Profile — McDonnell F-101 Voodoo

Design

McDonnell initially responded to the new outline with a proposal to enlarge the F-88 design to accommodate Allison J71s (62kN or 14,000lb). It was the air force that pushed for the bigger J57. McDonnell complied, the air force was finally happy and in October 1951 the company was asked to go ahead and build the revised, J57 powered machine, now designated F-101 in the century series but still called Voodoo. But the new Voodoo was a revised F-88 in the same way that perhaps the 747 is a revised 707: same layout, vastly different scale. The size of the new design was driven up massively by the new engines and the amount of fuel they would need and could lift. The J57s were installed in the same place but bulged out of the fuselage like some grotesque caricature, ostentatiously displaying the power available to the new Voodoo. The fuselage also had to be enlarged to fit in all that fuel, so it was expanded in all three dimensions, becoming wider, deeper and longer. Empty weight, the best measure of a fighter’s size, more than doubled to 11.9 tonnes (26,200lb). Cost must have risen at least proportionately. But the F-88’s general arrangement was retained. The biggest change was moving the tail plane up to the top of the fin in an attempt to get it out of wing downwash at high angles of attack. The attempt failed, and the Voodoo’s most serious performance fault was a tendency to suddenly pitch up at high angles of attack. This happened when the wake from the wing destroyed the tail’s lift: The tail then dropped, the aircraft stalled and the pilot started wondering when to eject, if he had the chance. The fix, not really satisfactory, was an automatic override to prevent the nose from going too high in the first place. The F-101 was also difficult to handle because of its high wing loading, which was one of the design’s most outstanding, indeed breathtaking, features. Despite the new Voodoo’s massively greater structure and fuel load, and the corresponding growth in loaded weight from the F-88’s 8.4 tonnes (18,400lb) to 22.2 tonnes (48,900lb), the original F-88 wing was retained almost unchanged. All McDonnell did to the F-88 planform was extend the chord (breadth) inboard, as it had done on two earlier jets, the original FH Phantom (not the F-4) and the F2H Banshee.

Wing area barely changed between the F-88 and F-101, rising from 32.5m2 (350sq ft) to just 34.2m2 (368sq ft). So wing loading at loaded weight skyrocketed from the F-88’s 258kg/m2 (53lb/sq ft) to an astronomical 648kg/m2 (133lb/sq ft) for the F-101A. The Voodoo had the highest wing loading of its day, higher even than the F-104s, which is an achievement in anyone’s book. I can find only one fighter wing loading higher than that, the MiG-31s 666 kg/m2 (136lb/sq ft). For comparison, an F-16s wing loading at takeoff weight for the air-to-air mission is 430kg/m2 (88lb/sq ft). The F-101s little wing, obviously kept small for the sake of minimum drag and maximum speed, was an important factor in expanding and limiting the Voodoo’s missions, as we will see later. With four times the F-88’s thrust, the F-101A could make 1618km/h (1005mph) at altitude, or Mach 1.5. More tellingly, initial climb was 171m/s (33,750ft/min), astonishing for the time and much better than the F-100As 66m/s (13,000ft/min).

The F-101 even outpaced the 115m/s (22,640ft/min) of the early model MiG-19S. Despite its colossal size, the F-101A had a high thrust/weight ratio for the mid 1950s: 0.61 at normal takeoff weight. Initial F-100As had a thrust/weight of only 0.48, although the MiG-19, that greatly overlooked hotrod of the mid 1950s, managed something over 0.8 (depending on which loaded weight one accepts). The F-101As range, the whole point of the exercise, was 2116km (1315 miles). Commensurate with its size, the Voodoo was planned to introduce a new standard of armament to fighter versus fighter combat: radar guided air-to-air missiles. As originally designed, the Voodoo was to have had an internal bay housing three GAR-1D Falcon AAMs (later called AIM-4A). This was another big step into the future; radar guided AAMs had previously been intended only as anti-bomber weapons to be deployed by specialist interceptors. Since the Voodoo they have become standard anti-fighter weapons. The first Voodoo model was also planned to have two retractable packs each housing six of the then fashionable 7cm (2.75in) unguided air rockets. And it was intended to carry four 20mm M-39 revolver cannon. Whether the design included the guns at the same time as the missiles and rockets is unclear. Space limits suggest that it did not, and the initial F-101A production model had guns only. But some authors imply that the original design had guns, rockets and missiles, giving the Voodoo a huge and versatile armament for a fighter of the day. And while the Voodoo was designed without a pound for air-to-ground, it must have been obvious that it could be adapted to haul plenty of bombs as well. For one of the first times, a fighter designed to shoot down fighters would also have a powerful radar – the APS-54 – something that has since become standard. In 1951 most fighters, such as the F-86 and F-100, had only a primitive ranging radar or none at all; others, such as the F3H Demon and F-102, had radar but were built to shoot down bombers. It must have seemed obvious that this unrivalled combination of speed, climb, range, radar and armament was heading towards a great future. In fact the Voodoo’s production and service career turned out to be only modest, perhaps because no-one realised that this vast lump of aluminium might have become the future in combat aircraft, the big multi mission fighter.

Development

The Voodoo’s great promise, and the failure to exploit it, is shown by the series of Pentagon decisions about how the aircraft would be used and developed. With these decisions, the Voodoo did get a quite complete allocation of fighter missions, but only in different versions and only in limited numbers. The development and production decisions – what the F-101 would do and how many would be built – also reflect how good, and bad, the Voodoo was. All these decisions were settled long before the first Voodoo entered service in 1957. As already related, the F-101 started as a long range fighter: a real fighter, intended to fight other fighters to get them off the backs of bombers. Development go ahead for this concept came in October 1951 and the first production order followed in January 1952. Initially the Voodoo was to be only an interim penetration fighter, to be replaced by some other aircraft later. But, perhaps because money dried up after the Korean War, the air force soon decided that the Voodoo airframe was good enough for the foreseeable future; a definitive penetration fighter would now be developed by progressively fitting the Voodoo with better equipment. Ironically, the Voodoo would eventually not serve as a penetration fighter at all. Early on, in 1952, it was decided that the Voodoo airframe would come in two versions: an initial structure that could cope with manoeuvres up to 6.3g; then, as production got into stride, a definitive version that would take 7.3g. All Voodoos, in whatever role, would subsequently be divided between 6.3g and 7.3g machines. Meanwhile the air force was looking at the first change of mission for McDonnell’s big fighter, tactical reconnaissance. This had been considered from the beginning of the F-101 project and in January 1953 McDonnell got a contract for a prototype RF-101 with a long camera filled nose replacing the radar. Sharing the same production line as the fighters, initial RFs would have the 6.3g structure while later ones got the 7.3g airframe. Another part of the air force, the Air Defense Command, was considering a third role for the Voodoo: interception. This was suggested as early as 1952. At the time the ADC was equipped with the Lockheed F-94 Starfire and the rather large Northrop F-89 Scorpion. ADC planning centred around a distant objective of a definitive interceptor (which eventually emerged as the Convair F-106 Delta Dart) and more immediate schemes for an interim interceptor to replace the low performance F-89. The Convair F-102 Delta Dagger was the interim interceptor, but ADC apparently considered the much larger Voodoo as an alternative: with two J57s instead of one the Voodoo had much better flight performance and more range. Initially, air force headquarters told ADC to stick with the F-102, but in 1953 the top brass accepted that another fighter might be handy for long range work on the periphery of the United States. After manufacturers had been asked to submit bids, the air force said in June 1954 that the Voodoo was, after all, the best prospect. It had beaten two aircraft that would never enter service: the swept wing Northrop F-89F and the North American F-100B Super Sabre, later designated F-107. A production decision followed in February 1955 with ADC ordering the two seat Voodoo to supplement (not replace) the F-102 as the interim interceptor. The second seat displaced some fuel but the missile armament and weapons bay, which the initial version had by now lost, was restored.

Initially the Voodoo interceptor would be designated F-109; later it became the F-101B. By that time the Voodoo had lost its first role of penetration fighter, and picked up a fourth, nuclear strike. This happened when SAC cancelled its penetration fighter order – on September 29, 1954, which coincidentally was the day of the first flight. The machines SAC had ordered instead went to the Tactical Air Command as low level nuclear strike aircraft. The aircraft had to be modified for the new mission, and it seems it was this that led to the deletion of the rocket packs and internal missiles. Whatever the reason, the first Voodoos, the tactical F-101A and C, were built with guns only. Other modifications included an external hardpoint for a single nuclear bomb and adaptation of the radar for air-to-ground work. Clearly, TAC took Voodoos into service not because they made good low level bombers but simply because the air force had already paid for them and had to find something for them to do. How often does history follow this line! The Voodoo was obviously suited to the new mission. But it is also obvious that the air force was not completely satisfied, and here we can list one more big decision taken in Voodoo development, probably the biggest: the decision to build only a few for tactical use. The air force bought just 124 tactical Voodoos: 77 F-101As, the initial 6.3 g model that entered service in May 1957, and 47 F-101Cs, with the 7.3g airframe. More tellingly, 96 C models were reordered as recce aircraft before being built. Production of these first Voodoo models, the big tactical fighters which in retrospect seem to have offered so much, finished with the last F-101C in October 1958,

just one year after the first F-101 had entered service. The recce Voodoo also entered service in May 1957 and was clearly seen as a more important part of the programme, since more were built for that role than for atomic mud moving. The RF-101 was the USAF’s standard tactical reconnaissance aircraft until, like most of its contemporaries, it was replaced by the Phantom in the 1960s. The two reconnaissance versions were the RF-101A and RF-101C with 6.3g and 7.3g airframes respectively. RF-101 production trailed the tactical fighter versions, so the bulk of the recce birds had the tougher 7.3g airframe. The first YRF-101A flew on May 10 1956 and McDonnell built 35 RF-101As and 166 RF-101Cs, 201 in all. (To put that in context, McDonnell later built 505 RF-4Cs.) The most numerous version turned out to be the strategic interceptor, the two seat F-101B. As the latest of the three models to move down the assembly line, the F-101B was built with only the 7.3g airframe – except for the prototype which flew in March 1957. The air force originally planned to buy 651 air defence Voodoos, greatly supplementing the purchase of 873 F-102As, but the final programme was 480, which was still considerable. The last F-101B was also the final new Voodoo and F-101 production finished on March 24 1961 after a total run of 807.

Service

The service career of the original Voodoos, the F-101A and F-101C, began in May 1957 when SAC accepted the first copies. Why any went to SAC at all is a mystery; the command had already decided it did not want the Voodoo and changes had given it strike capability at the expense of the fighter weaponry needed for bomber escort. Regardless, the F-101 lasted with SAC just two months and in July the first unit was redesignated as a Tactical Fighter Wing with TAC, which went to work training for the new strike mission. By the end of 1958 the Voodoos had moved to USAFE (US Air Forces Europe) in England and the 81st TFW at Bentwaters became the only operational user of the tactical Voodoo. The mission was to fly deep into enemy territory – as far as the Soviet Union itself – to toss nuclear bombs onto such targets as ports and airfields. The wing’s 54 aircraft, in three squadrons, were a mix of F-101As and Cs. The stronger Cs were more valuable, especially for strenuous toss bombing, but there were never enough to fully equip even a single wing. And with just one wing operating such a complicated aircraft, the Voodoo was a logistic inconvenience, so it is no surprise that the unit reequipped with F-4C Phantoms after only seven years. Sixty-one survivors were converted to reconnaissance aircraft, A models becoming RF-101Gs and Cs becoming RF-101Hs. These converted recce birds, now late into their economical service lives and not as fully equipped as the original RFs, were sent to the Air National Guard, surviving until 1972.

The original photo Voodoos had a far more glorious career, playing one of those vital but little publicised roles in Vietnam. The first RF-101 combat missions were conducted by the Taiwanese Air Force, of all people, in 1959 ( and probably 1958). The USAF lent Taiwan a number of RF-101As – up to eight – which were used for reconnaissance flights over mainland China. In 1962 US based RF-101s were used during the Cuban missile crisis, overflying Cuba to photograph the Soviet medium range ballistic missiles whose deployment there had taken the world to the brink of Armageddon. Other early RF-101s were sent to Europe where French based squadrons learnt the techniques to be used later in Vietnam. They also learnt that maintaining the Voodoo was a nightmare. South East Asian operations began as early as 1961, with detachments from Okinawa, and later settled down to full scale deployments in support of the American campaign. The Voodoo was used only in the first part of the air war, which finished with the bombing halt of October 1968, but it was worked hard. Of 166 RF-101Cs built, 37 were lost in Vietnam, 31 of them to enemy action. The roughest year was 1966. Apart from attrition, the threat from enemy fighters after 1967 led to the RF-4C, with its air-to-air armament, replacing the Voodoo in Vietnam and bringing the F-101s combat career to a close. Surviving RF-101Cs, largely worn out, continued to serve elsewhere for a few years. In 1971 the last frontline squadron handed over its recce Voodoos to the Air National Guard, which operated the type until 1979. The RF-101A, less numerous and with a weaker structure, survived with the ANG until only 1972. The interceptor Voodoo, the F-101B, lasted the longest. Development was not easy – the missile fire control system did not work well – but when it was ready the B was deployed at a breakneck pace. The first squadron did not receive its aircraft until January 1959 but by the end of 1960 there were 17 Voodoo squadrons in Air Defense Command. The F-101Bs were updated several times but phaseout began in 1968 and the last had been passed on to the ANG by mid 1971. The ANG kept them going until 1983, when the last were replaced by Phantoms. Canada, the only other operator of the Voodoo, initially rejected the F-101 when it was looking for a new interceptor in the early 1950s. But when their fantastic CF-105 Arrow interceptor was scrapped in 1959 the Canadians had little choice but to go back to the Voodoo. So from 1961 the USAF supplied 66 second hand F-101Bs to the RCAF, which traded them in for 66 updated Voodoos in 1970 and 1971. The USAF then converted 22 of the original Canadian aircraft into reconnaissance aircraft as RF-101Bs. The second batch of Canadian Voodoos remained in frontline service until 1985 – 14 years longer than the USAF F-101Bs – when CF-18s replaced the last of them. In Canadian service the aircraft was designated the CF-101. There was one other Canadian Voodoo, another second hand B model that was converted as an electronic warfare aircraft. Painted glossy black overall and called the Electric Voodoo, the EF-101B was the last of the breed. It flew until at least 1986, simulating enemy aircraft using electronic countermeasures.

Evaluation

And so, when it was all said and done, the Voodoo’s career was reasonable, but only reasonable. But that does not fairly judge the aircraft. To evaluate the Voodoo properly we have to look at what it could have done, as well as what it did do. And it could have done a lot more. It speaks volumes for the Voodoo that its late 40s, early 50s design was adapted to four roles: long range air superiority, low level strike, interception and reconnaissance. Its failure to actually serve in the long range air superiority role means nothing, because circumstances conspired against it. It was a tight mid 1950s budget that forced SAC to scrap its fighter force and drop the Voodoo. Besides, the whole notion of a penetration fighter was daft: what was the use of a fighter that could fly only 20% as far as the bombers it was supposed to escort? To assess the Voodoo’s air-to-air credentials, let’s instead compare it to such contemporaries as the F-100C, F-102A, F-104A, F-105B and MiG-19S. For flight performance, take these words of Captain Mark Forseille of the Canadian Armed Forces, quoted by author Robert F Dorr in 1986. “There is nothing to compare to the sound and feel of the burners kicking in at low level, especially on takeoff on a cold day. It would rattle all of the windows on the base, pound on your chest and echo in your ears.” The aircraft was less than perfect in the handling area. It had a very good roll rate but no nose authority. It couldn’t turn a complete circle without crossing at least two provincial borders and it had a terrifying tendency to pitch up at high angles of attack and low airspeeds. But it sure could accelerate. The data show that the Voodoo was as fast as most contemporary fighters and could outclimb all but the Starfighter. Manoeuvre was obviously weak but then that was not considered important. The initial model Voodoo (the F-101A and C) had weak armament, because it had lost its missiles during development. But with the missile system restored, as happened with the F-101B, the Voodoo had firepower at least comparable to any of those contemporary fighters’ and carried that armament over a far greater radius. Furthermore, if it had got a first class fire control system, such as that fitted to the F-106, and an expanded missile load, it would have had no peer in air-to-air roles until the arrival of the Phantom. So surely ADC was right back in 1952: fully developed and fully equipped, the Voodoo would have been the best aircraft to defend the North American continent, or indeed to perform any air-to-air mission. In summary, the Voodoo came close to being the greatest air-to-air machine of the 1950s; it was just never fully developed that way. But the Voodoo was an imperfect low level strike aircraft, because it was bigger than it needed to be and therefore cost too much. Its main assets for this mission were its little wing, or rather its high wing loading, its big internal fuel tankage and its radar. The wing ensured low gust response (fewer bumps from the thick, turbulent air near the ground), which meant it could fly fast at low level. Fuel capacity, always an enormous asset, gave it a long punch for distant targets and more time on afterburner to go in extra hard at difficult ones. But clearly this was not enough, because the air force built few tactical Voodoos and even reordered unbuilt ones as recce birds. A moment’s thought reveals that the air force preferred another plane: the Republic F-105 Thunderchief, which was about a year behind the Voodoo in development, entering service in May 1958. Whereas F-101C production lasted just another five months after that, Thuds kept rolling out of the factory door until 1964, more than 800 being built. The Thunderchief’s advantages are pretty obvious. At 10.8 tonnes (23,905lb) empty, it was a little smaller than the Voodoo and at least potentially cheaper.

Costs were also kept down by fitting it with just one engine, the P&W J75 (alias JT4, enlarged from the Voodoo’s J57 or JT3). But that engine and the advanced area ruled airframe made the Thud one of the few aircraft easily supersonic at low level, which the F-101 was not. The F-105B could also lift a similar load of ordnance and external fuel. If the Voodoo had had a bigger wing, it would have been able to lift much more. But it didn’t, so its thrust advantage was consequently wasted. In short, comparison with the F-105 reveals that the Voodoo was not properly adapted to strike. Given its size and complexity, the Voodoo was not good value compared to a specialist aircraft. One suspects that an RF-105, which was never built, would have equally outperformed the RF-101. It seems the RF-101 was used not because it was the best but, like the F-101A and C, it was available and paid for. So although the Voodoo could perform these non fighter functions, it wasn’t as good as the specialists. But the Phantom, a jack of all trades, replaced the masters of all of them because it managed to get into very large scale production, cutting costs. The Voodoo might have done the same if it had been bought for its forte, tactical air-to-air, in the first place. No one would argue that the Voodoo was as good as the Phantom, which came half a technology generation later. To compare, the Voodoo would have needed a bigger wing, area ruling, better engines, more advanced inlets and much more. But if in the mid 1950s TAC had wanted something that could shoot down other aircraft – and a quick look at its inventory shows that, amazingly, it did not – it would have placed big orders for a two seat Voodoo with missiles. A big production run would have cut unit costs and the Voodoo might have been pressed into all of the other jobs simply because its big, powerful airframe could perform the mission and had become cheap enough. All that happened to the Phantom instead – five years later when TAC suddenly discovered that it did need to shoot down enemy aircraft and, very conveniently, the Navy had just the plane for the job. The rest is history. But it might also have happened to the Voodoo first.