Here's his solution

According to the professor's calculations,they should be able to pull it off by a hair.The key is to maximize the support each assistant provides,not wasting a single kiloliter of fuel.It also helps us to think symmetrically so they can make shorter trips in either direction while setting the professor up for a long unsupported stretch in the middle.Here's his solution.All three planes take off at noon flying west,each fully loaded with 180 kiloliters.After 45 minutes, or one-eighth of the way around,each plane has 135 kiloliters left.