Ground Pattern Performance of the
Sims Rainmaker 2000-gallon Helibucket

The Wildland Fire Chemical Systems (WFCS) program tests a variety of fixed- and rotary-wing tankers to determine the parameters for optimal coverage over a wide range of fuel and fire conditions. The Sims Rainmaker 2000- gallon Helibucket Model SF 2000 is one of a family of helibuckets designed for use with a variety of helicopters. The Sims 2000-gallon helibucket is designed for use with Type I helicopters.

MTDC tested the Sims 2000-gallon helibucket (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—Sims 2000-gallon helibucket with the Sikorsky
CH-54 "Tarhe." The civilian version is the S-64 "Skycrane."

The helibucket is constructed of fiberglass. The door opening is actuated by a electric hydraulic system using 28 volts dc aircraft power. A series of holes with removable covers are arranged around the upper part of the bucket. These holes, when uncovered, allow for reduced loads. The drop tests were made with a volume of 1750 gallons.

The standard Sims 2000-gallon helibucket and a modified version were tested. The modified version had a door that opened faster, allowing a higher flow rate. Tests included air speeds from 19 to 98 knots (22 to 113 mph) and drop heights from 15 to 148 feet (measured from the bottom of the bucket to ground). The drops were made with three different materials: water, foam, and gum-thickened retardant.

Drop height and drop speed both have an effect on the drop pattern. Increasing drop height gradually widens the drop at the expense of higher coverage levels. This effect is modified by the ambient wind. Increasing wind speed widens the drop and decreases coverage levels. Drop speed has a much greater effect on the drop pattern. Figure 2 and Figure 3 show the effect of increasing the drop speed from 25 to 86 knots (29 to 99 mph). Drop heights are nearly identical, ranging from 106 to 119 feet.

Figure 2—Drop pattern characteristics for the Sims 2000-gallon helibucket
with a drop speed of 25 knots and a drop height of 106 feet. The contour
lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8 and 10
gallons per 100 square feet.

Figure 3—Drop pattern characteristics for the Sims 2000-gallon helibucket
with a drop speed of 86 knots and a drop height of 119 feet. The contour
lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8 and 10
gallons per 100 square feet.