Three planes, A, B and C, take off at the same time and travel in the same direction.

The flight 1/8 (one circle around the earth) just consumes 1/4 fuel, of which 1 aircraft A adds 2× 1/4 fuel tanks to the fuel tanks of aircraft B and C, and then takes 1/4 fuel to return safely. At this time, the fuel tanks of planes B and C are full.

The remaining two planes continue to fly within the range of 1/8, that is, within the range of 1/4. At this time, planes B and C still have 3/4 fuel tanks. Aircraft B added 1/4 fuel tank to aircraft C. The remaining 1/2 fuel tank was returned to aircraft B. The fuel tank of aircraft C was filled, and it continued to fly around the world, and it could fly for 3/4 flights.

On the flight from plane C to 1/2, three planes D, E and F took off from the same airport at the same time and flew in the opposite direction to planes A, B and C.

When planes D, E and F fly in the opposite direction 1/8, plane D adds 2× 1/4 fuel tank to planes E and F to return, and planes E and F fly forward 1/8, that is, 1/4 in the opposite direction and 3/4 in the positive direction. The two planes added 1/4 fuel tanks to aircraft C, and returned to the airport together with aircraft C. At this time, aircraft C, E and F all had 1/2 fuel tanks, just enough to fly the remaining 1/4 flights.

If the three planes D, E and F don't take off at the same time, they can save some fuel, but the number of flights is the same.