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Ground Pattern Performance of the National Guard Black Hawk Helicopter With the 660-Gallon SEI Industries Bambi Helibucket


Paul Solarz, Program Leader, and Cammie Jordan, Project Assistant

The Wildland Fire Chemical Systems (WFCS) Program tests a variety of fixed- and rotary-wing airtankers to determine the parameters for optimal ground-pattern coverage over a wide range of fuel and fire conditions. The National Guard Sikorsky S-70 (military version is the UH-60) Black Hawk helicopter with the 660-gallon SEI Industries Bambi helibucket (referred to as the National Guard Black Hawk with 660-gallon Bambi helibucket) is one of a family of helicopters designed for fire suppression with a helibucket. It is qualified as a Type 1 helicopter (figure 1).

Black Hawk
Figure 1-The National Guard Black Hawk with 660-gallon Bambi helibucket.

The helibucket is constructed of a heavy, coated fabric mounted to a collapsible frame. The dump valve (20 inches in diameter) is electrically actuated from the helicopter using 28 volts dc aircraft power. The bucket's maximum volume is 660 gallons with a maximum fill height of 53 inches. The volume of a given drop can be controlled by the rate at which the helibucket is lifted from the water (faster lift produces more volume) or by adjusting a cinch strap inside the helibucket.

The Missoula Technology and Development Center tested the National Guard Black Hawk with 660-gallon Bambi helibucket 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.

Tests included airspeeds from 40 to 88 knots (46 to 101 miles per hour) and drop heights from 73 to 170 feet from the bottom of the tank to the ground. The drops were made with three different materials: water, foam, and gum-thickened retardant.

Flow rate, drop height, and airspeed all affect the drop pattern. Because this type of helicopter is normally used over a narrow range of heights and speeds and because this system produces a single flow rate, information about an average drop is presented. Figures 2, 3, and 4 show the effect of drop height while maintaining airspeeds between 57 to 59 knots (65 to 68 miles per hour) with drop heights ranging from 83 to 128 feet while using gum-thickened retardant. Figures 5, 6, and 7 show the effect of increasing airspeed from 42 to 81 knots (48 to 93 miles per hour) while maintaining the drop height between 138 and 149 feet.

Chart showing the drop pattern of retardant at an airspeed of 57 knots
Figure 2-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket using gum-thickened retardant at an airspeed of 57 knots (66 miles per hour) and a drop height of 83 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

Chart showing the drop pattern of retardant at an airspeed of 56 knots and at a height of 117 feet
Figure 3-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket using gum-thickened retardant at an airspeed of 56 knots (64 miles per hour) and a drop height of 117 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

Chart showing the drop pattern of retardant at an airspeed of 59 knots and at a height of 128 feet
Figure 4-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket using gum-thickened retardant at an airspeed of 59 knots (68 miles per hour) and a drop height of 128 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

Chart showing the drop pattern of water at an airspeed of 42 knots and at a height of 138 feet
Figure 5-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket using water at an airspeed of 42 knots (48 miles per hour) and a drop height of 138 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

Chart showing the drop pattern of water at an airspeed of 50 knots and at a height of 143 feet
Figure 6-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket using water at an airspeed of 50 knots (58 miles per hour) and a drop height of 143 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

Chart showing the drop pattern of water at an airspeed of 81 knots and at a height of 149 feet
Figure 7-Drop pattern characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucketusing water at an airspeed of 81 knots (93 miles per hour) and a drop height of 149 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

The proper amount of fire-retarding materials to be applied (expressed as coverage level in gallons per 100 square feet) differs depending on the fuel model. Table 1 shows the coverage needed for specific fuel models using both the National Fire Danger Rating System (NFDRS) and Fire Behavior Fuel Model descriptions.

Table 1-The retardant coverage needed for specific fuel types.
Fuel Model    
National Fire Danger Rating System (NFDRS) Fire Behavior Coverage Level (gal/100 sq. ft) Description
A, L, S 1 1 Annual and perennial
western grasses, tundra
C 2   Conifer with grass
H, R 8 2 Shortneedle closed conifer;
summer hardwood
E, P, U 9   Longneedle conifer;
fall hardwood
T 2   Sagebrush with grass
N 3   Sawgrass
F 5 3 Intermediate brush (green)
K 11   Light slash
G 10 4 Shortneedle conifer
(heavy dead litter)
O 4   Southern rough
F, Q 6 6 Intermediate brush (cured),
Alaska black spruce
B, O 4   California mixed chaparral,
high pocosin
J 12 Greater than 6 Medium slash
I 13   Heavy slash

The results of drop tests allow managers to estimate the length of line a specific helicopter with a particular bucket produces at various coverage levels. Table 2 or figures 8 and 9 can be used to determine the drop height and airspeed of a water drop required to obtain the longest line at each coverage level. Table 3 or figures 10 and 11 can be used to determine the drop height and airspeed of a foam drop required to obtain the longest line at each coverage level. Table 4 or figures 12 and 13 can be used to determine the drop height and airspeed of a gum-thickened retardant drop required to obtain the longest line at each coverage level.

Table 2-Water tests producing the longest line at various coverage levels.
Coverage Level (gal/100 sq. ft) Line Length
(feet)		 Drop Height
(feet)		 Airspeed
(knots)
0.5 528 111 84
1 502 111 84
2 385 111 84
3 350 92 60
4 285 102 46
6 216 78 40
8 202 78 40
10 176 78 40

Chart showing the effect of drop height on length of line at various coverage levels for water
Figure 8-Use this graph to estimate the drop height needed to provide the longest line of water at various coverage levels.

Chart showing the effect of airspeed on the length of line at various coverage levels for water
Figure 9-Use this graph to estimate the airspeed needed to provide the longest line of water at various coverage levels.

Table 3-Foam tests producing the longest line at various coverage levels.
Coverage Level (gal/100 sq. ft) Line Length
(feet)		 Drop Height
(feet)		 Airspeed
(knots)
0.5 533 118 80
1 447 107 82
2 333 92 61
3 295 92 61
4 231 92 61
6 176 92 41
8 105 92 41
10 32 92 41

Chart showing the effect of drop height on length of line at various coverage levels for foam
Figure 10-Use this graph to estimate the drop height needed to provide the longest line of foam at various coverage levels.

Chart showing the effect of airspeed on the length of line at various coverage levels for foam
Figure 11-Use this graph to estimate the airspeed needed to provide the longest line of water at various coverage levels.

Table 4-Gum-thickened retardant tests producing the longest line at various coverage levels.
Coverage Level (gal/100 sq. ft) Line Length
(feet)		 Drop Height
(feet)		 Airspeed
(knots)
0.5 487 131 79
1 462 83 57
2 399 83 57
3 363 83 57
4 313 83 57
6 231 86 48
8 189 86 48
10 123 86 48

Chart showing the effect of drop height on length of line at various coverage levels for retardant
Figure 12-Use this graph to estimate the drop height needed to provide the longest line of gum-thickened retardant at various coverage levels.

Chart showing the effect of airspeed on the length of line at various coverage levels for retardant
Figure 13-Use this graph to estimate the airspeed needed to provide the longest line of gum-thickened retardant at various coverage levels.

The line-length graphs predict line length (in feet) as a function of drop height (in feet) and airspeed (in knots). The tables are constructed by selecting the drop producing the longest line at each coverage level. Either the graphs or tables may be used to estimate the drop height and airspeed required to produce the longest line for a given coverage level. The tables show an ideal case, while the graphs represent an average.

National Guard Black Hawk dropping water
Figure 14-Drop test of the National Guard Black Hawk with 660-gallon Bambi helibucket using water.
To select the proper drop height or airspeed, first use table 1 to determine the coverage level required by the NFDRS or Fire Behavior Fuel Model. The coverage levels in table 1 represent the coverage level required for average fire intensity for each fuel model. The required coverage level can be adjusted up or down depending on the actual fire intensity. Once the required coverage level is determined, the drop height and airspeed can be found. Use the table for the material dropped (water, foam, or gum-thickened retardant) to find the drop height and airspeed that produce the longest line for the desired coverage level. The same information can be found in the appropriate drop table.

For example, if a fire is burning in NFDRS Fuel Model H, R (Fire Behavior Model 8), represented by shortneedle closed conifer or summer hardwood, table 1 shows that a coverage level of 2 is required. The table for gum-thickened retardant (table 4) shows that for coverage level 2, a drop height of approximately 83 feet and airspeed of 57 knots (66 miles per hour) produces the longest line (399 feet).

The ground drop characteristics for the National Guard Black Hawk with 660-gallon Bambi helibucket were derived through controlled test drop procedures on flat ground (figure 14). This information is to serve only as a guide in assisting field personnel to determine the proper drop height and airspeed for delivering water, foam, or gum-thickened retardant. Actual coverage may vary depending on terrain, wind, weather, and pilot proficiency.

About the Authors

Cammie Jordan is a Project Assistant for the Wildland Fire Chemical Systems Program at MTDC. She is an elementary education student at the University of Montana and has worked for MTDC since 1998.

Paul Solarz is Program Leader for the Wildland Fire Chemical Systems Group. He received his bachelor's degree from Eastern Oregon State College in 1986. Paul has worked in Aviation and Fire Management since 1973, serving at seven Ranger Districts and in two Forest Supervisor's offices. He has an extensive operational background in fire, fuels, and aviation.

Additional single copies of this document may be ordered from:

USDA Forest Service
Missoula Technology and Development Center
5785 Highway 10 West
Missoula, MT 59808
Phone: 406-329-3978
Fax: 406-329-4811
E-mail: wo_mtdc_pubs@fs.fed.us

For additional Information contact:

Greg Lovellette, Project Leader
Missoula Technology & Development Center
5785 Highway 10 West
Missoula, MT 59808
Phone: 406-329-4719
Fax: 406-329-4811
E-mail: glovellette@fs.fed.us
Lotus Notes: Greg Lovellette/WO/USDAFS

The Forest Service, United States Department of Agriculture, has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies, and is not responsible for the interpretation or use of this information by anyone except its own employees. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader, and does not constitute an endorsement by the Department of any product or service to the exclusion of others that may be suitable. The United States Department of Agriculture (USDA), prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should phone USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write: USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, DC 20250-9410, or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

This page last modified June 14, 2002

Visitor since June 14, 2002