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B-29 Superfortress, U.S. Heavy Bomber


Aerial photograph of
          B-29 Superfortress

USAF


Boeing B-29A Superfortress


Specifications:


Crew
10-14
Dimensions 141’3” x 99’ x 29’7”
43.05m by 30.18m by 8.46m
Wing area 1739 square feet
161.6 square meters
Weights 74,500-135,000 lbs
33,800-61,200 kg
Maximum speed       358 mph (576 km/h) at 25,000 feet (7620 m)
295 mph (475 km/h) at 5000 feet (1524 m)
Cruising speed 230 mph
370 km/h
Landing speed 105 mph
169 km/h
Climb rate to 25,000 feet (7620 m) in 43 minutes
Service ceiling 31,850 feet
9708 m
Power plant 4 2200 hp (1640 kW) Wright R-3350-23 Duplex Cyclone 18-cylinder radial engines each with two exhaust-driven turbochargers driving four-bladed propellers
Armament Two dorsal and two ventral GE twin-0.50 machine gun turrets, sighted remotely.
Bell tail turret with one 20mm cannon and twin 0.50 machine guns
Bomb load 5,000 lbs (2270 kg) over 1,600 mile (2600 km) radius at high altitude
12,000 lbs (5440 kg) over 1,600 mile (2600 km) radius at medium altitude
20,000 lbs (9100 kg) maximum over short distances at low altitude
Could be modified to carry two 22,000 lb (10 tonne) Grand Slam bombs externally.
The “Silverplate” version delivered the first nuclear bombs.
Could carry a 2560 gallon (9691 liter) auxiliary fuel tank
Range 3250 miles at 25,000 feet (7620 m) with 5000 lb (2270 kg) bomb load
4100 miles at 25,000 feet (7620 m) with 5000 lb (2270 kg) bomb load and auxiliary fuel tank
4700 miles (7600 km) max
Fuel 8,198 gallons (31,030 liters) on early models, carried in four wing tanks.
9,548 gallons (36,140 liters) after the installation of extra tanks in the wing center section.
6,988 gallons (26,450 liters) only under operational conditions if the semi-permanent fuel tanks in one of the bomb bays were removed.
Sensors
AN/APQ-13 airborne radar
Production 3970 from 1943-9 to 1944-6 at Boeing Airplane Company, Seattle and Renton, Washington and Wichita, Kansas.These included 49 "Silverplate" nuclear bombers.
Variants The F-13 was a photoreconnaissance version equipped with six or more cameras. These first saw operational use in early November 1944.

The Silverplate variant removed the armor and all but the tail guns to save enough weight to deliver nuclear bombs.The bomb bays were also modified and the propellers were reversible to reduce landing length. The aircraft also carried multiple radar jammers, including APT-1, APT-4, and ARQ-8.

The B-29B was equipped with the precision AN/APQ-7 Eagle bombing radar, which used a small radome under the fuselage that slightly reduced speed.


The B-29 Superfortress is usually regarded as the ultimate strategic bomber of World War II. It saw service only in the Pacific theater. It was also the world's first nuclear-capable bomber (in its Silverplate variant) and dropped the two nuclear bombs on Hiroshima and Nagasaki that contributed to ending the war. It was a very sophisticated aircraft for its day, having fully pressurized crew compartments, sophisticated bombing radar, and remote-controlled gun turrets with computing sights.

Extreme measures were taken to ensure maximum streamlining. The design featured two bomb bays to keep the fuselage narrow, and the bombs were released alternately from each bay by intervalometer to avoid throwing the aircraft off balance. The gun turrets were designed for minimum drag, and all of the gun turrets (except for the rear guns) could be controlled remotely from any of the gunner stations, which were deliberately located some distance from the turrets to isolate the gunners from the noise and vibration of the guns. The entire aircraft was operated electrically, with 54 kilowatts of power generated by six generators and distributed through a new kind of aircraft wiring with superb mechanical and chemical resistance properties at extreme temperatures.

The beginnings of the B-29 program can be traced back to June 1939, when the Kilmer Board called for a very long-range bomber to be procured by 1944. "Hap" Arnold initiated the design program for the new bomber on 10 November 1939 and the Air Corps published a formal specification the next month. Boeing had been working on a new advanced bomber design to replace the B-17 since March 1938, and the company immediately began revising their design to meet the new specification. The Air Corps awarded Boeing a contract for the B-29 in September 1940 and the first prototype flew on 21 September 1942.

The B-29 was a huge gamble. The program ultimately cost $3 billion dollars, versus $2 billion for the Manhattan Project that developed the nuclear bomb. Hap Arnold was understandably determined to do whatever was necessary to make the program succeed. His deputy, Lauris Norstad, later said that "Arnold's life was that B-29 ... he was into every damn detail of that B-29" (Wolk 2010). Corners were cut in development and procurement, included ordering 500 production aircraft at the same time as the prototype. These began coming off the assembly line in September 1943.

It is perhaps unsurprising that the first production aircraft still had many design flaws. LeMay said that the B-29 "had as many bugs as the entomological department of the Smithsonian" (Hastings 2007). Of these, the worst was a regrettable tendency towards engine fires during takeoff, due to the use of magnesium alloy engine components to save weight. The fire extinguishing system proved inadequate, failing to extinguish engine fires 87 percent of the time. The second prototype crashed after two engines caught fire, killing the entire test crew and twenty persons on the ground. The third prototype nearly crashed due to crossed control cables. Of the first 96 aircraft to come out of the factories, only 16 were rated as flyable. The "Battle of Kansas" waged at Boeing's Wichita plant reached its climax in March and April 1944, and by late March the first B-29s departed for XX Bomber Command.

This did not end the difficulties with the new aircraft. Five of the new B-29s crashed near Karachi (in what is now Pakistan) in a single two-day period due to engine failure in the hot desert conditions. The first raid, mounted on 15 June 1944 from Chengtu, saw only 47 of the original 68 aircraft reach the target, Yawata. One pilot recorded that "The airplane always felt like it was straining every rivet to be up there when you had it over 25,000 feet" (ibid.) In addition, the B-29 was a challenge to new crews, and it took some time for pilots to learn to milk the full range out of the aircraft. For all this, the B-29 was a terrifying threat to Japan. Japanese fighter pilots were stunned by its huge size, which often caused the pilots to underestimate the range and fail to hit the aircraft during firing runs.

Bombing accuracy was initially unimpressive. Strike photography revealed that bombing accuracy during daylight precision raids in January 1945 was 12 percent of the bombs within 1000 feet (300 meters) of the target. However, by June 1945, this figure had improved to 40 percent of the bombs within 1000 feet of the target.

The aircraft imposed a serious logistical burden even when operations were moved from remote China to the Marianas, from which the first raid was launched on 24 November 1944. The Navy struggled to find shipping and escorts to convoy the necessary supplies. Each aircraft flew an average of eight missions a month, each of which consumed 6400 gallons (24,200 liters) of gasoline and expended eight tons of bombs. By June 1945 over 100 cargo ships were required to meet these logistical requirements.

The maximum bomb load given in the specifications, 20,000 lbs or 9.1 metric tons, is an upper limit for a relatively short flight at low altitude (8000 feet or 2400 meters). The long flight to Japan from the Marianas  required a trade of bomb weight for fuel weight, and the climb to altitude for high altitude attacks consumed prodigious quantities of fuel. Wolk (2010) states that a B-29 at high altitude could carry only 35% of the load of a B-29 at modest altitude. 

In a curious role reversal, a small number of B-29s were fitted out as navigation escorts for P-51 Mustangs making the long flight to Japan. These aircraft carried homing beacons to allow the Mustangs to home on them for the return flight.

One must question whether these aircraft were cost effective. Each aircraft was hideously expensive, at over half a million dollars, or five times as much as a Lancaster. Each required over thirteen tons of aluminum, half a ton of copper, 600,000 rivets, nine and a half miles (15 km) of wiring, and two miles (3 km) of tubing. In addition to the regular crew, each aircraft required 74 relief and ground crew. Great things were expected from the aircraft, but they were judged a failure in their original design role as conventional high-altitude daylight strategic bombers. They were more successful as low-altitude nighttime fire bombers, but only because Japanese air defenses were pitifully inadequate. (Losses to interceptors averaged just 0.24% of sorties.) Their employment as the world's first nuclear bombers, albeit in the Silverplate variation, has probably muted what would otherwise be justified criticism of the B-29 program. No other aircraft could  have delivered the nuclear bombs to Japan.

Photo Gallery


Ventral view of B-29s in flight

USAF

B-29s fly past Mount Fuji

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Bombs away

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Forward pressure cabin of B-29

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Panoramic view of B-29 cockpit

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Pilot's controls on B-29

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Side gunner with computing gunsight on B-29

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Bomb bay on B-29

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Tail gunner position on B-29

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Replacing an engine on a B-29

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Diagram showing turrets and gunner stations on
                B-29

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Diagram showing low drag of B-29 turrets

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B-29 factory floor

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Propaganda leaflet dropped on Japan

CIA

References

B-29 Memorial (accessed 2011-6-25)

Frank (1999)
Gunston (1986)

Hastings (2007)

Klein (2013)

Morison (1959)

Price (2005)

Tillman (2010)

Wolk (2010)



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