After 15 years of hard work by hundreds of volunteers, a restored B-29 bomber finally rolled out of its hangar in Wichita, Kans., in late March. Upon its inaugural flight later this year, the big four-engine bomber will become only the second B-29 in the world still in operation. The nonprofit group Doc’s Friends has invested more than 300,000 hours of volunteer labor to rebuild and restore the airframe, install new engines, and get the airplane ready to fly again. Doc was the original name given to the aircra…