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Ground Pattern Performance of the Airspray Electra L-188with Aero Union Constant Flow Tank

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

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

Figure 183.4%

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0057-2851-MTDCSeptember 2000

5100/5700

United States Department of Agriculture

Forest Service

Technology & Development Program

Drop Guides

he Wildland Fire ChemicalSystems (WFCS) program testsa variety of fixed- and rotary-

wing tankers to determine the parametersfor optimal coverage over a wide rangeof fuel and fire conditions. The AirsprayElectra L-188 (similar to the Orion P-3A), with an Aero Union Corporationtank, is a Type I airtanker used for firesuppression.

The Airspray Electra L-188 contains aRADS II constant flow tank approved bythe Interagency Airtanker Board (IAB) tohold 3000 gallons. The constant flowsystem distributes the retardantuniformly, minimizing the possibility ofthe fire burning through the appliedretardant. The tank has a singlecompartment with bulkhead dividers tominimize fluid movement forward andbackward and to provide structural

Airtanker

Figure 1 — The Constant flow tank of the Airspray Electra L-188.

integrity. Two opposing doors, which runthe length of the tank, are used to controlthe fluid flow. The tank doors aremechanically linked. They open from thecenter and operate in unison. The doorsoperate with full or partial tank fluidlevels. The controller senses the level ofretardant and constantly adjusts the dooropening to maintain selected flow rates.Flow rate is controlled by varying theangle of the door opening. The volumereleased depends on how long the doorsare opened. The computerized digitalcontrol logic used to operate the doorsenables the pilot to control coveragelevel and quantity, producing the desireddrop pattern. Drop tests were conductedat airspeeds from 111 to 144 knots (128to 166 mph) and drop heights from 133to 229 feet (measured from the bottomof the tank to ground). The drops weremade with two different materials: water

and gum-thickened retardant. Due tolimitations in the size of the grid andthe number of assistants, the testmatrix used volumes less than 1500gallons. Smaller volumes wereselected in combination with lowflow rates.

TT

The Missoula Technology and DevelopmentCenter tested the Airspray Electra L-188(Figure 1) with a series of drops over an arrayof plastic bowls much like Cool Whipcontainers. The quantity of material in eachbowl was measured and the data were used todetermine the drop pattern.

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Table 2–Water tests producing the longest line at various coverage level settings usinga constant flow tank.

Table 3–Gum-thickened retardant tests producing the longest line at various coveragelevel settings using a constant flow tank.

Coverage Level Flow Rate Coverage Level Line Length(gal/100 sq. ft) (gal/sec) (setting) (feet)

0.5 1011 Max. 6731.0 1011 Max. 5662.0 1011 Max. 4513.0 1011 Max. 3714.0 1011 Max. 2646.0 1011 Max. 1868.0 1011 Max. 85

10.0 1011 Max. 39

Coverage Level Flow Rate Control Setting Line Length(gal/100 sq. ft) (gal/sec) (feet)

0.5 90 0.5 16841.0 261 1 14122.0 261 1 6523.0 698 Max. 4084.0 698 Max. 3496.0 698 Max. 2388.0 698 Max. 63

10.0* 318 Max. 39

*Drop used less gum-thickened retardant

Flow rate, drop height, and airspeed affect thedrop pattern. Increasing drop height graduallywidens the drop while decreasing coveragelevels. This effect is modified by the ambientwind. Increasing windspeed widens the dropand decreases coverage levels. Airspeed alsoaffects the drop pattern. Because this

airtanker has eight selectable flow ratesettings, it can produce specific coveragelevels needed for effective drops. Figure 2shows a 974-gallon water drop with acoverage level of 4, airspeed of 122 knots(140 mph), and drop height of 152 feet.Figure 3 shows a 995-gallon gum-thickened

retardant drop with a coverage level of 4,airspeed of 129 knots (148 mph), and dropheight of 162 feet.

The proper amount of fire-retardingmaterial (expressed as coveragelevels in gallons per 100 square feet)

differs depending on the fuel model.Table 1 shows the coverage neededfor specific fuel models using boththe National Fire Danger RatingSystem (NFDRS) and the FireBehavior Fuel Model.

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

Fuel ModelNational Fire

Danger Rating System Coverage Level(NFDRS) Fire Behavior (gal/100 sq. ft) Description

A,L,S 1 1 Annual and perennialwestern grasses, tundra

C 2 Conifer with grass

H,R 8 2 Shortneedle closedconifer; summerhardwood

E,P,U 9 Longneedle conifer; fallhardwood

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 blackspruce

B,O 4 California mixedchaparral, high pocosin

J 12 Greater than 6 Medium slash

I 13 Heavy slash

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Figure 2–Drop pattern characteristics for the Airspray Electra L-188 with a coverage level setting of 4, carrying 995 gallons with an airspeed of 122 knots (140 mph) and a dropheight of 152 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 Airspray Electra L-188 with a coverage level setting of 4, carrying 974 gallons with an airspeed of 129 knots (148 mph) and a dropheight of 162 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.

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Airspray Electra L-188 With Aero Union Constant Flow TankCoverage Level Setting 4 Using Water

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Airspray Electra L-188 With Aero Union Constant Flow TankCoverage Level Setting 4 Using Gum-Thickened Retardant

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Effect of Flow Rate on Length of Line at Various Coverage LevelsAirspray Electra L-188 With Constant Flow Tank Using Water

CL = 0.5CL = 1CL = 2CL = 3CL = 4CL = 6CL = 8CL = 10

CL = Coverage Level

Figure 4–Use this graph to estimate the flow rate needed to produce the longest line ofwater at various coverage levels while dropping 1500 gallons.

The results of drop tests allow managersto estimate the length of line a specificairtanker produces at various coveragelevels. Table 2 or Figure 4 can be usedto estimate the coverage level setting ofa water drop for the longest line at thedesired coverage level. Table 3 orFigure 5 can be used to estimate the

coverage level setting of a gum-thickened retardant drop for the longestline at the desired coverage level.The graphs predict line length (in feet) asa function of flow rate (in gallons persecond). The tables are constructed byselecting the drop producing the longestline (on the ground) at each coverage

level. The tables may be used to estimatethe flow rate required to produce thelongest line for a given coverage level.The tables show an ideal case, while thegraphs represent an average.

To select the proper flow rate, first useTable 1 to determine the coverage level

required by the NFDRS or FireBehavior Fuel Model. The coveragelevels in Table 1 represent the coveragelevel required for average fire intensityfor each fuel model. The requiredcoverage level can be adjusted up ordown depending on the actual fireintensity.

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Effect of Flow Rate on Length of Line at Various Coverage LevelsAirspray Electra L-188 With Constant Flow Tank Using Gum-Thickened Retardant

CL = 0.5CL = 1CL = 2CL = 3CL = 4CL = 6CL = 8CL = 10

CL = Coverage Level

Figure 5–Use this graph to estimate the flow rate needed to produce the longest line ofgum-thickened retardant at various coverage levels while dropping 1500 gallons.

Once the required coverage level isdetermined, the flow rate can befound. Use the graph for the materialdropped (water or gum-thickenedretardant) to find the flow rate thatproduces the longest line for thedesired coverage level. The sameinformation can be found in the

appropriate drop table.For example, if a fire is burningin NFDRS Fuel Model G (FireBehavior Model 10), represented byshortneedle conifer (heavy deadlitter), a coverage level of 4 isrequired (Table 1). The graph forgum-thickened retardant shows that

for coverage level 4, a flow rate of698 gal/sec, using 1500 gallonsproduces the longest line (349 feet).

The ground drop characteristics forthe Airspray Electra L-188 werederived through controlled drop testprocedures on flat ground (Figure 6).

This information is to serve onlyas a guide to help field personneldetermine the proper drop height,airspeed, and door opening fordelivering water or gum-thickenedretardant. Actual coverage may varydepending on terrain, wind, weather,and pilot proficiency.

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Cammie Jordan is a Project Assistantfor the Wildland Fire Chemical SystemsProgram at MTDC. She is an elementaryeducation student at the University ofMontana and has worked for MTDCsince 1998.

Paul Solarz is Program Leader for theWildland Fire Chemical Systems Group.He received his bachelor’s degree fromEastern Oregon State College in 1986.Paul has worked in Aviation and FireManagement since 1973, serving atseven Ranger Districts and in two ForestSupervisor’s offices. He has an extensiveoperational background in fire, fuels, andaviation.

Additional single copies of thisdocument may be ordered from:

USDA Forest ServiceMissoula Technology andDevelopment Center5785 Highway 10 WestMissoula, MT 59808Phone: (406) 329-3978Fax: (406) 329-3719

Figure 6–Drop test of the Airspray Electra L-188.

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The Forest Service, United States Department of Agriculture, hasdeveloped this information for the guidance of its employees, itscontractors, and its cooperating Federal and State agencies, and isnot responsible for the interpretation or use of this information byanyone except its own employees. The use of trade, firm, or corporation

2600 (voice and TDD). To file a complaint of discrimination, write: USDA,Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400Independence Avenue, SW, Washington, DC 20250-9410, or call (202)720-5964 (voice and TDD). USDA is an equal opportunity provider andemployer.

names in this publication is for the information and convenience ofthe reader, and does not constitute an endorsement by the Departmentof any product or service to the exclusion of others that may besuitable. The United States Department of Agriculture (USDA), prohibitsdiscrimination 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 basesapply to all programs.) Persons with disabilities who require alternativemeans for communication of program information (Braille, large print,audiotape, etc.) should phone USDA’s TARGET Center at (202) 720-

About the Authors

For additional technical information,contact Greg Lovellette at the addressabove.

Phone: (406) 329-4815Fax: (406) 329-4811Internet: glovellette@fs.fed.usLotus Notes: Greg Lovellette/WO/

USDAFSInternet: glovellette@fs.fed.usAn electronic copy of this document isavailable on the Forest Service sFSWeb Intranet at:

http://fsweb.mtdc.wo.fs.fed.usFor additional information contact:Greg Lovellette, Project LeaderMissoula Technology & DevelopmentCenter5785 Highway 10 WestMissoula, MT 59808Phone: 406-329-4815Fax: 406-329-4811E-mail: glovellette@fs.fed.usLotus Notes: Greg Lovellette/WO/USDAFS