Keeping grapes warm with ... helicopters?

Spin Echo · Post by **Spin Echo** » 2007-10-18 03:10pm

Cold blast calls for aerial rescue
5:00AM Friday October 19, 2007
By David Eames

While the rest of us were looking forward to a holiday weekend, staff of Auckland's Heletranz joined up to 100 other helicopter pilots providing frost protection for the grapes that will become next year's vintage.

Managing director Tony Monk dispatched two aircraft to Marlborough and expected to have to send them back to the wine region tonight.

The helicopters' heavy blades provide the down draft that keeps delicate vines from freezing - a job sparked by the cold blast that swept up the South Island yesterday and threatens to send a shiver through the North Island today.

Mr Monk said: "If they get one frost, that could kill the whole year's production."

Heletranz is also ready to send helicopters to Hawkes Bay if the cold weather continues up the country.

An excert from an article about the cold weather blowing over the country here. I don't get this. How exactly does the down draft of the helicopter rotors protect the grapes from freezing? Isn't the air just as cold, if not colder up above the helicopter? Are they being had by helicopter pilots?

Post by **Sea Skimmer** » 2007-10-18 03:15pm

Its not a matter of the air being cold, the plants can endure that relatively easily, it’s a matter of moisture directly freezing on the plants, which then pulls out heat much more rapidly thanks to superior conduction. Blowing a lot of air around should be effective at preventing that from happening.

Lord of the Abyss · Post by **Lord of the Abyss** » 2007-10-18 07:54pm

Besides what Sea Skimmer said, the air moderately above the ground is warmer than lower air, usually. Plenty of growers of grapes and other cold intolerant crops use wind machines; towers topped with large fans that blow air downward. Helicopters should work as well, if more expensively.