This photo shows the Ion Tiger in flight. The 550-watt fuel cell is show in the box in the lower left corner. Credit: Naval Research LaboratoryFrom Live Science:
Robot spy planes are harnessing alternative energy to make them more covert and longer lasting than ever.
Such drones could also find use in civilian life to help monitor the earth or wildlife as well, researchers noted.
Increasingly, the military is deploying unmanned aerial vehicles, or UAVs, as eyes in the sky to scan the ground for targets and threats, especially for missions that are too dangerous for manned aircraft.
The problem with using internal combustion engines for these spy drones is how noisy they are.
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My comment: Since it is all about the noise that present UAVs produce, they should take the submariner motto .... run silent, run deep .... and change it into the following .... run silent, run high.