0157-2807-MTDC
January 2001
5100/5700
Airtanker
United States Department of Agriculture
Forest Service
Drop Guides
Technology & Development Program
Ground Pattern Performance of the California Department of Forestry Bell S205 and
National Guard UH-1 Helicopters With the 240-Gallon SEI Industries Bambi Helibucket
Paul Solarz, Program Leader, and Cammie Jordan, Project Assistant
T
he Wildland Fire Chemical
Systems (WFCS) Program tests
a variety of fixed- and rotarywing airtankers to determine the
parameters for optimal ground-pattern
coverage over a wide range of fuel
and fire conditions. The CDF Bell
S205 helicopter (operated by the
California Department of Forestry and
Fire Protection) and the National
Guard Bell UH-1 Iroquois Huey
(operated by the National Guard) were
tested with the 240-gallon SEI
Industries Bambi helibucket. Both
helicopters (referred to as the CDF
Bell S205 and National Guard UH-1
with 240-gallon Bambi helibucket)
belong to a family of helicopters
designed for fire suppression with the
use of a helibucket. They qualified as
Type 2 helicopters.
The Bambi helibucket is constructed
of a heavy, coated fabric mounted to a
collapsible frame (figure 1). The dump
valve (16 inches in diameter) is
electrically actuated from the
helicopter using 28 volts dc aircraft
power. The helibucket’s maximum
volume is 240 gallons with a
maximum fill height of 38 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 CDF
Bell S205 and National Guard UH-1
with 240-gallon Bambi helibucket
using 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—The CDF Bell S205 with 240-gallon Bambi helibucket.
Tests included airspeeds from 18 to 84
knots (21 to 97 miles per hour) and
drop heights from 27 to 86 feet from
the bottom of the tank to the ground.
The drops were made with three
different materials: water, foam, and
gum-thickened retardant.
For additional information, contact: Greg Lovellette, Project Leader; Missoula Technology & Development Center; 5785 Highway 10 West; Missoula, MT 59808. Phone: 406–329–4815; Fax: 406–
329–4811; Lotus Notes: Greg LovelletteWO/USDAFS; E-mail: glovellette@fs.fed.us
1
Width (feet)
150
Water with airspeed of 38 knots
4.0
6.0 6.0 3.0
75
4.0
2.0
0.51.0
75
0
0
0
125
250
Line Length (feet)
375
500
Figure 2—Drop pattern characteristics for the CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using water at an airspeed of 38 knots
(44 miles per hour) and a drop height of 42 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.
150
CDF Bell S205 and National Guard UH-1 With 240-Gallon Bambi Helibucket
Foam with airspeed of 37 knots
3.0
8.0
0.0 8.100.0
1
6.0
4.0
75
1.
2.00 3.0
4.0
150
75
0.5
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.
CDF Bell S205 and National Guard UH-1 With 240-Gallon Bambi Helibucket
150
Width (feet)
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 material dropped with
airspeeds of 37 to 40 knots (43 to 46
miles per hour) and drop heights
ranging from 38 to 50 feet using
water, foam, and gum-thickened
retardant.
0
0
0
125
250
Line Length (feet)
375
500
Figure 3—Drop pattern characteristics for the CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using foam at an airspeed of 37 knots
(43 miles per hour) and a drop height of 38 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.
2
CDF Bell S205 and National Guard UH-1 With 240-Gallon Bambi Helibucket
Gum-thickened retardant with airspeed of 40 knots
Width (feet)
150
150
75
75
0.5
4.0 3. 1.0
0 2.0
8.10
6.00.0
0
0
0
125
250
Line Length (feet)
375
500
Figure 4—Drop pattern characteristics for the CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using gum-thickened retardant at an
airspeed of 40 knots (46 miles per hour) and a drop height of 50 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 results of drop tests allow
managers to estimate the length of line
a specific airtanker produces at
various coverage levels. Table 2 or
figure 5 can be used to determine the
airspeed required to obtain the longest
line of water at each coverage level.
Table 3 or figure 6 can be used to
determine the airspeed required to
obtain the longest line of foam at each
coverage level. Table 4 or figure 7 can
be used to determine the airspeed
required to obtain the longest line of
gum-thickened retardant at each
coverage level.
The line-length graphs predict line
length (in feet) as a function of
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
airspeed required to produce the
longest line for a given coverage
level. The tables show an ideal case,
while the graphs represent an average.
To select the proper airspeed, first use
table 1 to determine the coverage
level required by the NFDRS or Fire
Behavior Fuel Models. 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
airspeed can be found. Use the table
for the material dropped (water, foam,
or gum-thickened retardant) to find
the airspeed that produces 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 K (Fire Behavior
Model 11), represented by light
slash, table 1 shows that a coverage
level of 3 is required. The table for
water (table 2) shows that for
coverage level 3, an airspeed of about
38 knots produces the longest line
(128 feet).
The grounds drop characteristics for
the CDF Bell S205 and National Guard
UH-1 with 240-gallon Bambi
helibucket were derived through
controlled test drop procedures on flat
3
Table 1—The retardant coverage needed for specific fuel types.
Table 2—Water tests producing the longest line at various coverage levels.
Fuel Model
National Fire
Danger Rating System
(NFDRS)
Fire Behavior
Coverage Level
(gal/100 ft2)
A, L, S
1
1
C
2
H, R
8
E, P, U
9
Longneedle conifer; fall
hardwood
T
2
Sagebrush with grass
N
3
Sawgrass
F
5
K
11
G
10
O
4
F, Q
6
12
I
13
Airspeed
(knots)
0.5
1
2
3
4
6
8
10
288
262
173
128
117
68
64
59
76
76
44
38
38
18
18
18
Description
Annual and perennial
western grasses, tundra
Conifer with grass
2
3
Shortneedle closed
conifer; summer
hardwood
Effect of Airspeed on the Length of Line at Various Coverage Levels
CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using water
Intermediate brush (green)
CL = 0.5
CL = 1
CL = 2
CL = 3
CL = 4
CL = 6
CL = 8
CL = 10
Light slash
4
300
Shortneedle conifer
(heavy dead litter)
Southern rough
6
4
J
Line Length
(feet)
Intermediate brush
(cured), Alaska black
spruce
California mixed
chaparral, high pocosin
Greater than 6
Medium slash
Heavy slash
250
CL = Coverage Level
Line Length (feet)
B, O
Coverage Level
(gal/100 ft2)
200
150
100
50
ground (figure 8). 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 gumthickened retardant. Actual coverage
may vary depending on terrain, wind,
weather, and pilot proficiency.
0
20
35
50
65
80
Airspeed (knots)
Figure 5—Use this graph to estimate the drop height needed to provide the longest line of water at
various coverage levels.
4
Table 3—Foam tests producing the longest line at various coverage levels.
Table 4—Gum-thickened retardant tests producing the longest line at various coverage levels.
Coverage Level
(gal/100 ft2)
Line Length
(feet)
Airspeed
(knots)
Coverage Level
(gal/100 ft2)
Line Length
(feet)
Airspeed
(knots)
0.5
1
2
3
4
6
8
10
333
285
180
125
117
83
61
48
78
78
78
37
37
37
37
37
0.5
1
2
3
4
6
8
10
292
253
220
115
94
68
42
19
82
82
82
55
38
38
25
25
Effect of Airspeed on the Length of Line at Various Coverage Levels
Effect of Airspeed on the Length of Line at Various Coverage Levels
CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using foam
CDF Bell S205 and National Guard UH-1 with 240-gallon Bambi helibucket using gum-thickened retardant
CL = 0.5
CL = 1
CL = 2
CL = 3
CL = 4
CL = 6
CL = 8
CL = 10
300
CL = 0.5
CL = 1
CL = 2
CL = 3
CL = 4
CL = 6
CL = 8
CL = 10
300
250
CL = Coverage Level
Line Length (feet)
Line Length (feet)
CL = Coverage Level
200
200
150
100
100
50
0
0
20
35
50
65
80
Airspeed (knots)
Figure 6—Use this graph to estimate the drop height needed to provide the longest line of foam at various
coverage levels.
20
35
50
65
80
Airspeed (knots)
Figure 7—Use this graph to estimate the drop height needed to provide the longest line of gum-thickened
retardant at various coverage levels.
5
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.
For additional technical information,
contact Greg Lovellette at the Center’s
address.
Phone: 406–329–4815
Fax: 406–329–4811
Lotus Notes: Greg Lovellette/WO/
USDAFS
E-mail: glovellette@fs.fed.us
Electronic copies of MTDC’s
documents are available on the
Forest Service’s FSWeb Intranet at:
http://fsweb.mtdc.wo.fs.fed.us
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
Figure 8—Drop test of the CDF Bell S205 with 240-gallon Bambi helibucket using gum-thickened
retardant.
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, D.C. 20250-9410, or call (202)
720–5964 (voice and TDD). USDA is an equal opportunity provider and
employer.
6