Although bearing an earlier suffix letter, the F-101B interceptor was predated by the F-101C.
New features to the F-101B included an elongated cockpit, permitting sitting of an observer behind the pilot, different armament (missiles and rockets carried by and launched from a hydraulically actuated rotary armament door), and a fire control system providing automatic search and track. The engines of the F-101B interceptor - two J-57-P-55 turbojets - also differed from those of both the F-101A and F-101C tactical fighter bombers by being fitted with longer afterburners.
The Air Force officially designated the interceptor version of the F-101 as the F-101B.
Development of the F-101B program was generated by a combination of factors. First, by Convair's failure to satisfy quickly the Air Force's "ultimate" interceptor requirements. Secondly, by the difficulties encountered with the same contractor's interim F-102, yet to be delivered in August, 1953, when Russia exploded a thermonuclear bomb - less than a year after the US first successfully demonstrated one. Finally, by ADC's insistence for the greater security that two new interceptors would provide, pending availability of Convair's "ultimate" F-106.
Impressed by McDonnell's revised version of the F-88 Voodoo (rechristened F-101 in November 1951), ADC in October 1952 suggested the possibility of modifying the aircraft to serve as an interceptor. Headquarters USAF, mainly because of the Voodoo's high cost, rejected the plan and decided to attempt solving the interceptor problem by increasing the numbers of F-86Ds and "putting the heat" on the F-102. The suggestion was revived, however, with ADC's proposal in April 1.953 to use the long range F-101 as an interceptor on the perimeter of the United States and in areas where ground radar was inadequate. The Air Force Council late in 1953 directed that the aircraft industry be invited to compete in determining the characteristics required by an interceptor other than the F-102 that would help fill the gap between the F-89 and F-106.
ADC announced that of the three aircraft proposals that might meet its requirements an advanced F-89, offered by Northrop, and interceptor versions of North American F-100 and McDonnell F-101 the F-101 was the best. Soon afterwards, the Air Force decided that the aircraft (titled F-101B in mid 1955), if produced, would include the MG-13 fire control system of the F-102 and would carry Falcon missiles.
Almost 6 months elapsed between the F-101's first flight and the Air Force official endorsement of the F-101 interceptor program. Interim predictions that the interceptor, equipped with the advanced J-67 engine, would be ready to fly by the middle of 1956, that production could begin in 1957, and that the aircraft could be made available to active interceptor squadrons in early 1958 proved wrong or too optimistic. Nevertheless, later events wholly vindicated the production decision.
Just as with other F-101s, procurement was initiated by letter contracts, the first of which, issued in March 1955, covered 28 aircraft. Four months later, a formal contract, released on 12 July, increased the fiscal year 1956 program to a total of 96 interceptors. However, in December 1956 the Air Force curtailed the peak monthly production rate originally projected for the aircraft and significantly reduced future procurement.
The Air Force officially designated the interceptor version of the F-101 as the F-101B.
Mockup Inspection came on 14-15 September 1955
Two of the alterations requested were of particular import. The first involved the aircraft's armament rack. The second dealt with the replacement of the F-101B's initial engines--two advanced but unproven J-67 turbojets developed by Pratt and Whitney.
A Production Hold Order came in May 1956.
The production restrictions imposed on the F-101A were extended to the F-101B. In the latter case, however, the Air Force restrictions were more drastic. The hold order remained totally in force through the end of 1956, at which time the projected armada of 651 F-lO1Bs was reduced by almost one quarter.
The first flight took place at Lambert Municipal Airport in St. Louis, Mo. on March 27, 1957, nearly a year later than predicted in early 1955.
The Air Force spent close to 2 years of extensive testing and accepted 50 F-101Bs before allowing the Voodoo interceptors to enter operational service. Category I flight tests, conducted at Edwards AFB, started immediately upon delivery of the first F-101B March 1957. Category II and Category III flight tests, conducted at Eglin and at Otis AFB, respectively, were completed on 15 March 1959.
Despite modifications that resulted from the experience with the basic F-101A, two serious flaws surfaced during flight tests of the B model. Both were unique to the interceptor version. The radar observer's cockpit had been badly designed and little could be done except to make minor changes. Too, the MG-19 fire control system developed by the Hughes Aircraft Company was not as advanced as the airframe in which it was placed. The MG-13 was merely a refinement of the E-6 fire control system of the F-89D and could not control the weapons of an interceptor as fast as the F-101B. Headquarters USAF denied replacement of the MG-13 with the MA-1 system of the F-106 because of the cost involved. This left only one course of action: to improve the Central Air Data Computer that was the heart of the MG-13 system.
This was a 6 month delay from latest estimates, 18 months later than first expected and almost 2 years after USAF acceptance of the first F-101B. On the other hand, the F 101B received by the 60th Fighter Interceptor Squadron at Otis AFB, the first ADC unit to be so equipped, was a thoroughly tested aircraft, capable of advanced performance.
Although support of the F-101B had been initially handicapped by shortages of parts, it improved during the later part of 1959, and by mid 1960 supply and maintenance problems were well under control. Other difficulties remained, however, including all Voodoos' susceptibility to corrosion and the skin cracks discovered in the rudder area of the F-101B model series. All the same, in December 1960 nine of ADC's 17 squadrons of F-101Bs were rated C-l the highest degree of combat readiness and seven were G2. Only one squadron was considered deficient, and this was due to a temporary shortage of qualified personnel. On the average, 70 percent of the 371 F-101Bs, then assigned to the combat forces, were operationally ready.
Despite the extensive flight tests of the 1957-1959 period, two separate testing programs were conducted at the Air Force Missile Development Center at Holloman AFB. One of the test programs further investigated the F-101B compatibility with both Falcon guided missiles and MB-1 nuclear Genies. The other was an overall review of the entire weapon system. Representatives of McDonnell and Hughes as well as Douglas, the producer of the MB I unguided nuclear rockets, participated in the latter.
Other configurations of the F-101B included TF-101Bs--F-101Bs with dual controls for pilot training. Contrary to plans, and because McDonnell took longer than promised to install the dual control kits, only one out of every four F-101Bs produced was so equipped. When fitted out as a trainer, the F-101B retained its original operational capability. The trainer versions entered ADC service in 1959. In April 1960 several of them were allocated to TAC for the training of tactical reconnaissance aircrews. F-101Fs were late F-101B productions that included modifications accomplished on the production line. Technically referred to as block 115-120 configurations (Because of the increasing complexity of aircraft being developed, modifications no longer necessarily entailed a change of the letter suffix in the aircraft model series designation. Since 1941, the aircraft being built with the same specifications were grouped into blocks as they were assembled on the production lines. The blocks were numbered beginning with 1, b, and subsequently with sequential multiples of five. The intermediate figures were reserved for the identification of aircraft modified after production at a modification center or in the field. In general, block numbers were only allocated to combat aircraft and transports. Exceptions occurred, however. F-4s and C-123s left their assembling plants with consecutive block numbers. On the other hand, T-33 and T-38 trainers received block numbers.)
These aircraft were first identified as F-101Fs in 1961 as arrangements were made to transfer 66 of them to the Royal Canadian Air Force (RCAF), where they acquired still another designation and became CF-101Bs. The trainer version of the block 115-120 F-101E configuration, the TF-101F, was known in RCAF service as the CF-101F. Ten TF-101Fs were included in the 66 Voodoo interceptors transferred to Canada in exchange for that country's operation and maintenance of 14 radar sites.
Production ended in March 1961 with delivery of the last three aircraft. A total of 480 F-101B/Fs were accapted.
One Voodoo interceptor was accepted in FY 57, 15 in FY 58, 133 in FY 59. 241 in FY 60, and 90 in FY 61.
Flyaway Cost Per Production Aircraft (F/TF-101B/F/TF-101F) was $1,754,066.00--airframe, $1,105,034; engines (installed), $332,376; electronics, $52,770; ordnance, $1,001; armament, $262,885. This total price did not include $13,333 of RDT&E costs and $52,922 in Class V modifications, spent on every F-101 interceptor.
Average cost per flying hour was $1,004.00. The average maintenance cost per flying hour was $501.00.
Because of the threat from airbreathing aircraft and missiles, the Air Force began planning modernization of its aging interceptor systems. The Interceptor Improvement Program increased the ability of the F-101B/F to thwart electronic countermeasures and to employ radar to search for and track low flying aircraft. The two phase program initiated in early 1963 was completed in mid 1966.
The unreliability of the F-101 engine starter (unimproved despite all efforts until the end of 1964) caused a number of incidents and personnel injuries. The problem was finally solved by installing a separate pneumatic cartridge starter for each of the two engines.
The Pitch Control System (PCS) of the MB-5 Automatic Flight Control System (AFCS) in the F-101B/F interceptors also had been a source of difficulties for many years. In April 1968 Headquarters USAF approved the installation of a modifying kit which had been thoroughly tested by Honeywell, builder of the AFCS. The new kit completely eliminated use of the poorly designed PCS.
The Air Force lost about one fifth of its Voodoo interceptors in some 10 years of operation. Accounting for most of these losses - the majority of which occurred during the early years of the aircraft's operational use - was the F-101's addiction to spins, a definite hazard to inexperienced pilots.
The Voodoo interceptors began leaving USAF operational inventory sooner than expected because of the economy-induced accelerated inactivation of seven ADC F-101 squadrons in 1968. This action produced a surplus of 163 aircraft, 30 of which were converted to the reconnaissance configuration and transferred to the Tactical Air Command. Another 66 of these Voodoos were allocated to Canada to replace the older F-101Bs, previously furnished to the northern partner in the North American Air Defense Command (NORAD). Such allocations left a residue of 67 aircraft for storage at Davis-Monthan AFB, Ariz. Because of continued budgetary restrictions, three of the last six F-101 squadrons in the regular interceptor force were inactivated in mid-1969. Phaseout of the entire F-101B/F fleet was concluded in the spring of 1971.
Aside from five TF-101B aircraft allocated in 1966 for training, the Voodoo interceptors did not reach the Air National Guard until December 1969. Once underway, however, the conversion of ANG F-102 fighter groups to more modern F-101Bs proceeded smoothly. The three units involved the 101st, 119th, and 141st Fighter Groups resumed their alert posture actually ahead of schedule. The Guard proved itself further in 1970 by taking first place in the William Tell F-101 competition. Three other ANG fighter groups (the 142d, 148th, and 107th) began converting to the F-101B/F aircraft in March and April 1971, also without trouble. The 147th Fighter Group (Training) received some F-141Fs in June 1971 but retained its F-102s to train crews for both the F-101B and the F-102--a task turned over to the Guard by ADC.
|Join the GlobalSecurity.org mailing list|