| XB-55 | |
|---|---|
 Artist impression of the XB-55 bomber proposal | |
| General information | |
| Type | Strategic bomber |
| Manufacturer | Boeing |
| Status | Canceled |
| Primary user | United States Air Force |
| Number built | 0 |
TheBoeing XB-55 (company designationModel 474) was a proposedBoeing aircraft designed to be astrategic bomber. The XB-55 was intended to be a replacement for the BoeingB-47 Stratojet inUnited States Air Force (USAF) service.
The XB-55 concept was contained in a Request for Proposal (RFP) issued by the United States Air Force in October 1947, two months before the first flight of the XB-47 prototype. Several United States manufacturers responded to the RFP. Boeing was selected from among this group and given a contract on 1 July 1948 to conduct further engineering studies. Boeing's initial approach was to mount fourturboprop engines on an airframe similar to its B-47: the wing would have less sweepback; theAllison T40-A-2 engines would drive three-bladecontra-rotating propellers,i.e., six blades per engine; the engines were to be mounted innacelles hung from the wings, two per side; the landing gear was to be similar to the B-47's tandem gear with outriggers retracting into the outboard engine nacelles. The XB-55 had a projected top speed of 490 mph (790 km/h) and a cruising speed of 435 mph (700 km/h), with a maximum weight of 153,000 lb (69,000 kg), a wingspan of 135 ft (41 m), and length of 118.9 ft (36.2 m).[1]
There was a major disagreement between the engine manufacturer and the propeller manufacturer over whether the Allison T40-A-2 driveshaft was strong enough to take the forces caused at highrevolutions per minute of the propellers. Allison was predicting that it would be at least four years before a successful powerplant would be delivered. In October 1948, a conference inDayton, Ohio was addressing the problems of the XB-55 when it was proposed over lunch that the XB-52 (Boeing Model 464), which until that point had been planned with turboprop engines, could be equipped with the forthcoming Pratt & Whitney J57 turbojet engines. Within a week, it was clear that not only would the XB-52 outperform the XB-55, it could be flying at least a year before the XB-55 could be expected to have reliable engines. Also bearing on the decision to abandon the XB-55 program were government funding constraints and the growing realization that the B-47 was becoming more successful than first projected. On 29 January 1949, theAir Materiel Command was directed to cancel the Boeing XB-55 contract.
Under a revised contract, the Boeing Project 474 was converted into the Boeing Project 479, which included a study of using six J40 turbojet engines in place of the turboprops on a similar wing platform, but with a thicker root section. Work on detailed engineering andmockup construction was canceled, although Boeing was contracted to continue conceptual studies andwind tunnel investigations. These studies proved valuable in development of theBoeing B-52 Stratofortress, which first flew on April 15, 1952.
The XB-55 project did not result in construction of a prototype.
Data fromAir Force Museum Fact Sheet[2]
General characteristics
Performance
Armament
Related development
Aircraft of comparable role, configuration, and era
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