In this issue, we examine proposals submitted to the Army Air Force heavy bombardment competition of 1946, which ultimat...
A ME R ICA N A ERO SPAC E A RC H I V E 3
THE B-52 COMPETITION OF 1946 ...and Dark Horses from Douglas, 1947-1950
Jared A. Zichek
n the third issue of The American Aerospace Archive, we take an indepth look at two of the original three proposals for the B-52 competition of 1946; offer speculation on the third based on available evidence; and examine some later dark horse contenders from Douglas. This is not a comprehensive history of the complicated evolution of the Boeing B-52 design - that would require an entire book, and the general story of that evolution has already been ably told elsewhere. Instead, the aim is to shed more light on some of the design submissions connected to the competi-
tion and inspire researchers to dig further into the tumultuous developmental history of this legendary aircraft.
Background The origins of the B-52 can be traced back to August 15, 1944, when the engineering division at Wright field recommended that a design study for a jet-propelled/turboprop heavy bomber be undertaken in FY1946; the study was to cost $650,000 and development of the airplane to cost $16 million between FY1947 and FY1949. The type
Cover: Artist's impression of Convair's extraordinary Long Range Heavy Bombardment Airplane, one of the losing contenders in the heavy bombardment competition of 1946. This and all other images in this publication are scanned from original documents found in RG 341 of the National Archives in College, Park, MD, unless otherwise indicated. 1) Artist's impression of the Boeing Model 462, winner of the competition. It would subsequently be replaced by the Model 464, which underwent a radical evolution before emerging as the swept wing, jetpowered XB-52 in 1951.
The American Aerospace Archive is published periodically by Jared A. Zichek (6021 La Jolla Hermosa Ave, La Jolla, California 92037) and is printed and distributed by MagCloud (www.jaredzichek.magcloud.com). American Aerospace Archive Number 3 (ISSN 1943-9636) is copyright 2009 by Jared A. Zichek. All rights reserved. All featured text and images are copyright 2009 their respective copyright holders. Reproduction of any material in part or in whole without its creator's permission is strictly forbidden. The American Aerospace Archive accepts no responsibility for unsolicited manuscripts, photos, art or other materials. Submissions are considered on an invitational basis only. Email your comments and suggestions to [email protected]
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was sought as an eventual replacement for the Convair XB-36, work on which had started in early 1941. Before its first flight on August 8, 1946, the Army Air Force (AAF) was already concerned that the giant bomber would not meet its mission radius requirement or be able to survive over enemy airspace without escort fighters. In April 1945, the AAF requested Boeing to undertake a design study for a heavy turboprop successor to the B-36. Boeing and its competitors declined to submit proposals because the desired characteristics were “so completely out of line with the state of the art." On November 23, 1945, the AAF released "Military Characteristics for Heavy Bombardment Aircraft," requirements for a “high speed, high altitude, long range, land airplane” shown in the table at right.1 In February 1946, the Air Technical Service Command (ATSC) issued a Request for Proposals (RFP) to the aviation industry for designs to “meet or approximate” the November 1945 2) General arrangement drawing and basic characteristics of the Model 462 taken from the brochure dated June 27, 1946.
characteristics. At the time, the requirements were beyond the state of the art, with a suitable turboprop engine taking up to 10 years to develop, according to some experts. Due to the lack of a suitable engine, the AAF asked the industry to approximate the requirements as best as it could, with emphasis being placed on meeting the high speed requirement.2 Boeing, Convair and Martin would each submit proposals to fulfill these demanding requirements. The first one we will examine is the winner, the Boeing Model 462.
Military Characteristics for Heavy Bombardment Aircraft November 23, 1945 High speed at tactical operating altitude
Tactical operating altitude
Tactical operating radius (take off point to target) at design gross weight with 10,000 lb bomb
5,000 statute miles
Average speed for above radius
Maximum (internal) bomb load
Crew accommodations for at least 12: pilot, copilot, flight engineer, one bombardier-navigator, one radio operator, the minimum number of fire control operators deemed necessary, and a six person relief crew.
Boeing Model 462 In the first half of 1946, Boeing submitted its Model 462 to the heavy bombardment competition. The following information about the design comes from the proposal brochure dated June 27, 1946.3 Boeing noted that significant advances in heavy bombardment airplane design were contingent upon concerted
efforts toward development and coordination of developmental activities surrounding many component elements, particularly power plants. Derived from a series of design studies and based on the results of extensive operational experience with the B-29, this conclusion was exemplified by the Model 462, which Boeing described as "...the most practical airplane possible with developments available for a design program initiated at this time." Only through full utiliza2▼
tion of design potentialities was it possible to propose an airplane with characteristics approaching those established by the design directive. In selecting basic design parameters such as power plants, gross weight and wing area, primary consideration was given to speed and range characteristics. Boeing believed that the Model 462 was the largest and hence the longest range airplane which would satisfy speed requirements with the selected engines. Provision for external droppable fuel tanks effectively increased the range without sacrifice in speed at gross weight less one half fuel. The configuration and basic design of the Model 462 was optimized within the limitations imposed by existing elements and development considerations.
The Boeing Model 462 was a high wing monoplane powered by six Wright T-35 combustion turbine engines geared to 20 ft diameter tractor propellers. The exterior configuration was characterized by particular attention to aerodynamic cleanness in basic layout as well as detail considerations, and by control and stabilizing surfaces designed to maintain the reputation of Boeing airplanes for stability and ease of control. The crew of ten was accommodated in a single pressurized compartment forward of the wing from which all flight and combat functions of the airplane were conducted. The large bomb bay was located under the wing center section near the center of gravity of the airplane. Self-sealing fuel tanks were installed in areas forward of, above, and behind the bomb
3) Another artist's impression of the Boeing Model 462, the general design of which owed a great deal to the company's experience with the B-29.
bay. Access to the bomb bay during pressurized flight was available to crew members through an air lock to a tunnel which joined the crew compartment and the forward section of the bomb bay. In order to simplify nacelle and landing gear design problems, it was proposed to study carefully a main landing gear configuration in which one of 4 landing gear units retracted into each of the four inboard nacelles. Power Plant
The Model 462 was powered by six Wright T-35 combustion turbine engines rated at 5,000 hp each. Driving 20 ft di-
ameter, single rotation, four blade high activity propellers, these engines were mounted in nacelles arranged to permit complete interchangeability of power sections in the form of a quickly changeable power package. Thus, although nacelles had increased in number from the B-29, problems related to maintenance and overhaul were greatly minimized. Boeing planned an extensive preliminary study devoted to the determination of optimum spinner, cowl, and propeller cuff configurations such that the most efficient air inlet conditions would be achieved. In addition, the basic problems surrounding combustion turbine installation would be given thorough initial consideration in order to assure availability of the latest devel-
opments in fuel systems, cooling provisions, jet exhaust arrangements, fire detection and prevention, etc. Fuel capacity was divided between the wings, the fuselage and the bomb bay. Of the 16,040 gallons carried in the wing fuel system, 9,700 gallons were protected by self-sealing tanks. The fuselage contained provisions for 8,370 gallons in self-sealing tanks and capacity for 7,850 gallons of fuel in self-sealing droppable bomb bay tanks, increasing the potential fuel capacity to a total of 32,260 gallons. In addition, provision was made for droppable wing tanks to accommodate approximately 6,500 gallons.
The effectiveness of the Model 462 was increased by its ability to deliver bomb combinations in all sizes up to and including the 44,000 lb “Grand Slam.” The 36 ft bomb bay provided ample space for consideration of advanced methods of bomb loading and release.
4) Cutaway view of the Model 462; note the massive 44,000 lb T12 bomb shown in the bomb bay. 5) Close-up cutaway of the giant bomber's nose section. The Model 462 would have carried a crew of 10, though only 9 are shown here.
Defensive armament consisted of 4 two-gun turrets and 1 four-gun tail turret, all of which were armed with 20 mm guns. All guns were controlled from four stations in the crew compartment between which operation of the turrets could have been exchanged. Turret locations provided a 3600 field of fire with at least four guns, with the exception of a very small area which was covered by two guns. Since performance of the Model 462 was based upon minimum drag, full consideration was given to the development and utilization of flush turrets and radar. Summary
It was anticipated that an extended program of aerodynamic, power plant, equipment installation, and structural development would proceed as a part of Phase I. Only through this coordination in early design stages could the AAF be assured of satisfactory progress in carrying out Phase II. The airplane performance estimated by Boeing was premised on a program of extensive and thorough investigation of new materials, new manufacturing techniques and innovations such as sandwich type construction, different methods of joining structure, new means of increasing the efficiency of stressed skins, and study of aerodynamic devices such as sealed, low drag control surfaces and full span flaps. The use of combustion turbine power necessitated an exhaustive study of cowling, induction system, cooling, and other design problems associated with the relatively unexplored field of turbine engine installation. Boeing argued for the adoption of such a plan early in Phase I, as it would substantially reduce the time required for later development phases and would be of tremendous assistance in the creation of prototype models, a factor of paramount consideration relating to the development of an aircraft in this class. Boeing believed that the Model 462, as basically conceived in the brief studies conducted up to that point and supplemented by the above type of research, would represent the optimum 6) Side views of the Model 462 engine nacelles. The aircraft was powered by 6 Wright T-35 turboprops producing 5,000 hp each. The forward sections were interchangeable to simplify maintenance and overhaul. 7) Illustration showing various bomb load possibilities, ranging from eighty-four 500 pound bombs to one enormous 44,000 lb bomb. 8) Weight breakdown of the Boeing Model 462. With a design gross weight of 360,000 lbs, it was the heaviest of the three contenders.
configuration for a heavy bombardment airplane designed to fulfill the requirements of the AAF as expressed in the requirements set forth on February 13, 1946. Victory
Although the high gross weight of 360,000 lbs was necessary to attain the range and speed proposed, Boeing’s model fell short of the range required (5,000 miles radius/13,000 miles range).
As will be seen later in this monograph, Boeing’s model was, by far, the largest aircraft proposed, even heavier than the B-36, which was less than a year away from its first flight. On May 23, 1946 General Craigie, Chief of the Engineering Division, recommended that the AAF accept the Boeing Model 462 for Phase I development “in view of the results of this evaluation and the outstanding record of Boeing Aircraft Company in the building of heavy bombardment aircraft….” Craigie
9) Artist's impression and top view of the Model 462. The defensive gun turrets retracted flush into the fuselage and contributed to the type's overall aerodynamic cleanness.
believed that Boeing's proposal represented the best performance per dollar, in addition to “most nearly [meeting] the requirements set forth in the Military Characteristics than either of the other two proposals, and further has far greater potentialities.” During the 7