The Commemorative Air Force in the US flies the only two airworthy Boeing B-29s, the most expensive weapon of World War Two. One pilot tells BBC Future what it feels like to fly them.

They are two of the most celebrated aircraft still flying today. The two Boeing B-29s flown by the Commemorative Air Force (CAF) in the US are the last airworthy examples of nearly 4,000 built in the mid-1940s, the largest bomber in the world at that time and a design which pushed aviation technology to the limit.

The aircraft, nicked "Fifi" and "Doc" by the CAF, take part in airshows across the US during the summer, where aviation fans can pay to ride along in 30-minute-long demonstration flights.

The Boeing B-29 was the most advanced bomber in the world when it entered service in 1945: it was the first mass-produced aircraft to have pressurised compartments for the crew, and it could fly higher and further than any other aircraft thanks to its four enormous engines. These engines also helped it fly almost as fast as the fighter planes of the time. Designing and building it cost more than the atomic bombs that B-29s would eventually drop on Japan to end World War Two.

Bringing the B-29 into service was a colossal industrial project that at times overwhelmed Boeing. Its engines were powerful but temperamental, and keeping them in line required the full-time attention of a dedicated flight engineer, who kept a beady eye on engine temperatures to avoid the engines catching fire from overheating. Even getting a B-29 airborne for its mission over Japan required great effort in the humid air of tropical airfields. So, 80 years after the B-29 helped bring the world's most costly conflict to a close, what is it like to fly one now?

Randall Haskin, 52, is one of the lucky few who knows. When he isn't flying freight planes for one of the world's biggest delivery companies, he swaps an airliner's seat for the rather more intensive controls of "Fifi".

"Flying the Superfortress is like leadership by committee," says Haskin over Zoom from his home in Las Vegas. "I have a flight engineer who's responsible for essentially all manner of engine operation and management. In the world of professional flying, it's normal to have two pilots interacting with one another. But now to have a flight engineer who is the key component of all aspects of engine operation makes being the pilot in command a leadership exercise."

The flight engineer's job was vital in a B-29 because there was no way the pilot or co-pilot could monitor the engine readings at the same time as doing everything else needed to get the aircraft into the air. "Think about when you first learn to drive, and think about when how you drive now, you make inputs with your foot on the accelerator all the time, and you don't think about how much or how little you're pushing," Haskin says. "You're just simply looking at either the speedometer or you're looking at your relative motion with other cars, and you're making inputs, right? Normally, when you fly any other aircraft without a flight engineer, that's the same thing that happens."

For example, in other big World War Two bomber planes Haskin has flown, like the Consolidated B-24 Liberator, if the pilot wants to add more power then he simply moves the throttle levers for the engines.

Not so on the B-29. "Instead of me just simply saying, 'Okay, I'm going to give it a little bit less power, because I want to slow down'. Well, now I have to tell the flight engineer what power to set. And it's not just, 'Hey, I want a little bit less,'" says Haskin. The pilot has to tell the flight engineer exactly how much extra power according to the manifold pressure gauge, which measure the pressure of the air around a crucial part of the wing. Too much power – or too little – and it can end in disaster.

This means Haskin has to be aware of things he is not usually aware of in any other airplane he flies, he says. "We're talking about having to use parts of my pilot brain in real time while I'm trying to fly this 90,000lb (40 tonnes) beast around........

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