Aviation Department Tech Tips Logo of USDA Technology & Development Program
September 1995
5700 9557 1307 - SDTDC


Fixed Tank Systems for Type II and III Helicopters

Melinda Seevers, Phoenix Design Engineering

Background
Helicopter fixed tank suppressant systems have been used successfully for over 25 years. Fixed tanks are externally attached underneath the helicopter. Systems for use with a variety of helicopter models exist today with features such as foam injection and hover refill capability. Tanks can be filled either on the ground by hydrant, with snorkel fill from shallow natural sources, or from open-top dip tanks. Water, foam, or approved long-term retardants can be used with fixed tanks.

Operational Considerations
Fixed tanks are noted for being well suited for use with brush and grassland wildfires, but can also be used for building line and in timber areas. There is no oscillation with a fixed tank, which contributes to accurate drops. Fixed tanks typically are capable of split drops, and the type of drop can be varied by controlling the drop doors and airspeed. When choosing a landing site for a helicopter with a fixed tank installed, pilots must consider the reduced ground clearance. If there is sufficient space, the pilot can hover, using in ground effect (IGE) power when flying with a fixed tank installed. Tanks are fairly easy to remove, and there is no problem in meeting the 5-minute removal requirement. However, fixed tanks can be difficult to install, especially without ground handling wheels. Most tank installations require the efforts of three or four people. A tank must be removed to use the aircraft cargo hook, unless there is a provision for access.

Summarized USDA Forest Service Contract Requirements
At present, the USDA Forest Service contract requirements for fixed suppressant/retardant delivery tanks for use with Type II or Type III helicopters require that:

  • The maximum gross weight of the tank (filled with suppressant) must not exceed the maximum rated lifting capability of the helicopter at sea level on a normal day.
  • The empty tank weight is not to exceed 12.5 percent of the weight of the water capacity of the tank.
  • The tank must be removable from the aircraft in 5 minutes or less.
  • If equipped with hover fill, the fill time is not to exceed 90 seconds.
  • The ground fill port must be a 3-inch Kamlock fitting located on the right side of the aircraft.
  • Tanks are to be equipped with an independent emergency dump system that can allow the entire load to be dropped in six seconds or less.
  • Controls, doors, venting, and construction quality should meet additional requirements.

 Manufacturers
At this time four manufacturers, Conair Aviation Ltd., Isolair, Sheetcraft, and Simplex Manufacturing Co., are marketing helicopter fixed tank systems for Type II and Type III helicopters. Specifications and performance claims for each model included in this Tech Tips were provided by the manufacturers and have not been independently tested or verified by the San Dimas Technology & Development Center (SDTDC). Because prices for the systems can vary significantly, it is recommended tha potential purchasers obtain current prices and system features by contacting the manufacturers.

Conair Aviation Ltd.
Conair Aviation Ltd. manufactures helicopter tank suppressant delivery systems for the Bell Model 205A-1/212, Bell 206L3/L4, and Eurocopter AS350 and SA315B helicopters. Conair's tank systems are certified for operations in a variety of countries. The AS350 system and the B205A-1/212 system are certified in both the Restricted and Transport Categories for rotocraft of the Federal Aviation Regulations. The AS350 system is available with a Federal Aviation Association (FAA) Supplemental Type Certificate (STC) in both categories. The other systems can be provided with a STC.

The tanks are constructed of aluminum with fiberglass fairings. Tank installation requires that the aircraft be equipped with standard high-skid landing gear. For added ground clearance with the Bell 205A-1/212, Conair provides modified aft saddle fittings that are approved for use with the Bell high gear. In addition, both the B205A-1/212 and the B206L3/L4 tank systems have internal opening doors that provide greater clearance for maintenance and for landing when the doors are open, following actuation of the emergency load release system. All tanks can be removed by four people in 5 minutes or less.

The tanks are each equipped with two electrically controlled hydraulically actuated doors that may be operated independently or in tandem by depressing a button on the cyclic. Each tank is equipped with a mechanical emergency load release system to allow the pilot to jettison the load, following failure of the main door control system. Drop-type selection and systems status information using annunciators are provided by the cockpit control panel. Control and status indication of the auxiliary hydraulic system is also provided by switches, annunciators, and gauges housed in a cockpit console.

Each of the tank systems can be hover or ground filled. For hover filling, a water source must be at least 1-foot deep. The hover fill pumps are hydraulically powered, using auxiliary systems that are independent of aircraft systems. A pneumatically powered hover fill system is also under investigation by Conair.

Options available for the Bell 205/212 model include:
  • An aft door load release system for filling portable ground reservoirs when hovering in ground effect
  • An off-load pump system for filling portable ground reservoirs when hovering in ground effect
  • A variable flow control (VFC) system allowing variable door positions to achieve different discharge flow rates
Foam injection is available for all tank systems. With the exception of the B205A-1/212 system, the foam injection tank and pumping components are integral with the fixed tank. The B205A-1/212 foam injection system is installed in the aft section of the helicopter cabin. A quick-disconnect hose transfers the concentrate from the aircraft to the fixed tank.

With the exception of the Bell 205 tank with optional cargo hook installation, cargo hooks are not accessible with the tanks installed.
Bell 212 helicopter with a Conair tank.
Figure 1—Bell 212 helicopter with a Conair tank.

Specifications for the Conair helicopter tanks are shown in table 1.
Table 1 - Specifications of Conair helicopter tank systems.
Helicopter Model Bell 205A-1/212 Bell 206L3/L4 Eurocopter AS350 Eurocopter SA315B
Tank: Height 15-in (.38 m) 14.4-in (.366 m) doors closed: 14-in (.36 m) doors closed: 15.5-in (.394 m)
      doors open: 21-in (.53 m) doors open: 21-in (.53 m)
Width 61.5-in (1.56 m) 50.0-in (1.27 m) 55.1-in (1.40 m) 50.0-in (1.27 m)
Length 176-in (4.47 m) 66.5-in (1.69 m) 119-in (3.02 m) 141-in (3.58 m)
Net weight 582 lb (264 kg) 254 lb (115 kg) 441 lb (200 kg) 320 lb (145 kg)
  without options      
Net weight with options 683 lb (310 kg) N/A N/A N/A
Gross weight        
with options (max.) 3677 lb (1668 kg) N/A N/A N/A
Water capacity 359 US gal (1360 L) 159 US gal (600 L) 211 US gal (800 L) 238 US gal (900 L)
Foam concentrate        
capacity 54.2 US gal (205 L) 6.6 US gal (25 L) 20 US gal (75 L) 21 US gal (80 L)
Hover fill rate (max.) 430 gpm (1630 L/m) 238 gpm (900L/m)* 430 gpm (1630 L/m) 408 gpm (1543 L/m)
Hover fill time,        
(approx. field avgs.) 50 sec 40 sec* 35 sec 35 to 40 sec

* Estimated using the pneumatic hover fill system. Hover fill system not available at present.

1 Basic configuration without options includes: 1360 L tank, new aft landing gear saddle fittings, hover-fill system, auxiliary hydraulic system, emergency load release system.

2 Configuration with options includes these additional items in addition to the basic items listed above: VFC system, aft door, off-load system, quantity measuring system, foam injection system, dual mirror kit, 2,000 lb (900 kg) cargo hook system.

Isolair
In the Type II and Type III category, Isolair Eliminator II fixed tank systems are available for the Bell 206B and 206L series, 204, 205, 212, 412, and 214, and the Eurocopter 350 series of helicopters. Isolair tanks are primarily constructed of fiberglass. Some of the systems have received FAA Supplemental Type Certification.

The systems are currently being modified with the addition of ground handling wheels which will allow 1-person installation. Cargo hooks are still accessible for emergency use with the system in place.

All of the tank systems can be hover filled from a water source that is at least 1-foot deep, or the tanks can be ground filled. The hover probe contains a pump at the lower end of the assembly. The refill pump is driven by an electric motor and requires 24VDC and 90 amps. For the 204, 205, and 212/412 models, electric power is taken from an added nonessential bus, and for the Astar tanks electric power is pulled from the aircraft main bus and is circuit protected. An optional hydraulic driven pump is available only for the military version of the Bell 205/212 ships.

With the exception of the smallest model for the 206B series, all tanks have split doors for flexibility in drop pattern and volume control. Dump doors are hydraulically actuated and individually controllable. Separate foam concentrate storage is contained within the tank, and the pilot can control the mix ratio. Drop length is also pilot controllable for a given airspeed.

Each system enables the pilot to control hover loading, foam mix ratios, dump volume, and drop length. Emergency dump, primary dump, hover refill pump initiate, and foam pump initiate switches are located on the cyclic. The display box houses the foam injection timer, monitor for percent of foam concentrate, and door-select switches. Annunciators on the display box detail quantity of water and foam concentrate, door close position, foam timer sequence operation, and condition of hover refill pump, such as overheat and proper connection.

Specifications for some of the Isolair tank systems are shown in table 2.
Table 2 — Specifications for selected Isolair fixed tank systems.
Tank Model 4600-206L-3 4600-350 4600-350B2 4600-205
Helicopter Bell 206L-3 Eurocopter 350 Eurocopter 350B2 Bell 205
Tank:     Height 14-in 15-in 13-in 14-in (.36 m)
              Width 48-in 49-in 52-in 88-in (2.2 m)
              Length 77-in 97-in 96-in 90-in (2.3 m)
Net weight 184 lb 247 lb 247 lb 336 lb (152 kg)
Gross weight 1,486 lb 1,898 lb 2693 lb 3,260 lb (1480 kg)
Water capacity 146 US gal 198 US gal 270 US ga 351 US gal (1330 L)
Foam concentrate capacity 10 US gal 15 US gal 15 US gal 27 US gal (102 L)
Hover fill rate, max        
with electric pump 350 gpm 400 gpm 400 gpm 400 gpm (1500 L/m)
Hover fill time 20 to 25 sec 25 to 30 sec 35 to 40 sec 55 to 75 sec

Sheetcraft
Sheetcraft's Skyhydrant fixed tank firefighting systems are available for use with the Bell 205/212, Bell 214B/412, Bell 206B/206L3/204, and MD 500 series helicopters. Both Los Angeles County and City Fire Departments have been flying with the Sheetcraft 205/212 style tank for 25 years. FAA Supplemental Type Certification is pending for the 205/212 tank.

All of the tanks can be ground filled, and the 360-gallon capacity tank for the Bell 205/212 and 214B/412 helicopters have optional hover refill capability. The 360-gallon tank also has optional foam injection. A Sheetcraft 360-gallon tank installed on a Los Angeles County Fire helicopter is shown in figure 2. The tank systems for the MD 500 and Bell 206B series helicopters have a 125-gallon capacity, and the 206L3 tank holds 150 gallons. All Sheetcraft tanks are fabricated of aluminum.
Sheetcraft tank on a Los Angeles County Fire Bell 412 helicopter.
Figure 2—Sheetcraft tank on a Los Angeles County Fire Bell 412 helicopter.

The hover refill system for the Sheetcraft 360-gallon tank was developed with ERA Helicopters, and is hydraulically operated and interfaced with the helicopter electrical power system. The system can hover refill from water sources that are at least 1-foot deep.

System installation requires that the aircraft have standard high-skid gear. The tank can be removed by three people in less than 5 minutes. The cargo hook remains installed, but is not accessible with the tank in place. Water can be emergency released in less than 3 seconds.

System controls include door actuation (the two doors for the 360-gallon tank can be opened simultaneously or singularly), foam injection mix ratio, and emergency release. The operation selector panel is located on the console, with actuating switches are located on the collective. Door position indicator lights are located on the glare shield in front of the pilot, and a DOOR OPEN audible warning is located behind the pilot.

Specifications for the 360-gallon tank system are shown in table 3.
Table 3— Specifications for Sheetcraft tank for Bell 205/212 and 2148/412 helicopters.
Tank system height 17-in
Tank system width 96-in
Tank system length 106-in
Total system weight 337 lb
Water capacity 369 gal (US)
Electrical power required (for tank doors) 35 A maximum
Door actuation operating system Electric/Pneumatic
Hover fill time 1 min 11 sec
Snorkel recommended duty cycle 1 min running time, then 3 min rest
Foam reservoir capacity 12.5 gal (10 to 15 drops) (47.3 L)

Simplex Manufacturing Co.
Simplex Fire Attack fixed tank systems for Type II and Type III helicopters are available for the Bell 206L and Bell 205/212, Eurocopter AStar series, and the BK-117. The Bell 205 model 10400 tank installation has FAA Supplemental Type Certification, and certification is pending for the Bell 212. The Bell 205/212 installation is shown in figure 3.

The Fire Attack tanks are constructed of reinforced fiberglass. Each of the tank systems are equipped with built-in foam retardant tanks, and have hydraulically actuated dump door assemblies. Dump volume and drop length for a given airspeed and foam/retardant ratio mixing are pilot controllable. Tanks can be installed and removed by a 2-person crew, and removal can be accomplished within 5 minutes.

All of the tank systems can be hover filled from a water source that is at least 6 inches deep, or the tanks can be ground filled. Hover refill pumps are either electrically or hydraulically driven, depending on the tank system model. Electric power is taken from the aircraft main electric bus, and hydraulic power for the model 10400 (Bell 205/212) is taken from the helicopter transmission offset quill drive. Power requirements during filling are approximately 100 amps, 2.5 horsepower for the electric pumps and 8.5 hp for the hydraulic pump. Simplex is developing an electrical pump that will produce higher volume for the same amperage draw.

Each system includes an onboard microprocessor, which controls the system, based on pilot input. Total volume loaded, foam injection ratio, and door settings are input by the pilot, and then all operations are recorded on a data card from which data can be printed. Other recorded data includes total flight time, number of loads, water volume, foam consumed, and start/stop time.
Simplex tank installation for Bell 205 and 212 helicopters.
Figure 3—Simplex tank installation for Bell 205 and 212 helicopters.

A summary of Fire Attack models and specifications is shown in table 4.

Table 4 — Specifications of Simplex Fire Attack Tank Systems.
Tank Model 10300 10400 10600 11000
Helicopter Bell 206L, L1, L3 Bell 205, 212 Eurocopter Eurocopter BK117
      AStar AS350B,C,D  
Tank:     Height 16 in 18 in 22 in 10 in
              Width 57 in 58 in 49 in 69 in
              Length 100 in 144 in 96 in 106 in
              Net weight 290 lb 640 lb 290 lb 286 lb
Water capacity 155 US gal 360 US gal 155 US gal 211 US gal
Foam concentrate        
capacity 14 US gal 25 US gal 20 US gal 14 to 20 US gal
Hover fill rate 120 gpm 380 gpm 120 gpm 120 gpm
        1 min 18 sec       57 sec       1 min 18 sec       1 min 46 sec
Snorkel pump power Electric motor Hydraulic motor Electric motor Electric motor

SUMMARY
A summary of the fixed tank systems from the four suppliers discussed in this Tech Tips and their respective features are provided in table 5.
Table 5 — Summary of Fixed Tank Systems.
Helicopter Model/Co. Conair Isolair Sheetcraft Simplex
(tank empty weight),        
capacity, features        
Bell 205/212, 214/412 582-683 lb*     359 gal** 336 lb     351 gal 337 lb     360 gal 640 lb     360 gal
  H,   Fm,   C****,   Al H,   Fm,   C,   Fbr H,   Fm,   Al H,   Fm,   Fbr
Bell 206L series 254 lb     159 gal 184 lb     146 gal 85 lb     125 gal 290 lb     155 gal
  H,   Fm,   Al H,   Fm,   C,   Fbr Al H,   Fm,   Fbr
Eurocopter AS350 series 441 lb     211 gal 247 lb     270 gal N/A 290 lb     155 gal
  H,   Fm,   Fbr,   Al H,   Fm,   C,   Fbr   H,   Fm,   Fbr
Eurocopter SA315 320 lb     238 gal N/A N/A N/A
  H,   Fm,   Al      
Eurocopter BK117 N/A N/A N/A 286 lb     211 gal
        H,   Fm,   Fbr
MD 500 Series N/A N/A 85 lb 125 gal N/A
      Al  
* Tank empty weight.

** Tank capacity.

*** Key for features:

**** Has optional cargo hook attached to the tank.

Has hover refill = H

Foam injection = Fm

Cargo hook access = C

Primarily constructed of aluminum = Al, fiberglass = Fbr

ADDITIONAL INFORMATION
Current pricing and additional product information can be obtained from the manufacturers at the following addresses and telephone numbers.

Conair Aviation Ltd.
P.O. Box 220
Abbotsford, BC
Canada V2S 4N9
Phone: 604–855–1171
Fax: 604–855–1017

Isolair
1620 Northwest Perm Way
Troutdale OR 97060
Phone: 503–492–2756
Email: sales@isolairinc.com
URL: http://www.isolairinc.com

Sheetcraft
447 South Ojai
Santa Paula, CA 93060
Phone: 805–525–3942
Fax: 805–525–2598
Email: bill.sheetcraft@verizon.net

Simplex Manufacturing Co.
13340 Northeast Whitaker Way
Portland, OR 97230
Phone: 503–257–3511
Fax: 503–257–8556
TD logo
For Additional Information Contact:
Aviation Program Leader
San Dimas Technology and Development Center
444 East Bonita Avenue, San Dimas CA 91773-3198
Phone 909-599-1267; TDD: 909-599-2357; FAX: 909-592-2309
E-mail: mailroom_wo_sdtdc@fs.fed.us

Information contained in this document has been developed for the guidance of employees of the Forest Service, United States Department of Agriculture (USDA), its contractors, and cooperating Federal and State agencies. The USDA assumes no responsibility for the interpretation or use of this information by other than its own employees. The use of trade, firm, or corporation names is for the information and convenience of the reader. Such use does not constitute an official evaluation, conclusion, recommendation, endorsement, or approval of any product or service to the exclusion of others that may be suitable.

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