0057-2849-MTDC
September 2000
5100/5700
Airtanker
United States Department of Agriculture
Forest Service
Drop Guides
Technology & Development Program
Ground Pattern Performance of
the Aero Union SP-2H
Paul Solarz, Project Leader, and Cammie Jordan, Project Assistant
T
he 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 Aero Union
Corporation SP-2H is one of a family of
airtankers that are used for initial attack
fire suppression and defined as a Type II
airtanker.
The Aero Union SP-2H constant flow
system contains a single compartment that
is certified by the Interagency Airtanker
Board to carry 2000 gallons. The tank
contains bulkhead dividers to minimize
fluid movement from front to back and to
provide structural integrity. Two opposing
doors, which run the length of the tank, are
used to control the fluid flow. The doors
are controlled by a servo controller with a
MOOG valve, which interprets fluid
height information from sensors in the
forward and aft compartments and adjusts
the door opening to produce a constant rate
of flow from the tank. The flow rate and
volume for any individual drop can be
adjusted to meet Interagency Airtanker Board
criteria by programming the controller. Any
fraction of the load can be released by
holding down the drop button. When the
operator lets go of the button, the doors will
close. Tests included airspeeds from 112 to
134 knots (90 to 100 mph) and drop heights
from 112 to 315 feet (measured from the
bottom of the tank to ground). The drops
were made with water and with gumthickened retardant.
The Missoula Technology and
Development Center (MTDC) tested the
Aero Union SP-2H (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
110%
4.875 x 2.137
Original Photo 5 x3.5
Print to Outside Edge of Borders
No Not Print Borders
Figure 1 —The constant flow tank for the AeroUnion SP-2H.
Flow rate, drop height, volume, and
airspeed affect the drop pattern.
Increasing drop height gradually widens
the drop while decreasing the coverage
levels. This effect is modified by the
ambient wind. Increasing windspeed
widens the drop, decreasing coverage
levels. Increasing airspeed increases the
line length while reducing the coverage
level. Because this airtanker has variable
volume and flow rates, it can use specific
coverage levels needed for accurate
drops. Figures 2 and 3 show the effect of
using water and gum-thickened retardant
at a coverage level setting of 3. These
drops were made at speeds of 125 and
126 knots (144 and 145 mph) and drop
heights of 162 and 164 feet.
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; E-mail: glovellette@fs.fed.us; Lotus Notes: Greg Lovellette/WO/USDAFS
1
Table 1—Retardant coverage levels needed for specific fuel models.
Fuel Model
National Fire
Danger Rating System
(NFDRS)
Fire Behavior
Coverage Level
(gal/100 sq. ft)
A,L,S
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
B,O
4
J
12
I
13
The proper amount of fire-retarding
material (expressed as coverage levels in
gallons per 100 square feet) differs
depending on the fuel model. Table 1
shows the coverage needed for specific
1
Description
Annual and perennial
western grasses, tundra
Conifer with grass
2
3
Shortneedle closed
conifer; summer
hardwood
Intermediate brush (green)
Light slash
4
Shortneedle conifer
(heavy dead litter)
Southern rough
6
Intermediate brush
(cured), Alaska black
spruce
California mixed
chaparral, high pocosin
Greater than 6
Medium slash
Heavy slash
fuel models using both the National Fire
Danger Rating System (NFDRS) and the
Fire Behavior Fuel Models.
The results of drop tests allow managers
to estimate the airspeed, drop height, and
Table 2–Water tests producing the longest line at various flow rate settings using the
constant flow tank.
Coverage Level
(gal/100 sq. ft)
Flow Rate
(gal/sec)
Coverage Level
(setting)
Drop Length
(feet)
0.5
1.0
2.0
3.0
4.0
6.0
8.0
10.0
234
225
225
607
607
476
476
-
2
2
2
6
6
4
4
-
2244
1970
870
372
114
13
1
-
Table 3–Gum-thickened retardant tests producing the longest line at various flow rate
settings using the constant flow tank.
Coverage Level
(gal/100 sq. ft)
Flow Rate
(gal/sec)
Coverage Level
(setting)
Drop Length
(feet)
0.5
1.0
2.0
3.0
4.0
6.0
8.0
10.0
221
221
353
476
585
607
607
607
2
2
3
4
5
6
6
6
1816
1478
1184
755
545
273
74
28
flow rate that provide the retardant
coverage level required for a given fire
intensity represented by the applicable
fuel model. Table 2 or Figure 4 can be
used to estimate the flow rate of a water
drop for the longest line of the desired
coverage level. Table 3 or Figure 5 can
be used to estimate the flow rate of a
gum-thickened retardant drop for the
longest line of the desired coverage level.
2
Aero Union SP-2H With Constant Flow Tank
200
200
100
1.0
Width (feet)
Coverage Level Setting 3 Using Water
1.0
1.0
1.0
100
1.0
0.5
0
0
0
200
400
600
800
1000
Length (feet)
1200
1400
1600
1800
Figure 2–Drop pattern characteristics for the Aero Union SP-2H using water with a coverage level setting of 3, an airspeed of 85 knots (98 mph), and a drop height of 46 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 graphs predict line length (in feet) as a
function of flow rate. The tables are
constructed by selecting the drop
producing the longest line (on the ground)
at each coverage level. Either the graphs or
tables may be used to estimate the flow
rate 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 flow rate, 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 flow rate can be found.
Use the graph for the material dropped
(water or gum-thickened retardant) to
find the flow rate that produces the
longest line for the desired coverage
level. The same information can be
found in the appropriate drop table.
3
Aero Union SP-2H With Constant Flow Tank
Width (feet)
Coverage Level Setting 3 Using Gum-Thickened Retardant
200
200
33..00 2
.0
100
2.0
1.0
0.5
2.0
3.0 2.0
3.0
3.0
100
0
0
0
200
400
600
800
1000
1200
1400
1600
1800
Length (feet)
Figure 3–Drop pattern characteristics for the Aero Union SP-2H using gum-thickened retardant with a coverage level setting of 3, an airspeed of 85 knots (98 mph), and a drop height of 90 feet. The
contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.
For example, if a fire is burning in
NFDRS Fuel Model F (Fire Behavior
Model 5), represented by intermediate
brush (green), a coverage level of 3 is
required (Table 1). The graph for
gum-thickened retardant shows that for
coverage level 3, a coverage level
setting of 4 produces the longest line
(755 feet).
The ground drop characteristics for the
Aero Union SP-2H were derived
through controlled drop test
procedures on flat ground (Figure 6).
thickened retardant. Actual coverage
may vary depending on terrain, wind,
weather, and pilot proficiency.
This information is to serve only as a
guide to help field personnel determine
the proper airspeed, drop height, and
flow rate for delivering water or gum-
4
Effect of Flow Rate on Length of Line at Various Coverage Levels
Effect of Flow Rate on Length of Line at Various Coverage Levels
Aero Union SP-2H With Constant Flow Tank Using Gum-Thickened Retardant
Aero Union SP-2H With Constant Flow Tank Using Water
2000
2000
CL = 0.5
CL = 1
CL = 2
CL = 3
CL = 4
1800
1600
1800
1600
CL = Coverage Level
1400
CL = 0.5
CL = 1
CL = 2
CL = 3
CL = 4
CL = 6
1400
Line Length (feet)
Line Length (feet)
CL = Coverage Level
1200
1000
800
1200
1000
800
600
600
400
400
200
200
0
200
310
420
530
640
750
Average Flow Rate (gal/sec)
Figure 4–Use this graph to estimate the flow rate needed to produce the longest line of water at
various coverage levels.
0
200
310
420
530
640
750
Average Flow Rate ( gal/sec)
Figure 5–Use this graph to estimate the flow rate needed to produce the longest line of gumthickened retardant at various coverage levels.
5
Figure 8
83%
4.875 x 2.914
Original Photo 5 7/8 x 4
Print to Outside Edge of Borders
No Not Print Borders
Figure 6–Drop test of the Aero Union SP-2H.
About the Authors
Cammie Jordan is a Project Assistant
for the Wildland Fire Chemical Systems
Program at MTDC. She is currently
enrolled at the University pursuing a
bachelorís degree in Elementary
Education with a Special Education
Endorsement. She has worked for
MTDC in Missoula since 1998.
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) 329-3719
Internet: wo_mtdc_pubs@fs.fed.us
For additional technical information,
contact Greg Lovellette at the address
above.
Phone: (406) 329-4815
Fax: (406) 329-4811
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.
Paul Solarz is Program Leader for the
Wildland Fire Chemical Systems Group.
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
Lotus Notes:Greg Lovellette/USDAFS/WO
Internet: glovellette@fs.fed.us
An electronic copy of this document is
available on the Forest Service s
FSWeb Intranet at:
http://fsweb.mtdc.wo.fs.fed.us
6