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. Designing and building it cost more than the atomic bombs that B-29s would eventually drop on Japan to end World War Two. 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?