Method for reducing the fuel consumption of aircraft, and aircraft

Abstract

The invention relates to a method (100) for reducing the fuel consumption of aircraft (1) in particular during cruising, and to an aircraft (1) designed to carry out the method (100). The method (100) according to the invention for reducing the fuel consumption of aircraft (1) in particular during cruising, which aircraft (1) comprises at least two separate fuel tanks (12s, 12b), the lateral distances of the centers of gravity of which from the longitudinal axis (1') of the aircraft (1) are different, comprises the following steps: – identifying the current attitude and the control deflections of the individual control surfaces (6, 7) [step 120]; – determining the current fuel distribution of the existing quantity of fuel among the fuel tanks (10, 11, 12s, 12b) of the aircraft (1) [step 130]; – calculating an optimized fuel distribution of the existing quantity of fuel in the fuel tanks (10, 11, 12s, 12b) for reducing the control deflections of the control surfaces (6, 7) [step 140]; and – adjusting the fuel distribution in the fuel tanks (10, 11, 12s, 12b) from the the current fuel distribution to the calculated fuel distribution [step 160]. The aircraft (1) according to the invention comprises a controller for carrying out this method.

Description

[0001] Methods for reducing fuel consumption of aircraft and aircraft

[0002] The invention relates to a method for reducing the fuel consumption of aircraft, particularly during cruising flight, as well as to an aircraft designed to carry out the method.

[0003] Due to manufacturing tolerances, aircraft are often not aerodynamically symmetrical relative to their longitudinal axis even when delivered. This aerodynamic asymmetry is often further exacerbated during operation and through maintenance and repair work. This aerodynamic asymmetry results in moments acting on the aircraft during flight that must be compensated for by appropriate control deflections of the controls – particularly the ailerons and / or rudder. Further moments compensated for by the ailerons and / or rudder during flight can arise from an uneven weight distribution relative to the longitudinal axis of an aircraft.

[0004] If the ailerons and / or rudder must be deflected continuously to compensate for the moments acting on the aircraft, the aircraft is in a continuous sideslip, with increased aerodynamic drag due to the deflected ailerons and / or rudder. This increased aerodynamic drag directly results in increased fuel consumption.

[0005] The object of the present invention is to create a method and an aircraft in which the disadvantages and problems known from the prior art no longer occur or only occur to a reduced extent. This object is achieved by a method according to claim 1 and an aircraft according to claim 8. Advantageous further developments are the subject of the dependent claims.

[0006] The invention accordingly relates to a method for reducing the fuel consumption of aircraft, particularly during cruising flight, the aircraft having at least two separate fuel tanks whose respective centers of gravity are at different laterally distances from the longitudinal axis of the aircraft, comprising the steps of: a) detecting the current flight attitude and the control deflections of the individual rudders; b) determining the current fuel distribution of the available fuel quantity across the fuel tanks of the aircraft; c) calculating an optimized fuel distribution of the available fuel quantity to reduce the control deflections of the rudders; and d) adjusting the fuel distribution in the fuel tanks from the current fuel distribution to the calculated fuel distribution.

[0007] The invention further relates to an aircraft with separate fuel tanks comprising at least two fuel tanks, whose respective centers of gravity are at different laterally distances from the longitudinal axis of the aircraft, and a fuel system for the controlled removal of fuel from the individual fuel tanks, wherein a controller connected to the fuel system is provided which is designed to carry out a method according to one of the preceding claims. The invention has recognized that by changing the weight distribution of an aircraft relative to its longitudinal axis during flight, the compensation of disturbing moments acting on the aircraft can be reduced by suitable rudder deflection, thereby reducing aerodynamic drag and consequently also fuel consumption. The method can generally be carried out without additional sensors or the like.be applied provided that the aircraft has at least two fuel tanks, the centres of gravity of which are at different laterally distances from the longitudinal axis of the aircraft.

[0008] According to the invention, the current flight attitude and the control deflections of the individual control surfaces are recorded. In modern aircraft, in particular commercial aircraft, the corresponding information is already regularly recorded for other reasons and is available in the form of data that can be used directly for the method according to the invention. From the data recorded in this way, it can be deduced whether disturbing moments are acting on the aircraft about its longitudinal axis which must be compensated for by control surface deflections. This is fundamentally possible in any flight attitude, but can be illustrated using a simple example: During precise straight-ahead flight of the aircraft, ideally no control surface deflection would be recorded; however, if a control surface deflection is detected, this obviously serves exclusively to compensate for disturbing moments in view of the straight-ahead flight.

[0009] Furthermore, the current fuel distribution of the total available fuel quantity across the aircraft's fuel tanks is recorded. In principle, all of the aircraft's fuel tanks can be taken into account in this analysis, including fuel tanks arranged along the aircraft's longitudinal axis - and thus not laterally spaced from it. However, those fuel tanks whose respective centers of gravity are laterally spaced from the aircraft's longitudinal axis are particularly relevant for the present invention, with the centers of gravity of at least two fuel tanks being laterally spaced from the longitudinal axis at different laterally spaced distances. In this context, "differently laterally spaced" means that the distance between the longitudinal axis and the center of gravity in the plane defined by the longitudinal and transverse axes is different when viewed scalarly and / or vectorially.In particular, two fuel tanks arranged symmetrically with respect to the longitudinal axis, for example in the wings, are laterally spaced differently from the longitudinal axis, even if the scalar distance between the respective center of gravity and the longitudinal axis may be identical.

[0010] Based on this information, a fuel distribution optimized for the current fuel distribution is then calculated. This is based on the finding that by changing the fuel distribution, particularly in the fuel tanks spaced laterally from the longitudinal axis, a weight moment can be generated around the aircraft's longitudinal axis, which can at least partially compensate for the aforementioned disturbance moments. As a result, the rudder deflections otherwise required for this purpose can be reduced, thus also reducing aerodynamic drag and ultimately fuel consumption.

[0011] Various factors can be taken into account when calculating the optimized fuel distribution. Firstly, the current fuel consumption and the current fuel withdrawal from the individual fuel tanks can be taken into account in order to anticipate any short-term changes in the fuel distribution when determining the optimized fuel distribution. Furthermore, if the position of the center of gravity of individual fuel tanks depends on the amount of fuel they contain, the actual or expected position of the center of gravity of the individual fuel tanks can be taken into account. This depends not only on the distance between the center of gravity of a fuel tank and the longitudinal axis of the aircraft. The center of gravity of a fuel tank can also "wander" in a direction parallel to the longitudinal axis of the aircraft depending on the fill level.This can be compensated for by changing the fuel distribution in fuel tanks located along the longitudinal axis. The center of gravity of individual fuel tanks may also change depending on the aircraft's attitude, which can also be taken into account, especially if the procedure is not performed exclusively during straight flight.

[0012] Once an optimized fuel distribution has been determined, the actual fuel distribution is then adjusted from the current fuel distribution to the optimized fuel distribution so that the rudder deflections to compensate for the disturbance moments can be reduced and the fuel savings can actually be achieved.

[0013] The adjustment of fuel distribution can usually be achieved directly with the fuel system available on board aircraft, especially modern commercial aircraft. For reasons of redundancy in the fuel supply to the engine(s), the continuous fuel withdrawal can be concentrated on individual fuel tanks, for example, by selectively operating fuel pumps and controlling fuel valves, or the fuel withdrawal from the individual fuel tanks can be specifically controlled in terms of withdrawal or flow rate.By adjusting the current fuel withdrawal accordingly, whereby more fuel is withdrawn from tanks that require a smaller relative amount of fuel for the optimized fuel distribution compared to the current fuel distribution, the current fuel distribution can be changed towards the optimal fuel distribution in the fuel tanks.

[0014] Alternatively, it is possible to adjust the fuel distribution in the fuel tanks at least partially with the help of one or more cross-feed pumps. If suitable cross-feed pumps are available, fuel can be pumped directly from a fuel tank which, according to the optimal fuel distribution, should have a smaller amount of fuel than currently present, into a fuel tank which contains too little fuel with regard to the optimized fuel distribution. With the help of suitable cross-feed pumps, the optimized fuel distribution can generally be achieved more quickly and flexibly than by simply adjusting the fuel withdrawal from the individual fuel tanks. However, suitable cross-feed pumps must be present between the fuel tanks which are spaced laterally at different distances from the longitudinal axis of the aircraft.

[0015] Once optimized fuel distribution is achieved for the individual fuel tanks, particularly in those located laterally spaced from the aircraft's longitudinal axis, the disturbance torques caused by the control surfaces are reduced, allowing the control surface deflection to be reduced to maintain the current flight attitude. Consequently, fuel consumption is also reduced.

[0016] The detected flight attitude used to calculate the optimal fuel distribution preferably includes the aircraft's roll and yaw attitude, although it may even be sufficient to use only the aircraft's roll and yaw attitude. Regarding the control deflections of the individual control surfaces to be detected, the ailerons and rudder are primarily important, and should at least be detected, while the elevator, if at all, plays only a subordinate role in the method according to the invention.

[0017] As already mentioned, it is fundamentally possible to carry out the inventive calculation of an optimized fuel distribution of the available fuel quantity in a large number of different flight attitudes. The adjustment of the fuel distribution in the fuel tanks can also fundamentally be carried out in any flight attitude. However, in order to avoid such an adjustment taking place while a flight maneuver is being carried out, which could possibly lead to irritation of the pilot or other undesirable consequences for the flight maneuver, it is preferred that the method comprises a detection of flight maneuvers and the calculation of an optimized fuel distribution and / or the adjustment of the fuel distribution is only carried out if no flight maneuvers or only certain flight maneuvers are detected.For example, the method according to the invention can be limited to a flight condition in which the aircraft is at the intended cruising altitude and in straight-ahead flight, i.e. no flight maneuver is carried out.

[0018] In order to avoid any undesirable interference with the flight behavior of the aircraft, but also to enable the procedure to be carried out on existing aircraft where an automated adjustment of the fuel flow from individual fuel tanks may not be provided, it can be provided that the actual adjustment of the fuel distribution is carried out by settings made by the pilot on the

[0019] The provided instructions are based on the current and calculated fuel distribution. For example, the pilot can be shown fuel system settings on cockpit monitors or other displays, allowing a previously calculated, optimized fuel distribution to be achieved. The pilot then simply has to implement these settings at an appropriate time.

[0020] Alternatively, it is of course possible for the actual adjustment of the fuel distribution to be carried out automatically. This only requires a suitable control system for the fuel system, which can automatically achieve the calculated, optimized fuel distribution. However, it is preferable to obtain pilot approval before the fuel distribution adjustment is actually carried out. This ensures that the fuel distribution adjustment only occurs in flight phases and situations that are, from the pilot's perspective, truly non-critical.

[0021] For an explanation of the aircraft according to the invention, reference is made to the above explanations.

[0022] The control system provided for carrying out the method according to the invention on board the aircraft can be designed as a separate computer module that is suitably connected to other systems of the aircraft in order to receive the necessary data and information from them and, if necessary, to be able to issue control signals. However, the control system can also be designed as a pure software module that is executed on a computer already provided in the aircraft and suitably connected.

[0023] In the aircraft according to the invention, a transverse feed pump can be provided as part of the fuel system in at least one compensating line between two fuel tanks spaced at different lateral distances from the longitudinal axis of the aircraft. With a corresponding transverse feed pump, an adjustment of the fuel distribution in the individual fuel tanks can be achieved more quickly, if necessary, than a corresponding adjustment solely by changing the fuel withdrawal from the individual fuel tanks.

[0024] The invention will now be described by way of example using an advantageous embodiment with reference to the accompanying drawings. They show:

[0025] Figure 1: a schematic representation of an aircraft in

[0026] Straight flight without application of the method according to the invention;

[0027] Figure 2: a schematic representation of an aircraft according to the invention in straight flight after application of the method according to the invention; and

[0028] Figure 3: a schematic representation of the sequence of the method according to the invention.

[0029] Figure 1 schematically shows an aircraft 1 in straight flight, which has a total of four fuel tanks 10, 11, 12s, and 12b. The fuel tank 10 is arranged centrally in the fuselage 2 of the aircraft 1, while the fuel tank 11, as a trim tank known from the prior art for the control surface 3 of the elevator, is designed symmetrically to the longitudinal axis 1' of the aircraft 1, which runs perpendicular to the blade plane. Furthermore, fuel tanks 12s, 12b are located in both the starboard wing 4s and the port wing 4b.

[0030] The aircraft 1 has a distributed fuel system 15, only schematically indicated in Figure 1, with which the engines 5 of the aircraft 1 can be supplied with fuel as required from any of the four fuel tanks 10, 11, 12s, and 12b. The fuel system 15 has corresponding pumps and controllable valves for this purpose. A cross-feed pump (not shown) is also arranged between the fuel tank 10 in the fuselage 2 and the fuel tank 11 in the control surface 3 of the elevator in order to be able to establish a desired trim by appropriately distributing the amount of fuel in these two fuel tanks 10, 11. Furthermore, an optional compensating line 16 can be provided, which is intended to ensure that the two fuel tanks 12s, 12b in the two wings 4s, 4b basically have the same fill level. This is known from the prior art.

[0031] According to the state of the art, the two fuel tanks 12s, 12b in the wings 4s, 4b are essentially filled evenly. Consequently, the weight forces of the two fuel tanks 12s, 12b, indicated by arrows 90s and 90b, are also identical to the fuel they contain.

[0032] For example, due to an aerodynamic asymmetry, deflections of both the rudder 6 and the ailerons 7 are required to maintain the straight flight desired in Figure 1 (the deflections in Figure 1 being significantly exaggerated for illustrative purposes). Regardless of the extent of the control deflections, they increase the aerodynamic drag and thus the fuel consumption of the aircraft 1, particularly in the straight flight illustrated in Figure 1, which typically accounts for a large portion of a commercial aircraft's flight.

[0033] Based on the state outlined in Figure 1, the method 100 according to the invention, as schematically illustrated in Figure 3, can be carried out. The method 100 can be executed, at least in large part, by a controller not illustrated in Figure 1. The controller can, for example, be a separate computer module that has a data connection to other systems of the aircraft 1. However, the controller can also be designed as a pure software module that is executed on a computer already provided in the aircraft 1.

[0034] In a first step 110, a check is made to determine whether a flight maneuver is currently being performed or whether the aircraft 1 is in straight-ahead flight at cruising altitude, i.e. whether no flight maneuver is being performed. The corresponding check can be made using current flight parameters provided by the corresponding on-board instruments or suitable information from an autopilot, if present on the aircraft. In the exemplary embodiment shown, the further steps of the method only run if this is the case. Otherwise, the check is repeated until straight-ahead flight at cruising altitude is actually determined. This prevents the method 100 from being executed during a flight maneuver.

[0035] If straight-ahead flight at cruising altitude is determined, the current flight attitude and the control deflections of the individual control surfaces are first recorded (step 120), with this information also being provided by corresponding on-board instruments of the aircraft 1. The flight attitude comprises at least information on the current yaw and roll angle, and the control deflections at least information on the deflection of the ailerons and rudder 6, 7.

[0036] In step 130, the current fuel distribution of the available fuel quantity across the fuel tanks 10, 11, 12s, 12b of the aircraft 1 is also recorded. For the method 100, the fuel quantities in the fuel tanks 12s, 12b that are spaced horizontally from the longitudinal axis 1' of the aircraft 1 during straight-ahead flight—that is, those in the wings 4s, 4b—are particularly important; however, the fuel quantity in the other fuel tanks 10, 11 can also play a role in the method 100, so that their fuel quantity is also recorded. The flow rate at which fuel is currently being withdrawn from the individual fuel tanks 10, 11, 12s, 12b is also recorded.

[0037] Based on the data thus recorded and determined, an optimized fuel distribution of the available fuel quantity in the fuel tanks 10, 11, 12s, 12b is then calculated in step 140, which leads to a reduction in the control deflections of the rudders 6, 7. In particular, by changing the fuel distribution in the fuel tanks 12s, 12b and the associated change in the weight forces 90s, 90b, a moment about the longitudinal axis 1' of the aircraft 1 is created, with which at least the control deflection of the ailerons 7 (see Figure 1) can be reduced. Due to flight dynamics, the control deflection of the rudder 6 (see Figure 1) can also be reduced.

[0038] Changing the amount of fuel in the fuel tanks 12s, 12b also changes their center of gravity. Due to the usual sweep of the wings 4s, 4b and the corresponding design of the fuel tanks 12s, 12b, this not only changes laterally but also longitudinally of the aircraft 1, which may need to be compensated for by changing the fuel distribution in the fuel tanks 10, 11. When calculating the optimized fuel distribution of the existing fuel quantity in the fuel tanks 10, 11, 12s, 12b, these and any other changes in the center of gravity positions are taken into account. In a next step 150, the pilot of the aircraft 1 is informed of the optimized fuel distribution, e.g., by displaying it on a suitable screen in the cockpit of the aircraft.The pilot can then—depending on the configuration of the aircraft 1—confirm the optimized fuel distribution, whereupon the fuel distribution is adjusted automatically, or he can receive instructions on how to adjust the fuel system 15 to achieve the desired fuel distribution, which he can then implement. If the pilot decides against adjusting the fuel distribution, e.g., because a flight maneuver is imminent, the method 100 begins again until it returns to step 150.

[0039] Regardless of whether the adjustment of the fuel distribution is automated or occurs with the active assistance of the pilot, there are basically two ways to adjust the fuel distribution. Firstly, the fuel can be adjusted by at least temporarily changing the fuel withdrawal from the individual fuel tanks 10, 11, 12s, 12b; secondly, the fuel can be adjusted by using suitable transverse feed pumps. In addition to the transverse feed pump already known from the prior art between the fuel tanks 10, 11 arranged along the longitudinal axis, a compensation line 16 equipped with a transverse feed pump (not shown) can also be provided between the two fuel tanks 12s, 12b in the two wings 4s, 4b, with which a change in the fuel distribution is possible by direct fuel transfer between the individual fuel tanks 10, 11, 12s, 12b.

[0040] Using the options provided by the aircraft 1 for adjusting the fuel distribution in the various fuel tanks 10, 11, 12s, 12b, after release by the pilot and / or by suitable adjustment of the fuel system 15 by the pilot in accordance with the specifications in

[0041] Step 160 the actual adjustment of the fuel distribution.

[0042] Once the adjustment of the fuel distribution in the fuel tanks 10, 11, 12s, 12b is complete, i.e., the fuel distribution corresponds to the calculated optimized fuel distribution, the method 100 can begin again from the beginning. Subsequently, repeated checks are carried out to determine whether any further control deflections of the rudders 6, 7 occur that can be reduced by suitably altering the fuel distribution.

[0043] Figure 2 shows the aircraft 1 according to Figure 1 after the method according to Figure 3 has been fully run through. As can be seen from the arrows 90s, 90b, a fuel distribution has been set between the two fuel tanks 12s, 12b in the wings 4s, 4b, in which the fuel tank 12b contains a higher quantity of fuel than the fuel tank 12s. With the help of the optimized fuel distribution in the fuel tanks 10, 11, 12s, 12b, the control deflections of the ailerons and rudder 7, 6 (cf. Figure 1) required for straight flight can be greatly reduced, if not completely avoided. The aerodynamic drag in the status of the aircraft 1 shown in Figure 2 is lower than in the status according to Figure 1. As a result, fuel consumption is also reduced.

Claims

Patent claims 1. A method (100) for reducing the fuel consumption of aircraft (1), in particular during cruising flight, wherein the aircraft (1) has at least two separate fuel tanks (12s, 12b), the respective centers of gravity of which are spaced differently laterally from the longitudinal axis (1') of the aircraft (1), comprising the steps: - Recording the current flight attitude and the control deflections of the individual rudders (6,7) [step 120] ; - Determination of the current fuel distribution of the available fuel quantity over the fuel tanks (10, 11, 12s, 12b) of the aircraft (1) [step 130] ; - Calculating an optimized fuel distribution of the available fuel quantity in the fuel tanks (10, 11, 12s, 12b) to reduce the control deflections of the rudders (6, 7) [step 140]; and - Adjustment of the fuel distribution in the fuel tanks (10, 11, 12s, 12b) from the current fuel distribution to the calculated fuel distribution [step 160].

2. Method according to claim 1, characterized in that the adjustment of the fuel distribution in the fuel tanks is carried out at least partially by adjusting the current fuel withdrawal from the fuel tanks (10, 11, 12s, 12b).

3. Method according to one of the preceding claims, characterized in that the adjustment of the fuel distribution in the fuel tanks (10, 11, 12s, 12b) is carried out at least partially by a transverse feed pump.

4. Method according to one of the preceding claims, characterized in that the detected instantaneous flight attitude includes, preferably is, the roll and yaw attitude of the aircraft (1).

5. Method according to one of the preceding claims, characterized in that the method (100) comprises a detection of flight maneuvers and the calculation of an optimized fuel distribution in the fuel tanks (10, 11, 12s, 12b) and / or the adaptation of the fuel distribution in the fuel tanks (10, 11, 12s, 12b) is only carried out if no or only certain flight maneuvers are detected.

6. Method according to one of claims 1 to 3, characterized in that the actual adjustment of the fuel distribution in the fuel tanks (10, 11, 12s, 12b) is carried out by settings of the pilot on the basis of instructions made available to him on the basis of the current and calculated fuel distribution.

7. Method according to one of claims 1 to 3, characterized in that the actual adjustment of the fuel distribution in the fuel tanks (10, 11, 12s, 12b) is carried out automatically, preferably after release by the pilot.

8. Aircraft (1) with separate fuel tanks (10, 11, 12s, 12b) comprising at least two fuel tanks (12s, 12b) whose respective centers of gravity are arranged on the longitudinal axis (1') of the Aircraft (1) are spaced apart laterally at different distances, and a fuel system (15) for the controlled removal of fuel from the individual fuel tanks (10, 11, 12s, 12b), characterized in that a controller connected to the fuel system (15) is provided, which is designed to carry out a method (100) according to one of the preceding claims.

9. Aircraft according to claim 1, characterized in that a transverse feed pump is provided as part of the fuel system (15) in at least one compensating line (12) between two fuel tanks (12s, 12b) spaced differently laterally from the longitudinal axis (1') of the aircraft (1).

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