JET BOMBERS

are limited to short ranges… the Boeing studies indicate that… the range of jet propelled aircraft may exceed that of conventional aircraft”.

The big catch here was that, according to Boeing, jet engines would be more efficient if a speed of 600mph could be achieved – but at the time nobody knew how to make a bomber able to fly that fast. Nevertheless, Air Materiel Command (AMC) got excited about the possibilities and approved an informal request for proposals. This resulted in Boeing and North American submitting initial designs in January 1944.

Boeing progressively refined their ideas over a series of models (413, 422, 424, 425 and 426) to end up with a turboprop, rather than a turbojet, concept to make maximum use of the better range over the pure jet. Because the AAF was also interested in speed, Models 424 and 425 featured turbojets. Unaddressed, largely because nobody knew a great deal about it, was the compressibility effect experienced close to the transonic zone. Added to the uncertainty was the sluggish development of the TG-180 engine.

Desperate to get a high-performance bomber, the AAF asked Wright Field to verify the engineering assessment and confirm that such a high-speed jet bomber could be built within two years, which it was not able to do. So little was known about the aerodynamics of highspeed cruise conditions that scientists and engineers were unable to provide the guarantees sought.

In November 1944, the AAF issued a requirement for a bomber with a top speed of 550mph – almost 200mph faster than the B-29 – carrying an 8,000lb bomb load on a 3,500 mile mission and with a service ceiling of 40,000ft. Questioned by politicians about the strident push for a new jet bomber, the AAF explained that the technical requirement would be set above the requirement for early service introduction and that, by issuing a formal request to industry, higher levels of funding could be released for development.

While Boeing was highly sceptical about a high-speed jet bomber, the AAF was emphatic in its desire to have one and brooked no compromise in the requirement – though it was prepared to accept a delay of up to two years in getting prototypes into the air.

Proposals

As the AAF moved toward a procurement strategy, confidence in the strategic bomber concept was at an all-time high. Across Nazi-occupied Europe, German industry was being pounded into dust, marshalling yards and railroads were being destroyed and cities across Japan were suffering a massive onslaught from the B-29. The atomic bomb had already been tested at Alamogordo, New Mexico. Bids for the new bomber were requested and four companies had responded by January 1945. Attracted by the prospect of lucrative development contracts, industry quickly switched from an attitude of cynicism over the jet bomber concept to one of enthusiasm. With the Me 262 operational over occupied Europe, the Ar 234 bomber/ reconnaissance aircraft rolling off the line and Britain putting the Gloster Meteor into production, American aircraft manufacturers were beginning to relish the challenge of building the nation’s first jet bomber.

The procurement strategy would follow a three-phase programme. The first phase would assess the feasibility of meeting the requirement and examine technical hurdles, risks and potential show-stoppers. The second would see designs fully completed, with engineering drawings made and mock-ups of specific proposals constructed.

The third phase involved construction, flight testing and competitive evaluation of prototypes. The emphasis here would be on configuration, flying qualities and actual performance compared to the requirement. There would be less focus on ancillaries and supplementary equipment.

Prototype dimensions and weights would represent those of a definitive, production aircraft but spaces would be left for electrical systems, weapons and general ergonomics of the flight deck.

This was to be a welcome departure from the existing ‘concurrency’ concept, where development and production ran together, the early airframes off the assembly line having to be retrofitted with any modifications or improvements highlighted as desirable through the development process. This method got aircraft to the front line and in quantity more quickly in theory but it had proven an administrative nightmare on the B-29 and would plague the B-36 too.

The phased development programme shifted the burden of administrative micro-management from the military to the contractor, but there was no other way to run a programme in which so many design and construction variables were unknown. It also made it easier to cancel a competing prototype, since no production had yet commenced.