Boeing B-29

Posted with permission of Ted Rushton

b-29-fifi-mar-5-2013Contrary to persistent conservative nonsense about democracies never preparing for national defence, Boeing began work in 1938 on design of the B-29 in response to a U.S. Army Air Corps request.

The goal was to develop a pressurized version of the B-17 with a tricycle leanding gear, instead of the tail-dragger B-17. The result was a design study for the Model 334, which provided many basic ideas for the B-29.

The Air Corps did not have money to pursue the design in 1938, but Boeing continued work as a private venture. In December 1939, the Air Corps issued a formal specification for a so-called “superbomber” capable of delivering 20,000 lb of bombs to a target 2,667 miles away and capable of flying at a speed of 400 mph.

Boeing submitted its Model 345 on May 11, 1940, competing with Consolidated Aircraft, Lockheed, and Douglas. Douglas and Lockheed soon abandoned work on their projects, but Boeing received an order on Aug. 24, 1940, for two flying prototypes, the XB-29 models, plus an airframe for static testing. A third flying test aircraft was added August 24, 1940. Consolidated continued to work on its Model 33, a backup in case of problems with Boeing’s design.

An initial order for 14 service test aircraft and 250 production bombers was placed in May 1941, and increased to 500 aircraft in January 1942. The B-29 featured a fuselage design with circular cross-section for strength. The need for pressurization also led to the B-29 having the only “stepless” cockpit design for an America combat aircraft in World War II, without a separate windscreen for the pilot.

Manufacturing the B-29 was complex. It involved four main-assembly factories: a Boeing factory in Renton, Wash., one at Wichita, Kan., a Bell plant at Marietta, Georgia, and a Martin plant at Omaha, Neb. Thousands of subcontractors were involved; parts and sub-assemblies flowed among the four plants. The first prototype flew from Boeing Field, Seattle, on Sept. 21, 1942.

Because of the aircraft’s highly advanced design, challenging requirements and immense pressure for production, development was
deeply troubled. The second prototype, fitted with a Sperry armament system using remote-controlled gun turrets sighted by periscopes, first flew on Dec. 30, 1942. This flight was terminated due to a serious engine fire. On Feb. 18, 1943, the second prototype experienced an engine fire and crashed, with Boeing’s chief test pilot among the fatalities.

Changes came so often and so fast that in early 1944, B-29s flew from the production lines directly to modification depots for extensive rebuilds. Engines were the most common maintenance headaches and catastrophic failures. The Wright R-3350 Duplex Cyclone radial engine was beset with dangerous reliability problems.

This problem was cured when the aircraft were fitted with the more powerful Pratt & Whitney R-4360 “Wasp Major” engine - - after World War II. In combat, the uppermost five engine cylinders were to be replaced every 25 hours; in practice, mechnics in the field replaced the entire engine and scrapped the old one.

For the first time in a bomber, the crew had full-pressurized comfort, developed by Garrett AiResearch. The nose and the cockpit were pressurized, bomb bays were not, so a long tunnel was installed over the two bomb bays so crews could crawl between the pressurized fore and aft sections.

Pilots, including those who fly Fifi, describe flight after takeoff as an urgent struggle for airspeed — generally, after takeoff in
other aircraft the striving is for altitude. However, radial engines need airflow for proper cooling, and faults with early engines meant
failure to quickly get up to speed could result in engine failure and risk of fire.

One great advantage is the clean design of the aircraft which greatly reduces airflow drag. Once the landing gear is up, the drag is
reduced by 50 percent. Part of this is reflected in fuel consumption; for full power at take-off, the B - 29 uses 100-octane fuel at the rate of 200 gallons per hour. At normal cruising speed, its about 60 gallons per hour. (Fuel costs are now about $6 per gallon.)

In wartime, the B-29 was capable of flight up to 31,850 feet at speeds of up to 350 mph. This was its best defense, because Japanese fighters rarely reached that height, and even then few could catch it. Only the heaviest of anti-aircraft weapons could reach it, and without proximity fuzes it was difficult to inflict damage.

The B-29’s revolutionary Central Fire Control system included four remotely controlled turrets each armed with two .50 Browning M2
machine guns. All weapons were aimed electronically from five sighting stations located in the nose and tail positions and three Perspex blisters in the central fuselage.

Five General Electric analog computers compensated for factors such as airspeed, lead, gravity, temperature and humidity. They also allowed a single gunner to operate two or more turrets simultaneously. The gunner in the upper position acted as fire control officer, switching turrets among other gunners during combat.

On some early missions, bombs hit far from the targets. Flight disciplines was blamed, so early B - 29 squadron commanders were fired and crews were raked over the coals. It wasn’t until after the war that people learned about jet stream winds of up to 200 mph, which scattered bombs caught in the jet stream like confetti at a raucous wedding.

The “solution” came in early 1945, when Gen. Curtis LeMay took command of the B - 29s and changed their role from high-altitude day bomber to low-altitude night bomber. LeMay ordered the removal of most of the defensive armament and remote-controlled sighting equipment so they could carry greater fuel and bomb loads. Instead of high explosives, the emphasis was switched to incendaries and area bombing of cities.

By Aug. 1, 1945, about 80 percent of major Japanese cities were destroyed by fire. Then came two nuclear bombs, dropped by B - 29s on Hiroshima and Nagasaki, two relatively unimportant cities that had not been fire-bombed. The result was the most dramatic ending of any war in history.

Photo: - - Trouble sometimes comes in beautiful shapes . . . as one pilot said after seeing ‘Fifi’ at Deer Valley, “I know where’s
another 30 of those - - in the ocean right off the end of the runway at Tinian.” But doesn’t beauty always include a risk? Tinian, I
believe, is where the runway ended at the edge of a cliff. If the aircraft wasn’t airborne by the end of the runway, it went off the
cliff and perhaps had enough speed to fly . . . . .

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