GB2300843A - Aircraft fuel system - Google Patents

Abstract

The present invention provides an aircraft fuel system comprising a multiplicity 16 of tubes 30 defining a fuel store, and a manifold 18, collector tank 12, and pump 14 for supplying fuel from the fuel store for use by the or an aircraft engine. The tubes may be constrictable, flexible or made from an expandable material whereby fuel can be expelled therefrom by fluid pressure or due to volume variation.

Description

AIRCRAFT FUEL SYSTEM The present invention concerns a fuel system for an aircraft.

Current aircraft fuel systems comprise a plurality of fuel tanks arranged at different locations within the aircraft structure and connected by a system of pipes, valves, pumps and gauges. In use, the tanks are individually emptied for supplying the aircraft engine or engines with fuel, and likewise refuelling involves the individual filling of each of the tanks.

Substantial amounts of fuel are contained in each tank and therefore measures have to be taken to prevent the fuel from sloshing around during take off, powered flight and landing and to prevent major shifts in the centre of gravity of the aircraft at these times.

Furthermore, in military applications, measures have to be taken to minimise the effect of battle damage, for example measures for explosion suppression and for attenuation of hydrodynamic ram effect, which is the effect caused by a bullet or fragment entering a liquid at supersonic speed and causing a shock wave to travel through the liquid, which may damage the surfaces of the tank holding the liquid.

The present invention seeks to overcome the problems of current aircraft fuel systems by removing the need for at least some of the separate tanks previously employed.

The present invention also seeks to provide a new aircraft fuel system which takes advantage of previously inaccessible aircraft volume for storing fuel.

The present invention provides an aircraft fuel system comprising a multiplicity of tubes defining a fuel store, tubes and means for supplying fuel from the tank and/or from the fuel store for use by an aircraft engine.

The present invention also provides an aircraft fuel system comprising a collector tank for fuel and a plurality of fuel tubes connected to the collector tank as a supplementary fuel store.

In a preferred embodiment, the additional fuel store comprises a multiplicity of flexible tubes connected at one end to the collector tank and sealed at the other end.

The tubes may run throughout the aircraft structure, i.e. along the fuselage, along the wings as far as the wing tips, and along the fins.

This arrangement is simple and reliable, and has a number of other significant advantages. In particular, the flexible tubes prevent fuel sloshing around and the overall aircraft fuel system is much less dependent on the structural design of the aircraft than in the case of a system employing a plurality of tanks. The tubes, being flexible and relatively narrow, can take advantage of previously inaccessible air frame volume for storing the fuel, and provide a storage arrangement in which the centre of gravity in the aircraft during take off, powered flight and landing can be readily maintained since the fuel can be stored uniformly along the length of each tube.

By employing the flexible tubes as a fuel store, minimum fuel loss is also ensured in the event of battle damage. Furthermore, shock resulting from hydrodynamic ram effect is also prevented.

The invention envisages various possibilities for supplying fuel from the flexible tubes for use by the aircraft engine or engines. For example, means may be provided to constrict each tube for pressurising the fuel within the tube. Such means may be internal in the form of an inflatable air chamber or other expandable material within the tube. However, they may also be external and in the form of an arrangement for compressing the wall of the tube from the outside. Another possibility for extracting the fuel is to connect the tubes to one or more vacuum chambers for withdrawing fuel from the tubes by way of a suction force.

Such an arrangement removes the need for the known transfer pumps for supplying the fuel and simplifies fuel volume monitoring. It also has the advantagepf efficient use of fuel in that only a negligible volume of fuel remains unusable.

In a preferred embodiment of the invention described below, fuel is scavenged from the flexible tubes by inflating a respective air chamber within each tube. By monitoring the flow and/or the pressure of the air supplied to each flexible tube, it is possible to detect when the respective tube is empty and needs refuelling.

The invention is described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of an aircraft fuel system according to the present invention; and Figures 2a to 2c illustrate possible arrangements for flexible tubes of the aircraft fuel system shown in Figure 1.

As illustrated in Figure 1, an aircraft fuel system 10 comprises a collector tank 12 for fuel incorporating a pump 14 for supplying the fuel to the or each engine of the aircraft.

A multiplicity of flexible tubes 16 extend throughout the airframe of the structure and are connected by way of a manifold 18 to the collector tank 12. In particular, one set 20 of the tubes 16 extends along the fuselage of the airframe to the furthest extremities of the fuselage. Further sets 22 of the flexible tubes 16 extend along the lengths of the wings to the wing tips and still further sets 24 extend to the tips of the fins. For the sake of simplicity, Figure 1 shows only a few of the tubes 16 and they are all depicted by means of straight lines. It should be appreciated that in practice there may be as many as 10,000 or more of the flexible tubes 16, depending on the optimum tube diameter, and the layout of the flexible tubes 16 may be quite irregular and circuitous in order to bypass structural elements of the airframe.The flexible tubes 16 are sealed at their ends remote from the manifold 18.

In order to reach remote and less accessible areas of the airframe, a number of the flexible tubes may be connected end to end by way of adaptors, or indeed may be connected as branch lines by means of T-piece connectors. In this instance, the flexible tubes connected to the manifold 18 are preferably of the largest diameter, and the tubes are arranged to be of increasingly small diameter the more remote they are from the manifold 18.

The flexible tubes 16 spread about the structure of the aircraft constitute a plurality of small fuel stores arranged to supplement or even remove the need for the storage of fuel in the collector tank 12.

In order to extract fuel from the flexible tubes 16, each tube 16 is associated with a respective inflatable air chamber 28 arranged so as to constrict the volume of the flexible tube 16 on being inflated. Air from the aircraft engine or engines is supplied by way of an air duct 26 to the manifold 18 for inflating the respective air chambers 28.

Alternatively, the air may be supplied to the manifold 18 by way of a compressor (not shown) for communication with the respective air chambers 28.

In either event, inflation of the respective air chamber 28 has the effect of constricting the flexible tube 16 and pressurising the fuel therein. This forces the fuel from the flexible pipe 16 back through the collector tank for supply to the aircraft engine or engines, eventually scavenging the fuel from the flexible tubes. The fuel is extracted uniformly along the length of each tube and hence there is no centre of gravity shift within the aircraft during take-off, powered flight and landing. By monitoring the flow andlor the pressure of the air supplied to each of the flexible tubes 16, it is possible to detect and then record when each tube 16 becomes empty.

Turning to Figure 2, various possible arrangements for the flexible tube 16 and associated inflatable air chamber 28 are illustrated.

In Figure 2a, the flexible tube 16 has an inner fuel passage 30 surrounded by a concentric inflatable air chamber 28, the two being separated by a flexible wall 32. In Figure 2b, the converse is true, and the flexible tube 16 constitutes an outer annular fuel chamber 30 around an inner inflatable air chamber 28, the two being separated by a flexible wall 32. Figure 2c shows a further possibility, in which the flexible tube 16 is divided by a flexible inner wall 32 into a first chamber 30 containing fuel and a second chamber providing the inflatable air chamber 28.

A still further possibility for extracting fuel from the flexible tubes 16, is to incorporate in each tube a "smart" material, which is expandable in order to constrict the remainder of the tube 16 carrying the fuel. More particularly, a "smart" material constitutes a material within which an electrostrictive or magnetostrictive element is embedded, and on application respectively of an electrical or magnetic signal the element changes shape, for example it expands, and thus exerts a force on the surrounding material causing this also to change shape and expand. As the "smart" material expands, so the passage for fuel is constricted and the fuel is pressurised and forced from the tube into the collector tank 12.

In each case, the quantity of fuel remaining in the flexible fuel tubes 16 may be monitored by counting the number of empty tubes 16.

Various other possibilities may also be envisaged: Instead of applying pressure to the flexible tube 16 to pressurise the fuel therein and force the fuel from the pipes 16, a vacuum pump arrangement may be employed.

Instead of the described arrangements involving flexible walls 32, the flexible tubes 16 may themselves be collapsible, and an external arrangement may be provided for collapsing the tubes 16 for pressurising the fuel for supply to the aircraft engine or engines. The external means may be mechanical or involve some alternative pressurised fluid arrangement.

Further, the arrangement described above envisages the use of plural individual tubes but it is equally possible to envisage an arrangement involving multiple elongate passages or a network of passages within a single elongated flexible mat or cushion.

According to another possibility, the fuel pump 14 for supplying fuel to the or each engine of the aircraft may be located in the manifold 18 instead of the collector tank 12.

In this instance, the collector tank 12 may be omitted altogether.

The invention as described provides a number of significant advantages: Firstly, the use of tubes as the fuel store permits the utilisation of previously unusable airframe volume with all the attendant advantages of uniform weight distribution and efficiency.

Furthermore, no shifts occur in the aircraft centre of gravity during fuel use provided that uniform fuel extraction is maintained along the lengths of the tubes.

The use of tubes avoid the need for inter-tank fuel transfer, with all the requisite pumps, pipes, valves and sensors and results in a simpler and more reliable fuel system In addition, a gradual degradation of the overall fuel system would occur in the event of damage, by contrast with the known arrangements, so that protective measures are easier to implement.

Claims (17)

1. An aircraft fuel system comprising a multiplicity of tubes defining a fuel store, and means for supplying fuel from the fuel store for use by the or an aircraft engine.

2. An aircraft fuel system according to claim 1 in which the tubes are constrictable for the supply of fuel.

3. An aircraft fuel system according to claim 2 in which the tubes are at least partially defined by flexible walls.

4. An aircraft fuel system according to any preceding claim in which each tube incorporates an air chamber whose volume is variable for extracting fuel from the tube.

5. An aircraft fuel system according to any one of claims 1 to 3 in which each tube incorporates an expandable material whose volume is variable for extracting fuel from the tube.

6. An aircraft fuel system according to any preceding claim in which the tubes are flexible.

7. An aircraft fuel system according to any preceding claim in which each tube is sealed at an end remote from the means for supplying fuel.

8. An aircraft fuel system according to any preceding claim in which respective ones of the tubes are connected by adaptors to respective further tubes of differing diameter.

9. An aircraft fuel system according to any preceding claim in which the means for supplying fuel comprise a manifold to which the tubes are connected.

10. An aircraft fuel system according to claim 9 in which the means for supplying fuel comprise a collector tank arranged downstream of the manifold.

11. An aircraft fuel system according to claim 9 or claim 10 in which the means for supplying fuel comprise a fuel pump located in the manifold or in the collector tank.

12. An aircraft including an aircraft fuel system according to any preceding claim.

13. An aircraft according to claim 12 in which the tubes are arranged to extend along the fuselage of the aircraft.

14. An aircraft according to claim 12 or 13 in which the tubes are arranged to extend along the wings of the aircraft.

15. An aircraft according to any of claims 12 to 14 in which the tubes are arranged to extend along fins of the aircraft.

16. An aircraft fuel system substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.

17. An aircraft substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.