Exterior aircraft light with cover erosion monitoring, aircraft comprising such exterior aircraft light, and method of monitoring erosion of a light transmissive cover

An exterior aircraft light with cover erosion monitoring, the exterior aircraft light comprises: a support; at least one light source, arranged on the support; a light transmissive cover, arranged over the at least one light source, the light transmissive cover having a forward facing portion and a rear-ward facing portion; a first light sensor, arranged to receive light emitted by the at least one light source and reflected towards the first light sensor by the forward facing portion of the light transmissive cover; and a second light sensor, arranged to receive light emitted by the at least one light source and reflected towards the second light sensor by the rearward facing portion of the light transmissive cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, EP Patent Application No. 23150120.6, filed Jan. 3, 2023 and titled “EXTERIOR AIRCRAFT LIGHT WITH COVER EROSION MONITORING, AIRCRAFT COMPRISING SUCH EXTERIOR AIRCRAFT LIGHT, AND METHOD OF MONITORING EROSION OF A LIGHT TRANSMISSIVE COVER,” which is incorporated by reference herein in its entirety for all purposes.

FIELD

The present invention relates to an exterior aircraft light, to an aircraft comprising such an exterior aircraft light, and to a method of monitoring erosion of a light transmissive cover of an exterior aircraft light.

BACKGROUND

Almost all aircraft are equipped with exterior aircraft lights. In particular, large passenger air planes are provided with a wide variety of exterior aircraft lights. The exterior aircraft lights are provided for a wide variety of different purposes, such as for allowing the passengers and/or air crew to view the outside, for passive visibility, for signaling purposes, etc. Examples of such exterior aircraft lights are navigation lights, also referred to as position lights, red-flashing beacon lights, white strobe anti-collision lights, wing scan lights, take-off lights, landing lights, taxi lights, runway turn-off lights, etc.

Exterior aircraft lights are exposed to very hazardous conditions. They have to withstand large aerodynamic forces, excessive particle impacts at high travelling velocities, as well as large temperature variations. The hazardous conditions, in particular the particle impacts at high travelling velocities, cause erosion of light transmissive covers of exterior aircraft lights. Erosion of the light transmissive cover may eventually degrade the light output of the exterior aircraft light in an unacceptable manner, leading to the exterior aircraft light no longer being considered airworthy. Up until now, erosion of light transmissive covers has been assessed mainly by highly subjective observations with naked eyes.

Accordingly, it would be beneficial to provide an exterior aircraft light with highly reliable integrated monitoring of the erosion of the light transmissive cover. Further, it would be beneficial to provide an aircraft with such an exterior aircraft light and to provide an according method of monitoring erosion of a light transmissive cover of an exterior aircraft light.

SUMMARY

Exemplary embodiments of the invention include an exterior aircraft light with cover erosion monitoring, the exterior aircraft light comprising: a support; at least one light source, arranged on the support; a light transmissive cover, arranged over the at least one light source, the light transmissive cover having a forward facing portion and a rearward facing portion; a first light sensor, arranged to receive light emitted by the at least one light source and reflected towards the first light sensor by the forward facing portion of the light transmissive cover; and a second light sensor, arranged to receive light emitted by the at least one light source and reflected towards the second light sensor by the rearward facing portion of the light transmissive cover; wherein the exterior aircraft light is configured to provide an indication regarding an extent of erosion of the light transmissive cover on the basis of sensor measurements of the first light sensor and sensor measurements of the second light sensor.

Exemplary embodiments of the invention allow for a highly reliable monitoring of the erosion of the light transmissive cover of an exterior aircraft light. As compared to previous approaches, the cover erosion monitoring does not rely on a human estimate of the erosion of the light transmissive cover. Rather, an automated monitoring of the light transmissive cover of the exterior aircraft light may become possible, with said automated monitoring having comparably low complexity, high ease of use, and high reliability. By monitoring the light, reflected by a forward facing portion of the light transmissive cover, and the light, reflected by a rearward facing portion of the light transmissive cover, a highly reliable monitoring of the erosion of the light transmissive cover may be achieved. Due to erosion predominantly or exclusively taking place at the forward facing portion of the light transmissive cover and due to the reflective action of the forward facing portion of the light transmissive cover increasing for light, coming from within the exterior aircraft light, the spread between the sensor measurements of the first light sensor and the sensor measurements of the second light sensor increases with erosion of the light transmissive cover.

Providing the indication regarding the extent of erosion of the basis of both the sensor measurements of the first light sensor and the sensor measurements of the second light sensor allows for a highly reliable determination of the extent of erosion. By comparing the sensor measurements of the first light sensor and the sensor measurements of the second light sensor, i.e. by comparing first sensor measurements that depend on erosion and second sensor measurements that are substantially independent of erosion of the light transmissive cover, the monitoring of the erosion of the light transmissive cover may be made substantially or even completely independent of other factors that may otherwise prevent accurate measurements. For example, an ambient light component of the sensor measurements may be present in both the sensor measurements of the first light sensor and of the second light sensor, and its disturbance of sensor measurements may be reduced or eliminated. As another example, a degradation of the at least one light source, such as an aging of LED light source(s), and/or a temporary reduction in light output due to a high operating temperature of the at least one light source may be present in both the sensor measurements of the first light sensor and of the second light sensor, and their disturbance of sensor measurements may be reduced or eliminated. A differential approach on the basis of sensor measurements of the first light sensor and sensor measurements of the second light sensor may provide for highly reliable results, while having a manageable complexity.

The exterior aircraft light is an exterior aircraft light with cover erosion monitoring, i.e. an exterior aircraft light with an integrated monitoring of the erosion of the light transmissive cover. It may also be said that an exterior aircraft light with cover erosion monitoring is an exterior aircraft light that has components for the monitoring of the erosion of the protective cover integrated into the exterior aircraft light. The exterior aircraft light has sensor and evaluation capacities to monitor the erosion of the light transmissive cover.

The exterior aircraft light is configured to provide an indication regarding an extent of erosion of the light transmissive cover on the basis of sensor measurements of the first light sensor and sensor measurements of the second light sensor. In particular, the exterior aircraft light may have a controller that is coupled to the first light sensor and to the second light sensor. Said controller may receive the sensor measurements of the first light sensor and the sensor measurements of the second light sensor and may have an evaluation logic to provide the indication regarding the extent of erosion of the light transmissive cover. The controller may further have a memory to store the sensor measurements of the first and second light sensors over time. The controller may be embodied in hardware or in a suitable combination of hardware and software.

The exterior aircraft light is configured to provide an indication regarding an extent of erosion of the light transmissive cover. The indication may be provided in the form of a signal that may be communicated to an entity outside of the exterior light, such as to a board computer of the aircraft. The signal may be communicated in a wired or wireless manner. It is also possible that the indication regarding the extent of erosion of the light transmissive cover is stored in the exterior aircraft light, such as in the memory of a controller of the exterior aircraft light, and may be read out via a suitable portable diagnostic device. It is further possible that the indication is given in a visual manner, such as via a status indication light source that is visible from outside the exterior aircraft light and that may for example be checked in the pre-flight routine. The indication regarding the extent of erosion of the light transmissive cover may be a quantitative indication regarding the extent of erosion. However, it is also possible that the indication is a binary indication, solely indicating whether the light transmissive cover is still considered airworthy or not.

The exterior aircraft light is configured to provide an indication regarding an extent of erosion of the light transmissive cover on the basis of sensor measurements of the first light sensor and sensor measurements of the second light sensor. In particular, the exterior aircraft light may be configured to relate the sensor measurements of the first light sensor to the sensor measurements of the second light sensor. Further in particular, said relating of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor may take place over time. In that case, respective sensor measurements of the first and second light sensors, taken substantially at the same time, may be related. In this way, a time line regarding a relative behavior of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor may be provided and may be used for evaluating the extent of erosion. With said comparative/relative approach of looking at the sensor measurements of the first light sensor and the sensor measurements of the second light sensor and with monitoring the development of the comparative/relative information over time, a highly reliable monitoring of the erosion of the light transmissive cover may be achieved. Details regarding different approaches for comparing/relating the sensor measurements of the first and second light sensors will be given below.

The exterior aircraft light has a light transmissive cover, arranged over the at least one light source. The light transmissive cover may be arranged over the at least one light source only or may be arranged over the support and the at least one light source. The light transmissive cover is a protective cover for the interior of the exterior aircraft light. In particular, the light transmissive cover may protect the interior of the exterior aircraft light from hazardous exhaust gases, from rain/snow, from excessive moisture, from particle impact caused by the impinging air stream during flight, and/or from impact of larger objects, such as birds. The light transmissive cover may be releasably mounted to the remainder of the exterior aircraft light, such that the light transmissive cover may be replaced when reaching an unacceptable extent of erosion or another type of major damage.

The exterior aircraft light has a first light sensor, arranged to receive light emitted by the at least one light source and reflected towards the first light sensor by the forward facing portion of the light transmissive cover. The forward facing portion of the light transmissive cover may be defined as that part of the light transmissive cover where the tangent to the outer surface of the light transmissive cover has an angle of more than 35° with respect to the impinging air stream during flight, i.e. an angle of more than 35° with respect to the forward flight direction. It has been found that most erosion takes place in this part of the light transmissive cover, i.e. in the part of the light transmissive cover where the impinging air stream hits the light transmissive cover in an orthogonal or substantially head-on manner.

The exterior aircraft light has a second light sensor, arranged to receive light emitted by the at least one light source and reflected towards the second light sensor by the rearward facing portion of the light transmissive cover. The rearward facing portion may be defined as that part of the light transmissive cover that is not exposed to an impinging air stream during flight. In particular, the rearward facing portion may be defined as that part of the light transmissive cover where the air stream is parallel to the tangent to the outer surface of the light transmissive cover, i.e. where the air stream passes along the outer surface of the light transmissive cover, or where the air stream detaches from the outer surface of the light transmissive cover, i.e. where the air stream diverges from the tangent to the outer surface of the light transmissive cover. For the example of fuselage-mounted light transmissive covers, the rearward facing portion may be the rear half of the light transmissive cover.

The light transmissive cover has a forward facing portion and a rearward facing portion. The forward and rearward facing portions may in particular be opposite portions of the light transmissive cover.

The exterior aircraft light has at least one light source, arranged on the support. The exterior aircraft light may have exactly one light source or may have a plurality of light sources. In the latter case, the light that is eventually received by the first light sensor and by the second light sensor does not have to come from all of the plurality of light sources nor from the same one or same ones of the plurality of light sources. In particular, it is possible that the light that is eventually received by the first light sensor originates from generally forward directed light source(s) and that the light that is eventually received by the second light sensor originates from generally rearward directed light source(s). The terminology that the exterior aircraft light has at least one light source, that the light sensor is arranged to receive light emitted by the at least one light source and reflected towards the first light sensor by the forward facing portion of the light transmissive cover, and that the second light sensor is arranged to receive light emitted by the at least one light source and reflected towards the second light sensor by the rearward facing portion of the light transmissive cover is not meant to imply a restriction regarding which particular light source emits the light that is eventually received by the respective light sensors.

The at least one light source may be at least one LED. In particular, each of the at least one light source may be an LED.

The first/second light sensor is arranged to receive light emitted by the at least one light source and reflected towards the first/second light sensor by the forward/rearward facing portion of the light transmissive cover. The first light sensor may be said to be oriented towards the forward facing portion of the light transmissive cover, and the second light sensor may be said to be oriented towards the rearward facing portion of the light transmissive cover. This terminology is not meant to imply that the first/second light sensor only receives light emitted by the at least one light source and reflected directly towards the first/second light sensor. Rather, the first and second light sensors may also pick up other light, such as ambient light, stray light within the exterior aircraft light, etc. However, with the provision of the first and second light sensors and their orientation towards the forward and rearward facing portions of the light transmissive cover, it may be possible to monitor the erosion of the light transmissive cover largely independent from such disturbing light components.

According to a further embodiment, the exterior aircraft light is configured to provide the indication regarding the extent of erosion of the light transmissive cover on the basis of ratio values of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor. Determining the indication regarding the extent of erosion on the basis of ratio values may provide for a particularly effective way of eliminating disturbing factors that affect the sensor measurements of the first and second light sensors in the same or similar manner. For example, ratio values may be particularly effective in reducing or eliminating the influence of ambient light and/or stray light within the exterior aircraft light and/or light source degradation and/or light output reduction due to high operating temperatures of the light source(s) and/or other factors that may be detrimental to the measurement accuracy between the first and second sensors and/or detrimental to the comparability of measurement values over time.

According to a further embodiment, the exterior aircraft light is configured to provide a worn cover indication when the ratio values of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor are above a worn cover threshold value. The worn cover indication may indicate that the light transmissive cover of the exterior aircraft light is to be replaced at the next possible time, such as at the next scheduled maintenance or at an extra-curricular maintenance. The worn cover threshold value may correspond to an extent of erosion at which the exterior aircraft light is no longer considered airworthy. It is also possible that the worn cover threshold value indicates an extent of erosion at which the exterior aircraft light is still considered airworthy, but not far away from no longer being considered airworthy. In this way, the worn cover indication may provide for a timely planning of a replacement of the light transmissive cover.

According to a further embodiment, the exterior aircraft light is configured to provide the worn cover indication when the ratio values of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor are on average above the worn cover threshold value within a predetermined erosion monitoring time interval. In this way, outside conditions that temporarily make the provision of meaningful sensor measurements impossible may be prevented from triggering a worn cover event. Examples of such conditions may be snow or excessive icing on the light transmissive cover, bird feces on the light transmissive cover, excessive dirt from exhaust gases on the light transmissive cover, etc.

According to a further embodiment, the exterior aircraft light is configured to provide the worn cover indication when at least a predefined percentage of the ratio values of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor are above the worn cover threshold value within a predetermined erosion monitoring time interval. Said predefined percentage may be 70% or 80% or 90% or 95% or another suitable percentage value. This binning of ratio values with respect to the worn cover threshold value may be employed as an alternative or additional means for preventing a wrong triggering of the worn cover event, as compared to the monitoring of the average described above.

The erosion monitoring time interval may cover a predetermined time interval from a momentary point in time into the past. In other words, the erosion monitoring time interval may be a moving window with respect to the sensor measurements taken over time, i.e. a moving window with respect to the time series of sensor measurements generated by the first and second light sensors.

According to a further embodiment, the predetermined erosion monitoring time interval is between 1 week and 3 months. In particular, the predetermined erosion monitoring time interval may be between 2 weeks and 2 months. The given time intervals have been found to provide a good trade-off between obtaining a highly reliable determination regarding the extent of erosion of the light transmissive cover, while reacting to the process of erosion of the light transmissive cover in an adequate time frame.

According to a further embodiment, the worn cover threshold value is between 1.5 and 4. This worn cover threshold value is applied under the assumption that the ratio value of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor is normalized at 1, when the exterior aircraft light is put into service, i.e. when the light transmissive cover is in a non-eroded state. The given value range has been found to provide a particularly reliable determination of a worn light transmissive cover, i.e. of a light transmissive cover that is to be serviced/maintained/replaced, while maintaining a long service life of the light transmissive cover.

According to a further embodiment, the exterior aircraft light is configured to provide the indication regarding the extent of erosion of the light transmissive cover on the basis of difference values of the sensor measurements of the first light sensor and the sensor measurements of the second light sensor. Evaluating difference values of the sensor measurements of the first light sensor and sensor measurements of the second light sensor may also provide for a highly effective way of monitoring the state of erosion of the light transmissive cover of the exterior aircraft light. In particular, evaluating difference values may also allow for reducing or eliminating an undesired disturbance of the sensor measurements by ambient light, stray light within the exterior aircraft light, light source degradation, temporary light output reduction due to high operating temperatures of the light source(s), etc. The additional features, modifications, and effects, as described above with respect to the usage of ratio values, may be applied to the indication regarding the extent of erosion of the light transmissive cover on the basis of difference values in an analogous manner.

According to a further embodiment, the exterior aircraft light further comprises: a first shutter, arranged over the first light sensor, wherein the first shutter has a first light entry port oriented towards the forward facing portion of the light transmissive cover; and/or a second shutter, arranged over the second light sensor, wherein the second shutter has a second light entry port oriented towards the rearward facing portion of the light transmissive cover. In this way, the influence of disturbing light components, such as ambient light, stray light within the exterior aircraft light, etc., on the sensor measurements of the first and second light sensors may be kept particularly low. A particularly high reliability in determining the extent of erosion of the light transmissive cover may be achieved.

According to a further embodiment, the first shutter encloses the first light sensor, with the exception of the first light entry port, and/or the second shutter encloses a second light sensor, with the exception of the second light entry port.

According to a further embodiment, the first light sensor and/or the second light sensor are arranged on the support. In this way, the at least one light source, the first sensor, and the second light sensor may be jointly supported by the support. The support may be a circuit board, in particular a printed circuit board (PCB). In this way, the support may provide the mechanical support for the at least one light source and the first and/or second light sensors and may provide the electric connections for the at least one light source and the first and/or second light sensors. The controller of the exterior aircraft light may also be arranged on the support. Other electric components of the exterior aircraft light, such as a status indication light source, may also be arranged on the support.

According to a further embodiment, the exterior aircraft light is configured to provide an indication regarding an extent of degradation of the at least one light source on the basis of sensor measurements of the second light sensor. In particular, the exterior aircraft light may be configured to provide an indication regarding aging/long term degradation of the at least one light source on the basis of sensor measurements of the second light sensor. The aging/long term degradation of the at least one light source may be due to thermal and/or electric stresses over time. As the sensor measurements of the second light sensor are largely or fully independent of the erosion of the light transmissive cover, the sensor measurements of the second light sensor may allow for a highly reliable determination of the degradation of the at least one light source. In order to make said determination largely or fully independent of other variables, such as different levels of ambient light, it is possible to obtain the sensor measurements for the indication regarding an extent of degradation under laboratory conditions, e.g. by placing a cover/hood over the exterior aircraft light. It is also possible to compare the lowest sensor measurements within respective degradation monitoring time intervals over time. It may be assumed that, within each degradation monitoring time interval, there is at least one instance of an operation of the exterior aircraft light under well-defined environmental conditions, such as a night flight. The degradation monitoring time interval may be between 1 week and 3 months, in particular between 2 weeks and 2 months. With the described set-up, it may be possible to carry out an erosion monitoring of the light transmissive cover and a degradation monitoring of the at least one light source with two sensors only. As compared to previous approaches, which used three sensors for providing the two functionalities, the sensor capacities may be reduced by 33%.

According to a further embodiment, the exterior aircraft light is a fuselage-mounted aircraft beacon light. The aircraft beacon light may be a red-flashing aircraft beacon light, such as an aircraft beacon light with red light sources that emit sequences of red light flashes in operation. The terminology of the exterior aircraft light being a fuselage-mounted aircraft beacon light means that the exterior aircraft light is configured/adapted to be mounted to the fuselage of an aircraft.

The fuselage-mounted aircraft beacon light may have a bowl-shaped/cup-shaped light transmissive cover. The light transmissive cover may have another suitable shape, such as teardrop shape, as well. With these kinds of shapes of the light transmissive cover, the forward facing portion and the rearward facing portion of the light transmissive cover may be conveniently positioned on opposite sides of the light transmissive cover in the longitudinal direction of the fuselage of the aircraft. Accordingly, such fuselage-mounted aircraft beacon lights may provide for ample room for providing and suitably orienting the first and second light sensors.

According to a further embodiment, the exterior aircraft light comprises a plurality of light sources, arranged on the support. In particular, the plurality of light sources may be arranged in an annular configuration on the support, and the first light sensor and the second light sensor may be arranged laterally outwards of the annular configuration of the plurality of light sources. The annular arrangement of the plurality of light sources may be particularly suitable for fuselage-mounted aircraft beacon lights. The plurality of light sources, the first light sensor, and the second light sensor may in particular be arranged in a rotationally symmetric arrangement.

According to a further embodiment, the exterior aircraft light comprises an optical system for shaping the desired exterior aircraft light output, such as the desired beacon light output, from the light emitted by the at least one light source/by the plurality of light sources. The optical system may comprise one or more lenses and/or one or more reflectors and/or one or more shutters. In a particular embodiment, the optical system may comprise a unitary lens structure that is arranged over the plurality of light sources and, optionally, over the first and second light sensors and that is rotationally symmetric with respect to the center axis of the annular configuration of the plurality of light sources.

According to a further embodiment, the exterior aircraft light is a wing-end-mounted exterior aircraft light. When mounted to the end of a wing, an exterior aircraft light may take over part of the forward lighting functionalities and part of the rearward lighting functionalities of an exterior aircraft lighting system. The light transmissive cover of such an exterior aircraft light may be a three-dimensional structure, in particular a three-dimensional structure having a substantially semi-circular or semi-elliptical horizontal cross-section. In this way, the light transmissive cover may have a forward facing portion and a rearward facing portion that are highly suitable for implementing the erosion monitoring described herein.

According to a further embodiment, the wing-end-mounted exterior aircraft light is a wing-end-mounted aircraft navigation light or a wing-end-mounted red-flashing beacon light or a wing-end-mounted white strobe anti-collision light or a wing-end-mounted multi-function light providing the functionalities of two or all of an aircraft navigation light, a red-flashing beacon light, and a white strobe anti-collision light.

Exemplary embodiments of the invention further include an aircraft, comprising at least one exterior aircraft light in accordance with any of the embodiments described above. The aircraft may be an airplane or a rotorcraft. The additional features, modifications, and effects, as described above with respect to the exterior aircraft light, apply to the aircraft in an analogous manner.

According to a further embodiment, the aircraft comprises an upper fuselage-mounted aircraft beacon light, as described in any of the embodiments above, mounted to an upper portion of a fuselage of the aircraft, and/or a lower fuselage-mounted aircraft beacon light, as described in any of the embodiments above, mounted to a lower portion of the fuselage of the aircraft.

Exemplary embodiments of the invention further include a method of monitoring erosion of a light transmissive cover of an exterior aircraft light having at least one light source, the method comprising: obtaining first sensor measurements with a first light sensor, the first light sensor arranged to receive light emitted by the at least one light source and reflected by a forward facing portion of the light transmissive cover; obtaining second sensor measurements with a second light sensor, the second light sensor arranged to receive light emitted by the at least one light source and reflected by a rearward facing portion of the light transmissive cover; relating the first sensor measurements and the second sensor measurements; and providing an indication regarding an extent of erosion of the light transmissive cover on the basis of said relating of the first sensor measurements and the second sensor measurements. The additional features, modifications and effects, as described above with respect to the exterior aircraft light, apply to the method of monitoring erosion of a light transmissive cover in an analogous manner.

According to a further embodiment, said relating of the first sensor measurements and the second sensor measurements comprises determining ratio values of the first sensor measurements and the second sensor measurements.

According to a further embodiment, the method comprises providing a worn cover indication when the ratio values are above a worn cover threshold value.

DETAILED DESCRIPTION

FIG.1shows a schematic top view of an aircraft100according to an exemplary embodiment of the invention. In the exemplary embodiment ofFIG.1, the aircraft is a commercial passenger airplane100.FIG.2shows a schematic front view of the aircraft100.

The aircraft100comprises a fuselage160and two wings170a,170bextending laterally from the fuselage160. A respective engine180a,180bis attached to each of the wings170a,170b. The aircraft100further comprises two horizontal stabilizers140a,140band a vertical stabilizer150, which are mounted to an aft portion of the fuselage160.

The aircraft100is equipped with a variety of exterior aircraft lights.

Out of all the exterior aircraft lights, which may be provided at the exterior of the aircraft100, only three white strobe anti-collision lights128a,128b, and128cand two red-flashing beacon lights120a,120bare depicted inFIGS.1and2. The air-craft100may be equipped with additional exterior lights, which may in particular include at least one or any subset or all of navigation lights, logo lights, wing scan lights, engine scan lights, cargo loading lights, take-off lights, taxi lights, landing lights, and/or runway turn-off lights. For clarity and simplicity of illustration and de-scription, these additional types of exterior lights are not depicted inFIGS.1and2. It is, however, pointed out that the white strobe anti-collision lights128a,128b, and128cmay be combined aircraft navigation and white strobe anti-collision lights. In this case, the exterior aircraft light128awould provide a white strobe anti-collision light output and a green navigation light output, the exterior aircraft light128bwould provide a white strobe anti-collision light output and a red navigation light output, and the exterior aircraft light128cwould provide a white strobe anti-collision light output and a white navigation light output.

The aircraft100shown inFIGS.1and2is equipped with an upper red-flashing beacon light120a, which is installed in an upper portion of the aircraft100, in particular on top of the fuselage160. In an alternative configuration, the upper red-flashing beacon light120amay be installed in an upper portion of the vertical stabilizer150, in particular on top of the vertical stabilizer150.

The aircraft100further comprises a lower red-flashing beacon light120b, which is installed in a lower portion of the aircraft100. The lower red-flashing beacon light120bmay in particular be mounted to the bottom of the fuselage160.

Although only one lower red-flashing beacon light120bis depicted inFIGS.1and2, the aircraft100may comprise two or more lower red-flashing beacon lights, which may be installed at different positions along the longitudinal extension of the fuselage160. A first lower red-flashing beacon light may, for example, be mounted to a front portion of the fuselage160close to the front gear of the aircraft100, and a second lower red-flashing beacon light may, for example, be mounted to a middle portion of the fuselage160close to the main gear of the aircraft100and/or to an aft portion of the fuselage below the horizontal and vertical stabilizers140a,140b,150.

In alternative configurations, red-flashing beacon lights may be installed at the tips of the wings170a,170band at the tail110of the aircraft100, potentially supplemented by red-flashing beacon lights on the side walls of the fuselage160and/or on the bottom of the fuselage160.

In the exemplary embodiments ofFIGS.1and2, the upper red-flashing beacon light120aand the lower red-flashing beacon light120bare exterior aircraft lights in accordance with exemplary embodiments of the invention. An exemplary embodiment of such fuselage-mounted aircraft beacon lights is described below with respect toFIGS.3to7.

Commonly, the red-flashing beacon lights120a,120bare switched on when the engines180a,180bare started, such that the emitted sequences of red light flashes may help to inform and warn ground personnel in the vicinity of the aircraft100that the engines180a,180bhave been started.

As mentioned, the aircraft100is equipped with three white strobe anti-collision lights128a,128b, and128c. First and second white strobe anti-collision lights128a,128bare installed in the wings170a,170b, in particular in the respective tips of the wings170a,170b. A third white strobe anti-collision light128cis installed at the tail110of the aircraft100.

The white strobe anti-collision lights128a,128b,128cemit respective sequences of white light flashes during normal operation of the aircraft100. It is also possible that the white strobe anti-collision lights128a,128b,128care only operated during the night and in bad weather conditions.

FIG.3shows a schematic vertical cross-sectional view of an exterior aircraft light according to an exemplary embodiment of the invention. In the exemplary embodiment ofFIG.3, the exterior aircraft light is a fuselage-mounted aircraft beacon light2. The aircraft beacon light2may for example be employed as the upper air-craft beacon light120aand/or as the lower aircraft beacon light120, depicted inFIGS.1and2.

The aircraft beacon light2ofFIG.3has a mounting portion40, which is configured for mounting the aircraft beacon light2to the aircraft100, in particular to the fuselage160of the aircraft100, as it is depicted inFIGS.1and2.

The aircraft beacon light2further comprises a disk-shaped support4. The support4has a central portion. A plurality of light sources6are arranged on the support4around the central portion of the support4. The plurality of light sources6may in particular be arranged in an annular configuration around the central portion of the support4, with two of said plurality of light sources6being depicted in the cross-sectional view ofFIG.3. The light sources6may be LEDs.

The support4is in turn supported by a support structure42, which is arranged between the mounting portion40and the support4. The mounting portion40may be formed integrally with the support structure42. The support structure42provides mechanical support to the support4. It may further provide a cooling structure and a cooling space for transferring heat, which is generated by the plurality of light sources6in operation, away from the plurality of light sources6.

FIG.4shows a schematic perspective view of selected components of the air-craft beacon light2ofFIG.3.FIG.4depicts the disc-shaped support4and the annular configuration of light sources6in a perspective view. Various components of the aircraft beacon light2ofFIGS.3and4have rotational symmetry with respect to a central axis of symmetry20. In particular, the support4and the annular configuration of light sources6have rotational symmetry.

The vertical cross-sectional view ofFIG.3is a longitudinal cross-sectional view through the aircraft beacon light2. The cross-sectional view ofFIG.3may in particular be taken along the longitudinal axis of the fuselage of the aircraft, when the aircraft beacon light2is mounted to the fuselage. In other words, the cross-sectional view ofFIG.3is a longitudinal cross-sectional view in the aircraft frame of reference. The forward flight direction of the aircraft is indicated via arrow70inFIG.3.

In the exemplary embodiment ofFIGS.3and4, the plurality of light sources6are arranged in a circular manner around the axis of symmetry20. The plurality of light sources6are in particular arranged between the central portion of the support4and a circumferential periphery of the support4. It is pointed out that other arrangements of light sources are possible as well. It is also possible that only one light source is present. Said one light source may for example be provided in the central portion of the support4.

In the exemplary embodiment ofFIGS.3and4, the plurality of light sources6are red LEDs. Optionally, the plurality of light sources6may comprise a combination of red LEDs and white LEDs and/or infrared LEDs. It is also possible that the plurality of light sources6are white LEDs and a red color filter is provided in the aircraft beacon light2.

The aircraft beacon light2further comprises a lens structure8. The lens structure8is arranged and configured for forming a beacon light output from the light emitted by the plurality of light sources6. The lens structure8is shown inFIG.3, but not inFIG.4.

In the exemplary embodiment ofFIG.3, the lens structure8is a unitary, rotationally symmetric component, which is arranged within the aircraft beacon light2for conditioning the light output of the aircraft beacon light2. The lens structure8is arranged over the plurality of light sources6. The lens structure8may be made from silicone or from PMMA or from another suitable material, and it may be molded over the plurality of light sources6onto the support4. In other words, during manufacture, the material of the lens structure8may be brought into its eventual shape in a molding process right over the plurality of light sources6and the support4. It is also possible that the lens structure8is molded as a separate element, which is later attached to the support4, enclosing the plurality of light sources6between the support4and the lens structure8.

The lens structure8is a rotationally symmetric component and has various annular optical surfaces, which will be described in detail below. The cross-sectional view ofFIG.3shows two mirror-symmetrical portions of the lens structure8towards the left and towards the right of the central portion of the support4. It is understood that the individual surfaces and portions of the lens structure8, which will be described below, extend around the central portion of the support4in a revolving manner. It is further understood that the lens structure8may or may not be continuous through the central portion of the support4and may thus cover a large portion of the support4.

The lens structure8has a light entry surface, which is the boundary surface with respect to the plurality of light sources6, a first total internal reflection surface82, which is distal from the support4and positioned laterally outwards of the plurality of light sources6, a second total internal reflection surface86, which is distal from the support4and positioned laterally inwards of the plurality of light sources6, a first light exit surface84, which is substantially orthogonal to the support4and forms the laterally outermost part of the lens structure8, and a second light exit surface88, which is close to orthogonal with respect to the support4and which is positioned between the plurality of light sources6and the central portion of the support4, i.e. laterally inwards of the plurality of the light sources6and the second total internal reflection surface86.

In addition, the lens structure8of the exemplary embodiment ofFIG.3comprises a refractive portion90, which forms the most distal part of the lens structure8with respect to the support4and which is arranged between the second light exit surface88and the second total internal reflection surface86, when considering the distance from the axis of symmetry20. The optical effects of the various surfaces and portions of the lens structure8will be described below with respect toFIG.5.

The aircraft beacon light2further comprises a light transmissive cover10, which is also shown inFIG.3, but not inFIG.4. The light transmissive cover10is mounted to the mounting portion40and forms an inner space between the mounting portion40and the light transmissive cover10. The support4, the plurality of light sources6, and the lens structure8are arranged in said inner space. The light transmissive cover10protects the lens structure8, the plurality of light sources6, and the support4during flight of the aircraft and on the ground.

The light transmissive cover10may be made from a transparent, color-less material, such as PMMA. The light transmissive cover10may also be made from an-other suitable material. In case white light sources are used for providing a red beacon light output, the light transmissive cover10may comprise a red color filter or may be made from a red, light transmissive material.

In the exemplary embodiment ofFIG.3, the light transmissive cover10is bowl-shaped/cup-shaped and encloses the support4, the plurality of light sources6, and the lens structure8. The light transmissive cover10has a forward facing portion12and a rearward facing portion14. In the cross-sectional view ofFIG.3, the forward facing portion12and the rearward facing portion14are depicted as substantially straight line portions of the light transmissive cover10. It is understood that the forward facing portion12and the rearward facing portion14are extended portions of the light transmissive cover10around the front end and around the rear end of the light transmissive cover10.

The aircraft beacon light2further comprises a first light sensor22, a first shutter32, a second light sensor24, and a second shutter34. The first light sensor22and the first shutter32are arranged at a forward end portion of the support4. The second light sensor24and the second shutter34are arranged at a rearward end portion of the support4. The first light sensor22, the first shutter32, the second light sensor24, and the second shutter34are depicted in cross-section inFIG.3and in a three-dimensional view inFIG.4, wherever visible in the viewing direction ofFIG.4.

The first light sensor22is arranged to receive light emitted by one or more of the plurality of light sources6and reflected by the forward facing portion12of the light transmissive cover10. The first shutter32is shaped and arranged to enclose the first light sensor22, with the exception of a first light entry port36. The first shutter32contributes to the orientation of the first light sensor22towards the forward facing portion12of the light transmissive cover10. In other words, the first shutter32helps that the first light sensor22predominantly senses light that arrives from the forward facing portion12of the light transmissive cover10.

The second light sensor24is arranged to receive light emitted by one or more of the plurality of light sources6and reflected by the rearward facing portion14of the light transmissive cover10. The second shutter34is shaped and arranged to enclose the second light sensor24, with the exception of a second light entry port38. The second shutter34contributes to the orientation of the second light sensor24towards the rearward facing portion14of the light transmissive cover10. In other words, the second shutter34helps that the second light sensor24predominantly senses light that arrives from the rearward facing portion14of the light transmissive cover10.

The first shutter32and the second shutter34may have a low profile on top of the support4. In this way, the first shutter32and the second shutter34may disturb/block the beacon light output of the aircraft beacon light2to a low degree or not at all. In a particular embodiment, the first shutter32and the second shutter34extend from the support4by at most 5 mm, in particular by at most 3 mm. The extension from the support4is understood as the extension in the dimension orthogonal to the support4.

In the exemplary embodiment ofFIG.3, the lens structure8is molded over the first light sensor22, the first shutter32, the second light sensor24, and the second shutter34. In other words, the first light sensor22, the first shutter32, the second light sensor24, and the second shutter34are enclosed by the transparent lens structure8. It is also possible that the first light sensor22, the first shutter32, the second light sensor24, and the second shutter34are arranged outside of the lens structure8, for example laterally outwards of the lens structure8.

With the first light sensor22and the second light sensor24, the erosion of the light transmissive cover10, in particular the erosion of the forward facing portion12of the light transmissive cover10, can be monitored. Exemplary details of such monitoring will be described below with respect toFIGS.6and7.

The aircraft beacon light2further comprises a controller50. In the exemplary embodiment ofFIG.3, the controller50is arranged on the support4, in particular arranged on a back side of the support4. The controller50may also be provided in or at the support structure42. The controller12may also be provided in other locations in the aircraft beacon light2.

The controller50is coupled to the plurality of light sources6. The controller50is configured for effecting a pulsed power supply to the plurality of light sources6in operation. In this way, the plurality of light sources6may provide for a red-flashing beacon light output of the aircraft beacon light2.

The controller50may be coupled to an on-board power supply network or to an according power adapter (not shown), and it may pass on the received electric power to the plurality of light sources6. The controller50may be embodied entirely in hardware or it may comprise a suitable combination of hardware and software for achieving the desired control of the plurality of light sources6.

The controller50is further coupled to the first light sensor22and to the second light sensor24. The controller50is configured to evaluate the sensor measurements of the first light sensor22and the second light sensor24. In particular, the controller50is configured to determine an extent of erosion of the light transmissive cover10by relating the sensor measurements of the first light sensor22and the sensor measurements of the second light sensor24. Details of said determination will be described below with respect toFIGS.6and7.

Once the controller50has determined that the light transmissive cover has de-graded to an unacceptable extent, herein also referred to as a worn cover event, the controller50may control a status indication LED52to provide a visual indication of the worn cover event. For example, the status indication LED52may be a yellow LED and the controller50may control the status indication LED52to light up when the aircraft is on the ground. With the status indication LED52being arranged at a rear end of the support4and being visible through the light transmissive cover10, the visual indication regarding the worn cover event may become apparent to ground personal and/or crew members that do a pre-flight check or a regular comprehensive aircraft check after a certain number of operating hours or a full aircraft check in the course of scheduled maintenance. As an alternative/in addition to providing the visual indication via the status indication LED52, the controller50may transmit a worn cover signal to an outside entity, such as to the aircraft board computer and/or to a portable diagnostic device, via a suitable wired or wire-less communication channel.

FIG.5shows the aircraft beacon light2ofFIG.3in the same cross-sectional view.FIG.5additionally shows exemplary light rays63,65,67,69, as emitted by the light source6depicted on the left hand side ofFIG.4. For enhancing the clarity of the illustration, no light rays emitted by the light source6on the right hand side ofFIG.4are shown.

In order to draw better attention to the exemplary light rays63,65,67,69, the reference numerals to the individual surfaces and portions of the lens structure8are omitted fromFIG.5. It is pointed out that the reference numerals ofFIG.3ap-ply toFIG.5in complete analogy.

For ease of illustration, the principal light emission directions60of the light sources6are indicated as dashed lines inFIG.5, with the principal light emission directions60being oriented orthogonal to the support4. The light sources6are directed light sources, with the principal light emission direction60extending orthogonal to the support4.

A first portion of the light, emitted by the light sources6, enters the lens structure right after exiting the light sources6, reaches the first total internal reflection sur-face82, experiences total internal reflection at the first total internal reflection sur-face82, and is reflected laterally outwards. The exemplary light rays63, which il-lustrate said first portion of light, hit the first light exit surface84in an orthogonal manner and, therefore, pass the first light exit surface84without further refraction.

While being reflected laterally outwards, the first portion of light is collimated in a direction parallel to the support4, i.e. it is collimated within the horizontal plane in the aircraft frame of reference. For achieving said collimation, the first total internal reflection surface82has a parabolic shape in cross-section, as illustrated inFIGS.3and5. The first portion of light encompasses the light as output by the plurality of light sources6in an angular range of about 45° between the principal light emission directions60and 45° laterally outwards thereof.

A second portion of light enters the lens structure8from the plurality of light sources6, reaches the second total internal reflection surface86, experiences total internal reflection at the second total internal reflection surface86, and exits the lens structure8for a first time at the second light exit surface88. The second portion of light is illustrated via exemplary light rays65.

The second total internal reflection surface86is also parabolic. However, the parabolic shape is tilted in such a way with respect to the support4that the exemplary light rays65are not collimated parallel to the support4, but somewhat angled up-wards with respect to the support4. The exemplary light rays65of the second portion of light experience an additional refraction at the second light exit surface88. The second portion of light, after passing the second light exit surface88, re-enters the optical structure8at the refractive portion90. The refractive portion90refracts the second portion of light to be parallel or close to parallel with respect to the support4. In this way, the second portion of light is also emitted in or close to the horizontal plane of the aircraft100in the aircraft frame of reference. The second portion of light encompasses the light as output by the plurality of light sources6in an angular range of about 30° between the principal light emission directions60and 30° laterally inwards thereof.

A third portion of light emitted by the light sources6, which is illustrated by exemplary light rays67, enters the lens structure8after being emitted by the light sources6and propagates right to the first light exit surface84. There, the third portion of light is refracted into various angular directions. The third portion of light encompasses the light as output by the plurality of light sources6in an angular range of about 45° between 45° laterally outwards of the principal light emission directions60and parallel to the support4.

A fourth portion of light, which is illustrated by exemplary light rays69, enters the lens structure8after being emitted by the light sources6and propagates right to the second light exit surface88and the refractive portion90. There, the fourth portion of light experiences refraction into various angular regions. The fourth portion of light encompasses the light as output by the plurality of light sources6in an an-gular range of about 60° between 30° laterally inwards of the principal light emission directions60and parallel to the support4.

With the given lens structure8, a highly efficient fulfilling of the FAR requirements for aircraft beacon lights2, requiring a high intensity peak in the horizontal plane in the aircraft frame of reference and requiring a decreasing intensity for larger angles with respect to the horizontal plane, can be achieved.

The total internal reflection at the first and second total internal reflection surfaces82,86may allow for providing the peak in the horizontal plane in a particularly space-efficient and energy-efficient manner. As compared to other approaches, where complex optical systems, based on metallic reflectors, were used, an FAR-compliant beacon light output may be achieved with up to 80% reduction in beacon light volume and up to 60% reduction in height over the fuselage104. In this way, aerodynamic drag can be reduced, and the exposure to damaging particles and larger objects, such as birds, can be reduced.

It is, however, explicitly pointed out that the formation of the beacon light output may also be achieved with other optical structure designs and that exemplary embodiments of the present invention may also employ such other optical structure designs.

FIG.6shows an enlarged version of a rear portion of the aircraft beacon light2ofFIG.3in the same cross-sectional view, with exemplary light rays illustrating part of the light sensing for monitoring erosion of the light transmissive cover10. In particular,FIG.6shows that portion of the aircraft beacon light2that is depicted to-wards the right of the central axis of symmetry20inFIG.3.

As described with respect toFIG.5, a first portion of light, as emitted by the plurality of light sources6, leaves the aircraft beacon light2substantially parallel with respect to the support4. As inFIG.5, said first portion of light is illustrated via exemplary light rays63. When examining said first portion of light closely, not all of the light passes through the rearward facing portion14of the light transmissive cover10in an unimpeded manner. A small fraction of the first portion of light experiences Fresnel reflection at the outer surface of the light transmissive cover10. This reflection may be due to surface imperfections at the inner and outer surfaces of the light transmissive cover10and/or due to non-perfect collimation of the first portion of light and a reflection of angled light rays on the light transmissive cover10and/or due to other factors. Part of said small fraction of the first portion of light reaches the second light sensor24and gives rise to sensor measurements at the second light sensor24. This part of light is indicated with reference numeral74inFIG.6.

The rearward facing portion14of the light transmissive cover10is not hit by an impinging air stream in operation. Therefore, the rearward facing portion14of the light transmissive cover10does not experience erosion or only a minimal amount of erosion in use. When, hypothetically, assuming the light output of the plurality of light sources6to be constant and when, hypothetically, assuming a constant amount of ambient light, the sensor measurements of the second light sensor24would stay substantially constant over time. In other words, the sensors measurements of the second light sensor24reflect the fact that only minimal or no erosion takes place at the rearward facing portion14of the light transmissive cover10.

FIG.7shows an enlarged version of a front portion of the aircraft beacon light2ofFIG.3in the same cross-sectional view, with exemplary light rays illustrating part of the light sensing for monitoring erosion of the light transmissive cover10. In particular,FIG.7shows that portion of the aircraft beacon light2that is depicted towards the left of the central axis of symmetry20inFIG.3.

As described with respect toFIG.5, a first portion of light, as emitted by the plurality of light sources6, leaves the aircraft beacon light2substantially parallel with respect to the support4. However, said highly collimated light output through the forward facing portion12, substantially in parallel with the support4, only takes place, as long as the light transmissive cover10is in a non-eroded state. When the forward facing portion12of the light transmissive cover10has experienced some erosion, as it is depicted inFIG.7, the outer surface of the forward facing portion12of the light transmissive cover10takes on a complex shape in terms of its optical properties. While some light still passes the forward facing portion12straight, some light experiences refraction at various angles, and some light experiences reflection at various angles. Part of the latter portion of light, i.e. part of the portion of light being reflected at the outer surface of the forward facing portion12of the light transmissive cover10, reaches the first light sensor22and gives rise to sensor measurements at the first light sensor22. This part of light is indicated with reference numeral72inFIG.7.

Over the course of time and with an ongoing erosion of the forward facing portion12of the light transmissive cover10, the portion of light that is reflected at the outer surface of the forward facing portion12of the light transmissive cover10increases. Similarly, the part of the light that reaches the first light sensor22after being reflected at the outer surface of the forward facing portion12of the light transmissive cover10increases as well.

When considering both the substantially constant reflection of light towards the second light sensor24, as described above with respect toFIG.6, and the increasing reflection of light towards the first light sensor22due to a progressing erosion of the forward facing portion12of the light transmissive cover10, as described above with respect toFIG.7, it can be appreciated that the spread between the sensor measurements of the first light sensor22and the second light sensor24increases with an increase in erosion. The relation between the sensor measurements of the first light sensor22and the second light sensor24may be monitored over time, and a highly reliable determination with respect to the extent of erosion of the light transmissive cover10may be obtained.

The increasing spread between the sensor measurements of the first light sensor22and the sensor measurements of the second light sensor24may be monitored in terms of ratio values or difference values of the sensor measurements of the first and second light sensors22,24. By looking at ratio values or difference values, the sensor measurements of the first and second light sensors22,24may be combined into a single metric. Said single metric may then by compared to a suitable threshold value for determining whether the extent of erosion of the light transmissive cover10has reached a critical level, such as a level where the light transmissive cover10is to be replaced.

Basing the determination regarding the extent of erosion of the light transmissive cover10on ratio values or difference values of the sensor measurements of the first and second light sensors22,24may additionally allow for eliminating or reducing the measurement uncertainty that may be created by different levels of ambient light and/or by stray light within the aircraft beacon light2and/or by light components of other origin and/or by light output variations due to aging of the light sources4and/or temporary light output reductions due to thermal stresses on the light sources4. It may become possible to use measurement values, obtained un-der vastly different environmental conditions and/or at very different points in time, in a meaningful manner. The data basis for monitoring erosion of the light transmissive cover may be greatly increased.

The controller50, as described above with respect toFIG.3, may carry out above described evaluation of the sensor measurements of the first and second light sensors22,24. In particular, the controller50may store the sensor measurements and/or the ratio/difference values and may determine the extent of erosion from the time series of sensor measurements and/or ratio values and/or difference values. Further in particular, the controller50may monitor whether the ratio/difference values are above a worn cover threshold value for a predetermined erosion monitoring time interval, at least on average, and/or whether a predefined percentage of the ratio/difference values are above the worn cover threshold value within a predetermined erosion monitoring time interval. In this way, the controller50may ensure that the slow process of erosion of the light transmissive cover10is reliably monitored, while disregarding temporary disturbances of the sensor measurements, such as snow, excessive icing, dirt, light output reductions due to high operating temperatures of the light sources, or temporary sensor malfunctions.

The controller50may also carry out a degradation monitoring. In particular, the controller50may evaluate the sensor measurements of the second light sensor24over time and may deduce the level of degradation of the light sources6therefrom. With the sensor measurements of the second light sensor24being largely or fully independent of the erosion of the light transmissive cover10, a highly reliable de-termination of the degradation/aging of the light sources6may be achieved.

FIG.8shows a schematic top view of an aircraft100according to an exemplary embodiment of the invention. In the exemplary embodiment ofFIG.8, the aircraft100is a smaller size airplane, such as a private airplane for recreational or sports purposes. In particular, the airplane may be an airplane of less than 20 passengers. The aircraft has a fuselage160, a right wing170a, and a left wing170b. Each of the right and left wings170a,170bis equipped with a propeller engine.

Further, the aircraft100ofFIG.8has two exterior aircraft lights2in accordance with exemplary embodiments of the invention. The exterior aircraft lights2are wing-end-mounted exterior aircraft lights and are provided on a left lateral end portion of the left wing170band a right lateral end portion of the right wing170a. Each of the exterior aircraft lights2has a light transmissive cover10, which is substantially circular in the top view ofFIG.8and/or substantially circular in a horizontal cross-section. With this shape, the light transmissive cover10has a forward facing portion12and a rearward facing portion14. The principles of obtaining sensor measurements with a first light sensor, oriented towards the forward facing portion12, and a second light sensor, oriented towards the rearward facing portion14, and of determining an extent of erosion of the light transmissive cover10on the basis of the sensor measurements of the first and second light sensors, as described above, are applicable to the exterior aircraft lights2of the aircraft100ofFIG.8in an analogous manner. It is understood that the number, arrangement, and colors of light sources may be different in such an embodiment, as compared to the exterior aircraft light2ofFIGS.3to7.

In the exemplary embodiment ofFIG.8, the exterior aircraft lights2are combined navigation, white strobe anti-collision and red-flashing beacon lights. It is also possible that the exterior aircraft lights2have only one or any two of said functionalities.