Method and computer program product for estimating the weight of an aircraft
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- LUFTHANSA TECHNIK AG
- Filing Date
- 2024-08-30
- Publication Date
- 2026-07-08
Smart Images
Figure EP2024074254_06032025_PF_FP_ABST
Abstract
Description
Method and computer program product for estimating the weight of an aircraft
[0001] The invention relates to a method and a computer program product for estimating the weight of an aircraft.
[0002] In the case of aircraft, and especially commercial aircraft (i.e., aircraft designed for the commercial transport of passengers and / or cargo), it is known to carry out a so-called performance analysis during or after one or more flights, in which key figures are determined from the flight data currently being determined and / or recorded, based on which the performance characteristics of the aircraft can be determined.
[0003] An example of such a parameter is the actual drag coefficient of an aircraft in flight—not the one calculated during the aircraft's design. Changes in the actual drag coefficient over time allow for the detection of deteriorations in an aircraft's aerodynamic performance. These changes can then be used, for example, to initiate maintenance and / or cleaning work aimed at improving the aircraft's aerodynamic performance. Furthermore, the actual drag coefficient of an aircraft, or changes in it, can be used to determine whether aerodynamic modifications, such as the addition of winglets or aerodynamically functional film, are actually producing the desired effect.
[0004] A large proportion of the key performance indicators used for performance analysis, such as the actual resistance coefficient, are based on calculations with various input variables. A crucial parameter here is the Actual weight of an aircraft at the time of determining the other input variables.
[0005] To estimate the actual weight of an aircraft at a specific point in time during a flight, the prior art uses the following methods: starting from the aircraft's base weight, the initial fuel weight, and the estimated weight of the payload, which is derived from the so-called "load sheet" and determined, for example, based on standard weights per passenger, the weight is subtracted from the weight of the fuel consumed up to that point in time.
[0006] Particularly due to the regularly rough estimation of the payload weight, the aircraft's initial weight, or the weight determined at any given time during flight according to current technology, is quite inaccurate. This inaccuracy also affects those parameters whose determination takes the aircraft's weight into account, ultimately leading to large variations in the parameters in question between different flights of the same aircraft. Consequently, minor changes in the parameters do not reveal whether an aircraft's performance characteristics have actually deteriorated or improved, or whether the change is merely due to an inaccurate estimate of the aircraft's weight, which forms the basis for determining the parameters.
[0007] This means, for example, that deteriorations in performance characteristics are only reliably detected as such when a performance characteristic changes significantly beyond its usual range. Until this point, the aircraft is operated without the deterioration being detected and potentially rectified. The aircraft may then be operated in a suboptimal condition, which in The result is regularly higher fuel consumption.
[0008] The object of the present invention is to create an improved method and a computer program product for estimating the total weight of an aircraft, so that, as a result, parameters relating to the performance characteristics of the aircraft can be determined with higher accuracy.
[0009] This problem is solved by a method and a computer program product according to the independent claims. Advantageous further developments are the subject of the dependent claims.
[0010] Accordingly, the invention relates to a method for estimating the weight of an aircraft, in particular a commercial airliner, during flight, wherein the relationship between the total aircraft weight, the lift coefficient (cl), and the angle of attack (a) is known for the aircraft, and the angle of attack and the amount of fuel are determined during flight, characterized by the steps: a) determining at least two instantaneous total aircraft weights at different times during a flight based on the respective instantaneous angle of attack and the relationship between the lift coefficient, the angle of attack, and the total aircraft weight; b) determining the respective dry total weights by subtracting the weight of the respective instantaneous amount of fuel from the determined total aircraft weights; c) averaging the dry total weight over all dry total weights determined for the same flight; and d) Estimating an instantaneous total weight at any given time during the flight by adding the weight of the fuel quantity at that time to the average dry total weight.
[0011] Furthermore, the invention relates to a computer program product or a set of computer program products comprising program parts which, when loaded into a computer or into interconnected computers, are designed to carry out the method according to the invention.
[0012] The invention recognizes that, based on the relationship between the total aircraft weight, lift coefficient, and angle of attack, as well as state parameters already determined during flight for other reasons, an estimate of the aircraft's weight can be achieved that is significantly more accurate than the prior art estimation based, among other things, on standard payload weights. Consequently, aircraft performance indicators that depend on the actual weight of the aircraft can be determined with greater accuracy.
[0013] The invention takes advantage of the fact that the relationship between total aircraft weight, lift coefficient, and angle of attack is generally known. Even if the relationship between these three quantities is not directly available, for example, in the form of a table of values that may include further input values, the relationship between lift coefficient and angle of attack is regularly provided by the aircraft manufacturer (either as a mathematical function or in the form of a table of values). This is particularly relevant when considering the aircraft's attitude angles—and, if applicable, additionally taking into account the dynamic pressure, the aircraft's airspeed, and the density of the surrounding air. The lift force can be determined from the lift, which is either measured or derived from the altitude, thus increasing accuracy. Taking into account acceleration forces on the aircraft, which can be determined using suitable accelerometers (but are usually negligible in the case of commercial aircraft, at least during phases without special flight maneuvers such as takeoff or landing), the total weight force, and thus ultimately the weight of the aircraft, can be calculated from the lift.
[0014] Due to potentially insufficient accuracy of the input variables used, such as sensor data that may be accurate enough for their original intended purpose but not for determining the total weight force, the total weight force calculated in this way is often inaccurate. For example, attitude angles and angles of attack are regularly only recorded with the accuracy required for aircraft control. A similar issue arises when determining the density of the surrounding air if the pressure sensor used has a low numerical resolution. Furthermore, various deformations of the fuselage and wings, as well as atmospheric fluctuations in temperature and air density, are not always fully captured.These inaccuracies, which are insignificant for the actual operation of the aircraft, can affect the input variables used to determine the total weight of the aircraft as well as the relationship between lift coefficient and angle of attack.
[0015] The invention recognizes that the total weight of an aircraft during flight has a constant and a variable part, the variable part being formed almost entirely by the fuel consumed during flight. The invention, as described above, The weight referred to as the "dry weight" of the aircraft can be determined by subtracting the current weight of fuel from the aircraft's weight. This dry weight can then be considered constant during flight and used to eliminate or at least reduce various influencing factors in determining the total aircraft weight.
[0016] According to the invention, the dry total weight is determined from the calculated total weight by subtracting the weight of the fuel present at the time the total weight was determined. The quantity and thus the weight of the fuel on board an aircraft is generally known at any given time during a flight.
[0017] Assuming that this total dry weight remains constant at least over one flight of the aircraft, all total dry weights determined over the course of a flight can be averaged. With a suitable number and temporal distribution of the total dry weights to be averaged, various disturbances in the determination of the total aircraft weight described above can be compensated for and reduced.
[0018] In order to determine the weight of the aircraft at any given time during flight, starting from the average dry weight, the instantaneous fuel weight at the desired time of flight must be added back to the average dry weight, so that the instantaneous total aircraft weight at the desired time is obtained.
[0019] In other words, an averaging of the proportion of the aircraft's total weight considered constant is carried out during of a flight, to which the weight of the fuel at any desired point during the flight is added to obtain the aircraft's weight at that point in time. Based on this total weight, key performance indicators for the aircraft can then be calculated for that specific flight. The more total aircraft weights are determined at different times during a flight, and thus the more data points are considered in this averaging process, the more accurate the estimate can be.
[0020] A calculation using the method according to the invention provides an estimated value. However, it has been shown that an aircraft weight estimated according to the invention, including in particular the consideration of a repeatedly determined instantaneous total aircraft weight, exhibits higher accuracy compared to the prior art, and consequently, key performance indicators based on it also regularly exhibit higher accuracy. As a result, compared to the prior art, even minor deviations in the key performance indicators from flight to flight of an aircraft allow conclusions to be drawn about the aircraft's condition and, if necessary, required maintenance or cleaning work to be initiated. This ensures the most optimal possible condition of the aircraft, which in turn leads to lower fuel consumption. Even minor improvements that may result from modifications to the aircraft, such as...the application of aerodynamically effective (riblet) foil, to be clearly demonstrated and proven.
[0021] The method according to the invention can, in principle, be carried out after an aircraft flight in order to, for example, evaluate modifications to the aircraft based on parameters derived from, among other things, the total weight determined according to the invention. For this purpose, data on the aircraft can be used. For other reasons, the time-resolved data log, which is already regularly provided for and must include at least the angle of attack and the amount of fuel or fuel consumption for this purpose, can be used.
[0022] However, it is also possible for the inventive method to be carried out at regular intervals and / or on an event-driven basis during a flight, so that the total weight thus determined can be taken into account when calculating parameters that are, for example, displayed directly to the pilot. The averaging of the dry total weight is then carried out in each case based on the dry total weights already determined for the current flight, and the determination of the current total weight is based on the actual current fuel quantity. The method can be carried out in particular at regular intervals during a flight, with the exception of certain flight maneuver phases, such as takeoff, landing, and turns.By not performing the procedure during the exemplary flight maneuvers mentioned, it can be ensured that regularly occurring disturbances related to the lift coefficient, angle of attack, and total aircraft weight do not influence the aircraft weight estimation according to the invention. However, starting from a previously determined dry weight for the flight, the current total weight can still be estimated using the current fuel quantity.
[0023] The angle of attack can be determined using an angle-of-attack sensor and / or an attitude sensor on board the aircraft. If several suitable sensors are available, an average angle of attack can be used to determine the instantaneous total aircraft weight.
[0024] The current amount of fuel, which is used to determine dry total weights as well as the current The total weight required at any given time during the flight can be determined based on a known initial fuel quantity and the actual fuel consumption over time and / or with the help of fuel quantity sensors.
[0025] The relationship between total aircraft weight, lift coefficient, and angle of attack can be at least partially defined in the form of a table of values. "At least partially" in this context means that a table of values is provided for at least two interrelated values underlying this relationship, from which the remaining values can then be derived using formulas. For example, as described above, a table of values can be provided for the relationship between lift coefficient and angle of attack, from which, taking into account further input variables and a known formula, other quantities, such as the total aircraft weight, can be calculated. However, it is also possible, of course, for one or more tables of values and / or a multidimensional table of values to directly provide an estimate of the total aircraft weight as a function of the lift coefficient and angle of attack.
[0026] It is preferred that, when averaging the total dry weight, only those total dry weights are considered that lie within a confidence interval around a previously determined averaged total dry weight or a predetermined total dry weight. By not including total dry weights lying outside such a confidence interval in the report, outliers, which may arise, for example, due to sensor malfunctions or influences not accounted for when determining a momentary total aircraft weight, such as those that can occur during certain flight maneuvers, cannot affect the averaged total dry weight and thus the The invention provides an estimation of the weight of an aircraft. As a starting point for the confidence interval, either a previously determined dry weight for the flight can be used, or alternatively, an estimated aircraft weight based on the prior art can be used. Even if a corresponding aircraft weight, which can be determined based on a load sheet and thus, for example, standard weights per passenger, does not have an accuracy comparable to an aircraft weight estimated according to the invention, such a determined aircraft weight is sufficiently close to the actual total weight to be used as a starting point for defining the confidence interval.
[0027] As already explained, the higher accuracy achievable according to the invention in estimating the weight of an aircraft enables the determination of other aircraft parameters based on this weight with greater accuracy. In particular, the weight estimated according to the invention can be used in a method for determining the drag coefficient of an aircraft, especially a commercial airliner. Corresponding methods for determining the drag coefficient are known in the art and require no further explanation here. However, these known methods all have in common that the actual weight of the aircraft is used as an input. By enabling a significantly more accurate estimation of this weight according to the invention, the accuracy of relevant parameters, such as the drag coefficient, is also increased.
[0028] It has been shown that the accuracy in determining the drag coefficient can be increased solely on the basis of the inventive estimation of the aircraft's weight to such an extent that, compared to the prior art, even smaller changes in the drag coefficient between two flights are possible. can be directly attributed to a decrease in aerodynamic efficiency or to aerodynamic modifications of the same aircraft.
[0029] Although it is already evident from the preceding explanations, it should be pointed out again that the method according to the invention relates to the estimation of the weight of the aircraft for a single flight.
[0030] If the inventive method is carried out on a large number of flights of the same aircraft, possible correction factors for the inventive estimation of the aircraft's weight can be derived from the respective results, thereby making the result even more accurate.
[0031] Assuming that the aircraft weight estimated according to the state of the art, as shown in the load sheet, varies around the actual weight over a large number of flights, the mean of the load sheet weights over a large number of flights should, in principle, be identical to the mean of the weights estimated for the same flights. When averaging the load sheet weights, potentially known passenger- and / or route-specific influences, such as the primary use of a route for business or leisure travel or the average weight of passengers in the departure and / or destination region, can already be taken into account.
[0032] Any remaining difference between the calculated mean values can, in principle, be related to the aircraft's total weight, dry weight, temperature, Reynolds number, and / or center of gravity. By determining and comparing corresponding mean values for different subgroups of flights, which may be grouped according to predefined criteria, the individual relationships can generally be elucidated more precisely. determine. From the dependencies thus determined, correction factors for the inventive estimation of the aircraft's weight can then be determined.
[0033] The method can be implemented in the computer program product or set of computer program products according to the invention.
[0034] The invention will now be described by way of example with reference to the accompanying drawings. These show: Figure 1: a schematic flow diagram for an exemplary embodiment of the method according to the invention for a flight of an aircraft; Figure 2: an exemplary diagram of the total aircraft weight determined in step 110 during one flight; Figure 3: an exemplary diagram of the fuel weight during one flight, as determined in step 115; Figure 4: an example diagram of the total dry weight determined in step 120 during one flight; Figure 5: an exemplary diagram of the total dry weight determined according to Figure 4 during one flight according to step 120; Figure 6: an example diagram for averaging the Total dry weight during the one flight according to step 130; and Figure 7: an exemplary diagram of the weight of the aircraft determined according to the invention over one flight according to step 140.
[0035] The inventive method 100 is explained below by way of example with reference to Figures 1 to 7. The method 100 is carried out for a completed flight of a commercial aircraft, namely a wide-body passenger aircraft, using a data record of the aircraft, as is regularly created. The data record contains, in time resolution, all the information required in the method 100 described below. Furthermore, information from the flight's "load sheet" is known for the execution of the method 100, in particular the total aircraft weight estimated therein according to the prior art based on standard weights.
[0036] In the first step of procedure 100, the instantaneous total aircraft weight is determined for each point in time of the flight under investigation, with the exception of takeoff and landing, from the data in the data log. For this purpose, various data points are accessed, such as the instantaneous angle of attack, instantaneous airspeed, altitude, ambient pressure, and / or instantaneous density of the air surrounding the aircraft. Using a predefined relationship between angle of attack and lift coefficient, the instantaneous lift force is first determined. This lift force, apart from special flight maneuvers (which are largely excluded by takingoff and landing), can be equated to the total aircraft weight force, from which the total aircraft weight can then be determined.Alternatively, any accelerations experienced by the aircraft at the time the current total aircraft weight is determined, which are also regularly included in the data record, can be used in the determination of the. The total aircraft weight force is taken into account, so that the take-off and landing phases, as well as any phases with larger flight maneuvers, can be considered when determining the total aircraft weight.
[0037] The total aircraft weight determined in this way is shown in Figure 2 over the duration of the cruise phase of the flight, excluding takeoff and landing. As is immediately apparent, the total aircraft weight determined based on the data log and the underlying sensor data does not exhibit the continuous downward trend that would be expected. This is regularly due to the insufficient resolution of the sensor data for determining the total aircraft weight, as the sensors typically only have the accuracy required for their original intended purpose, which is often inadequate in this case. Furthermore, the sensor data is subject to inaccuracies due to the inherently turbulent atmosphere.
[0038] The data log also allows the determination of the current amount of fuel or its weight. (Step 115). In addition to any information that may be available regarding the absolute fuel level, the actual instantaneous fuel consumption is regularly recorded in the data log. Together with the knowledge of the initial fuel quantity, which is also usually known, the instantaneous fuel weight can be determined over the entire cruise phase of the flight, as shown in Figure 3.
[0039] Under the assumption, regularly valid for commercial aircraft, that only the weight of the fuel on board changes due to its continuous consumption, while the weight otherwise remains constant, it can be determined in step 120 from the calculated instantaneous The instantaneous dry weight of the aircraft is determined from the total aircraft weight (see Figure 2) and the instantaneous fuel weight (see Figure 3) (see Figure 5). To do this, as schematically illustrated in Figure 4, the determined instantaneous total aircraft weight is divided into a variable and a constant part, where the variable part consists solely of the fuel weight present at the respective time, and the constant part represents the instantaneous dry weight. In other words, the instantaneous fuel weight must be subtracted from the instantaneous determined total aircraft weight to obtain the instantaneous dry weight.
[0040] As can be seen directly from Figure 5, the dry total weight determined on the basis of the determined instantaneous total aircraft weight is not constant, which is again due to the low accuracy of the incoming sensor data from the data log.
[0041] According to the invention, step 130 provides for averaging the determined time-resolved total dry weights over the cruise phase of the flight under investigation. To exclude extreme outliers, which can generally only be explained by individual singularities in the data record, from the averaging process and thus avoid distorting the result, only those values for the instantaneous total dry weight that lie within a confidence interval (shown as dotted lines in Figure 6) are considered. The confidence interval is formed around the total dry weight that can be determined from the information in the load sheet according to the prior art. Even if the weight in question does not have the accuracy achievable according to the invention, experience has shown that it is nevertheless sufficiently close to the ultimately desired value to be sufficient to define the present confidence interval. can be used. As shown in Figure 6, in the present embodiment all dry total weights lie within the confidence interval, so that all values can be taken into account when averaging the dry total weight.
[0042] The corresponding average dry total weight is shown as a dashed line in Figure 6. In this example, it lies above the weight determined from the load sheet to establish the confidence interval.
[0043] Starting from this average dry weight, the instantaneous total weight of the aircraft over the entire considered period of the flight can be estimated in step 140 by adding the instantaneous fuel weight (see Figure 7).
[0044] It has been shown that the estimated weight of the aircraft regularly exhibits a significantly higher accuracy over the entire flight than the instantaneous total aircraft weight determined according to the state of the art, since averaging the dry total weight reduces a large proportion of the inaccuracies based on the use of sensor data.
[0045] Due to the increased accuracy in estimating the weight of an aircraft achieved with the aid of the method according to the invention, the accuracy of those aircraft parameters whose determination requires consideration of the aircraft's weight is also increased. Consequently, even changes in such parameters compared to several flights of the aircraft, which in the prior art did not result in any actual change to the aircraft due to inaccuracies in determining the total aircraft weight, can be detected. These could be attributed to changes that would allow conclusions to be drawn about an actual change, e.g., in the aerodynamic efficiency of the aircraft.
Claims
Patent claims 1. Method (100) for estimating the weight of an aircraft, in particular a commercial aircraft, during a flight, wherein the relationship between total aircraft weight, lift coefficient and angle of attack is known for the aircraft and the angle of attack and fuel quantity are determined during the flight, characterized by the steps: a) determining at least two instantaneous total aircraft weights at different times during a flight based on the respective instantaneous angle of attack and the relationship between lift coefficient, angle of attack and total aircraft weight (step 110); b) determining the respective total dry weights by subtracting the weight of the respective instantaneous fuel quantity from the determined total aircraft weights (step 120); c) averaging the total dry weight over all total dry weights determined for the same flight (step 130);and d) estimating an instantaneous total weight at any time during the flight by adding the weight of the fuel load at that time to the averaged dry total weight (step 140); 2. Method according to claim 1, characterized in that the method (100) is carried out on the basis of a time-resolved data record of the aircraft comprising at least the angle of attack and the fuel quantity.
3. Method according to one of the preceding claims, characterized in that the method (100) is carried out at regular intervals and / or in relation to events during the flight. 4 . Method according to one of the preceding claims, characterized in that the angle of attack is determined by means of an angle of attack sensor and / or an attitude sensor.
5. Method according to one of the preceding claims, characterized in that the fuel quantity is determined on the basis of a known initial fuel quantity and the actual fuel consumption and / or with the aid of fuel quantity sensors. 6 . Method according to one of the preceding claims, characterized in that the relationship between total aircraft weight, lift coefficient and angle of attack is specified at least partially in the form of a table of values and / or one or more mathematical functions.
7. Method according to one of the preceding claims, characterized in that when averaging the total dry weight, only those total dry weights are taken into account which lie within a confidence interval around a previously determined averaged total dry weight or a predetermined total dry weight. 8 . Method according to one of the preceding claims, characterized in that in the determination of at least two instantaneous Total aircraft weights are taken into account by taking into account correction factors derived from an analysis of the estimated weights for the aircraft over a large number of flights.
9. Method for determining the drag coefficient of a Aircraft, in particular a commercial aircraft, characterized in that the necessary estimation of the weight of the aircraft is carried out using a method (100) according to one of the preceding claims.
10. A computer program product or set of computer program products comprising program parts which, when loaded into a computer or into networked computers, are designed to estimate the total weight of an aircraft according to the method according to any one of the preceding claims.