Delivering things by drone began as a stunt in 2012, when a model airplane dropped a burrito by parachute to a hungry customer waiting below. The concept then graduated, first to a proof-of-principle venture in Iceland using multicopters, then to a well-funded Amazon project in the United Kingdom. But these and similar attempts to solve the last-mile problem?the mile leading to the customer?have largely been disappointing. Amazon recently scaled back its drone-based delivery project in the U.K.