Commercial and military transport aircraft are typically designed to carry a given load of passengers, cargo or both, at a given range and/or at a given endurance. Occasionally, the range and/or endurance of the aircraft may need to be increased. Such extended range and/or endurance can be accomplished by installing additional or auxiliary fuel tank systems in the aircraft, typically by positioning fuel tanks physically within the aircraft's fuselage cargo space (i.e., that space within the aircraft's pressurized fuselage which is below the passenger deck). Conventional auxiliary fuel tank systems are typically comprised of additional fuel tanks and their respective equipment, manifolds, and harnesses necessary to manage the additional fuel carried in the tanks.
These additional fuel tanks and systems may be embodied in diverse configurations, for example, with tanks installed under the wings external to the aircraft or with tanks internal to the fuselage. These additional fuel tanks and systems may be configured to directly supply fuel to the engines or to transfer the fuel to other tanks and from there to feed the aircraft engines and/or to be used to control aircraft center of gravity or even to transfer fuel to other aircraft in flight or to other vehicles on the ground.
Auxiliary fuel tank systems are in and of themselves known. For example, it has been proposed in U.S. Pat. Nos. 6,889,940, 7,040,579 and 7,051,979 (incorporated fully by reference herein) to provide auxiliary fuel tank systems that contemplate providing various separate manifold assemblies (e.g., fuel inlet and outlet manifolds, vent manifolds and the like) internally of each tank. By positioning the tank assemblies in adjacent side-by-side configuration, their respective internal manifolds may be connected together to provide a tank system that can be operatively interconnected with the aircraft's on-board fuel management systems.
A difficulty that may be encountered in the conventional auxiliary fuel tank systems noted previously relates to the manifolds that interconnect one tank to another so as to transfer fluids in both directions (i.e., into and out of a respective tank). In case of high accelerations or decelerations in a direction generally parallel to the longitudinal axis of the aircraft (and hence parallel to the row of auxiliary fuel tanks positioned within the aircraft's fuselage), if the fuel tanks are fluid-connected to one another through one or more manifolds and fuel is allowed to migrate from one fuel tank to another in a cascade fashion, the pressure that responsively develops in the last fuel tank(s) in the row of tanks may reach values well above the tank's structural limits. As a result, a real risk of potentially damaging or even rupturing the fuel tank exists.
More recently, U.S. Pat. No. 7,648,103 (the entire content of which is expressly incorporated hereinto by reference) has disclosed an auxiliary tank assembly having a relief manifold assembly mounted internally within the tank body so as to prevent an overpressure condition occurring within the interior space of the fuel tank body due to an excess volume of fuel being introduced thereinto which exceeds the maximum allowable volume of fuel permitted therewithin. The relief manifold assembly thus includes a buffer vessel which defines an internal buffer chamber within the tank body extending upright between the upper and lower walls of the tank body. The buffer vessel includes an aperture located at a lower end thereof near the lower wall of the tank body and exposed directly to the fuel held in the interior space of tank body. A relief valve associated with a relief branch conduit maintains an air column under pressure within the buffer vessel. When the maximum allowable fuel within the tank body is attained, the pressure of the air column will cause the relief valve to open thereby venting the air column therethrough and allowing some fuel to enter the internal buffer chamber and thereby relieve the overpressure condition.
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