The hand-launched Tactical Long Endurance Unmanned Aerial System (TALEUAS) is being developed at the Unites States’ Naval Postgraduate School in Monterey, California. It needs an electric propeller to get airborne, but give it a few minutes to reach a reasonable altitude and TALEUAS can fly all day just by riding rising currents of warm air called thermals.
When TALEUAS encounters a thermal it senses the lift and spirals around to take advantage of it. Vultures and eagles use the same technique, and Kevin Jones, who is in charge of the project, says he has often found TALEUAS sharing the air with these raptors. On some occasions, indeed, the birds found that the thermals they were attempting to join it in were too weak for their weight, as the drone is more efficient than they are at gliding.
TALEUAS’s endurance is limited only by the power requirements of its electronics and payload, for at the moment these are battery powered. Dr Jones and his team are, however, covering the craft’s wings with solar cells that will generate power during the day, and are replacing its lithium-polymer battery with a lithium-ion one capable of storing enough energy to last the night. That done, TALEUAS will be able to stay aloft indefinitely.
TALEUAS does, however, depend on chance to locate useful thermals in the first place. Roke Manor Research, a British firm, hopes to eliminate that element of chance by allowing drones actively to seek out rising air in places where the hunt is most likely to be propitious. As well as thermals, Mike Hook, the project’s leader, and his team are looking at orographic lift, produced by wind blowing over a ridge, and lee waves caused by wind striking mountains. Their software combines several approaches to the search for rising air. It analyses the local landscape for large flat areas that are likely to produce thermals, and for ridges that might generate orographic lift. It also employs cameras to spot cumulus clouds formed by rapidly rising hot air. Such software replicates the behaviour of a skilled sailplane pilot—or a vulture—in knowing where to find rising air and where to avoid downdraughts.
SOURCES - Economist, RC Soaring Digest
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