1. Field of the Invention
The invention relates to a collapsible liquid container, particularly for storing and transporting helicopter fuel, which can be easily transported by a helicopter.
2. Prior Art
A helicopter is severly limited in its range of operations by the volume of fuel consumed. Small helicopters can rarely carry sufficient fuel on board for normal work, and commonly the helicopter is required to carry external fuel, e.g. to sling steel fuel drums from the cargo hook, for transporting fuel to the work area. Commonly, at a work site where there has been extensive use of helicopters, many empty fuel drums accumulate and become a hazard due to residual fuel which is difficult to empty completely, and furthermore require considerable storage space. Because returning empty fuel drums back to base is time consuming, they are commonly left behind and it is estimated that there are millions of empty fuel drums scattered across the northern portions of Canada and Alaska.
Flexible, pillow bladder tanks have been used to store fuel but such tanks are prone to a rupture by rough handling and thus require extra protection. Such tanks are also difficult to empty completely of fuel as the discharge opening is not always at a lowermost point. If the bladder tanks are merely fitted in a conventional net sling beneath the helicopter, the tanks are commonly damaged when the helicopter lands, due to puncturing by sharp objects on the ground. To avoid this problem, the pillow tanks have been transported on pallets suspended from cables, but this arrangement can exhibit poor aerodynamic characteristics requiring the helicopter to fly at lower cruise speeds. Also, when the helicopter is returning to base with empty pillow tanks, the pillow tanks are bulky and do not fold easily, and thus are returned as an external load. If the empty pillow tanks are strapped to the pallet, they also exhibit poor aerodynamic characteristics requiring a relatively slow cruise speed.