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."