. The armament installation was to have been a quartet of 20-mm M-24 cannon carried in a nose-mounted turret. Two different turret designs were to have been considered. One was a Martin design which allowed the guns to be stowed out of sight inside the nose when not needed. When needed, the guns would be elevated and moved forward into firing position. The Martin turret could rotate 360 degrees and the guns could elevate 105 degrees. The other turret design was a Northrop project, which was similar in concept to the Martin design but had only a 30-degree cone of fire.

The USAAF looked favorably upon the Northrop proposal and issued a development contract on May 3, 1946. Two prototypes were ordered under the designation XP-89 in December of 1946. Serials were 46-678 and 46-679.

In the meantime, the Cold War between the West and the Soviet Union was beginning to get underway. It was generally conceded that the acquisition by the Soviet Union of nuclear weapons was only a matter of time. The appearance of the Tupolev Tu 4 (a copy of the B-29) at the 1947 Tushino air display was a shock to American intelligence, since the USSR would now have a means to deliver nuclear bombs onto continental US targets. There were no all-weather jet-powered interceptors yet available to counter this threat. The US was extremely worried about an all-weather fighter "gap" opening up, leaving the continental US defenseless for several years against an onslaught of nuclear-armed Soviet bombers.

Something needed to get to the squadrons right away. Since neither the Curtiss-Wright nor the Northrop designs promised to be immediately available in quantity for several more years, the USAF approached Lockheed in March of 1948 and asked them to see if the TF-80C two-seat trainer could be adapted as an all-weather fighter, with first deliveries to operational squadrons being made before the end of 1949. Lockheed quickly came up with a design which was eventually to emerge as the F-94 Starfire.

The Northrop XP-89 (46-678) rolled out of the factory 9 months later than expected in early June of 1948. The XP-89 was powered by a pair of Allison J35-A-9/-15 engines of 4000 lb.s.t. each. Neither the Martin nor the Northrop turrets were ready, so the prototype carried no armament. The aircraft was equipped with conventional ailerons which drooped for takeoff and landing, adding extra lift.For rollout, the XP-89 did not carry its jettisonable 600-gallon wingtip tanks. It was painted gloss black overall.

Even before the new Northrop fighter made its first flight, on June 11, 1948, the P-for-pursuit designation was replaced by the F-for-fighter designation, and the XP-89 became the XF-89.

Following a number of ground taxi and brake tests at Northrop Field, the XP-89 was disassembled and trucked out to Muroc Dry Lake (later Edwards AFB). The XP-89 made its maiden flight there on August 16, 1948, with test pilot Fred Bretcher at the controls. Flight test results were generally positive, but the aircraft proved to be seriously underpowered. For the first 32 flights, conventional ailerons were fitted, but on February 1, 1949 a new series of trials began with Northrop-invented "decelerons", which was a split surface that could be operated in one piece as a conventional aileron but which could be opened up to serve also as an airbrake. This feature was made standard on all subsequent F-89s.

Even though the flight test crews were enthusiastic about the XF-89, the USAF ordered that a flyoff take place between the XF-89, the Curtiss XF-87, and the Navy's Douglas XF3D-1 Skyknight. The Curtiss XF-87 with its side-by-side seating arrangement was judged to have the best cockpit arrangement, with the XF3D-1 coming in second. The tandem seating arrangement in the XF-89 made communication between pilot and radar operator difficult. Ease of maintenance was found to be the best in the XF3D-1, with the XP-87 coming in second. However, the evaluation team judged the XF-89 as being the superior fighter and having the best development potential.

Since the Northrop XF-89 was judged as having the superior potential as a fighter, on October 10, 1948, the USAF officially cancelled the Curtiss XF-87 project. The failure of the XF-87 to win any production orders was the end of the line for the Aeroplane Division of Curtiss-Wright. Shortly thereafter, the Aeroplane Division of Curtiss-Wright declared bankruptcy, sold all of its assets to North American, and closed its doors forever.

Even though the XF3D-1 did not succeed in obtaining any USAF orders, it nevertheless did receive orders from the US Navy and the US Marine Corps, and went on to serve as both a land-based and carrier-based interceptor fighter for many years.

In January of 1949, President Harry Truman authorized the Air Force to make an initial purchase of 48 F-89As. The second XF-89 would be converted into a service test aircraft under the designation YF-89.

In March of 1949, the name "Scorpion" was officially applied to the XF-89, the suggestion being originally made by ground crews at Edwards who thought that the parked plane with its upward-curving rear fuselage and its high tail looked a lot like the dangerous creature with the deadly stinger in its tail.

On July 14, 1949, the USAF made the order of 48 production F-89A aircraft official. Serials 49-2431/2478 were assigned. An additional 27 aircraft were added to the contract on September 19, 1949.

The second prototype (46-679) made its maiden flight on November 15, 1949. Modifications made when the airframe was almost 90 percent complete led to a change in designation to YF-89, as it was envisaged as being a test vehicle for the production F-89A fighter. The XF-89 had been painted black, but the YF-89 was finished in natural metal overall.

The XF-89 had been unarmed, pending the availability of the nose turret. However, the nose-mounted turret was eventually abandoned as being too complicated, and a more conventional armament of six forward-firing 20-mm Mk 24 cannon was chosen for the Scorpion.

Since the USAF wanted the Scorpion in service right away, production of the F-89A got underway immediately, even before testing of the prototypes was completed. This commitment to production proved to be premature. On February 22, 1950, the XF-89 prototype crashed while making its 102nd flight. During a high-speed low altitude run in front of Air Force officials, the right horizontal stabilizer peeled off, and the aircraft tore itself apart in midair. Pilot Charles Tucker was thrown clear during the breakup and he was able to parachute to safety, but flight engineer Arthur Turton was killed. The cause of the crash was later found to be a failure of the horizontal stabilizer due to excessive flutter.

The YF-89 was grounded for changes, and production of the F-89A was halted. As a result of the grounding, the YF-89 was extensively modified. The nose was completely redesigned. It was reconfigured to be more tapered and was increased in length by three feet. An AN/ARC-33 radar set was fitted in the nose, along with a Hughes E-1 fire control system. Since the XF-89 was somewhat underpowered and had poor takeoff characteristics, more powerful engines were fitted--Allison J35-A-21s, rated at 5200 lb.s.t. dry and 6800 lb.s.t with afterburners. The engine air intakes were redesigned to include external boundary layer bleed ramps and auxiliary pop-in doors were added to the nacelle sides to allow additional air to be supplied to the engine during ground runups. The engineers believed that pulsating exhaust gases from the engine were responsible for the tail flutter problems that had wrecked the XF-89, and the engine exhaust area was redesigned by adding deflector plates to the fuselage to direct the exhaust away from the tail. The pitot tube was moved from the vertical tail and installed in the nose. The jettisonable 300-gallon wingtip tanks of the XF-89 were replaced by permanently-attached more-streamlined 300 gallon tanks.

The heavily-modified YF-89 was redesignated YF-89A (Model N-49), and made its first flight on June 27, 1950, and the Scorpion flight test program was resumed.

Serials:


46-678 	Northrop XP-89 Scorpion - redesignated XF-89 in 1948.  
46-679 	Northrop YF-89 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.

  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.