The present invention concerns a refuel valve assembly and a method for refuelling an aircraft. More particularly, this invention concerns a refuel valve assembly and a method for refuelling an aircraft with two or more tanks.
More specifically, the invention concerns a refuel valve assembly for refuelling a first and a second fuel tank on an aircraft, wherein the refuel valve assembly comprises an inlet for receiving fuel from an orifice in a structure of the aircraft, a first and a second outlet for delivering fuel from behind the structure to the first and second fuel tanks.
The invention also concerns a method of refuelling an aircraft with two or more fuel tanks, the method comprising the steps of delivering fuel to an orifice in a structure of the aircraft, then receiving the fuel in an inlet of a refuel valve assembly behind the structure, and providing a plurality of outlets in the refuel valve assembly for delivering the fuel to the fuel tanks.
The structure of the aircraft may be a spar of the aircraft, for example the forward spar. The structure of the aircraft may be a wing skin, for example a lower wing skin. The location of orifice takes into account a mandatory safety distance from hot surfaces such as engine exhausts and wheel brakes. Also the structure which the orifice is in must be able to react a load that may be experienced from the refuelling equipment. Typically on a large passenger aircraft with a dihedral wing this would place the orifice outboard of the (outboard) engine and as a result, place it high above ground level. So access to the refuel valve assembly becomes important and for this reason the lower wing skin (aft of the forward spar) and the forward spar itself become candidates for placement of the orifice. Notably, locating the orifice in the aft spar is more difficult as it is usually smaller than the forward spar and includes flaps and ailerons etc. In addition, some civil aircraft also have a gravity feed for fuel, for which is located on the upper wing surface. In this case, the orifice would be in the upper wing skin.
Existing refuel systems for refuelling two or more tanks fall broadly into two categories; (i) a gallery system and (ii) a system using a refuel manifold and separate delivery lines.
In both systems, fuel is supplied from ground equipment such as a fuel bowser, or similar. During refuel, the fuel is passed from the ground equipment to a refuel coupling on the aircraft through a fuel pipeline. The refuel coupling is generally located at the wing leading edge, in front of the wing front spar.
In a gallery system, as shown in FIGS. 1a, 1b and 1c, there is generally one hole in the front spar 13 of the aircraft wing 10. The refuel coupling 20 is connected to this hole in front of the front spar 13, behind the wing leading edge 12 and is covered by a refuel coupling cap 21 (shown in FIG. 1c) when refuel is not taking place. The refuel coupling 20 can also be accessed by an access panel 14 on the underside of the wing for maintenance. The refuel coupling 20 connects to the ground equipment during refuel.
Behind the front spar 13, a fuel tank delivery line 30 is connected around the hole. The fuel tank delivery line 30 splits using connector joints at various points to connect to the different fuel tanks 11 on board the aircraft. At each connector joint there is a ball valve that controls flow of fuel from the fuel tank delivery line 30 into the designated fuel tank 11. Tank 11a is the right wing tank, tank 11b is the centre tank and tank 11c is the left wing tank. There is also a solenoid controlled shut-off valve (not shown) on the fuel delivery line 30, near the hole in the front wing spar 13. This shut-off valve can either be open, to allow fuel to be delivered to the fuel tanks 11, or closed, to prevent fuel being delivered to the fuel tanks 11. During fuel delivery, fuel is pumped into the fuel delivery line 30 through the refuel coupling 20 and the hole in the front wing spar 13.
It is essential to balance fuel delivery to the different tanks so that the fuel flow to each tank is proportionate to the tank volume. It is also essential that the fuel tanks are not over-pressurised and that there is no fuel spillage due to over-filling of the tanks. This is achieved by providing fixed orifice plate restrictors 31a, 31b in various places on the fuel delivery line. Shut-off valves (not shown) are also provided at the branching of the line 30 into different tanks 11. The fixed orifice plate restrictors 31a, 31b act to restrict fuel flow and reduce pressure in the fuel delivery line 30 downstream of the restrictor. A fixed orifice plate restrictor 31b (shown in FIG. 1b) with a small orifice is in place towards the end of the fuel delivery line 30 in the branch line to the left wing tank 11c to restrict fuel delivery into left wing tank 11c, the downstream most tank on the delivery line 30. A larger orifice restrictor 31a is in place further upstream on the delivery line 30 in the branch line to the right wing tank 11a. 
These restrictors 31a, 31b act to increase the refuel time as they reduce the fuel flow.
In addition, their presence causes Electro-Static Discharge (ESD) to build up in the fuel. This is because the restrictors disturb the fuel flow. Fuel flowing through a restrictor has increased flow turbulence and suffers from a shearing effect and a pressure drop. As a result, the fuel has an increased charge density.
In the gallery system, the restrictors 31 are placed as far away from a diffuser in the tanks 11 as possible to give the fuel maximum length of delivery line to “relax”. This “relaxing” of the fuel reduces the ESD in the fuel. However, the distances between the restrictors and the diffusers are governed by the location of the shut-off valve to each tank, the location of the diffuser (located at the lowest point of the tank 11) and trying to achieve a minimised system weight. Hence, the distances of the restrictors from the diffusers are, in fact, relatively small when compared to the total length of the delivery line 30.
Furthermore, the presence of connector joints in the delivery line 30 causes additional turbulence to the fuel, and therefore additional ESD is built up in the fuel.
In order to keep the level of ESD acceptably low, the fuel flow rate has to be purposefully reduced. This obviously increases the refuel time.
Furthermore, the fuel flow rate must also be kept low in order to prevent downstream surge pressures upon shutting of the control valve or shut-off valves. These downstream surge pressures can be caused when the valves are closed and causes a low-pressure region adjacent to the valve. This can cause the column of fuel downstream of the low-pressure region to return and impact on the valve.
In addition, upstream surge pressures are also created when the valves are shut too quickly. There are methods of trying to reduce these surge pressures such as shutting the—valves slowly, limiting fuel flow rate, using flexible delivery line hosing and using pressure reducing valves. However, each of these has their own disadvantages.
Any surge pressures must be accommodated by the refuel system components and this adds weight and complexity to the system.
In the separate delivery lines system, as shown in FIG. 2, there are many holes 115a, 115b, 115c in the front wing spar 113, each hole being connected to a separate delivery line 130a, 130b, 130c leading to one of tanks 111 on the aircraft. Hence, there is a hole in the spar for each tank that is to be refuelled. A manifold 122 is connected to the front of the front wing spar 113 and covers all of the holes in the wing spar. The manifold 122 has a solenoid valve 123a, 123b, 123c associated with each spar hole 115a, 115b, 115c. The solenoid valves 123 can either be open or closed to control delivery of fuel into the different delivery lines 130. The manifold 122 is connected to a refuel coupling 120 that connects to the ground equipment during refuel.
During fuel delivery, fuel is pumped from the ground equipment to the refuel coupling 120 and into the manifold 122. The fuel is then delivered to the different fuel tanks 111 by opening the corresponding solenoid valves 123 in the manifold 122. In addition, flow restrictors (not shown) are also required in the individual delivery lines 130 leading to the fuel tanks. This is because actual restriction requirements are dependent upon the different tank 111 volumes and the wing tank vent system.
This manifold and separate delivery lines system requires the wing front spar 113 to be provided with a hole 115 for each tank that needs to be refuelled. To enable sufficient structure to react the load applied to the wing spar, there must be a minimum separation between the holes in the wing spar. This distance is called the pitch. With a larger pitch and/or more holes in the spar, the manifold must be longer in length. This means that the weight of the manifold, and therefore the aircraft as a whole, is increased. In addition, for each hole, there is an area of re-enforcement (not shown) around the hole in order to stabilise the spar structure. This also increases the weight of the aircraft for each hole.
Furthermore, if an aircraft is provided with a later additional fuel tank, modification of the wing spar 113 is needed in order for an additional hole to be cut in the spar 113 to allow the additional fuel tank to be refuelled. For example, if the aircraft is manufactured with three tanks and an additional cargo tank (ACT) is then desired, a fourth hole would need to be provided in the wing spar 113, a certain minimum pitch from any of the existing holes. The additional hole needs to be provided with re-enforcement. The manifold 122 then also requires modification in order to cover the additional hole. Both of these add to the weight of the aircraft. If a further ACT is desired, this again requires a further additional hole, adding again to the weight of the aircraft. Furthermore, where numerous ACT's are to be added, adaptation of the wing spar 113 in production or service may give rise to complications that could prevent installation of the required additional equipment. It is not generally considered feasible to modify the wing spar for the above-mentioned reasons. Hence, another method of adding the additional tanks must be found, which involves modifying the existing refuel system, which may make it inefficient.
If the wing is made from a metallic structure (for example, aluminium alloy), it is fairly simple to modify the spar to provide additional holes for any additional tanks required, as long as the changes are within the scope of structural change allowed by the metallic wing. However, this obviously adds to the cost of providing additional tanks, either during production or in service.
If the wing is made from a composite material, such as Carbon Fibre Re-enforced Plastic (CFRP), it is especially difficult to modify the spar to provide additional holes for any additional tanks. This is because the re-enforcement required for the holes needs to take the form of composite layers being added across and along the structure and not just locally to the hole, as in metallic structures. Hence, additional holes in a composite wing structure and the subsequent re-enforcement, may add more weight than in a comparative metallic structure. It also means that, due to the production method of a composite spar, post-production modification is extremely difficult. Hence, the number of holes in the wing must be minimised (to minimise weight). The number of holes must also provide for any foreseeable addition to the number of fuel tanks so that a whole new spar is not required. For example, an aircraft may have six ACT's to be installed as an option. This means that the manifold and separate delivery lines system is not particularly suitable for use in composite wing structures, as any weight reduction due to the use of composites is negated by the increase in weight (estimated at 1.5 kg) for each of the required holes. The estimate of 1.5 kg is based on a spar for a single-aisle aircraft such as an Airbus A320.
In addition, both systems utilise solenoid control valves. However, the use of solenoid valves has disadvantages. For example, the solenoid valve represents a convoluted route for the fuel and so results in a pressure drop across the valve. The solenoids of the valves must be mounted on the valves and this means that they may be difficult to access for maintenance purposes. Also, the solenoids require a constant drain on the aircraft electrical system during refuel as at least one solenoid in each valve must be powered during refuel. In addition, the powered solenoid will get heated up which can cause decreased reliability.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved refuel valve assembly and method for refuelling an aircraft with two or more tanks.