The Fire Boss: An Air Tractor for Drenching Fires
By Max Trescott, EAA Sport Aviation technology columnist
February 24, 2011 — Any pilot worth his salt knows of the Air Tractor line of agricultural spraying aircraft. Yet few know of the Fire Boss, a seaplane version of the Air Tractor that can drop 800 gallons of water on a fire before dashing off to a lake or river to scoop up another load of water. Fewer still know of the AT-802U, an Air Tractor equipped with a 50-caliber mini-gun that can serve as an attack aircraft for counter insurgency operations. All are testimonies to the genius of Leland Snow, who passed away earlier this week at the age of 80.
The Fire Boss is an intriguing design that mates an Air Tractor 802 and its 800-gallon spray tank with a set of beefy floats from Wipaire, an aircraft float manufacturer. According to Fire Boss LLC chief pilot Mark Mathisen, the joint engineering project resulted from a dinner meeting between Snow and Wipaire President Bob Wiplinger.
Air Tractor contributed to the project by designing additional reinforcement and float attach points to its AT-802, powered by a 1600-hp PT6 turbine engine. Wipaire modified a set of floats originally designed for the Beaver by adding a 3-inch probe that a pilot can deploy to suck up water. When step taxiing on water at approximately 60 knots, 80 pounds per square inch of water pressure is generated at the probe. That enables the Fire Boss to fill its tank in 10-12 seconds, while traveling less than half a mile across the water’s surface.
When I met with Mark Mathisen this week, he was in Bartow, Florida, giving initial training to new pilots who will be flying the plane for the Canadian fire season that starts March 1. Of the pilots training, half come from an air attack firefighting background. The other half are experienced seaplane pilots.
Mathisen describes a demanding environment for pilots. It is critical that they have the landing gear in the correct position - down for runways and up for the water - and they need to deal with aircraft pitch movements associated with deploying the water scoop.
As the scoop enters the water, the aircraft pitches forward and pilots need to counter by pulling back on the stick. How much they need to pull back depends upon the aircraft’s ground speed and the condition of the water. In choppy water, the probe is not continuously in the water and pilots need only pull back a few inches. For glassy water, full aft movement of the stick is necessary.
When landing on water, the Fire Boss initially weighs 11,000 pounds. On takeoff with full tanks, it weighs 16,000 pounds. However it must remain on the step when loading its tank. If it gets too slow and comes off the step, it could sink, as the maximum permissible weight when off the step is 11,500 pounds.
To date, 55 of the planes have been sold, mostly to Australia, Europe, and Canada. Three of the aircraft are under contract to fight fires in the U.S. Look for more of these innovative aircraft to be deployed at firebases everywhere.
Fire Boss LLC is a division of Wipaire Inc.