Convair YF-102

Last revised March 17, 2003

The Convair F-102A Delta Dagger single-seat all-weather interceptor was the first delta-winged combat aircraft in the world to enter operational service. It was also the world's first all-weather interceptor capable of supersonic performance in level flight. It was the first fighter to have an all-missile armament provided as standard from the very start of the initial design stage. It was also the first manned interceptor designed from the outset as the principal component of a weapons system.

Following the end of the war in Europe, relations between the United States and the Soviet Union underwent a rapid deterioration. However, at that time, there seemed to be little direct threat from the Soviet Union against the continental United States itself. In October of 1947, several Tupolev Tu-4 heavy bombers (reverse-engineered B-29s) appeared at a Moscow airshow, and the newly-organized United States Air Force was now faced with a potential strategic bombing threat from the Soviet Union. 

The new Air Force Secretary, W. Stuart Symington III appointed a board of senior Air Force officers to look into selecting an interceptor fighter to protect United States airspace against Soviet bombers carrying nuclear bombs. At that time, the main contenders were the Curtiss XF-87, the Northrop XF-89, and the Navy's Douglas XF3D Skyknight.

The board of senior officers first met at Muroc AFB on October 7-8, 1948. Because of the urgency of the situation, they authorized the development of an interim night fighter based on the Lockheed TF-80C two-seat jet trainer that would be designated F-94A. The contract for the Curtiss F-87A was cancelled in November of 1948, and the production of 48 Northrop F-89As was authorized on January 10, 1949. The development of an interceptor version of the F-86A Sabre was recommended in January of 1949, and work on the resulting F-95 (later redesignated F-86D) was started in March of 1949.

However, the North American F-86D Sabre, the Northrop F-89 Scorpion, and the Lockheed F-94 were all subsonic aircraft, and were deemed to have insufficient growth potential to be able to meet the threat. At the end of their Muroc meeting, the board of senior officers recommended that the USAF organize a totally new competition to design a really satisfactory all-weather interceptor. This project came to be known as the "1954 interceptor", after the year that the new interceptor would supposedly be entering service.

Recognizing that the development of the new interceptor was going to challenge the state of the art, the Air Force took the unusual step of inviting representatives of the aircraft and electronics industry to meet together in May of 1949 and come up with a proposal. However, the traditions of design competitions based on customer specifications written by the Air Force in stone proved difficult to overcome, and the industry was not able to come up with anything useful.

Undaunted, the Air Force still recognized that innovative developmental approaches would be needed if the 1954 timetable was to be met. At that time, the Air Force recognized that the increasing complexity of modern weapons made it no longer practical to attempt to develop equipment, airframes, electronics, engines, and other components in isolation and expect them to work properly when they were put together in the final product. To address this problem, the Air Force decided to use the so-called "weapons system" concept for the new interceptor, in which components would be integrated with each other from the very beginning, making sure that the various systems would be compatible with each other when they were incorporated into the final aircraft. The project was given the designation WS-201A, where WS stood for "Weapons System". As originally conceived, WS-201A was a weapons system consisting of a primary armament of air-to-air guided missiles to be guided and directed by an all-weather search and fire control radar, all housed in an airframe capable of supersonic flight.

The electronics package for the new WS-201A system came first. Project MX-1179 was the designation given to that portion of the project which was dedicated to the armament and electronic fire-control system of the 1954 Interceptor. In January of 1950, no fewer than 50 firms were invited to submit proposals for the fire control system. Six firms made the short list--Bendix, General Electric, Hughes, North American, Sperry Gyroscope, and Westinghouse. In July of 1950, the Hughes Aircraft Company was named the winner of the MX-1179 contract. The Hughes proposal consisted of a MA-1 fire control system acting in conjunction with GAR-1 Falcon air-to-air guided missiles. For a brief time, the Falcon missile was known as the F-98, a fighter designation.

The airframe part of the project was designated MX-1554. Proposals for the airframe were requested by the Air Force on June 18, 1950. When the bidding closed in January of 1951, nine proposals had been submitted by six different manufacturers. Republic submitted three separate proposals, North American two, and single proposals were made by Chance-Vought, Douglas, Lockheed, and Convair.

On July 2, 1951, the Air Force announced that designs by Convair, Lockheed, and Republic had been selected to proceed with preliminary development. All three companies were to proceed with their designs all the way to the mockup stage, with the design being deemed most promising at that time being awarded a production contract. Later, the USAF deemed it too costly to carry through with three concurrent development programs, and it cancelled the Lockheed project in its entirety. The Convair and Republic entries were given the go-ahead to proceed.

The Republic entry bore the company designation of AP-57. It called for an extremely advanced aircraft capable of achieving a Mach 3 performance at altitudes of up to 80,000 feet. This was clearly a quantum leap in the state of the art for the early 1950s.

The Convair entry in the MX-1554 project was closely related to the experimental XF-92A which Convair had built in 1948 to provide data for the proposed F-92 Mach 1.5 fighter designed in consultation with Dr. Alexander Lippisch. Dr. Lippisch had done pioneering work on delta-winged aircraft in Germany during the war, and Convair had become convinced that the delta configuration provided a viable solution to the problems of supersonic flight. The XF-92A had been the first powered delta-wined aircraft to fly, but the F-92 project had itself been cancelled before any prototype could be built.

On September 11, 1951, Convair received a contract for its delta winged design which was designated F-102. Work on the competing Republic design was also authorized, and that aircraft was assigned the designation XF-103. However, the XF-103 was so far ahead of the state of the art that it was deemed too risky to be a serious contender for the 1954 Interceptor project, which made the F-102 for all practical purposes the winner of the contest.

The Air Force authorized the fitting of a Westinghouse J40 turbojet in the first few examples of the F-102, but later production aircraft were to have the appreciably more-powerful Wright J67 (a license-built version of the Bristol Olympus). The J40-powered F-102 was to be capable of a speed of Mach 1.88 at 56,500 feet, with the J67 production version capable of Mach 1.93 at 62,000 feet.

In order to expedite the development of its 1954 Interceptor program, the Air Force adopted the so-called "Cook-Craigie" program, named for its originators, Generals Laurence C. Craigie and Orval R. Cook. During the late 1940s, these two officers had developed a concept of an aircraft development program in which the usual prototype stage would be skipped. Instead of waiting to start full-scale production until the prototypes had passed flight testing and the bugs had been ironed out, the Cook-Craigie plan called for the delivery of a small number of production aircraft during the flight testing phase. Any major changes deemed to be necessary could be incorporated into permanent factory tooling in order for combat-ready aircraft to be delivered when mass production started. This program is inherently risky-- it can produce a new combat aircraft in a hurry if everything goes according to plan during flight testing, but can result in a lot of costly and time-consuming fixes in the field if unexpected problems turn up.

The Cook-Cragie plan is really viable only if there is a high degree of confidence that the aircraft is really going to go into production. Since the F-102 was basically a scaled-up XF-92A, the risk was deemed work taking.

By December of 1951, it was apparent that the J67 engine and the MA-1 fire-control system would not be ready in time. This forced the USAF to change its plans. At that time, the Air Force decided to proceed with an interim version of its 1954 Interceptor, one which could be introduced into service at an early date, pending the availability of the fully-developed version at a later time. The interim version was to be designated F-102A, with the fully-developed advanced version being designated F-102B.

The F-102A was to be equipped with an interim fire-control system, the Hughes E-9, which was a modified E-4. The E-9 was later renamed MG-3 after a number of changes had substantially improved its capability. The MG-3 was in turn supplanted by the MG-10 which incorporated the AN/ARR-44 data link, the MG-1 automatic flight control system, and the AN/ARC-34 miniaturized communication set.

The F-102B ultimately turned out to be so different from the F-102A that it was assigned the new designation of F-106 in 1956. It will be discussed in a later article.

The mockup of the F-102A was inspected in November of 1952. At that time, the Air Force decided that the F-102A should be capable of carrying external stores, and they recommended some rearrangement of the cockpit components.

All throughout the development cycle, the weight of the F-102A had been spiraling ever upwards, an all-too-familiar pattern. In 1951, the Westinghouse J40 engine was the most powerful turbojet in production, but it now lacked the thrust to give the F-102A its required performance. Consequently, the Air Force decided to switch to the Pratt & Whitney J57 turbojet, which was in the 10,000 lb.s.t class and was scheduled to enter production in early 1953. In retrospect, this change in powerplants was extremely fortuitous, since the J40 engine was to prove so troublesome and unreliable that it had to be cancelled.

Under the philosophy of the "Cook-Cragie" program, the prototype phase would be skipped altogether, and the program would begin with the production of a set of service test aircraft, designated YF-102. It was hoped that it would be possible to iron out any technical problems while production was actually underway, bringing the aircraft to active service as soon as possible in order to meet the 1954 service debut commitment. Manufacture of a preliminary order for ten YF-102s (two Model 8-80s, 52-7994/7995) and eight Model 8-82s (53-1779/1786) began in April of 1952.

The first 32 F-102A production aircraft were ordered on December 17, 1952, under a contract approved on June 12, 1953. First service was planned for December of 1955, almost two years later than originally planned.

The YF-102 was basically a scaled-up XF-92A with a slim nose and lateral air intakes replacing the nose intake. A strong skeleton of milled aluminum spars and longerons covered with aluminum skins carried the fuel in wing spaces. The electronics was carried in the fuselage. The armament was to consist of six Hughes GAR-1 Falcon air-to-air missiles carried internally in a ventral bay. In addition, twenty-four 2-inch FFAR rockets were to be carried in channels contained inside the missile-bay doors. A maximum speed of 870 mph at 35,000 feet was promised.

A severe problem cropped up early in 1953, one which was potentially fatal for the entire program. At that time, wind tunnel testing discovered that the initial drag estimates of the YF-102 had been way off, and that the F-102 would be unable to exceed Mach 1. In addition, the maximum altitude would be only 52,400 feet, versus the predicted 57,600 feet, while the combat radius would be reduce from 350 to 200 nautical miles.

Even though early wind tunnel tests had indicated that there would be a problem with excessive drag, it took a long time to convince the Convair engineering staff that there was a problem with their basic design. It was not until August of 1953, that Convair engineers reluctantly agreed to redesign their aircraft. By that time, it was too late to incorporate the required changes in the first ten YF-102 aircraft that had been ordered.

In the meantime, work on the first YF-102s was proceeding at a rapid pace. The first YF-102 was finally completed in the autumn of 1953. It was powered by a J57-P-11, rated at 10,900 lb.s.t. dry and 14,500 lb.s.t. with afterburning. It was trucked from San Diego out to Edwards AFB. It took off at Edwards on its maiden flight on October 24, 1953, with Richard L. Johnson at the controls. In initial tests, severe buffeting was encountered at Mach 0.9. Even more serious, the aircraft proved to be incapable of exceeding the speed of sound in level flight, fully confirming the results of the wind tunnel testing. Additional problems were encountered with the main landing gear, and the fuel system operated erratically. To make matters even worse, the J57-P-11 engine did not develop its full rated power.

The first YF-102 was written off on November 2 in a forced landing following an engine failure. Test pilot Johnson was seriously injured. The cause of the accident was traced to a failure in the Bendix fuel control system. The second YF-102 flew on January 11, 1954. This aircraft was limited to Mach 0.99 in level flight. Dives at higher speeds resulted in severe yaw oscillations. Even in a 30-degree dive, the YF-102 was only able to reach Mach 1.24. Even though an altitude of 47,000 feet could be reached, handling difficulties limited the practical ceiling to only 40,000 feet.

The F-102 program was in BIG trouble. In fact, the performance of the YF-102 was not all that much better than the F-86D Sabre, which was already in production. If no cure could be found, the whole program would undoubtedly be cancelled.

YF-102 serial numbers:

52-7994/7995	Convair YF-102 Delta Dagger
53-1779/1786	Convair YF-102 Delta Dagger


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