F-89D "Scorpion"
New Features to the F-89D included different Allison J-35 engines and high-altitude afterburners; additional 262-gallon nose fuel tank; and improved fire control and armament--the 20-mm nose-mounted cannons of earlier F-89 model series were replaced by 104 2.75 in, folding-fin aerial rockets, carried in permanently mounted wing-tip pods.
The tentative military characteristics of early 1945, as revised in November of that year, were nearly satisfied in 1954 (after almost 10 years), when the F-89D became operational. Northrop met its latest target date of June 1952 by delivering two of the interceptor aircraft, but the Air Force grounded the entire F-89 force 2 months later. Full production of the F-89D was not resumed until November 1953 and that aircraft did not reach the Air Defense Command until 1964-a new setback of more than a year.
The initial F-89Ds were almost of the same configuration as the earlier, structurally deficient F-89 aircraft. Major changes, therefore, were phased into production in order to correct the faulty wing design that had been principally responsible for the series of F-89C mid-air disintegrations.
Only five F-89Ds had been accepted by the Air Force by November 1962, when the structural failings of the basic F-89 were finally ascertained, but another 120 F-89Ds had already left the production lines. Moreover, although Northrop daily programmed output of 17 aircraft came practically to a halt, several other F-89Ds were manufactured before the appropriate modifications could be merged into production. Hence, approximately 170 F89-Ds required some post-production modifications similar to those made on the 194 earlier model series.
On 7 January 1954, ADC's 18th Fighter Interceptor Squadron at Minneapolis, St. Paul, Minn., was the first to receive F-89Ds. At year-end, 118 F-89Ds were in the command's inventory, but these urgently needed aircraft lacked the E-6 fire control system and E-11 autopilot of subsequent D productions.
The F-89D, the most produced of the F-89 model series, actually epitomized the transition from WW II gun-armed interceptors to ADC's guided missile carriers of the late fifties. The transitional nature of the F-89 meant that engineering problems were all but certain to arise. The crash on 20 October 1963 of a structurally modified F-89B, that had been adapted to the D configuration and specially fitted for the testing of rocket firing equipment, offered an example of the complexity of the pioneering problems encountered. Examination of the YF-89D wreckage, while uncovering no evidence of structural failure, failed to reveal what part had been played by the rocket malfunctions, reported by the pilot prior to the accident. Ensuing testing of the E-6, Hughes' new fire control system, was further hampered by its scarcity-the E-6 was also being tested with North American F-86D and Lockheed F94C-and by the manufacturer's deficient spare part support. Similarly, the integration of new autopilot systems proved to be more difficult than anticipated. Beginning in July 1964, F-89Ds in production were equipped with E-11 autopilots (replacing the F-5 retrofitted in the P-89D and C aircraft and long considered a candidate for the first 193 F-89Ds, which like earlier F-89 productions had been delivered without autopilots), but use of the E-11 at speed in excess of Mach .75 had to be temporarily prohibited.
The F-89D also continued to suffer from the fact that the Northrop designers of the ground-attack F-89, in fashioning the aircraft as the high-altitude interceptor that the Air Force needed, had seemingly sacrificed the necessary structural features that would have enabled the plane to withstand low-level, high-speed flight maneuvers. Hence, despite the successive structural changes made between 1948 and 1953, all F-89Ds early in 1954 were still restricted from exceeding a speed of 425 knots at altitude of less than 20,000 feet-a restriction which essentially limited the F-89D's effectiveness to B-29 type targets. Subsequent improvements to the rudder and automatic pilot improved the maneuver capability of the aircraft but only to a degree.
Although the modified J-35-A 21A engines of the F-89B and C model series had already been replaced in the F-89D by the more powerful J-36-A-33s, engine troubles continued to plague the F 89. More specifically, "power droop" under certain conditions, particularly at altitudes in excess of 30,000 feet, induced a significant loss of thrust in both the 21A and -33. Substitution of yet another model in the d 35 series did not cure the problem immediately for "power droop" also began to affect the operation of the new -35 engine. Because of the basic difficulty in finding the precise cause of the improper engine operation, the problem was not resolved until early 1965. Shielding of the temperature-sensing element of the J-35-A-35 engine power control proved to be the answer. Yet, the use of another engine was considered for a time.
One of the new features of the F-89D aircraft was the addition of permanently mounted wing tip pods. This configuration, first flown in 1951 (on the modified F-89B, lost in October 1953), still proved troublesome 3 years later. The pods became excessively corroded after a few rocket firing missions and operational squadrons were sometimes required to dissemble and rebuild them. Moreover, corrosion and the damage it caused accounted on several. occasions for minor explosions which collapsed the rocket tubes. The problem seemed to solve itself, however, with the introduction of new "thick wall" rocket launcher pods, successfully tested by mid-1954.
The fate of the F-89 as prospective carrier of the Falcon a was still uncertain early in 1954-2 years after the F-86D and F-94 had been dropped as potential Falcon carriers in favor of the Northrop interceptor. Adaptation of the early F-89 productions to the Falcon-carrying mission was no longer considered, and although provisions for the E-9 fire control system and Falcon missiles were included in all F-89Ds (605 of which were in the production program by 1954), the original 1 January 1954 IOC for the F-89 Falcon combination had already slipped. In March 1954, after a 6 month review of the entire F-89 program, the Air Force decided to dispense entirely with plans for fitting the E-9 system and Falcon pods into the F-89Ds. The decision was accompanied by a new and final procurement order for 233 additional F-89s. The first 77 aircraft in this group would be identical to the F-89Ds then being produced, but the other 156 future productions would incorporate the E-9 fire control system and pods for 42 standard folding-finrockets and six Falcon missiles. The combination was officially dubbed F-89H in April 1954, to distinguish it from the earlier F-89D, which had provisions for the installation of this equipment but lacked the equipment itself.
Two F-89Ds were accepted in FY 52, 10 in FY 53, 191 in FY 54, 300 in FY 55, and 179 during the first 9 months of FY 56. Delivery rates were almost constant between February 1954 and December 1955, with a monthly average of 25 aircraft. This was done at a cost of: $801,802.00--airframe, $598,439; engines (installed), $101,954; electronics, $11,392; ordnance, $1,857; armament, $87,960. Production ended with delivery of the last seven aircraft in March 1956. The F-89D began its phaseout in 1958. ADC used the two-place F-89D until late 1958, then began to equip the ANG's 178th FIS.
The F-89D achieved some minor milestones. The aircraft was the initial carrier of Hughes' Falcon air-to-air missiles. The first firing (October 1953) was not entirely successful for the missile pod collapsed after firing. Necessary redesign postponed the operational date of Falcon-equipped F-89s (F-89Hs) from January 1954 to late 1955. 27 January 1955, an armed Falcon, also fired from a modified F-89D, downed a QB17 drone--the first GAR-1 armed with a warhead to strike an airborne aircraft. This time the operation was a complete success.
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