AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT DROP TANK Inventor: Geoffrey William Hall Inventor's Address: 23 Devonshire Road Aldgate SA 5154 The following statement is a full description of this invention, including the best method of performing known to me: Helitank Design Background Water carrying devices known as Helitanks have been used by helicopters to transport and release water on bush or wildfires since before the 1980's. In some cases Helitanks are the preferred alternative over the more traditional use of Helibuckets as unlike buckets that are attached to aircraft via the helicopters hook, tank's are fixed to the helicopter in a way that they cannot be released inadvertently from the aircraft, making their use over built-up areas safer for civilians and ground crews. There are several problems with existing tank systems. Tanks mounted to the underbelly of most Helicopters have a flat bottom to allow enough ground clearance for the aircraft to land unobstructed. This flat bottom creates a problem when the water doors open as the tank is unable to drain all of its contents quickly and evenly. Head pressure available is limited due to the height of the tank. One solution to these problems is to have many doors spread beneath the tank exposing most of the floor to an evacuation area so when the water doors open most of the water drains. This solution creates another problem. Water exiting these tanks tends to flow in a turbulent or broken fashion as the holes created by the open doors are unclean. A considerable area of exposed face, when the aircraft moves forward, causes the passing air to mix with the water being released. This mixing causes the water molecules to atomize, making the water stream misty and as light as the air around it. The mist reacts further with the surrounding air as it falls to the ground reducing the impact or penetration of the water and making it difficult for the pilot to hit the target with the full contents of the storage tank. On a windy day, a considerable amount of the total contents released drifts away. Another type of helicopter tank is a "V" shaped tank. These tanks are commonly fitted to aircraft that have enough ground clearance to enable a taller tank to be fitted. They may also be fitted to aircraft that have been modified to include an internal tank. These tanks are also known as "high head tanks." Typically they drain through long narrow doors at the base of the tank. The water column shape is streamlined with the air passing around it. One problem with this tank design is the high head aspect. Typically the tanks are around 4 to 8 ft in height. The pressure at the bottom of the tank, near the doors is much greater than the pressure at the top of the tank. When the doors open this pressure causes the water column to expand once clear of the doors. The expansion of the column causes water to mix with the air and atomize to, once again, result in drift. Fire can be extinguished when water is dropped on it, cutting off oxygen, removing one of the three (3) ingredients for combustion. If the water being released from the aircraft is allowed to mix with air then the fire will not be smothered. A system is needed that will allow the full contents of its tank to reach the ground as a liquid.
My invention allows the tank to change its shape allowing the aircraft to land with adequate ground clearance, to either fill on the ground, or at hover and maintain enough ground clearance to land immediately either during normal operations or/and in emergency landing. And finally, release its load to maintain an unbroken or non atomizing drop pattern by maintaining a constant head pressure causing its contents to flow through a single narrow door opening positioned in the middle of the tank. DROP TANK design and features The helicopter tank known as the "Drop Tank" is a light-weight composite tank constructed from carbon fiber and high density foam. Its total weight could be up to half that of similar aluminium or fiberglass tanks of the same capacity whilst maintaining suitable strength to be fully certified under CASA and FAA design standards. DROP TANK flight positions The Drop Tank has three (3) flight positions 1. Retracted/Empty Position 2. Fill Position 3. Deployed/Release Position Retracted/Empty Position In the starting position the tank is empty and fully retracted. In this position the tank can be transported to the fire with minimal drag and maximum ground clearance as the depth of the tank is approximately 4 to 10 inches, depending upon the size of the tank. Additionally, the aircraft requires no undercarriage modification to increase the ground clearance beneath the aircraft because of the tank's depth. Fill Position In the Fill position the tank still retains some ground clearance and can be filled to its full capacity. In this position the tank is held by cables connected to hydraulic cylinders or actuators. The cables allow upward movement of the tank with a full load of liquid in the tank should the aircraft need to land immediately on uneven ground. Deployed/Release Position The third position is the release position. The tank drops as the doors open and water exits the tank, timed with the water exit rate to maintain a constant head pressure.
DROP TANK'S CONSTANT HEAD PRESSURE FEATURE This is the most important feature of the Drop Tank's design. By maintaining a constant head pressure as the doors open, a constant flow rate is obtained. If the tank were to be dropped into a "V" shape first, before the doors open, the head pressure would diminish causing the water column to expand, then contract, leaving an uneven drop pattern on the ground. The initial expanding column would also atomize with the air flowing around it. The Drop Tank's design allows all of the contents within the tank to drain at a constant flow rate through the release doors. Once water dropping is complete, the tank automatically returns to the Retracted/Empty position. By maintaining a constant door opening and head pressure a narrow liquid column released from the tank is obtained, preventing atomization and drift.
DROP TANK structural features Inner Liner Liquid is held inside the tank by a light-weight liner supported by the carbon fiber walls of the tank. Hinges Lightweight molded polyurethane or plastic hinges overlaid with carbon fiber and attached to the panels enable the tank to move into 3 positions; retracted, fill and deployed. The use of piano-type hinges is not the only method of hinging 2 panels together. Another feasible method could be a membrane of composite material. Tank Single Mounting Point The Drop Tank is manufactured from carbon fiber, an extremely light weight material with qualities of extreme strength. Through the use of this material, the tank could be mounted from a single, central point to the fuselage of the aircraft. This design allows the tank to be removed and refit in minimal time (10 to 15 minutes). The Loading Systems The tank can be loaded two ways. First, through a standard 2 - 3 inch cam lock fitting (During ground loading) and second, through a quick fill, snorkel mounted pumping system. The snorkel pump is driven from a motor assembly mounted at the proximity of the tank. A flexible drive shaft connects the motor to a pump impeller mounted on the end of the snorkel hose. This design allows the system to function without a heavy motor pump assembly on the end of the snorkel hose. By placing the electric drive motor close to the tank, energy losses through voltage drop are kept to a minimum. A quick disconnect cam lock system allows the fight crew to disconnect the lightweight pump and snorkel hose from the heavier, permanently mounted drive motor when the system is needed to be stowed for long distance transport. The Frameless Doors The door system allows the doors to seal liquid inside the tank. When doors open, they reveal an opening with no central obstruction to upset liquid flow as the doors seal on themselves. The doors narrow opening and rate of speed in which they open allow for an optimal drop pattern. The doors are narrow (about 10 inches wide) and extend almost the full length of the tank. The liquid column flowing out of the tank is less influenced by air moving around the tank when compared to other tank designs because of the door opening dimension. Cross sectional area of the leading edge of the liquid column is greatly reduced by the Drop Tank's unique door system. By reducing the influence of the moving air around the column, the liquid column remains mostly unbroken. Molecules making up the liquid remain attached to each other and, therefore, its weight remains unchanged. This gives the column penetration, allowing the pilot to operate the aircraft at a higher altitude above the fire with less wind affected drift due to reduced atomization.