LEGACY CONTENDERS

The four manufacturers responding with proposals to the November 1944 jet bomber requirement were Boeing, Convair, Martin and North American. All four were given contracts to build flying prototypes for a competitive fly-off. There was only one production contract on offer though –the AAF had expressed a desire for just one in-service jet bomber.

The biggest ‘unknown’ was the engine itself, followed by uncertainties about compressibility and aerodynamic stability in the high-subsonic regime. The first was a technological challenge, the second and third could only be solved through scientific and engineering investigation.

The overall challenge of mathematically defining flying characteristics close to the transonic zone had already prompted the National Advisory Committee for Aeronautics (NACA, precursor to NASA which it became in October 1958) and the AAF to build the Bell XS-1 rocketplane. Hopes were high that the XS-1 would break through the misnamed ‘sound barrier’ and explore supersonic flight.

All four jet bomber proposals were ambitious and technically challenging –but to varying degrees. North American’s B-45 was the most conservative, adopting a conventional wing design with a proven NACA cross-section and four jet engines.

The Convair B-46 (Model 109) went further into the unknown with an aerodynamically unproven highaspect ratio wing set on a long, slender fuselage. Thanks to its small cross section, the fuselage had little bomb bay volume yet it weighed more than that of the proposed B-45.

Boeing’s B-47, at this stage simply the Model 432, featured a conventional, straight wing with four engines and main landing gear in nacelles. And the Martin B-48 was unusual in having six engines in two nacelles, one on each wing, which had a thickness-chord ratio so low that the landing gear had to go in the fuselage.

The relatively simple B-48 was liked best since it had no glaring flaws and promised an early in-service date. Although the AAF had put performance before availability, it began to see the possibility of an early introduction. Although the unusual features of Martin’s design would add a further 18 months to the development cycle, the company projected a top speed of 534mph compared to 486mph for the B-45 and 478mph for the B-46.

But the company had an aggressive and demanding marketing approach. Martin VP Harry T. Rowland wrote to the AAF demanding that his company’s design be given priority consideration. If he didn’t get it, he would take the design to the Navy!

In addition to the four bids from January 1945, there were three other bomber projects where jet propulsion was under consideration – the B-35, B-36 and B-42. The first two of these initially piston-engined types had emerged in the late 1930s and early 1940s during the Air Corps’ search for a very long range, strategic bomber. The B-42 had come slightly later as a result of a private company project.

The catalyst for the B-35 and B-36 was the belief that the US might have to fight Nazi Germany from North America – requiring a bomber able to fly to Europe and back without landing. This prospect came closer to reality in 1940 when German forces overran Norway, France and the Low Countries, only being halted short of an invasion of the British Isles by the natural barrier of the English Channel, the RAF and the threat of the Royal Navy.

At this date the only long-range US bomber, the B-17C had a combat radius