Boeing has been awarded a patent for an inflatable long-endurance unmanned air vehicle that is rechargeable mid-flight.

The patent was filed in March 2013 and was awarded by theUnited States Patent and Trademark Officeto the manufacturer on 2 June. It covers technology surrounding inflatable UAVs carrying a tether that would then charge when connected to a ground-based power supply through a ball and hook tether system.

“Aircraft, particularly smaller autonomous and semi-autonomous aircraft such as surveillance drones, blimps and quadrotors, may be launched from ground-based launch platforms,” the patent states. “There remains a need for autonomous aircraft which can operate autonomously over extended time periods.

“In one embodiment, a system comprises an electrically powered buoyant aircraft, a control system to manoeuvre the aircraft and a tether adapted to couple the aircraft to a ground-based power supply to provide power to the aircraft while the aircraft is coupled to the tether.

“The aircraft can disconnect autonomously from the tether in response to a command signal.”

The ground-based power supply provides alternating current (AC) power to the tether, while the aircraft features a power converter to convert the AC power to direct current power.

Patent Yogi - a patent support company - demonstrates how the in-flight charging system could work

Patent Yogi

Meanwhile, Boeing is also exploring technology that allows natural updrafts to power a UAV, for which it was awarded a patent in February.

Observing that glider pilots increase range and endurance by utilising the natural updrafts of air caused by the heating of the Earth’s surface, Boeing says that UAVs can benefit from these thermals in the same way – although there are limits on how much it can use them, in line with airspace restrictions.

“In many countries UAVs are prohibited from flying in controlled airspace and may therefore be subject to an artificial ceiling that is lower than the true theoretical maximum altitude,” the patent states. “As such, it is not always possible for a UAV to achieve the theoretically available height gains from updrafts.”

The statement says, therefore, that there is a requirement to provide a UAV that can derive benefit from an updraft while being prohibited from climbing above a certain outlined altitude.

“The unmanned aerial vehicle with a gliding capability comprises a generator arranged to be driven by a rotor, and a battery, wherein the unmanned aerial vehicle can operate in an energy-harvesting mode in which the motion of the unmanned aerial vehicle drives the rotor to rotate, the rotor drives the generator, and the generator charges the battery,” it says.

In the energy-harvesting mode, regenerative braking of the generator reduces the forward speed of the UAV to generate electricity and prevent the unmanned aerial vehicle from flying above a predetermined altitude, it adds.