In the summer of 1923, Army aviators began running a fuel hose from one biplane to another and setting endurance records. Technological leaps since then mean B-2 bombers can fly from Missouri to Korea and back, nonstop.
Here we see a US Navy F/A-18 Hornet getting itself into position behind a KC-10 Extender aerial tanker for a fill-up in 2010 while thousands of feet in the air over Afghanistan. But the story of aerial refueling stretches back a full 90 years. Let's travel back in time....
Two months later, in late August 1923, the two men who'd been in the receiving plane -- Lowell Smith and John Richter -- set an endurance record with a flight that lasted 37 hours, 15 minutes, with help from 16 midair refueling maneuvers, according to the National Museum of the US Air Force. In October of that year, the duo flew from the Canadian border to the Mexican border, with three aerial refuelings. The novelty was quickly becoming well-established reality.
So it was that an Atlantic-Fokker C-2A airplane was dubbed the Question Mark, in an exercise that was part research project, part publicity stunt. The question was this: just how long could this plane stay in the air before it finally had to come back down to Earth?
A year later, according to the National Museum of the US Air Force, a civilian plane carrying two men remained in the air for 647 hours, 28 minutes -- that is, 27 days.
Against that backdrop, in 1949 a US Air Force B-50A bomber known as the Lucky Lady II (seen here) carried out the first-ever nonstop round-the-world flight. The circumnavigation took 94 hours, 1 minute -- 2 hours less than four full days -- from February 26 to March 2, and required the assistance of four pairs of KB-29M tankers, which carried out an unspecified number of refuelings.
"The fuel delivery aircraft (KB-29M) would fly above and forward of the receiver aircraft (B-50A) and unreel a long refueling hose. The crew of the B-50A would extend an apparatus from the rear of the aircraft designed to snag the refueling hose trailing behind the KB-50M. Once the fuel hose was captured, it was reeled into the B-50A where the crew connected it to the refueling manifold. Once the fuel transfer was complete, the hose was released and the KB-29M reeled in back."
The P models were an upgrade over the M models, which had been in service for a couple of years at that point. The B-29M used a loop-and-hose system, the hose of which had a 2.5-inch-diameter refueling hose that transferred fuel at a relatively modest 110 gallons per minute. That would prove inadequate for the new high-speed, high-altitude bombers coming into service, on top of being tricky to operate.
"Interestingly enough, Boeing already had a better system in mind," according to an Air Force post describing the transition to the KB-29P. "The company developed a 'flying boom,' which featured a telescoping pipe with fins at the nozzle end. The fins were termed 'ruddervators' because they functioned as both rudders and elevators. The boom operator, sitting in the B-29's converted tail turret, literally flew the boom into a receptacle on the upper fuselage of the receiver aircraft. This design allowed more positive control of the air-to-air refueling operation and, with the boom's four-inch diameter, it offered much faster fuel transfer."
The KB-29Ms were later converted to a more modern probe and drogue system.
"During its final test flight," DARPA said, "two modified Global Hawk aircraft flew in close formation, 100 feet or less between refueling probe and receiver drogue, for the majority of a 2.5-hour engagement at 44,800 feet. This demonstrated for the first time that High Altitude Long Endurance (HALE) class aircraft can safely and autonomously operate under in-flight refueling conditions."
The Navy, meanwhile, had hoped to carry out aerial refueling tests with its X-47B drones in 2014, but it looks now like that will not come to pass.
This artist's rendering by Boeing shows what the aerospace giant had been calling, before the contract was awarded, the NewGen Tanker, refueling a B-2 Spirit stealth bomber.
Boeing on Friday laid out this timetable for the KC-46A: "The first test aircraft is expected to roll out of the factory in January 2014, while the second is scheduled to leave the factory in March. Boeing plans to fly the fully provisioned tanker for the first time in early 2015 and make the first delivery in 2016. The company expects to build and deliver the first 18 KC-46As by 2017 and a total of 179 by 2027 if all options under the contract are exercised."