Ground Pattern Performance of the Griffith Big Dipper Model 100 Helibucket, 0057-2839-MTDC

Image showing drop pattern characteristics at an airspeed of 47 knots and drop height of 42 feet.
Figure 3—Drop pattern characteristics for the Griffith 100-gallon helibucket
with an air speed of 47 knots 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.

Image showing drop pattern characteristics at an airspeed of 60 knots and drop height of 64 feet.
Figure 4—Drop pattern characteristics for the Griffith 100-gallon helibucket
with an air speed of 60 knots and a drop height of 64 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 gum-thickened retardant (expressed as coverage levels 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 the Fire Behavior Fuel Model.

Table 1—Retardant coverage levels needed for specific fuel models.

Fuel Model		Coverage Level (gal/100 sq. ft)	Description
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 air speed and height that provide the retardant coverage level required for the fire intensity represented by the appropriate fuel model. Table 2 or Figure 5 can be used to estimate the air speed of a water drop required to obtain the longest line of the desired coverage level. Table 3 or Figure 6 can be used to estimate the air speed of a foam drop to obtain the longest line of the desired coverage level. Table 4 or Figure 7 can be used to estimate the air speed of a gum-thickened retardant drop to obtain the longest line of the desired coverage level.

Table 2—Water tests producing the longest line at various coverage levels.

Coverage Level (gal/100 sq. ft)	Airspeed (knots)	Line Length (feet)
0.5	56	239
1	40	157
2	36	51
3	0	0
4	0	0
6	0	0
8	0	0
10	0	0


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