Boeing B-29 Superfortress (1944): pressurised bomber

1944·575 km/h·up to 9,100 kg·4× R-3350 turbocharged radials, 2,200 hp each·5,230 km·3,970

· THE STORY

The most expensive weapon of the war

The B-29 was the most expensive weapons programme of the war — three billion dollars, more than the atomic bomb it eventually carried — and the most advanced aircraft in it. Its crew sat in pressurised cabins at 9,000 m, its guns were aimed by computers from sighting stations, and its four engines each had two turbochargers. It was rushed into service with engines that caught fire, and then, in March 1945, its commander threw out the idea it was built for: the guns came out, it flew low at night, and it burned Tokyo. On 6 and 9 August 1945 two of them ended the war.

575 km/hTop speedup to 9,100 kgBomb load

· WHY IT MATTERED

A cabin you could breathe in

At 9,000 m the outside pressure is a third of sea level. The B-29’s nose and rear compartments were pumped up to the pressure of 2,400 m and joined by a tunnel over the bomb bays, which stayed at outside pressure because bomb doors cannot hold a seal. The crew flew eight-hour missions without oxygen masks, in a fuselage that was, in engineering terms, a pressure vessel with wings.

GO DEEPERSupercharger vs altitude, the full demo →A pressure vessel with wings →

· WHY IT MATTERED

Guns aimed by computer

Four remote turrets, each with two heavy machine guns, were aimed from sighting stations by gunners who never touched them; five analogue computers corrected for the aircraft’s speed, the bullet’s drop and the lead needed. One gunner could take over any turret. It was the first fire-control system of its kind in the air.

· WHY IT MATTERED

LeMay throws the concept away

Precision bombing from 9,000 m over Japan failed: the jet stream blew the bombs off target and the engines burned. In March 1945 General LeMay stripped the guns and gunners out, loaded incendiaries, and sent the B-29s in at 1,500–2,700 m at night. Sixteen square miles of Tokyo burned on the first night. The aircraft designed to be untouchable at altitude did its work low and unarmed.

· THE ENGINE

The Duplex-Cyclone: rushed to war, and it burned

Eighteen cylinders in two rows, 55 litres, 2,200 hp, and a cowling so tight that the rear row overheated. The R-3350 first ran in 1937 and flew in 1941, and it went to war before it was ready: it swallowed valves, its turbine blades failed in 800 °C exhaust, and its magnesium crankcase burned at 3,000 °C, through the wing spar in seconds. Take-off at 60 tonnes on a tropical runway was the most dangerous minute of a B-29 mission — and in spring 1944 the Air Force sent factory workers to the airfields in Kansas to make 150 aircraft fit to deploy.

4× Wright R-3350-23 · 18-cylinder two-row radial · 54.9 L · two-speed supercharger plus two GE turbochargers per engine · 2,200 hp each

GO DEEPEROpen the full demo →

· WEAPONS AND SPECIALITY

Ten remote guns, nine tonnes of bombs

Ten heavy machine guns under central fire control put about seven kilograms a second into a fighter that any two turrets could reach, and the tail carried a cannon as well until it was found to be useless. Its bomb bays held nine tonnes — five times a B-17’s usual load — and, on two aircraft modified under the Silverplate programme, one bomb each.

· TRY IT

Pressurisation: a cabin at 2,400 m inside a sky at 9,000

The lab computes the cabin: outside pressure from the barometric formula at cruising height, the differential the fuselage skin has to hold, and the hoop stress in a tube of that radius and gauge. It shows why the bomb bays stayed at outside pressure and the crew crawled between the cabins through a tunnel.

Readout

Power, 4 engines8,800 hp

Per engine2,200 hp

True airspeed575 km/h

Service ceiling9,710 m

A simplified model calibrated to the published rating and top speed — the shape of the curve is the point, not the third decimal.