Ground Pattern Performance of
the Marsh Turbo Thrush

The Wildland Fire Chemical Systems (WFCS) program tests a variety of fixed- and rotary-wing tankers to determine the parameters for optimal ground pattern coverage over a wide range of fuel and fire conditions. The Marsh Turbo Thrush, owned and operated by the Marsh Aviation Company, is an aircraft designed for use as an agricultural sprayer. It is converted for fire suppression by adding a fire door.

MTDC tested the Marsh Turbo Thrush (Figure 1) with a series of drops over an array of plastic bowls much like Cool Whip containers. The quantity of material in each bowl was measured and the data were used to determine the drop pattern.

Figure 1—View of the gate of the Marsh Turbo Thrush.

The standard fire door was replaced by the Marsh 60/40 fire door. The Marsh 60/40 door is designed with two adjacent doors, one opening 40 percent and the other opening 60 percent of the available area. The system provides three flow rates by opening either the 40 percent door, the 60 percent door, or both. The doors are hydraulically controlled. The aircraft's tank holds 380 gallons. Tests were conducted at air speeds from 80 to 86 knots (92 to 99 mph) and drop heights from 24 to 31 feet from the bottom of the door to ground. The drops were made with three different materials: water, foam, and gum-thickened retardant.