THE technique honeybees use to touch down smoothly could be an ideal way to
control pilotless planes as they land, say Australian scientists.
A team led by Mandyam Srinivasan of the Australian National University in
Canberra monitored the flight paths of six bees as they made over 100 landings
on a flat surface. They found that, as they descended, the bees鈥� flying speed
was always proportional to their height鈥攁nd this gave them the clue to the
simple trick they were using to land safely.
As you travel along, the closer an object is, the faster it seems to pass.
It鈥檚 the same for the bees: if they flew at a constant speed while descending,
the ground would appear to hurtle by faster and faster. In fact bees do the
opposite. They ensure that the image of the ground always crosses their field of
view at the same rate, and so automatically slow down as they land, making their
speed close to zero at touchdown.
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鈥淭he beauty of the system is that the bee is on autopilot. To land, it needs
no explicit knowledge of its flight speed or its height above ground,鈥� says
Srinivasan. 鈥淚t鈥檚 neat and economical,鈥� agrees Tom Collett, a neurobiologist at
the University of Sussex, Brighton.
To test their idea, the team equipped a computer-controlled gantry robot with
a downward-pointing video camera. They showed that simply by keeping the
velocity of the image of the ground constant they could bring the robot to a
standstill at touchdown. Their findings will be published in an upcoming issue
of Biological Cybernetics.
A system like this would be ideal for landing micro air vehicles (MAVs), says
team member Javaan Chahl. The US military, which helped fund the research, is
developing surveillance MAVs with wingspans as small as a few centimetres.
Soldiers could carry these tiny planes into battle, and send them out to perform
tasks such as reconnoitring nearby buildings
(快猫短视频, 5 April 1997, p 36).
The bees鈥� landing technique requires very little computing power. Cameras
already on board the plane could be used in conjunction with a tiny computer,
says Chahl. Srinivasan鈥檚 team is now building a larger pilotless aircraft with a
bee-like visual system that it will use to guide itself in to land.