Quest for Performance: The Evolution of Modern Aircraft
Chapter 12: Jet Bomber and Attack Aircraft
[355] Offensive military air operations against ground targets can be broadly divided into two major classes. First, strategic air power is employed to destroy the enemy's industrial base and necessary resources for conducting war, or for fear of reprisal, to deter military aggression by an unfriendly nation. Second, tactical air power is intended to provide broad support for military operations against specific targets in the battle area. The evolution of jet-powered aircraft optimized to fill these two vastly different military roles is discussed in this chapter.
The first tentative expression of the concepts of strategic air power can be found in the sporadic and relatively ineffectual German air raids against London in World War I. First Zeppelins and later the notorious multiengine Gotha bombers were used in these raids. (See chapter 2.) The ideas and methods of strategic air power were vigorously espoused, refined, and implemented during the period between the wars by the disciples of such visionary prophets of air power as Douhet, Trenchard, and Mitchell. During World War II, the concepts of strategic bombing were vigorously practiced by the air forces of the United States and Great Britain. The highly refined, four-engine propeller-driven bomber was the universal instrument employed for this purpose by both countries.
The ultimate long-range, strategic air weapon of World War II was the Boeing B-29 Superfortress (see chapter 5), which was used with such devastating effectiveness against the Japanese home islands during the last months of the war and which had the dubious distinction of dropping the first atomic bomb on Hiroshima in August 1945. Following the end of hostilities, this highly efficient, long-range aircraft became the backbone of the United States Strategic Air Command [356] (SAC). Equipped with atomic weapons, SAC served then and serves now as a nuclear deterrent to massive aggression in any part of the world. An improved version of the B-29, the Boeing B-50, entered SAC in 1948. Finally, the six-engine Convair B-36 (the six reciprocating engines were later augmented by four jet engines) became a mainstay in the SAC inventory in 1950.
As described for fighter aircraft in chapter 11, however, the advent of jet propulsion, together with advanced aerodynamic concepts, offered the promise of large increases in performance and operational capability of strategic bomber aircraft. These significant advances in technology sealed the fate of the large propeller-driven bomber and eventually banished it to total oblivion. Today, examples of this once ubiquitous class of military aircraft are primarily relegated to museums, with a few still being flown and demonstrated at air shows by enthusiastic (and well-financed) collectors of antique aircraft.
The German Arado 242 made its maiden flight in June 1943 and was the world's first jet-powered bomber; it saw limited action in the last year of World War II (ref. 201). The first operational jet bomber built in the United States entered service with SAC in 1948 and showed a speed advantage over the propeller-driven B-29 of more than 200 miles an hour. Phase-out of large propeller-driven bombers from first-line operational service, however, took place over a much longer period of time than was the case for the propeller-driven fighter; the last B-36 was retired from SAC in 1959, after which the United States heavy-bomber force was entirely jet powered.
In contrast to the diversity of jet-fighter types developed following the end of World War II, the evolution of the jet bomber in the United States has been characterized by the development and production of only a few types. Since the late 1950's, only two entirely new large bombers have been built in this country. Neither of these aircraft was put into production. Escalating costs, increased reliance on intercontinental ballistic missiles, doubts as to the ability of the manned bomber to penetrate enemy airspace and survive attack by increasingly effective surface-to-air missiles, all played an interrelated part in limiting development of new bombers. One body of opinion even suggested that the usefulness of the manned bomber had about reached an end. New aircraft concepts and operational techniques, new weapons, and new electronic capabilities now seem to assure the continued effectiveness of the manned bomber; production of at least one new aircraft type is now planned.
[357] The technical development of the large jet bomber for the USAF is traced in this chapter. Also included are brief descriptions of a number of jet-powered attack aircraft. Attack aircraft are employed in tactical and interdiction-type operations against enemy ground targets and have formed an integral part of military air power since the days of World War I. The lineage of these aircraft is more related to fighters than to strategic bombers, but they usually have lower performance than fighters and are not optimized for air-to-air combat. They are included here to complete the picture of Jet aircraft designed for offensive military operations against ground targets.
A number of the physical and performance characteristics of the 11 aircraft discussed are presented in table VI in appendix A. The quantities given are defined in the list of symbols provided in appendix B and, in most cases, require no further explanation. A further clarification of certain of the characteristics, however, seems desirable. A multitude of range-payload combinations are possible for all the aircraft. The value of the payload WP given for each aircraft is for one specified type of mission with a radius RD. The mission radius is the distance at which the payload (e.g., bombs) can be delivered with sufficient fuel remaining for a safe return to home base. The ferry range RF is the total distance that the aircraft can fly with no disposable weapons payload and with maximum internal and external fuel load. Finally, the values of zero-lift drag coefficient and maximum lift-drag ratio given in table VI for some of the aircraft are based either on information obtained from industrial sources or on estimates by the author according to the methods given in chapter 3 of reference 176.