杏吧原创

AS FIREFIGHTERS struggled to defeat the wildfires sweeping across Colorado last week, plans were emerging for a new, more efficient way of fighting such fires from the air.

Drop-planes and helicopters with their small water bombs can only cover small areas at each pass because their water supply is limited. They also have to fly dangerously low to have any effect at all, as water dropped from high altitude evaporates before it can get to the flames.

Now Ralph Pope and his team at Wetzone Engineering, a company based in Huntingdon Beach, California, think they have a better idea. Water will rain down continuously from gigantic airships, which will be kept topped up by passing drop-planes or helicopters. 鈥淚t鈥檒l be like having a non-stop artificial rainstorm,鈥� says Pope.

They suggest using 300-metre-long propeller-powered airships carrying just under one million litres of water and flying high above the flames. From there, adjustable valves on the underside of the balloon鈥攎uch like large shower heads鈥攚ill pump out a staggering 200,000 litres an hour over a large area of the fire. They could also have a few water cannon that can be directed over particularly persistent hot spots.

Currently, the largest drop-planes used in Colorado are converted Hercules military transporters that can carry up to 13,000 litres on a single trip, says Ron Meyer, firefighting aviation manager for Colorado鈥檚 Rocky Mountain area. Helicopters can only carry up to 600 litres. But they could still be used to replenish the airship鈥檚 water supply via an enormous catch basin on the top (see Graphic).

With a million litres of water in its tank, you would expect it to take some lifting to get the airship off the ground. But Thomas Gagliano, chief scientist of Wetzone, says one cubic metre of helium can lift over a kilogram of payload. Which means that roughly a million cubic metres of helium is needed to lift a million litres of water. As vast as this might seem, heavy lifting airship companies such as SkyCat already have craft capable of lifting such loads.

Meyer is intrigued by Wetzone鈥檚 idea but warns that wind might be a problem for airships. 鈥淭hese fires can be so big they create their own weather,鈥� he explains. 鈥淲e routinely shut down aircraft operations because of wind and turbulence from fires.鈥�

Gagliano says their airships would get round these conditions by moving to higher altitudes, typically 1200 metres. 鈥淎t higher elevations we will change the density of the rain,鈥� he says, ensuring that the water droplets from the 鈥渟hower head鈥� are large enough to be effective by the time they reach the fire.

Wetzone has another trick up its sleeve. 鈥淎fter the fire is out, we then have a device that will reseed the forest with millions of seedlings,鈥� says Pope. He envisages the crew dropping pouches of soil and fertiliser from the airship then using the elaborate firefighting equipment to water them. 鈥淲hen released from that altitude they penetrate the ground and [roots] sprout out.鈥�

But it will be at least three years before these airships are out fighting fires, says Gagliano. They are working on prototypes but the economics of running airship fleets are challenging to say the least. But the losses incurred in wildfires are pretty challenging, too. Every year, says Gagliano, the annual bill in the US for wildfire losses is around $2 billion. And that figure does not include the cost of fighting the fires themselves.