WO2001028853A1

WO2001028853A1 - An aircraft fuel system

Info

Publication number: WO2001028853A1
Application number: PCT/GB2000/003977
Authority: WO
Inventors: Maurice Tovey
Original assignee: Airbus Uk Limited
Priority date: 1999-10-20
Filing date: 2000-10-17
Publication date: 2001-04-26
Also published as: JP2003535738A; GB9924680D0; AU7808000A

Abstract

An aircraft fuel system comprises a fuel tank (10) and a pump (14) for pumping fuel (12) from the fuel tank (10) to an engine (22). A receptacle (16) is provided for receiving fuel from the pump (14) to provide a reservoir of fuel. A duct (20) is provided along which fuel (12) is fed by gravity from the receptacle (16) to an engine (22) when fuel feed from the pump (14) is interrupted or is not supplied at a sufficient rate with the aircraft in normal flight conditions.

Description

An Aircraft Fuel System

The invention relates to an aircraft fuel system and is particularly, but not exclusively, concerned with a fuel system of an aircraft having wing-mounted engines.

On certain aircraft, fuel is supplied to an engine by means of a pump which draws fuel from the lowest part of a fuel tank on the aircraft, for example in part of the aircraft wing. During flight, the fuel in the tank tends to move around and it is necessary to have a system which prevents the problem of an erratic supply of fuel to the engine due, say, to an inlet to the pump becoming uncovered. Negative "g" conditions of the aircraft can also have a similar effect on fuel feed. In such situations it is possible for air to enter the system and air release valves are normally provided to release the entrained air. Fuel supply pressure can be significantly reduced where air reaches the pump and the provision of air release valves do not prevent that.

An object of the present invention is to provide an improved fuel system which minimises the problem outlined above.

According to one aspect of the invention there is provided an aircraft fuel system comprising a fuel tank and a pump for pumping fuel from the fuel tank to an engine, a receptacle being provided for receiving fuel from the pump to provide a reservoir of fuel from which the engine can be fed by gravity when fuel feed from the pump is interrupted or not supplied at a sufficient rate with the aircraft in normal flight conditions.

With such an arrangement, the reservoir of fuel in the receptacle minimises the problem outlined above as the fuel flow from the receptacle will not be directly affected by temporary interruption of fuel flow from the pump. The provision of the reservoir of fuel will also help to avoid air reaching the engine and, as a result, air valves for the system may no longer be necessary.

Air entering the receptacle may escape through means therein thereby minimising the risk of air reaching the engine. The receptacle is preferably kept full of fuel when the aircraft is in a normal flight condition.

A duct leading from the receptacle to the engine may have an inlet positioned above a lower end of the receptacle. In the event of the aircraft experiencing a temporary negative "g" condition tending to raise the fuel above the lower end of the receptacle, there will be sufficient fuel in the receptacle between the inlet and the lower end of the receptacle to feed the engine for at least part of the duration of the negative "g" condition.

An inlet device may be provided on or otherwise associated with the receptacle to enable fuel to enter the receptacle from the fuel tank, for example in the event of pump failure.

In a preferred embodiment, the receptacle is arranged in the fuel tank itself with an inlet for the receptacle preferably immersed in the fuel.

Also in a preferred embodiment, the pump is arranged in the fuel tank and may be immersed in the fuel.

In order to maximise the available fuel, the receptacle may have a transverse section for fuel which may extend upwardly from a position at or adjacent its upper end.

According to a second aspect of the invention there is provided an aircraft wing having therein a fuel system according to the first aspect of the invention or to any of the consistory clauses relating thereto. In such a case, the receptacle may comprise upper and lower sections, the upper section being transverse to the lower section and extending, for example upwardly, from a position at or adjacent the upper end of the lower section.

An aircraft fuel system in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: -

Fig 1 is a diagrammatic elevation of an aircraft fuel tank illustrating a fuel system in accordance with the invention, Fig 2 is a diagrammatic elevation similar to Fig 1 but showing another version of a fuel system in accordance with the invention,

Fig 3 is a plan view of the fuel tank shown in Fig 2 and

Fig 4 is a diagrammatic cross section spanwise of an aircraft wing showing the way in which the fuel system of Figs 2 and 3 can be used in practice.

With reference to Fig 1, a fuel tank 10 contains aviation fuel 12 and a pump 14. The pump 14 is located on the bottom of the tank 10 although it can be equally placed elsewhere provided that it can draw fuel from the lowest point in the tank. An upstanding receptacle 16 is suitably mounted in the tank 10 and is closed off from the tank 10 at its lower end as viewed in Fig 1. The receptacle 16 is connected at its lower end to an inlet duct 18 and to a delivery duct 20. The inlet duct 18 is connected to the pump 14 and the delivery duct 20 is connected to an aircraft engine 22. The upper end of the receptacle 16 is provided with a small diameter pipe 24.

In use, the pump 14 (for example a rotodynamic pump) pumps fuel 12 to the engine 22 and fills the receptacle 16 with fuel 12. In normal flight conditions, the receptacle 16 is kept full of fuel by the fuel pump 14 and the pipe 24 permits any excess fuel fed to the receptacle to overflow back into the tank 10. In the event of a temporary interruption of fuel feed from the pump 14 due, for example due to movement of fuel 12 within the tank

10, the receptacle 16 provides a reservoir of fuel having a head H which is sufficient fuel to maintain a supply of fuel to the engine 22 for a short period. The head H, which decreases as fuel leaves the receptacle, causes the fuel in the receptacle to be delivered by gravity at a satisfactory feed rate to the delivery duct 20. If air enters the pump 14 as a result of an inlet port or suction pipe thereof becoming uncovered, the air will simply enter the receptacle 16 and bubble up through the column of fuel 12 therein, eventually escaping through the pipe 24. Where the aircraft is subjected to a negative g condition, an inlet 26 to the delivery duct 20 may become uncovered. In that case, there will be some fuel in the delivery duct 20 to power the engine 22 briefly. Where the inlet 26 to the deliver ' duct 20 becomes uncovered in that way, air may enter the duct 20. The system shown in Figs 2 and 3 helps to minimise that possibility.

Looking now at Figs 2 and 3, the tank 10 houses two pumps 14 which pump fuel 12 to a slightly different form of receptacle 16. It will be noted from Fig 2 that the inlet 26 of the delivery duct 20 is spaced by a distance S from the closed lower end of the receptacle 16 and the receptacle has a one way inlet valve 27 in a side wall adjacent the lower end. In the event of a temporary interruption of fuel flow from the pump 14 due, say, to the aircraft experiencing a negative g condition, the fuel 12 may rise in the tank so that its lower surface lies at the position indicated at 12a in Fig 2. 2 In such a case, the pump 14 will be uncovered leading to an interruption in flow from the pump to the receptacle 16. However, there is sufficient fuel in the receptacle 16 between the inlet 26 of the delivery duct 20 and the closed lower end of the receptacle 16 to maintain a supply of fuel 12 from the receptacle 16 to the engine 22 for a brief period, say twenty litres of fuel for five seconds. Although there may be some leakage of fuel from the receptacle through the pipe 24, the leakage will be insignificant as the cross-sectional dimension of the pipe 24 is tiny compared to that of the receptacle 16.

During an interruption in flow from the pump 14 in normal flight conditions, the inlet valve 27 can open to prevent the level of fuel 12 in the receptacle 16 falling below the level of the fuel in the tank 12. Once the flow from the pump 14 is resumed, the remaining fuel 12 required to fill the receptacle 16 completely is soon supplied by the pump 14. Also, in the event of pump failure, or if the pump has been switched off, the inlet valve 27 will enable the level of fuel 12 in the receptacle 16 to stay the same as that of the fuel in the tank 10. In that way, a measure of fuel feed can be maintained provided that the fuel level in the tank does not fall below the inlet 26 of the delivery duct 20. In Fig 4, it will be seen how the system can be arranged on an aircraft and, in particular, in an aircraft wing 29 extending from a fuselage 29a. Parts corresponding to parts shown in Figs 1 to 3 carry the same reference numerals and are not described in detail.

The pump 14 has a suction pipe 28 which picks up fuel 12 from the lowest point of the tank 10. One or more additional fuel tanks are provided as indicated at 10a, 10b and 10c. The receptacle 16 is similar to the receptacle shown in Fig 2 except that a lower section 30 thereof is extended at its upper end by means of a transverse upper section 30. The transverse section 31 has the pipe 24 at its upper end and receives fuel 12. Conveniently, the transverse section 31 is inclined upwardly at an angle similar to the dihedral angle of the wing 29 so that it can follow the inside surface of the adjacent wing skin 32. The delivery duct 20 is arranged as in Fig 2

The fuel system as shown in Fig 4 operates in the same way as that in Figs 2 and 3 but with the upwardly extending transverse section 30 providing a reservoir of fuel of greater volume.

Claims

1. An aircraft fuel system comprising a fuel tank and a pump for pumping fuel from the fuel tank to an engine, a receptacle being provided for receiving fuel from the pump to provide a reservoir of fuel from which the engine can be fed by gravity when fuel feed from the pump is interrupted or not supplied at a sufficient rate with the aircraft in normal flight conditions.

2. An aircraft fuel system according to claim 1 in which the receptacle has means which permits air to escape therefrom.

3. An aircraft fuel system according to claim 2 in which the said means is arranged to permit air to enter the receptacle when fuel flows from the receptacle to the engine.

4. An aircraft fuel system according to claim 2 or 3 in which the said means enables excess fuel fed to the receptacle to overflow therefrom, for example back to the fuel tank.

5. An aircraft fuel system according to any preceding claim in which the receptacle is normally kept full of fuel by the fuel pump.

6. An aircraft fuel system according to any preceding claim in which a duct leading from the receptacle to the engine has an inlet positioned above a lower end of the receptacle.

7. An aircraft fuel system according to any preceding claim in which an inlet device such as a valve is associated with the receptacle to enable fuel to enter the receptacle directly from the fuel tank when required.

8. An aircraft fuel system according to any preceding claim in which the receptacle is arranged in the fuel tank.

9. An aircraft fuel system according to claim 8 in which the lower end of the receptacle has an inlet which, in use, is immersed in the fuel.

10. An aircraft fuel system according to any preceding claim in which the pump is arranged in the fuel tank.

11. An aircraft fuel system according to claim 10 in which, in use, the pump is normally immersed in the fuel.

12. An aircraft fuel system according to any preceding claim in which the receptacle comprises upper and lower sections, the upper section being transverse to the lower section and extending, for example upwardly, from a position at or adjacent the upper end of the lower section.

13. An aircraft fuel system constructed and arranged substantially as described herein with reference to the accompanying drawings.

14. An aircraft wing having therein a fuel system according to any preceding claim.

15. An aircraft wing according to claim 13 in which the receptacle has a transverse section for fuel extending upwardly from a position at or adjacent its upper end at an angle substantially corresponding to a dihedral angle of the wing.