F-89C "Scorpion"
As a progressive development of the F-89B, the C presented few new features. However, elevators with internal mass balances replaced external mass-balanced elevators of previous model series. The aircraft was first accepted with the delivery of four aircraft in September 1951. The F-89C entered operational service in January 1952. ADC's 74th FIS at Presque Isle AFB, Maine, had received only 19 F-89Cs by March, when the Air Force stopped further allocations because of the aircraft's lack of structural reliability.
The F-89's J-36 engine continued to cause a great deal of difficulty. In addition, the low-slung engine of the F-89 earned a reputation as the "world's largest vacuum cleaner" by picking up litter from the runway. A vagrant piece of metal, on several occasions, was sucked into engine inlets, causing disintegration of the compressor blades. Pieces of the compressor then destroyed the remainder of the engine. Inlet screens were an answer of sorts, although it was discovered that at extremely high altitudes the inlet screen could become completely clogged with ice. Grounding orders, engine changes, inlet screen modifications, and similar actions seemed to have partially resolved the problem by mid-year.
While the F-89's propulsion problems were being tended, a far more serious crisis developed. Starting with a crash on 25 February, a whole series of almost identical accidents occurred. Despite increasingly severe speed restrictions, six F-89s-mostly F-89Cs had disintegrated in mid-air by 15 September. Accident investigations and study of the F-89 structure made it appear that the failures resulted from the stresses imposed by maneuvers, poor stability, and possible structural fatigue.
On 22 September, except for 13 aircraft that would be flight tested to identify needed structural and stability corrections, all F-89 aircraft including five new model series already accepted by the Air Force-were grounded. At year-end, the grounding was still in effect.
The structural failures of the early F-89 productions were finally attributed to a faulty design of the wing structure--a mistake, however, that most "aerodynamicists and structures designers" would not have recognized at the time it was made. All that could be done at that point was to redesign the F-89s already produced (at a cost of approximately $17 million) and apply the new knowl edge to aircraft to be produced. Modification of the F-89C received the highest priority, but by the middle of 1953 ADC still had only 31 of the modified F-89Cs available. Moreover, the modified air craft could be used at only 80 percent of. performance potential. This was true of the 194 early F-89s reworked by January 1954, when the modification program ended.
Production ended with the delivery of six aircraft. The design improvements directed in late 1952 did not find their way into the Northrop production line until April 1953 and all F-89Cs were modified after production.
Except for 48 aircraft delivered during the last 4 months of 1951, all F-89Cs were accepted during 1952-128 in FY 52 and 35 in FY 53 at a cost of: $797,202.00-airframe, $612,533; engines (installed), $95,110; electronics, $10,557; ordnance, $4,519; armament, $74,483.
The F-89C, in development for so many years, almost reached obsolescence before to become operational to a significant degree. Like the F-89As and Bs, the aircraft left the active inventory in 1954. The three model series were still being flown by the ANG in early 1960.
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