16:36 12 February 2007
NewScientist.com news service
Tom Simonite
An unpiloted helicopter that will function as an air ambulance on
the highest mountain in the world is being developed in New Zealand.
Tests on the aircraft will begin in April 2007 in the Southern Alps and
around Mount Everest in January 2008.
In
May 2007, the Everest Rescue Trust plans to start building a base at
Namche Bazar, the main town within Sagarmatha National Park, which
covers the southern half of Everest. As well as housing a medical
facility specialising in injuries as such frostbite, the base will be
home to two new 'Alpine Wasp' helicopters, currently being developed by
TGR Helicorp.
The
Alpine Wasp is controlled remotely by a pilot back on the ground using
information provided by onboard cameras and laser ranging sensors. Each
helicopter has six cameras on its fuselage and a total of 10 in its
nose - five looking forwards and five looking down.
"The
pilot sits in a virtual reality environment and could effectively be
considered to be sitting astride the bulbous nose with a wide angle of
view forward and down," explains Trevor Rogers, president of TGR
Helicorp.
Talk to the proboscis
Once
a stranded climber has been located, the Alpine Wasp communicates with
them using an 8.5-metre extendable "proboscis" with a camera and a
small speaker attached to its end. The proboscis also has a Kevlar loop
on the end capable of supporting any injured person.
"The
operator extends the proboscis out to the climber using laser
distancing equipment and, via the speaker, tells them to slip the
Kevlar loop over his head and under his arms," says Rogers.
After
the climber has tightened a simple clamp around themselves, the
helicopter can take off again. The weight of the climber detaches the
loop from the pole and they swing below the craft, before being winched
into a pod that closes behind them and provides oxygen and warmth.
Conventional
helicopters struggle at altitudes above about 4300 m (14,100 ft), at
which point normal engines suffer from a lack of oxygen and blades
experience reduced lift in the rarefied air. The Alpine Wasp will have
extra wide blades to provide more lift and an engine modified to cope
with thinner air, Rogers told New Scientist.
Sound barrier
It
will also spin its rotors at a lower speed than normal. This is to
avoid the rotor blades breaking the sound barrier - which is lower at
high altitudes. This could change the airflow and cause potentially
catastrophic instability.
Peter
Bunniss, a rotor craft researcher at Bristol University, UK, who also
works for helicopter manufacturer AgustaWestland, says the size of the
helicopter's rotors may need to be altered dramatically.
The
proportion of the circle described by a helicopter's blades that is
covered by the blades is known as the "solidity". "It is usually around
3% to 8%," Bunniss says. "I think they'll need two or three times more
than that, so it'll look quite an odd craft."
Having
to spin the blades slower to avoid the reduced speed of sound will also
reduce lift, Bunniss notes: "It's an interesting challenge to take on."
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