GB2586033A

GB2586033A - Measuring aerodynamic surfaces

Info

Publication number: GB2586033A
Application number: GB1910828.1A
Authority: GB
Inventors: Edwards Paul
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-07-30
Filing date: 2019-07-30
Publication date: 2021-02-03
Anticipated expiration: 2039-07-30
Also published as: GB2586033B; GB201910828D0

Abstract

Measurement system 2 and method of use for measuring steps (y, figure 1) and gaps (x, figure 1) at joints between adjacent skin panels of an aircraft wing component (45, figure 4a). The system comprises an apparatus configured to obtain data indicative of the height of the step (optionally a laser distance measurer 21), the width of the gap (optionally using a camera 22), and at least one environmental condition (i.e. temperature, humidity). A controller 24 may use these data to determine whether the surface of the wing component meets predefined acceptability criteria based either on the step and gap data, or on step, gap, and environmental data. This acceptability criterion may be indicative of the aerodynamic characteristics of the wing component. A positioning system (figure 5) may be used to move the apparatus along a predefined path enabling it the measurement of step and gap over the full length of every joint of the wing component (figure 4b).

Description

Intellectual Property Office Application No. GII1910828.1 RTM Date:14 November 2019 The following terms are registered trade marks and should be read as such wherever they occur in this document: -Spidercam Intellectual Property Office is an operating name of the Patent Office www.gov.uk /ipo

MEASURING AERODYNAMIC SURFACES

TECHNICAL FIELD

[0001] The present invention relates to a measurement system for measuring steps and gaps at joints between adjacent skin panels of an aircraft wing component, and to a method for use in checking the aerodynamic characteristics of a surface of an aircraft wing component.

BACKGROUND

[0002] The aerodynamic performance of an aircraft wing is affected by the smoothness of its outer surface. In particular, discontinuities such as steps and gaps between adjacent skin panels increase parasitic drag, thus increasing the amount of fuel spent to travel the same distance and reducing the overall fuel efficiency of the aircraft. Aircraft manufacturers therefore set acceptability limits for the sizes of steps and gaps on wing surfaces, and newly constructed wings must be checked to ensure that these limits are not exceeded.

SUMMARY

[0003] A first. aspect. of the present invention provides a measurement. system for measuring steps and gaps at joints between adjacent skin panels of an aircraft wing component. The system comprises a measurement apparatus configured to obtain first measurement data, second measurement data and third measurement data. The first measurement data is indicative of the height. of a step between adjacent. skin panels of the aircraft wing component. The second measurement data is indicative of the width of a gap between the adjacent skin panels. The third measurement data indicative of at least one environmental condition at the location of the measurement apparatus.

[0004] Optionally, the measurement system further comprises a positioning system configured to move the measurement apparatus along a predefined path relative to the aircraft wing component. Optionally, the predefined path is defined such that it enables the measurement apparatus to obtain first and second measurement data over the full length of every joint of the aircraft wing component.

[0005] Optionally, the measurement apparatus is configured to obtain substantially continuous first and second measurement data.

[0006] Optionally, the measurement apparatus comprises a distance sensor for obtaining the first measurement data and a camera for obtaining the second measurement data.

[0007] Optionally, the measurement apparatus comprises at least one environmental sensor for obtaining the third measurement data Optionally, the at least one environmental sensor comprises one or more of: a temperature sensor; a humidity sensor.

[0008] Optionally, the measurement system further comprises a controller configured to receive the first measurement data and the second measurement data and to determine whether the surface of the aircraft wing component meets predefined acceptability criteria, based on the received first measurement data and second measurement data. Optionally, the controller is configured to additionally receive the third measurement data, and to determine whether the surface of the aircraft wing component meets predefined acceptability criteria, based on the received first measurement data, second measurement data and third measurement data.

[0009] A second aspect of the invention provides a method for use in checking the aerodynamic characteristics of a surface of an aircraft wing component. The method comprises: (a) in respect of each joint between adjacent skin panels comprised in the wing component: measuring a first distance between the edges of the adjacent skin panels which define the joint, along a first direction; measuring a second distance between the edges of the adjacent skin panels which define the joint, along a second direction perpendicular to the first direction; and (b) measuring at least one environmental condition at the location of the wing component, substantially contemporaneously with performing (a).

[0010] Optionally, the first distance and the second distance are each measured over the full length of the joint.

[0011] Optionally, the method further comprises: [0012] (c) determining whether the aerodynamic characteristics of the surface of the wing component are acceptable based on the measured first distances and the measured second distances.

[0013] Optionally, performing (c) comprises: calculating an overall first distance value for the entire wing component and an overall second distance value for the entire wing component; and determining whether each of the calculated overall distance values meets a predefined acceptability criterion.

[0014] Optionally, performing (c) further comprises determining that the aerodynamic characteristics of the surface of the wing component arc unacceptable if at least one of the calculated overall distance values does not meet the predefined acceptability criterion.

[0015] Optionally, determining whether the aerodynamic characteristics of the surface of the wing component are acceptable is additionally based on the measured environmental condition.

[0016] Optionally, a set of predefined acceptability criteria corresponding to different environmental conditions are defined, and one or more acceptability criteria corresponding to the measured environmental condition are selected for use in determining whether the aerodynamic characteristics of the surface of the wing component are acceptable.

[0017] Optionally, the measurement system according to the first aspect comprises a controller configured to cause the measurement system to perform the method of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiments of the invention will now he described, by way of example only, with reference to the accompanying drawings, in which: [0019] Figure la is a plan view of an example aircraft wing; [0020] Figure lb is a plan view of a component of the example aircraft wing of Figure I a; [0021] Figure lc is a cross-section through an example joint comprised in the component of Figure l h; [0022] Figure 2 is a schematic view of an example measurement system according to the invention; [0023] Figure 3 is a schematic view of an example measurement system according to the invention and an example aircraft wing component; [0024] Figure 4a is a plan view of an example aircraft wing component; [0025] Figure 4b shows an example path tracing joints of the example aircraft wing component of Figure 4a; [0026] Figure 5 is a schematic top view of an example measurement system according to the invention and the example wing component of Figure 4a; and [0027] Figure 6 is a flow chart illustrating an example method according to the invention.

DETAILED DESCRIPTION

[0028] The following text describes example implementations of measurement systems according to the invention. Each example measurement system is suitable for measuring steps and gaps at joints between adjacent skin panels of an aircraft wing component, and comprises a measurement apparatus. In each example the measurement apparatus is configured to obtain first. measurement. data indicative of the height of a step between adjacent skin panels of the aircraft wing component; second measurement data indicative of the width of a gap between the adjacent skin panels; and third measurement data indicative of at least one environmental condition at the location of the measurement apparatus.

[0029] Measuring an environmental condition at the location of the measurement apparatus, simultaneously with obtaining the first and second measurement data, is advantageous because the shape and relative position of the panels comprised in the aircraft wing component may change in dependence on environmental conditions, e.g. due to thermal contraction/expansion of the materials forming the panels. Consequently, the size of the step and/or gap between adjacent panels may change in dependence on environmental conditions. It. may be the case that a step and/or gap which is unacceptable under the environmental conditions present at the lime of measuring the wing component. would become acceptable under the environmental conditions typically experienced during cruising fl ight, or vice versa. It will be appreciated, for example, that the temperature in a wing factory will generally be higher than the air temperature at. a cruising altitude of the aircraft.. Some examples of the invention are able to automatically determine whether the surface of a wing component is aerodynamically acceptable, based on the step and gap measurements and the measured environmental conditions at the time of those measurements.

[0030] To accurately determine the overall aerodynamic effect of steps and gaps on the surface of an aircraft wing component, it is required to know the size of all of the steps and gaps at any given time. Conventional step and gap measuring techniques are slow and labour intensive, so currently data is obtained only at discrete locations on a given joint. Moreover it takes a long time to obtain data for every joint of an aircraft wing component, which means that the environmental conditions may change during the measuring process. Thus, using conventional techniques it would he very difficult to obtain a global picture of the state of every step and gap of an aircraft wing component for a given environmental condition. Some advantageous embodiments of the invention enable all of the joints comprised in an entire aircraft wing component to be measured in a single process, such that all of the measurements are obtained under substantially the same environmental conditions.

[0031] Figure la is a plan view of an aircraft wing I. The wing 1 is in a fully assembled state and is attached to the fuselage of an aircraft (not shown). Moveable devices 14 (such as slats, flaps and spoilers) are mounted on the wing 1. An engine 12 and flap track fairings 13 are also mounted on the wing 1. The outer surface of the wing 1 is formed by multiple skin panels 11. Joints exist where adjacent skin panels 11 abut each other. The illustrated example wing 1 is a wing of a commercial airliner, although the invention may equally be applied to any other aircraft wing.

[0032] Figure lb shows the upper surface of a component 1' of the wing 1. The wing component 1' comprises a wing box formed from front and rear spars and upper and lower covers. The wing component l' may additionally comprise one or more fixed leading edge structures and one or more fixed trailing edge structures. The illustrated wing component 1' does not include any moveable devices, or a wing tip. The outer surface of the wing component 1' is formed by the skin panels 11. Each of the skin panels 11 may be formed from a metallic material, a composite material, or any other suitable material. The wing component 1' comprises substantially all of the joints 15 that are comprised in the full wing 1. The term "wing component" as used throughout this document is intended to refer to a component of an aircraft wing which makes up all or nearly all of the fixed structure of that aircraft wing, and therefore comprises substantially all of the joints between skin panels that are comprised in the complete wing.

[0033] Joints 15 between the skin panels 11 are circled on Figure lb. A cross-section through an example one of the joints 15 is shown in Figure lc. The example joint of Figure lc is between a first panel 1 la and a second panel lib of the skin panels 11. The first and second skin panels lla, 1 lb, may be any adjacent pair of skin panels 11 comprised in the component 1 ' . The joint 15 may be defined in terms of the width x of a gap between edges of the adjacent skin panels 11a, 11h, and the height y of a step between edges of the adjacent skin panels 1 l a, 11b. The gap width is measured in a first direction (which in Figure 1 c is the horizontal direction), and the step height is measured in a second direction (which in Figure 1c is the vertical direction) perpendicular to the first direction. In examples in which one or both of the adjacent skin panels 11a, 11 b is substantially planar, the gap width is the distance between the edges of the adjacent skin panels 11a, l lb in the plane of the substantially planar panel(s) and the step height is the distance between the edges of the adjacent skin panels l la, llb in the direction perpendicular to the plane of the substantially planar panel(s). Each joint 15 extends for a particular length, as can be seen on Figure lb. The gap width and the step height (that is, the values of x and y) may vary independently along the length of each joint 15.

[0034] Figure 2 shows an example measurement system 2 for measuring steps and gaps at joints between adjacent skin panels of an aircraft wing component. The system 2 comprises a measurement apparatus 20 configured to obtain first measurement. data indicative of the height of a step between adjacent skin panels of the aircraft wing component; second measurement data indicative of the width of a gap between the adjacent skin panels; and third measurement data indicative of at least. one environmental condition at. the location of the measurement apparatus. In the illustrated example the measurement apparatus 20 comprises a distance sensor 21 for obtaining the first measurement data, a camera 22 for obtaining the second measurement data, and at least one environmental sensor 23 for obtaining the third measurement data. The distance sensor 21, camera 22, and at least one environmental sensor 23 are contained within a housing 26.

[0035] The distance sensor 21 may be any type of sensor suitable for measuring the distance between the distance sensor 21 and a surface. In some examples the distance sensor 21 comprises a laser distance measurer. The distance sensor 21 is configured to simultaneously measure the distance between the distance sensor 21 and a surface of one of the adjacent. skin panels and the distance between the distance sensor 21 and a surface of the other one of the adjacent skin panels. For example, if the distance sensor 21 is a laser distance measurer, the laser beam may be configured as a line which extends across the gap such that one end of the laser beam is incident on one of the adjacent panels and the other end of the laser beam is incident on the other of the adjacent panels. The first measurement data obtained by the distance sensor comprises distance values. In particular, the first measurement data comprises pairs of distance values -one distance value for each of the adjacent skin panels which define the measured joint. Each pair of distance values corresponds to a different location along the length of the measured joint. The distance sensor 21 may be configured to obtain substantially continuous first measurement data. For example, the distance sensor 21 may be configured to output. a time-varying distance signal. Alternatively, the distance sensor 21 may he configured to obtain discrete distance values at a high enough frequency that the resulting measurement data is effectively continuous.

[0036] The camera 22 may he any type of camera suitable for obtaining high-quality images of the joints. In some examples the camera 22 is a high definition camera. The field of view of the camera 22 is sufficiently large to encompass the full width of any given joint comprised in an aircraft wing component to he inspected by the measurement system 2, when the measurement apparatus 20 is arranged at an intended operational distance from that joint. In some examples the camera 22 comprises a zoom function to enable the field of view to be adjusted. The second measurement data comprises images, each of which shows a section of the joint. The images each show the full width of the joint, to enable a controller to determine a gap width based on the images. The camera may he configured to obtain substantially continuous second measurement data. For example, the camera may be configured to output a video signal. Alternatively, the camera may be configured to obtain still images at a high enough frequency that the resulting measurement data is effectively continuous.

[0037] The at least one environmental sensor 23 comprises a temperature sensor and/or a humidity sensor, of any suitable design known in the art. Preferably the at least one environmental sensor 23 comprises both a temperature sensor and a humidity sensor. The third measurement data comprises temperature values and/or humidity values and/or values of any other environmental parameter. The environmental sensor(s) 23 may he configured to obtain one measurement of the environmental condition during a process of measuring a wing component. Provided the time required to complete the measuring process is sufficiently short, then it may be assumed that the environmental conditions remain substantially constant throughout. However; other examples are also possible in which the at least one environmental sensor 23 is configured to obtain third measurement data at multiple times during a process of measuring a wing component, or is configured to obtain substantially continuous third measurement data.

[0038] The example measurement system 2 further comprises a controller 24 configured to receive the first measurement data and the second measurement data In this example the controller 24 is disposed within the housing 26. Other examples are possible in which the controller 24 is located externally to the housing 26. In some examples the controller 24 may be located remotely from the measurement apparatus 20. The controller is linked to each of the distance sensor 21, camera 22 and environmental sensor(s) 23 by a communications link 25. Each of the communications links 25 is configured for the transmission of data to the controller 24. Any or all of the communications links 25 may also be configured for the transmission of control signals from the controller 24. In the illustrated example each communications link 25 is a wired communications link. In other examples, such as examples where the controller 24 is located remotely from the measurement apparatus 20, one or more of the communications links 25 may be a wireless communications link.

R10391 The controller 24 of the example measurement system 2 is configured to process the first and second measurement data in order to determine gap width and step height values. The first measurement data comprises pairs of distance values (one distance value for each of the adjacent skin panels which define the measured joint), each pair corresponding to a different location along the length of the measured joint. The controller 24 determines step height values for each location along the length of the measured joint by calculating, for each pair of distance values, the difference between the two distance values comprised in the pair.

[0040] The second measurement data comprises a set of images or video frames. The controller 24 may use edge detection techniques to detect, in each image or frame, the edges of the adjacent skin panels which define the joint being measured, and can then determine the number of pixels between the detected edges in the image. The controller 24 may calculate this number along the full length of the joint that appears in the image. Based on information about the distance between the camera 22 and the wing component being measured, and information about the properties of the camera 22, the controller 24 converts the gap widths in pixels to real world gap widths. The information about the properties of the camera 22 is stored in a memory of the controller 24. The information about the distance between the camera 22 and the wing component being measured is the set of first measurement data which corresponds to the section of the joint shown in the particular image (or is derived from that set of first measurement data).

[0041] The controller 24 is further configured to determine whether the surface of a wing component that has been measured meets predefined acceptability criteria. The determination is based on at least the first measurement data and the second measurement data (that is, the measured gap widths and step heights). The determination may, in some examples, be based only on the first and second measurement data In other examples the determination is additionally based on the third measurement data (that is. the measured environmental condition(s)).

[0042] The controller 24 is configured to calculate an overall gap width value and an overall step height value representative of the entire wing component. In some examples the controller 24 is configured to calculate an average (e.g. a mean) measured step height for the entire wing component, and an average measured gap width for the entire wing component, in which case those averages can be used as the overall gap width value and the overall step height. value. In other examples the controller may calculate an average in respect of each joint in the wing component, or may calculate an average in respect of a predefined group of joints. hi such examples the controller 24 may be configured to combine the different averages to arrive at an overall gap width value and an overall step height value for the wing component. For example, different joints or groups of joints may be given a different weighting to give them a higher or lower contribution to an overall value. This approach may be appropriate for wing designs in which certain joints or groups of joints have a disproportionately high or low impact on the aerodynamic performance of the wing.

[0043] The controller 24 is further configured to determine whether the overall gap width value meets a first predefined acceptability criterion, and to determine whether the overall step height value meets a second predefined acceptability criterion. The first and second acceptability criteria are stored in a memory of the controller 24. For example, the first acceptability criterion might he a maximum gap width, such that the overall gap width value meets this criterion if it is less than or equal to the maximum gap width. Correspondingly, the second acceptability criterion might he a maximum step height, such that the overall step height value meets this criterion if it is less than or equal to the maximum step height. Alternatively, one or both of the first and second acceptability criteria might be a range, such that a value falling within the range meets the criterion. If the overall gap width value meets the first predefined acceptability criterion and the overall step height value meets the second predefined acceptability criterion, the controller 24 is configured to determine that the measured wing component is aerodynamically acceptable. If the overall gap width value does not meet the first predefined acceptability criterion and/or the overall step height value does not meet the second predefined acceptability criterion, the controller 24 is configured to determine that the measured wing component is aerodynamically unacceptable. The measurement system 2 may output and/or store the determination of whether the wing component is acceptable or unacceptable in any suitable manner.

[0044] In some examples, the determination of whether the measured wing component is aerodynamically acceptable is based only on the first and second measurement data, as described above. In such examples, the third measurement data is output and/or stored by the measurement system 2, together with the first and second measurement data, and may be used for research and development purposes. For example, the set of first, second and third measurement data could he used to improve understanding of how environmental conditions affect the wing build process. Once a sufficiently large number of sets of first, second and third measurement data (each corresponding to a particular wing component) has been gathered, this may enable predefined acceptability criteria to he defined based on the third measurement data (environmental condition(s)) as well as the first and second measurement data.

[0045] Thus, in some examples the determination of whether the surface of an aircraft wing component that has been measured meets predefined acceptability criteria is based on the third measurement data as well as on the first and second measurement data. In such examples, the controller 24 may determine an overall gap width value and an overall step height value, in any of the ways described above. In some examples the controller may apply a correction factor to the overall gap width value and the overall step height value, before comparing these values to the predefined acceptability criteria, with the correction factor being based on the third measurement data. In other examples, a set of different predefined acceptability criteria corresponding to different environmental conditions are defined, and the controller 24 is configured to select. acceptability criteria corresponding to the measured environmental condition(s) (as indicated by the third measurement data) for use in determining whether the wing component is acceptable. That is, the overall gap width value is compared to a selected gap width acceptability criterion corresponding to the measured environmental condition(s), and the overall step height value is compared to a selected step height acceptability criterion corresponding to the measured environmental condition(s). In all other respects, the controller 24 may perform and output the determination in the same manner as described above for the case where the determination is based only on the first and second measurement. data.

[0046] Some example measurement systems according to the invention further comprise a positioning system configured to move the measurement apparatus relative to an aircraft wing component that is to he measured. Figure 3 shows an example measurement system 3 comprising the measurement apparatus 20 and such a positioning system. The wing component 1' is arranged to be measured by the measurement. system 3. In particular, the wing component I' is supported on jigs 32 such that it is within a measurement region defined by the positioning system of the measurement system 3. The jigs 32 may be configured to hold the wing component 1' in a fixed position and orientation throughout the measuring process. Alternatively, in some examples the jigs 32 may be configured to move the wing component l' during the measuring process. For example, the jigs 32 may he configured to rotate the wing component 1' about a spanwise axis of the wing component 1', to facilitate measuring all surfaces of the wing component F. [0047] The positioning system of the example measurement system 3 comprises one or more rails or wires 31a which extend between posts 31b. In the illustrated example there is a single wire 31a strung between two posts 31b, although more typically the arrangement of wires/rails 31a and posts 31b may be two-dimensional. The spacing between the posts 31b is selected such that the full length of a wing component that is intended to he measured by the measurement system 2 fits between the posts 3 lb. More generally, the posts 31b may be located on the boundary of a two-dimensional measurement region configured to encompass the aircraft wing component that is to be measured.

[0048] The measurement apparatus 20 is mounted on the wire/rail 31a by a drive mechanism (not shown) incorporated into the housing 26 of the measurement apparatus 20. The drive mechanism is configured to retain the measurement apparatus 20 on the wire/rail 31a and to controllably cause it to travel along the wire/rail 31a (in the axial direction of the wire/rail 31a). In some examples the drive mechanism may be configured to enable the measurement apparatus 20 to be controllably moved in a direction perpendicular to the axis of the wire/rail 31a. This feature may advantageously enable the measurement apparatus 20 to follow a zig-zag, sinusoidal, spiral, or any other non-linear shape of path as it travels along the wire/rail 31a. Various suitable drive mechanisms are known in the art. The detailed working of the drive mechanism is outside of the scope of the invention and will not be further described.

[0049] The drive mechanism of the measurement apparatus 20 is in communication with the controller 24 via a communications link, such that the controller 24 is able to control the operation of the drive mechanism. In particular, the controller 24 is configured to cause the drive mechanism to move the measurement apparatus 20 along the predefined path relative to the aircraft wing component that is to be measured. The controller 24 sends control signals to the drive mechanism to cause it to activate, deactivate, alter the driving speed, alter the driving direction, and the like.

[0050] The controller 24 is configured to accurately determine the position of the measurement apparatus 20 relative to the positioning system 31a,3 lb. During operation of the measurement system 3, the wing component to he measured will he accurately arranged in a known position and orientation relative to the positioning system 31a, 31b, so it follows that the controller 24 is able to accurately determine the position of the measurement apparatus 20 relative to the wing component during the measuring process. In some examples the controller 24 determines the position of the measurement apparatus based on inputs from the drive mechanism. For example, the drive mechanism may comprise a stepper motor which enables the distance travelled by the measurement apparatus 20 along the wire/rail 31a to be accurately commanded by the controller 24. In examples in which the measurement apparatus 20 is also moveable perpendicular to the axis of the wire/rail 31a, a similar motor or device may be used to enable the controller 24 to accurately command the distance travelled by the measurement apparatus in a direction perpendicular to the axis of the wire/rail 31a. In some examples the positioning system may comprise location indicators which are detectable by the measurement apparatus 20 (such as visual markers on the wire/rail 31a, or on the floor by which the positioning system is supported) and the measurement apparatus 20 may comprise a dedicated sensor for detecting such location indicators. The length of the wire/rail and the locations of the posts 31h may also be stored in a memory of the controller 24 for use in determining the position of the measurement apparatus 20. The controller 24 may use some or all of the above-described information to determine the position of the measurement apparatus relative to the positioning system 31a, 31b.

[00511 The positioning system is configured to move the measurement apparatus 20 along a predefined path relative to the wing component that is to he measured. The predefined path is defined such that it enables the measurement apparatus to obtain first and second measurement data over the full length of every joint of the aircraft wing component. The shape of the predefined path is defined based on the size, orientation and location of the joints comprised in the wing component that is to be measured. The predefined path is therefore specific to a particular design of wing component. The predefined path may additionally be defined based on properties of the measurement system 20 and/or properties the positioning system 31a, 3 lb, and/or properties of the jigs 32 used to support the wing component during the measuring process. Such properties may include, for example: the field of view of one or both of the sensors 21, 22; the distance between the measurement system 20 and the wing surface being measured; whether the drive mechanism is configured to move the measurement system 20 only axially along the wire/rail 31a or is configured to additionally move the measurement system 20 perpendicular to the axis of the wire/rail 31a; whether the jigs 32 are configured to move the wing component during the measuring process; and so on.

[0052] The predefined path is stored in a memory of the controller 24, which sends appropriate control signals to the drive mechanism to cause it to move the measurement apparatus 20 along the predefined path. It will be appreciated that the movement of the measurement apparatus 20 is constrained by the configuration of the wire/rail 31a, and that the shape of the wire/rail 31a must therefore be selected to enable the measurement apparatus 20 to travel along the predefined path. In some examples the shape of the wire/rail is selected to enable the measurement. apparatus 20 to travel along any one of multiple predefined paths. Each of the multiple predefined paths may, for example, correspond to a different wing component design.

[0053] The camera 22 and the laser measure 21 are generally required to he calibrated prior to commencing data acquisition. A calibration area 33 is therefore provided within the measurement region defined by the positioning system 31a, 3 lb. The calibration area comprises a target or marker having a known size and shape, at a known distance from the measurement apparatus 20. The camera 22 and laser measure 21 may be calibrated using any suitable conventional calibration procedures.

[0054] Figure 4a shows a particular example wing component 4' which is to he measured by a measurement system according to the invention (such as the example measurement system 3). The external surface of the wing component 4' is formed by multiple abutting skin panels 41. Between each pair of adjacent skin panels there is a joint 45. Figure 4h illustrates one possible predefined path 46 to he followed by a measurement apparatus (e.g. the measurement apparatus 20) such that the measurement apparatus is able to obtain measurements over the full length of every joint on the upper surface of the wing component 4'. It will be appreciated that various alternative paths could he defined to achieve the same outcome.

[0055] In Figure 4h the arrows indicate the direction of travel of a measurement apparatus following the predefined path 46 relative to the wing component. The start of the path 46 is at point 461, this is where the measurement apparatus would obtain the first measurements of gap width and step height. The end of the path 46 is at point 462, this is where the measurement apparatus would obtain the final measurements or gap width and step height. Environmental condition measurements may he obtained at any point on the path 46 (or at multiple points, or continuously). For simplicity, only the upper surface of the wing component 4' is shown, and the predefined path 46 only covers the joints 45 comprised in this upper surface. The lower surface will also comprise multiple joints, which must also he measured in a process of measuring all the joints of an aircraft wing component. The predefined path 46 can be extended to additionally travel along the joints of the lower surface in any appropriate manner, depending on the nature of the positioning system used to move the measurement apparatus and/or the jigs supporting the component 4'. For example, the positioning system may be capable of moving the measurement apparatus along a three dimensional path which travels over all surfaces of the component 4' whilst the component 4' remains stationary. Alternatively the positioning system may only be capable of moving the measurement apparatus along a two-dimensional path, or a three-dimensional path which only travels over the upper surface of the component 4'. Tn such examples the jigs supporting the component 4' may be configured to move the component 4' (e.g. by rotating it) to bring the lower surface into a region that. is scannable by the measurement apparatus.

[00561 A rail-based positioning system like that described above in relation to Figure 3 could be used to move a measurement apparatus along the predefined path 46, but. it would require a fairly complex system of rails/wires. Figure 5 shows an example measurement system 50 comprising an alternative type positioning system, which uses a "Spidercam" mechanism to move the measurement apparatus 20. The positioning system of Figure 5 may be particularly advantageous for applications where it is desired to move a measurement. apparatus along a complicated predefined path such as the example path 46. The positioning system is shown from above in Figure 5. It comprises four posts 51b arranged so as to define the corners of a rectangular measurement region large enough to encompass the wing component 4' that is to be measured. Four flexible cables 51a connect the measurement apparatus 20 to the posts 5 lb. More particularly, a motorized winch (not shown) is mounted on each post Slb and each cable Sla is connected to a different one of the winches. Each winch is individually controllable to alter the length of the cable 51a to which it is connected.

By controlling the lengths of the cables 51a, the system allows the measurement apparatus 20 to be positioned at any location in the three-dimensional cuboid defined by the posts 51b. There is a communications link (which may be wireless or wired) between each or the winches and a controller (not shown) of the measurement system 50. The controller can thereby send control signals to the winches to cause them to move the measurement apparatus 20 along a predefined path.

[0057] The use of an example measurement system according to the invention as part of a process of checking the aerodynamic characteristics of a surface of an aircraft wing component will now he explained with reference to Figure 6. Figure 6 illustrates an example method 600 for use in such a checking process, which may be implemented using any of the example measurement systems described above, or any other measurement system according to the invention. For example, a controller of any of the example measurement systems 2, 3, 4 may be configured to cause that measurement system to perform the method 600.

[0058] In a first block 601, a first distance between the edges of the adjacent skin panels which define a joint between adjacent skin panels of an aircraft wing component is measured along a first direction; and a second distance between the same edges of the same adjacent skin panels is measured along a second direction perpendicular to the first direction. The measuring of the first distance and the second distance is performed in respect of each joint between adjacent skin panels that is comprised in the wing component. The first distance and the second distance are preferably each be measured over the full length of the joint, such that the measurement. data generated comprises either a continuous signal or a set of high-frequency discrete measurements.

[00159] Measuring the first distance produces first measurement data, which may have the features of the first measurement data described above in relation to Figure 2. Measuring the second distance produces second measurement data, which may have the features of the second measurement data described above in relation to Figure 2. For example the first distance may he a step height, in which case it may he measured using a laser measurer of the measurement system that is implementing the method 600. The second distance may be a gap width, in which case it may be measured using a camera of the measurement system that is implementing the method 600. Measuring the first distance and/ or the second distance may comprise processing, using a controller of the measurement system implementing the method 600, sensor data obtained by a sensor (i.e. a camera or a laser measurer) of the measurement system. Such processing may comprise determining a first and/or second distance based on received sensor data (and optionally other information available to the processor), for example in the manner described above in relation to Figure 2.

R10601 In a second block 602, at least one environmental condition at the location of the wing component is measured. Block 602 is performed substantially contemporaneously with performing block 601. Measuring the at least one environmental condition produces third measurement data, which may have the features of the third measurement data described above in relation to Figure 2. The at least one environmental condition may be measured using an environmental sensor of a measurement system implementing the method 600, for example in the manner described above in relation to Figure 2.

I00611 The method 600 further comprises an optional block 603. Block 603 comprises determining whether the aerodynamic characteristics of the surface of the wing component are acceptable based on the measured first distances and the measured second distances. The determining may additionally be based on the measured environmental condition. Determining whether the aerodynamic characteristics of the surface of the wing component are acceptable may he performed, e.g. by a controller of the measurement system implementing the method 600, in the manner described above in relation to the operation of the controller 24.

R10621 The method 600 is performed as a single continuous process -that is, every joint in the wing component is measured in a continuous sequence without any significant pauses occurring in the data acquisition. Upon completion of the method 600, gap width values and step height values arc available for the entire wing component. together with data on the environmental conditions under which these gap width and step height values were obtained. Thus, a complete knowledge of the geometry of the joints of the wing component for a given set of environmental conditions is possible. As discussed above, this is advantageous as it permits a better informed and more accurate judgement as to whether the surface of the wing component is aerodynamically acceptable, and also because it provides a wealth of data to improve the understanding of how wing component surfaces and the wing build process is affected by variations in environmental conditions.

[0063] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, although the measurement systems and methods according to the invention have been described in the context of measuring wing components, such systems and methods could equally be applied to complete aircraft. wings.

[0064] Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.

[0065] Where the term "or" has been used in the preceding description, this term should be understood to mean "and/or", except where explicitly stated otherwise.

Claims

CLAIMS: 1. A measurement system for measuring steps and gaps at joints between adjacent skin panels of an aircraft wing component, the system comprising: a measurement apparatus configured to obtain: first measurement data indicative of the height of a step between adjacent skin panels of the aircraft wing component; second measurement data indicative of the width of a gap between the adjacent skin panels; and third measurement. data indicative of at least. one environmental condition at the location of the measurement apparatus; 2. A measurement system according to claim 1, further comprising a positioning system configured to move the measurement apparatus along a predefined path relative to the aircraft wing component.3. A measurement system according to claim 2, wherein the predefined path is defined such that it enables the measurement apparatus to obtain first and second measurement data over the full length of every joint of the aircraft wing component.4. A measurement system according to any preceding claim, wherein the measurement apparatus is configured to obtain substantially continuous first and second measurement data.5. A measurement system according to any preceding claim, wherein the measurement apparatus comprises a distance sensor For obtaining the first measurement data and a camera for obtaining the second measurement data.6. A measurement system according to any preceding claim, wherein the measurement apparatus comprises at least one environmental sensor for obtaining the third measurement data, the at least one environmental sensor comprising one or more of: a temperature sensor; a humidity sensor.7. A measurement system according to any preceding claim, further comprising a controller configured to receive the first measurement data and the second measurement data and to determine whether the surface of the aircraft wing component meets predefined acceptability criteria, based on the received first measurement data and second measurement data.8. A measurement system according to claim 6, wherein the controller is configured to additionally receive the third measurement data, and to determine whether the surface of the aircraft wing component meets predefined acceptability criteria, based on the received first measurement data, second measurement data and third measurement data.9. A method for use in checking the aerodynamic characteristics of a surface of an aircraft wing component, the method comprising: (a) in respect of each joint between adjacent skin panels comprised in the wing component: measuring a first distance between the edges of the adjacent skin panels which define the joint, along a first direction; measuring a second distance between the edges of the adjacent skin panels which define the joint, along a second direction perpendicular to the first direction; and (h) measuring at least one environmental condition at the location of the wing component, substantially contemporaneously with performing (a).10. A method according to claim 9, wherein the first distance and the second distance are each measured over the full length of the joint.11. A method according to claim 9 or claim 10, further comprising: (c) determining whether the aerodynamic characteristics of the surface of the wing component are acceptable based on the measured first distances and the measured second distances.12. A method according to claim 11, wherein performing (c) comprises: calculating an overall first distance value for the entire wing component and an overall second distance value for the entire wing component; and determining whether each of the calculated overall distance values meets a predefined acceptability criterion.13. A method according to claim 12, wherein performing (c) further comprises: determining that the aerodynamic characteristics of the surface of the wing component are unacceptable if at least one of the calculated overall distance values does not meet the predefined acceptability criterion.14. A method according to claim 11 or claim 12, wherein determining whether the aerodynamic characteristics of the surface of the wing component arc acceptable is additionally based on the measured environmental condition.15. A method according to claim 14, wherein a set of predefined acceptability criteria corresponding to different environmental conditions are defined, and one or more acceptability criteria corresponding to the measured environmental condition are selected for use in determining whether the aerodynamic characteristics of the surface of the wing component are acceptable.16. A measurement system according to claim 7 or claim 8, wherein the controller is configured to cause the measurement system to perform the method of any of claims 9 to 15.