Flexible Fuel Tanks

Flexible fuel tanks are reinforced rubberised bag type fuel tanks placed in a non fuel tight compartment.

The tank incorporates all the components as required for the rigid removable fuel tank such as a vent, drain and fuel quantity indicator etc.  The airframe compartment for the tank is used completely, with a small opening provided for the insertion of the tank.  When inserted into the compartment the tank is held in place by several ‘buttons’ or ‘snaps’ which attach the tank to the compartment.  These tanks are found on many medium sized aircraft.

Rigid Removable Fuel Tanks

A rigid removable fuel tank is a tank that is installed in a compartment designed to hold the tank.  The tank must be fuel-tight but the compartment in which it fits is not fuel tight.

The tank is usually constructed of aluminium components welded together.  A baffle or baffles may be installed inside the tank to reduce the free movement of fuel called ‘surge’.  The baffles are attached to the tank structure with apertures to allow a flow of fuel but reducing the ‘surge’ action of the fuel.

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The tank must be smaller than the tank compartment to fit into the compartment and therefore the best use of the available space is not utilized.

The rigid removable tank may be held in position by straps and/or screws.  An access panel is used to cover the fuel tank.  The tank has a fuel feed line located near to the lowest inboard point to ensure that most of the fuel load is utilized.

A fuel drain point is situated at the lowest point of the tank when the aircraft is in a landed and stationary mode.

A fuel filler cap and vent tube are fitted near the top of the tank and provision made for a fuel quantity indicator.  This type of fuel tank is found on light aircraft.