GB2373772A

GB2373772A - Aircraft undercarriage system

Info

Publication number: GB2373772A
Application number: GB0107437A
Authority: GB
Inventors: Philip Lawrence Webberley
Original assignee: BAE Systems PLC
Current assignee: BAE Systems PLC
Priority date: 2001-03-24
Filing date: 2001-03-24
Publication date: 2002-10-02
Also published as: GB0107437D0

Abstract

An aircraft undercarriage system comprises a fluid circuit 18, a pump 20 for pumping fluid through the fluid circuit 18, an undercarriage leg 10 which can be raised and/or lowered by means of a first fluid operable jack 12 arranged in the fluid circuit 18, and a shock absorber 24 for the leg 10 which defines a reservoir of fluid 20 for the fluid circuit. The circuit also includes a second fluid operable jack 30 for operating the undercarriage door 28, and the pump operates the two jacks substantially simultaneously or in timed relationship.

Description

Aircraft Undercarriage System The invention relates to an aircraft undercarriage system. The undercarriage is an essential part of an aircraft, but is only used when the aircraft is on the ground, or during take off and landing. Typically, during flight, the undercarriage is retracted into and stowed In the body of the aircraft. it is extended again for landing. Retraction and extension of the undercarriage are brought about by means of hydraulic actuators forming part of the main hydraulic system of the aircraft. The main aircraft hydraulics are therefore required to cope with both essential flight controls and utility systems as well as retraction and extension of the undercarriage, sometimes all at the same time. Whilst the main aircraft engines are able to power the hydraulics for both flight controls and undercarriage movement simultaneously the Auxiliary Power Unit (APU) of the aircraft has a limited power supply that cannot cope with both requirements In that way. Therefore ground maintenance staff are unable to run both hydraulic systems completely without using the main engines, or Aircraft Ground Equipment (AGE).

One object of the present invention is to provide an aircraft undercarriage system which IS controlled In an improved manner.

According to a first object of the invention there is provided an aircraft undercarriage system comprising a fluid circuit, a pump for the fluid circuit, an undercarriage leg which can be raised and/or lowered by means of a fluid

operable actuator in the fluid circuit and a shock absorber for the leg which defines a reservoir of fluid for of the fluid circuit.

According to a second aspect of the invention there is provided an aircraft undercarriage system on an aircraft, the aircraft having a fluid system comprising a first part in the form of a fluid circuit, a pump for pumping fluid through the fluid circuit, an undercarriage leg which can be raised and/or lowered by means of a fluid operable actuator arranged in the fluid circuit and a shock absorber for the leg which defines a reservoir of fluid for the fluid circuit and a second part operable independently of the first part for operating other fluid-operable circuitry of the aircraft which may or may not Include all the Flight Control systems.

With such an undercarriage system as set out in either aspect and where the fluid is a hydraulic fluid, the undercarriage is raised and lowered by a hydraulic system which is completely separate from the remaining aircraft hydraulics, used for flight controls and other utility systems. In this way it is possible for the ground maintenance staff to check the hydraulics system of the aircraft, without running the main engines, or using AGE. A main undercarriage shock absorber such as an Oleo shock absorber can contain up to ten litres of oil that is not used while the aircraft is airborne. By separating the undercarriage hydraulics from the remaining system the reservoir and pumps for the remaining hydraulic system can be made smaller. In certain aircraft reservoir capacities are about fourteen litres. In such cases the aircraft hydraulic system requires a large takeoff to drive the pump and the secondary power system, powered by the APU, can only operate one hydraulic system at a time. By powering the undercarriage system separately using its own pump the demands on the APU are reduced, such that the APU IS capable of powering all the other hydraulics systems simultaneously.

Separation of the hydraulic system for the undercarriage from that of the other functions IS also advantageous because It reduces the number of hydraulic lines and routes that currently exist. That is likely to increase aircraft survivability should it suffer damage whilst airborne.

Preferably the pump causes fluid to be drawn from and returned to the reservoir, to keep the volume of fluid in the reservoir substantially constant.

In a preferred embodiment a further fluid actuator is arranged in the fluid circuit for operating a component associated with the undercarriage, for example an undercarriage door.

Large transport and passenger aircraft have more than two main undercarriages and so have a potentially greater reservoir capacity. It is possible that the shock absorber reservoir in such cases could be the main hydraulic supply for all utilities, such as the undercarriage, brakes, ramps and in-flight refuelling probes, leaving a much smaller reservoir and engine driven pump to supply the flight controls. It is possible that these too may be supplied by the undercarriage.

In certain aircraft the main undercarriages are close together. In this type of aircraft the pump may be shared between both undercarriages. In other aircraft each undercarriage may have its own pump. Where each undercarriage leg is supplied with its own pump self-jacking and self-propulsion along the ground may be possible. These functions are useful to reduce what is known as the "logistic footprint"of the aircraft, such that the aircraft needs less support equipment.

An aircraft undercarriage system will now be described, by way of example only, with reference to the accompanying drawings which is a diagrammatic representation of an aircraft undercarriage and associated fluid circuit forming an undercarriage system in accordance with the invention.

An aircraft undercarriage 5 comprises a leg 10 which can be raised or lowered by means of a fluid-operable jack 12. The leg is pivotally connected to the body structure 14 of the aircraft at a hinge point 16. The leg can be pivoted between an extended position, as shown in figure 1 and a retracted position. The directions of movement are shown by arrow A.

The jack 12 forms part of a fluid circuit 18. The fluid circuit 18 is powered by an electro-hydraulic pump generally indicated at 20, which itself is driven from an electrical supply, generally indicated at 22. The leg 10, comprises an Oleo-type shock absorber 24. The shock absorber contains a reservoir of oil 26 which, in accordance with the invention, supplies the fluid circuit 18.

The undercarriage system further comprises an undercarriage door 28 which is raised and lowered by means of a second fluid-operable jack 30. The door 28 is pivotally connected to the body structure 14 of the aircraft and can be pivoted between an open position as shown in the drawing and a closed position. The door is pivotable in the directions shown by arrow B The jack 30 forms part of the fluid circuit 18.

In use and with the leg 10 extended and the door 28 open as shown in the drawing, the aircraft takes off from the ground. Once airborne, the aircraft pilot operates controls to activate the electro-hydraulic pump 20 to pump oil from the reservoir 26 in the shock absorber 24 through the fluid circuit 18, thereby operating jacks 12,30. Pumping oil into the jack 12 pivots the leg 10 about the hinge point 16 and raises the leg into its retracted position in the body structure 14 of the aircraft. Operation of the second jack 30, raises the undercarriage door 28, to enclose the undercarriage after the leg 10 has been retracted. The pump 20 can then be deactivated and the system left dormant.

To lower the undercarriage 5, the pilot activates the pump 20 and a valve (not shown) operates to reverse the directions of fluid flow to and from the jacks 12, 30. The pump 20 pumps oil from the reservoir 26 into the first and second jacks, 12 and 30 so that the second jack 30 lowers the undercarriage door 28 and the first jack lowers the leg 10 into the extended position for landing. Fluid exhausted from the jacks 12.30 during raising and lowering of the undercarriage leg 10 and undercarriage door 28 returns to the reservoir 26 in the shock absorber 24.

Claims

1. An aircraft undercarriage system comprising a fluid circuit, a pump for pumping fluid through the fluid circuit, an undercarriage leg which can be raised and/or lowered by means of a fluid operable actuator arranged in the fluid circuit and a shock absorber for the leg which defines a reservoir of fluid for the fluid circuit.

2 An aircraft undercarriage system on an aircraft, the aircraft having a fluid system comprising a first part in the form of a fluid circuit, a pump for pumping fluid through the fluid circuit, an undercarriage leg which can be raised and/or lowered by means of a fluid operable actuator arranged in the fluid circuit and a shock absorber for the leg which defines a reservoir of fluid for the fluid circuit and a second part operable independently of the first part for operating other fluid-operable circuitry of the aircraft.

3. An aircraft undercarriage system according to claim 1 or 2 In which the pump causes fluid to be drawn from and returned to the reservoir, to keep the volume of fluid in the reservoir substantially constant.

4. An aircraft undercarriage system according to claim 1,2 or 3 in which a further fluid actuator is arranged In the fluid circuit for operating a component associated with the undercarriage.

5. An aircraft undercarriage system according to claim 4 in which the said component is an undercarriage door

6. An aircraft undercarriage system according to claim 4 or 5 in which the pump operates the two actuators in timed relationship.

7 An aircraft undercarriage system according to claim 4 or 5 in the two actuators are operated substantially simultaneously.

8. An aircraft undercarriage system constructed and arranged substantially as described herein with reference to the accompanying drawing.