<p>Mention the 'Century Series' to an aviation enthusiast and the classic aircraft of the family will roll off the tongue. High on most lists would be the Convair F-106 Delta Dart, a sleek and powerful interceptor that protected American skies for nearly 30 years, and considerably outlasted its other illustrious contemporaries. Its engine and fire control system made it a very effective interceptor, while its broad delta wing turned it into a surprisingly good dogfighter. However, it is for its remarkable grace and beauty that the 'Six' will be best remembered.
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<p>Fewer were built than any other of the illustrious 'Century Series' fighters; it never fired a shot in anger; it was never exported; and it retired from active service in 1988: one could be forgiven for thinking such a curriculum vitae to be a description of a second-rate aircraft which has staggered through several years of secondary duties. In reality, these facts apply to the Convair F-106 Delta Dart, a super-sleek machine designed to knock out the Soviet bomber threat to the continental USA. The type notched up nearly three decades of round-the-clock air defense duties as part of the US Air Force's primary air-defense assets and outlived all of its contemporaries in an important and demanding role. And yet it is an aircraft that very nearly did not see the light of day: it was a product that ran the gauntlet of political and economic in-fighting through the 1950s and 1960s, and which did little to help its own cause in the early days of design and initial testing.
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<p>The urgent need perceived by the US Air Force in the late 1940s for a new and much more capable aircraft to counter the growing Soviet bomber threat was formulated in a 1951 proposal for a so-called 'Ultimate Interceptor'. This was to enter service in 1954, replacing earlier types such as the North American F-86 Sabre. Convair won the design competition, but it was soon apparent that the timescale was unrealistic as development work began to slip badly. The Air Force response was a two-stage interceptor development program with an interim limited-production design, the F-102A, giving way to the F-102B 'Ultimate Interceptor' in about 1954. Although the airframes would be the same, the F-102B would be linked with the MX-1179 Automatic Weapon Control System then under development by Hughes. Here, too, major problems arose. The F-102A did not live up to expectations and had to undergo a massive redesign to incorporate the 'area rule' principle as a means of lowering drag. While this had the desired effect of boosting performance, the F-102A's troubles were far from over. Development of the F-102B was being held back by problems with the Wright J67 powerplant and the MX-1179 fire-control system.
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<p>In desperation, the Air Force boosted F-102A production to over 700 units: it needed aircraft fast, even if the type did not match all expectations. Conversely, F-102B orders were restricted to a mere 17 aircraft for test purposes. It looked as though the 'Ultimate Interceptor' was being squeezed out of the USAF's future plans, but the desire at Convair to go back to the drawing board and get things right then caught the imagination of the Air Force which saw a new, more capable interceptor as the perfect link with the coast-to-coast Semi-Automatic Ground Environment (SAGE) direction centers then under construction as part of a new air-defense network. The F-102B survived. In September 1956, a Systems Development Directive called for the production aircraft to be available by August 1958. It should be able to intercept and destroy enemy aircraft at altitudes up to 70,000 ft (21,335 m) in all weather conditions, and have a combat radius of some 430 miles (692 km). The SAGE direction centers would guide the aircraft on an interception track via a datalink or by voice vectoring.
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<hi style=hdr1>Family Resemblance</hi>
<p>Redesignated F-106A in acknowledgement of the major design differences which distinguished it from the F-102A, the new aircraft was named Delta Dart and took to the skies for the first time on 26 December 1956. Powered by a single Pratt & Whitney J75 (the Wright J67 having been dropped), the Delta Dart bore a family resemblance to the Delta Dagger via its large delta wing, but there were many major design changes. Lessons learned the hard way resulted in a long 'Coke bottle' fuselage incorporating area rule; a large swept fin with a distinctive 'flat top' profile; revised and increased internal fuel tankage; and severely truncated though enlarged engine air inlets. Pitch and roll control was provided by elevons on the wing trailing edge, while clamshell speed-brakes were positioned at the rear base of the fin. This was an extremely sleek machine, aesthetically appealing but with a purpose. The clean lines were important if the aircraft were to perform at its best as an interceptor.
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<p>Such were the major airframe features. In terms of equipment within the airframe, the single most important item was the Hughes MA-1 (formerly MX-1179) AWCS. This highly complex system incorporated the first digital computer to go into service and, supplied with information from the SAGE centers, could automatically calculate the best intercept heading for the F-106 along with correct speed and height. The MA-1 displayed such information on cockpit instrumentation, along with target data such as altitude, speed, bearing and range. The aircraft was in continual but silent communication with its GCI director via a datalink, the F-106 pilot taking over only when target lock-on had been achieved. The MA-1 then selected the intercept steering geometry and the automatic or manual attack mode. Such a piece of equipment was fundamental to F-106 interception missions, but it had a checkered life with constant corrections during the early days in an attempt to make it fully effective. By the late 1980s, the MA-1 was getting very long in the tooth, and was a prime reason for the retirement of the F-106.
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<hi style=hdr1>Updates and Improvements</hi>
<p>Such 'tweaking' to the MA-1 was a characteristic of the F-106. The final production run of 277 F-106As and 63 two-seat F-106Bs may have been completed in less than three years, but there were major differences between the different batches of aircraft as modifications and improvements were incorporated as the aircraft were produced. Such was the scale of the production differences that the USAF detailed no fewer than 130 changes that it would have to make to bring early aircraft up to late production standards. So, in September 1960 Project Wild Goose began as the first of several conversion and/or update programs that have spanned the F-106's career. The installation of an IR search/track sight immediately ahead of the windscreen was a legacy of Project Broad Jump, a longer program which was completed during 1963. Running concurrently with this was Project Dart Board, which featured the introduction of a new supersonic ejection seat, a thermal flash hood for the pilot and fuel transfer modifications to arrest a series of engine flameouts.
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<p>In addition to these retrospective programs, the fleet also underwent progressive updating. In 1965, supersonic fuel tanks and an inflight-refueling receptacle were installed fleet-wide along with a new TACAN system, while an ambitious SLIM program in 1967 was eventually implemented as an MEISR. This covered some 250 F-106A and F-106B airframes, and introduced improvements to the radar, automatic flight controls and a DC electrical system. This took several years to implement, as did Project Sixshooter which included the replacement of the original heavily-framed main canopy by a clearer 'blown' example, better ECCM and a new RHAW receiver. Most significant of all was the introduction of the 20-mm Vulcan M61A1 six-barrel cannon, the whole package being housed in the rear of the internal weapons bay. Not all aircraft were thus fitted, but those which did receive the gun were identifiable by a tell-tale bulge in the underfuselage for clearance as the six barrels rotate. Introduction of the gun was an acknowledgment of the F-106's dogfighting abilities, a fact realized only after years of stand-off interceptions with the radar-guided and IR-seeking models of the AIM-4 Super Falcon (up to four being carried) and a single nuclear-tipped AIR-2A Genie rocket. The F-106 was unique until the YF-22 and YF-23 in that it never toted its ordnance on external pylons, the whole load always being carried internally in the long weapons bay.
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<hi style=hdr1>Delta Guardians</hi>
<p>With regard to the F-106 in operational service, its debut in mid-1959 was soon followed by the conversion to the type by late 1960 of another 13 squadrons, almost half of ADC's air defense assets. As the years progressed the number of squadrons increased, but by the late 1960s the Delta Dart was on the decline, with only 11 operational units. In 1972 the Air National Guard received its first (secondhand) examples of the Delta Dart in a force that was to peak at six squadrons in mid-1974. Since then it has been a gradual process of attrition and replacement by more modern types, most notably the McDonnell Douglas F-15 Eagle and General Dynamics F-16 Fighting Falcon.
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<p>These two designs eventually brought the curtain down on the F-106's long and illustrious career, the last being retired in 1988. Having spent many a mission intercepting and destroying pilotless drones over the years, the F-106 has assumed the role of the target in the form of converted QF-106s. And so the 'Six', 'The Cadillac of the Fighters' which improved with time, will bow out. The last of the delta-winged birds will be gone, but certainly not forgotten.
<item><hi format=bold>Powerplant:</hi> one Pratt & Whitney J75-P-17 turbojet rated at 24,500 lb thrust with afterburner
<item><hi format=bold>Performance:</hi> maximum speed 1,327 mph at 35,000 ft; service ceiling 45,000 ft; combat radius 730 miles
<item><hi format=bold>Weights:</hi> empty 24,315 lb; maximum take-off 39,195 lb
<item><hi format=bold>Dimensions:</hi> wing span 38 ft 31/2 in; length 70 ft 83/4 in; height 20 ft 31/2 in; wing area 697.8 sq ft
<item><hi format=bold>Armament:</hi> one AIR-2 Genie unguided nuclear rocket and four AIM-4 Falcon AAMs internally; Project Sixshooter aircraft had Genie replaced by M61A1 Vulcan 20-mm cannon
