Boeing B-29 Superfortress variants

The Boeing B-29 Superfortress was produced in a large number of experimental and production models.

XB-29

 * Section source: Baugher and National Museum 

The XB-29, Boeing Model 345, was the first accepted prototype or experimental model delivered to the Army Air Corps, incorporating a number of improvements on the design originally submitted, including more and larger guns and self-sealing fuel tanks. Two aircraft were ordered in 1940 August, and a third was ordered in December. A mock-up was completed in the spring of 1941, and it first flew on September 21, 1942.

Testing continued until February 18, 1943, when the second prototype crashed. Flown by Boeing's chief test pilot, Edmund T. "Eddie" Allen on a two-hour powerplant performance test, leaking fuel from a filler cap in the leading edge ran down inside the leading-edge and ignited spreading to the engines, due to the much reduced power the aircraft, unable to climb, crashed into the Frye meat-packing plant, demolishing the majority of the packing plant and killing all eleven crew, 22 employees at the plant and one fireman. The crash killed many élite Boeing personnel involved in the design; the pilot, Allen, was chief of the Research Division. After the crash, the United States Army Air Forces and a congressional committee headed by then-Senator Harry S. Truman investigated the B-29 program issuing a scathing report, prompting the Army Air Force to take over the program.

YB-29
The YB-29 was an improved XB-29 and 14 were built for service testing. Testing began in the summer of 1943, and dozens of modifications were made to the planes. The engines were upgraded from Wright R-3350-13s to R-3350-21s. Where the XB-29 had three-bladed props, the YB-29 had four-bladed. Various alternatives to the remote-sighted defensive systems were tested on a number of them, particularly the fourth one delivered. After alternative arrangements had been fully tested, defensive armament was standardised at ten .50-calibre machine guns in turret-mounted pairs. The YB-29 also featured a better fire control system.

B-29
The B-29 was the original production version of the Superfortress. Since the new bomber was urgently needed, the production design was developed in tandem with the service testing. In fact, the first B-29 was completed only two months after the delivery of the first YB-29. 46 B-29s of this variant built by the Glenn L. Martin Company at its Omaha plant were used as the aircraft for the atomic bomb missions, modified to Silverplate specifications. 2,513 B-29s were manufactured by Boeing-Wichita (1,620), Bell-Atlanta (357), and Martin-Omaha (536).

B-29A

 * Section source: Baugher and National Museum 

The B-29A was an improved version of the original B-29 production model. All 1,119 B-29A's were built exclusively at the Boeing plant in Renton, Washington, formerly used by the United States Navy.

Enhancements made in the B-29A included a better wing design and defensive modifications. Due to a demonstrated weakness to head-on fighter attacks, the number of machine guns in the forward dorsal turrets was doubled to four. Where the wings of previous models had been made by the sub-assembly of two sections, the B-29A began the trend of using three. This made construction easier, and increased the strength of the airframe. The B-29A was produced until May 1946, when the last aircraft was completed. It was much used during the Korean War, but was quickly phased out when the jet bomber became operational.

Washington B Mk 1 - This was the service name given to 88 B-29As supplied to the Royal Air Force.

B-29B

 * Section source: Baugher and National Museum 

The B-29B was a modification used for low-level raids, designed with the intent of firebombing Japan. Since fighter opposition was minimal over Japan in late 1944, many of the Army Air Force leadership — most notably Curtis LeMay, commander of the XXI Bomber Command — felt that a (lighter) faster bomber would better evade Japanese flak.

In the B-29B, all defensive armament was removed except for that in the tail turret. Initially the armament was two .50 in M2/AN machine guns and one 20 mm M2 cannon which was soon changed to three .50 in M2/ANs. The weight saved by removing the gun system increased the top speed from 357 mph to 364 mph (574 km/h to 586 km/h).

Also incorporated on this version was an improved APQ-7 "Eagle" bombing-through-overcast radar fitted in an airfoil shaped radome under the fuselage.

All 311 B-29Bs were built at the Bell plant in Marietta, Georgia ("Bell-Atlanta").

B-29C
The B-29C was a modification of the B-29A re-engined with improved Wright R-3350 engines. The Army Air Force originally ordered 5,000, but cancelled its request when World War II ended and none were built.

B-29D (XB-44)

 * Section source: Baugher and National Museum 

The B-29D was an improved version of the original B-29 design, featuring Pratt & Whitney R-4360-35 engines of 3500 hp (2600 kW) each — nearly 60% more powerful than the Wright R-3350. It also had a taller vertical stabiliser and a strengthened wing. The XB-44 was the testbed designation for the D model.

When World War II ended, drastic cutbacks were made in military spending, altering the outlook of the B-29 program. Because Congress was reluctant to continue funding wartime projects, the B-29D was redesignated B-50 to make it appear completely new. Congress fell for the trick, and the B-29D was kept alive, even though no planes flew under the original designation.

Test beds
A number of B-29s were converted to serve as test beds for new systems. These all received variant designation, even though many existed only as a single converted aircraft.

XB-29E
The XB-29E for fire-control systems (one converted) was a model B-29-45-BW.

XB-29F
The B-29F for cold-weather operation in Alaska were six converted B-29-BWs.

XB-29G
It was also used in the development of jet engines. Stripped of armament, a converted B-29B-55-BA (44-84043)(Bell) designated the XB-29G carried experimental jet engines in its bomb bay, which it would extend into the airstream for testing during flight. This plane was used to test the Allison J35, General Electric J47 and J73 jet engines.

XB-29H
The XB-29H to test armament configurations was a converted B-29A.

YB-29J, YKB-29J, RB-29J
Experimentation in engines continued. For example, six B-29s (redesignated YB-29J) of various designation were upgraded to R-3350-79 engines. Other engine-associated items were also upgraded, including new Curtiss propellers, and 'Andy Gump' cowlings, in which the oil coolers have separate air intakes. Two were later converted to aerial refueling tanker prototypes, and redesignated YKB-29J. The remainder were used for reconnaissance, and designated RB-29J. ''

EB-29

 * Section source: Baugher and National Museum 

The EB-29 (E stands for exempt), was used as a carrier aircraft in which the bomb bay was modified to accept and launch experimental aircraft. They were converted in the years following World War II. One EB-29 was converted to carry the famous Bell X-1 until it was replaced by a B-50. Another was used to carry and test the XF-85 'parasite fighter'. This fighter was intended to be carried by the Convair B-36 on long-range missions to protect it from Soviet fighters. Yet another EB-29 was used to carry two EF-84B Thunderjet fighters as part of Project Tom-Tom. All three Tom-Tom aircraft and their crews were lost in a crash on April 24, 1953.

RB-29J (RB-29, FB-29J, F-13, F-13A)

 * Section source: see Baugher and National Museum 

Early B-29/B-29As that were modified for photo reconnaissance carried the F-13/F-13A designations, with "F" meaning 'photo'. The aircraft (118 modified B-29BWs and B-29As) carried three K-17B, two K-22 and one K-18 cameras. Between the end of the war and 1948 the designation was changed to FB-29J. In 1948, the F-13/FB-29s were redesignated RB-29 and RB-29A.

Six B-29A/F-13As were modified with the Wright 3350-CA-2 fuel injected engines and designated at YB-29Js. These were then converted to RB-29Js.

In January 1949, RB-29s were assigned to the 91st Strategic Reconnaissance Wing and moved to Yokota AB, Japan in December 1950; to provide support to the Korean War and attached to the 15th Air Force, Far East Air Force.

SB-29

 * Section source: National and Birdsall 

The SB-29 'Super Dumbo' was a version of the B-29 adapted for air-sea rescue duty near the end of World War II. Sixteen 29s were modified to carry a droppable A-3 lifeboat under the fuselage, the SB-29 was used mainly as rescue support for air units that flew long distances over water. With the exception of the forward lower gun turret, all defensive armament was retained. They also carried a variety of radio equipment, provisions, survival kits, and extra crew. It was used throughout the Korean War into the mid-1950s. It received its nickname from "Dumbo", the Disney character, whose name was given to the aircraft used in previous missions to pick airmen up when they crashed at sea.

TB-29

 * Section source: National Museum 

The TB-29 was a trainer conversion of B-29 used to train crew for bombing missions; some were also used to tow targets, and the designation included B-29s modified solely for that purpose. Their most important role was serving as radar targets in the 1950s when the United States Air Force was developing intercept tactics for its fighters.

WB-29

 * Section source: National Museum 

The WB-29s were production aircraft modified to perform weather monitoring missions. An observation position was fitted above the central fuselage section. They conducted standard data-gathering flights, including from the UK over the Atlantic, but were also ordered to fly into the eye of a hurricane or typhoon to gather information. Following nuclear weapons tests, some WB-29s would use air sampling scoops to test radiation levels. On 3 September 1949, a WB-29 returning from Yokota AB, Japan, to Eielson AFB, Alaska, recovered radioactive debris in air sampling scoops from the cloud generated by the first atomic bomb test by the Soviet Union on 29 August.

Airborne Early Warning

 * Section source: National Museum 

In the middle of 1951, three B-29s were modified to participate in the Airborne Early Warning programme. The upper section of the forward fuselage was extensively modified to house an AN/APS-20C search radar, and the interior was modified to house radar and Electronic Counter Measures (ECM) equipment. This development led to production radar picket aircraft, including the EC-121 Warning Star. (×3, converted)

A Soviet-built copy of B-29, Tu-4, was used as the platform for a Chinese experimental airborne early warning aircraft, KJ-1 AEWC, in 1970s.

Navy P2B patrol bomber

 * ''Section source: Baugher

The U.S. Navy acquired four B-29-BWs from the U.S. Army Air Forces on March 14, 1947. These aircraft were modified for long-range patrol missions and given the designation P2B-1S with Navy Bureau Numbers (BuNo) 84028, 84029, 84030 and 84031.

BuNo 84029, previously AAF Ser. No. 45-21787, later went through modifications to carry the Navy's Douglas D-558-2 Skyrocket high-speed rocket-powered research aircraft. Modifications of the bomb bay were done to carry the Skyrocket II under the belly and dropped for Mach speed testing. The first Skyrocket test flight occurred on September 8, 1950 with test pilot William B. Bridgeman, and George Jansen flying the B-29. Scott Crossfield later broke Mach 2 with the Skyrocket on November 20, 1953; with the last Skyrocket flight in December 1956.

The P2B-1S "mother-ship" was nicknamed "Fertile Myrtle" and was assigned the NACA number 137. As of May 2013, this aircraft was in the collection of Kermit Weeks at his Fantasy of Flight aviation museum in Polk City, Florida. The forward fuselage section was restored and briefly displayed at the Florida Air Museum in Lakeland, Florida. It has since been relocated to Fantasy of Flight's "Golden Hill" storage facility along with the remainder of the disassembled aircraft and is awaiting full restoration to airworthy flying status at a future date.

BuNo 84030 and 84031 were later modified into anti-submarine patrol bombers and redesignated P2B-2S.

XB-39 Superfortress

 * Section source: see Baugher and National Museum 

The XB-39 Superfortress was a single YB-29 modified to use water-cooled Allison V-3420-17 inline engines. Since the Army Air Force was concerned that problems might develop with their first choice of engine, the Wright R-3350, they contracted General Motors to do testing on a modified aircraft to show that it could still be used even if the R-3350 failed. Since the R-3350 did not have significant enough problems to prevent its use, no XB-39s were ordered.

Tupolev Tu-4
In 1945, three B-29s were forced to land in Soviet territory after a bombing raid on Japan because of a lack of fuel. Since the Soviet Union was not at war with Japan at the time, the aircraft and crews were interned. Eventually, the B-29 crew members were returned, but the aircraft remained in Russian hands. Seeking a modern long-range bomber, Joseph Stalin ordered the Tupolev OKB to reverse-engineer the Superfortress.

The resulting aircraft first flew on May 19, 1947 and immediately began series production. Although largely identical in appearance to American B-29's the Tu-4 (Nato reporting name: "Bull"), had Soviet-designed defensive guns and had been re-engineered to suit production using metric tools; resulting in an aircraft that was slightly heavier and slower than the B-29. The Tu-4 presented a significant leap forward in Soviet strategic bombing. Not only did the Red Air Force have the means to deliver nuclear weapons, but Tu-4 had sufficient range to reach the United States on a one-way trip. On October 18, 1949, a Tu-4 was used in the first air-drop test of a Soviet atomic bomb.

In Soviet service, the Tu-4 had been phased out of service by the early 1960s, being replaced by more modern aircraft such as the Tupolev Tu-95. Although the "Bull" never dropped a bomb in anger, the Tu-4 influenced Soviet aircraft technology, particularly airframe construction and onboard systems. The People's Liberation Army Air Force of China is rumoured to still operate up to 15 upgraded Tu-4s, possibly as AWACS platforms.

Advanced transport and bomber variants of the Tu-4 design such as the Tu-70, 75, 80, and 85, were developed and built, but none of these achieved serial production.