Buckets or Belly Tanks?

Making the Right Choice
Ken Armstrong
July 10, 2007
By Ken Armstrong
184-bellyIf you are looking for an intense conversation between heli pilots bring up the pros and cons concerning relative performance between helicopter belly tanks and suppression buckets carried as external loads. In order to create a fair comparison, we will consider the installation of these systems on the ubiquitous Bell 205, 212, UH-1H series of medium helicopters that enjoy a great deal of suppression acceptance.

Although helicopter belly tankers were uncommon a few years ago, they are gaining an increasing share of the firefighter’s marketplace. Why? While there are a few advantages found among the tanks offered, their prime attraction for many is the fact they cannot be jettisoned…. Flying with a slung load (bucket) over populated areas is verboten in many countries with the result that markets such as Los Angeles and other cities surrounded by forests are turning to the fuselage mounted tanks. These tanks preclude the inadvertent dropping of a bucket on the tax paying populace with the result belly tanks are now spreading to the third world. Another reason for their growing popularity is the fact that many militaries and similar agencies with large helicopters are taking on the fire suppression role in their countries in the absence of civilian operators. The truth is, many of these armed forces pilots have never flown a slung load!

Previously, most belly tanks also offered other benefits in terms of door sequencing, partial load drops and the ability to easily carry mixed internal loads. These benefits have been matched with new options on equipment such as the Bambi Bucket and bucket evolution has closed the gap.

Installation Considerations
The most popular bucket system for the Bell 205 is the model 3542 Bambi Bucket system with a capacity of 350 gallons (1663 liters). The system weighs 176 pounds (76 kg) compared to 418 pounds (190 kg) for a competitor’s fiberglass belly tank with a capacity of only 269 gallons (1279 liters). The bucket only requires the installation of an electrical plug near the hook and the trigger button at a convenient location in the cockpit. It takes a couple of minutes to attach the bucket to the hook and plug and of course it can be jettisoned during an emergency in a second.

Belly tanks require approximately a half hour to bolt directly to the helicopter structure and add approximately 400 pounds to the basic weight of the helicopter. Moreover this weight cannot be eliminated during a forced landing - a touchdown that could easily damage the belly tank. Additionally, many helicopters allow higher gross weight operation with slung loads meaning pilots can carry more fire suppressant with a bucket.

The Bambi Bucket is electrically operated and can be installed on a standard fifteen amp circuit breaker. Belly tanks require the same 28 VDC power supply but draw 90-125 amps of current and therefore have more complex installation requirements for power.

The Bambi Bucket can be folded up and placed in its carrying bag in a few minutes and stowed in the helicopter whereas the belly tank requires a considerable time for a mechanic to remove and stow it in the hangar. During operations in the field, the belly tank hanging under the helicopter significantly reduces ground clearance and requires that the helicopter be mounted on high skid gear to minimize the risk of damage. With the doors open for inspection and maintenance, a belly tank has only a few inches of ground clearance. Conversely, the Bambi Bucket is designed to be lifted via the suspension cables directly from the ground.

The belly tank is considerably more complex with three opening doors, an electrically driven hydraulic pump, hydraulic reservoir and an additional hose and pump system of approximately 2 hp that draws water up the filling hose to replenish the belly tank.

Operational Considerations
A USA manufactured belly tank refill pump is capable of a maximum flow rate of 270- 300 U.S. GPM thereby requiring a fill time of 55 to 75 seconds. The Bambi Bucket fills in 3-5 seconds. As a result, belly tank equipped helicopters must hover at high power settings over the water for longer periods of time than bucket equipped helicopters. This is more challenging for pilots and perhaps as spray builds up on the windshield obscuring vision it can also be more dangerous. Of course, there is also the consideration that lengthy hover times create much more wear and tear on helicopter dynamic components. The Bambi Bucket is fast and easy to fill – assuming the pilot is trained on slung loads and pick-up techniques (not the kind used at the bar after hours…). My students are taught to fill buckets in less than three seconds.

Because buckets require a water depth of approximately 3 feet (1 metre) to completely fill, shallow water sources will result in only partial bucket loads – without special equipment or piloting techniques. Because belly tankers use an electric pump on the end of a 10-12 foot hose they can pump a full load of water from shallower water sources. (This tank benefit has recently been eclipsed by some buckets which have a capability of pumping themselves full in only a few inches of water.)

During fire suppression operations with belly tanks, the pilot has the option of dropping on two or three different spot fires by releasing only one door at a time whereas older style Bambi Buckets were limited to one drop with their large load. The recent introduction of the new Torrantula Valve equipped Bambi Bucket allows an infinite multiple drop capability with a pilot activated switch that can open and close the bucket exit drain over an infinite range.

During injected foam operations, a minor residue of foam will remain on the bucket walls when it is dipped into the water source thereby creating a minor amount of contamination. Although the concentration is extremely low, some countries are concerned with the possibility of damage to fish in the reservoirs – especially during an accidental spillage. Belly tank systems do not dip their tanks into the water so there is little chance of diluted foam dripping into the water source. As environmentalists become more active, this could become an issue in selecting a tank over a bucket.

The evolution of tanks provides a further benefit, i.e. slightly faster enroute times as the belly packs are more streamlined than yesteryear and produce less drag than a bucket. Depending on the distance between the fire and water source, this faster cruise speed can make up for the long fill time and perhaps even reduce cycle time over the fast filling buckets.

Belly tanks can be easier to use for pilots who are not conversant with sling load flying. Additionally, bucket pilots need to be trained in the efficient techniques for picking up water with a bucket. Moreover, with some buckets it is necessary for pilots to adjust airspeed and altitude to match their load to the burning trees below and these are techniques that don’t seem to come readily to every pilot. Using incorrect techniques with a bucket can result in wrapped lines and buckets that won’t empty or fill. To be sure, these are all due to pilot technique errors, but they can be avoided with belly tanks.

Some belly tanks negate the use of the cargo hook and would need to be removed to carry a slung load as they block access to/or require removal of the hook. This could impede revenue generation when the helicopter needs to be re-configured for a slinging task.

A significant benefit for buckets is their ability to be flown on a long line. This allows access to confined water sources, places the helicopter farther from flames and obstacles and avoids the helicopter “fanning the flames” as sometimes occurs during low and slow drops. In some instances, the ability to use a long line is the deciding factor to purchase a bucket.

Drop Considerations

During B.C. forestry testing the square edged doors of belly tank systems were found to break up the water or foam mix in an irregular manner. Unfortunately, the more the load breaks up in the free air-stream due to factors such as: airspeed, high ambient temperatures and low relative humidity the greater the evaporation of the load into the atmosphere. The rounded edges of the Bambi Bucket minimize water break-up and provide a more effective, concentrated load. Testing also indicated the bucket drop pattern would be more efficient for fire suppression activities. It should be noted that tank manufacturers have been improving their door geometry and this is becoming less of a consideration.

Durability and Reliability
Buckets (and there are many types around the world) are generally made from a tough, durable material that is impervious to most foam chemicals and they can therefore be dipped into the retardant pits often dug by forestry/agriculture agencies. Because of their resilient construction, pilots often drag buckets through tree tops or bushes with no resulting damage. Belly tank hoses and pumps are not so resilient and are much more likely to create mechanical problems in the field when they are subjected to the normal wear and tear of fire suppression operations. In fact at least one of the belly tank manufacturers recommends an extensive and expensive spares kit to keep the system serviceable. This spares kit costs more than a complete Bambi Bucket.

It is logical that the Bambi Bucket system with nothing more than a simple solenoid, spring reel and latching mechanism is less prone to failures than a complex system with high power demands, many moving parts, doors to seal and fabrication consisting primarily of fragile and frangible carbon fiber or fiberglass.

Buckets are less than 10% of the price of the belly tanks. Moreover, the recommended spare parts package is small, simple and inexpensive compared to the complex belly tanks’ requirements. With far fewer moving parts the maintenance demands of the buckets is far less than the belly tankers. Moreover down time for simple bucket systems will logically be less than belly tankers and this can have a major effect on generation of revenue during fire suppression operations.

For many pilots and operators, the bucket system is a hands down winner. However, for those operating from shallow water sources, over populated areas or in a location that forbids traces of foam in the water supply you will be motivated to consider the more expensive and complex belly tanks. Shop carefully and consider your needs to select the system that best suits your current and future requirements.

Editors Note: Kenneth Armstrong has flown more than 60 helicopter types and for the past 15 years traveled worldwide training foreign pilots in the art of aerial fire suppression. He has received numerous awards and medals for these suppression activities. He is based in Victoria. E-Mail This e-mail address is being protected from spambots. You need JavaScript enabled to view it

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