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Boeing XB-55

United States (1947)
Picture of Boeing XB-55 Strategic Bomber Proposal

The proposed Boeing XB-55 strategic bomber was being developed to succeed the in-development Boeing B-47 Stratojet - it was commissioned before the B-47 had even flown.


Detailing the development and operational history of the Boeing XB-55 Strategic Bomber Proposal.  Entry last updated on 4/25/2016. Authored by Staff Writer. Content ©www.MilitaryFactory.com

Not convinced of the reliability of, and promised performance from, early turbojet engines, the United States Air Force (USAF) looked beyond all-jet-powered forms in-development after the close of World War 2 (1939-1945). The Boeing B-47 "Stratojet" swept-wing strategic jet bomber was selected by the USAF to fulfill an earlier specification and was a product of the period - it eventually went on to find success as over 2,000 of the type were built and flown until the late-1970s.

However, even before the B-47 prototype went airborne in 1947, USAF authorities penciled out a new request in October of that year for an insurance-minded strategic bombing platform relying on more conventional propulsion power. The usual participants responded and this crop included Boeing whose submission was selected for further development under the designation of "XB-55" (Company Model 474).

Boeing engineers elected for a form that was not unlike their B-47 proposal save for the use of Allison T40-A-2 turboprop engines over turbojets. These systems would be underslung at the wings in the usual way (the wing mainplanes being of reduced sweepback when compared to the B-47) and drive three-bladed contra-rotating propeller units. Four engines would be used to power the large bomber and output up to 5,600 horsepower. Estimated performance included a maximum speed of 490 miles per hour (cruising at about 450 mph), a range out to 5,000 miles and a ceiling of 42,000 feet. In comparison, the B-47 (B-47E) managed a maximum speed of 607mph, cruised at 557mph, flew out to 4,650 miles and reached up to 33,100 feet of altitude.

The XB-55 would be crewed by ten personnel and the airframe was to hold an overall length of 119 feet, a wingspan of 135 feet and a height of 33.7 feet. Maximum Take-Off Weight (MTOW) was listed at 168,000lb. As in the B-47, the XB-55 was to feature a "bicycle" undercarriage arrangement in which the main legs were held inline under the mass of the body and outrigger legs were used to support the wings. Standard, defensive armament was to include 10 x 20mm cannons while the bomb load reached 24,000lb of stores. The B-47 was defensed by 2 x 20mm cannons and carried around 25,000lb of stores.
In many ways the XB-55 was an insurance policy against the B-47 - it was far more conventional in design and held qualities for a bomber influenced by the recent World War but the USAF could at least understand what it was getting without pinning all their hope on the success (or failure) of unreliable, underpowered and thirsty turbojet engines of the time.

Eventually there proved delays with the expected Allison engines which prompted a look into an all-turbojet-powered form by way of the "XB-52" initiative - this design promised considerably better performance figures from the impending arrival of the Pratt & Whitney J57 turbojet engine. Couple this with waning interest on the part of the USAF over the XB-55 (the B-47 was seeing success in service by this point) and the XB-55 project contract was terminated in 1949. It, too, dawned on the USAF that it required a fleet of fast bombers and turboprop-powered forms were not going to be sufficient.

The XB0-55 endeavor lived a short time longer as "Model 479" which studied the use of 6 x Westinghouse J40 turbojet engines along a revised wing element and this data then served the upcoming Boeing B-52 "Stratofortress" strategic heavy bomber program. Leftover funding for the XB-55 went into pursuit of a supersonic strategic bomber under the Boeing "XB-59" designation (Model 701).

As no functional prototype of the XB-55 was ever completed, specifications reported in this article and on this page are purely estimates based on engineering data.






Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.

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Relative Maximum Speed Rating
Hi: 500mph
Lo: 250mph
    This entry's maximum listed speed (491mph).

    Graph average of 375 miles-per-hour.
City-to-City Ranges
NYC
 
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LON
 
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PAR
 
  BER
BER
 
  MOS
MOS
 
  TOK
TOK
 
  SYD
SYD
 
  LAX
LAX
 
  NYC
Graph showcases the Boeing XB-55's operational range (on internal fuel) when compared to distances between major cities.
Aviation Era
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Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units
0
0


  * Commercial Market High belongs to Cessna 172.

  ** Military Market High belongs to Ilyushin Il-2.


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Origin: United States
Year: 1947
Type: Strategic Bomber Proposal
Manufacturer(s): Boeing - USA
Production: 0
Global Operators:
United States (cancelled)
Historical Commitments / Honors:

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* Ribbons not necessarily indicative of actual historical campaign ribbons. Ribbons are clickable to their respective campaigns/operations.
Measurements and Weights icon
Structural - Crew, Dimensions, and Weights:
Unless otherwise noted the presented statistics below pertain to the Boeing XB-55 model. Common measurements, and their respective conversions, are shown when possible.

Operational
CREW


Personnel
10


Dimension
LENGTH


Feet
118.93 ft


Meters
36.25 m


Dimension
WIDTH


Feet
135.01 ft


Meters
41.15 m


Dimension
HEIGHT


Feet
33.63 ft


Meters
10.25 m


Weight
EMPTY


Pounds
99,208 lb


Kilograms
45,000 kg


Weight
LOADED


Pounds
167,992 lb


Kilograms
76,200 kg

Engine icon
Installed Power - Standard Day Performance:
4 x Allison T40-A-2 turboprop engines developing 5,600 horsepower each and driving three-bladed propellers in contra-rotating fashion.

Performance
SPEED


Miles-per-Hour
491 mph


Kilometers-per-Hour
790 kph


Knots
427 kts


Performance
RANGE


Miles
5,005 mi


Kilometers
8,055 km


Nautical Miles
4,349 nm


Performance
CEILING


Feet
42,651 ft


Meters
13,000 m


Miles
8.08 mi

Supported Weapon Systems:

Graphical image of an aircrat automatic cannon
Graphical image of an aircraft conventional drop bomb munition
Armament - Hardpoints (0):

STANDARD:
10 x 20mm cannons

OPTIONAL:
Up to 24,000lb of drop stores.
Variants: Series Model Variants
• XB-55 - Base Series Designation