Take a Japanese scientist, two assistants, and three advanced airplanes. One of them wants to fly around the world in just six hours, but his plane only carries enough fuel for half the journey. To make it even harder, all three planes can only take off and land at a single airport on the equator, and every plane and pilot must survive. How can they pull it off?
The Impossible Challenge
Professor Fukanō (whose name comes from the Japanese for "impossible") has designed an unprecedented airplane with extraordinary speed and maneuverability. Flying over the equator, it covers one degree of longitude per minute, which means it could theoretically complete a full circle in six hours. However, the plane does not carry enough fuel. It can hold only 180 kiloliters and burns one kiloliter per degree of longitude, so a full tank equals half a trip. The professor could have designed a larger tank, but he deliberately made this limitation part of the challenge.
The Solution
The first part of the plan relies on his assistants, Fugōri and Orokana, piloting two additional planes to refuel him in mid-air. Thanks to the plane's extraordinary capabilities, it can change direction instantly and transfer fuel to another plane while flying together, all without losing speed.
The mission is already complicated, but the professor faces another constraint: only one airport on the equator has authorized takeoff and landing. That airport is the starting point, the finish line, and the only place where the assistants can refuel. And there is no room for sacrifice: all pilots and airplanes must survive.
The Flight Plan
The journey demands extraordinary efficiency, so much so that the planes will be on the verge of running out of fuel more than once. Here is the plan: The three planes take off at noon heading west. Forty-five minutes later, Orokana transfers 45 kiloliters of fuel to Fugōri and the professor. Both planes are full again, and Orokana has just enough fuel to return to the airport. Another 45 minutes pass (and Orokana lands), and then Fugōri sends 45 kiloliters to the professor, refilling his tank. With 90 kiloliters in his own plane, Fugōri turns around and heads back. This gives the professor 180 additional minutes of flight. Ninety minutes later, Fugōri lands, and Orokana immediately takes off with a full tank, heading east. Ninety minutes after that, at the exact moment the professor's fuel tank is about to be completely empty, Orokana catches up and transfers 45 kiloliters. With perfect coordination, Fugōri takes off heading east. Forty-five minutes later, the professor and Orokana are about to run dry, but Fugōri saves the day by sending 45 kiloliters to each. With 45 minutes left and 45 kiloliters in their tanks, all three planes arrive safely at the airport, having flown on fumes more than once.
Note: This riddle has more than one solution; the video presents the most efficient one.
Source: TED Education
