PhotonFirst has extensive experience in aerospace applications. Please find below a number of cases:

  • Landing gear load sensing
  • Helicopter blade monitoring
  • UAV load monitoring
  • Structural health monitoring in aircraft structures
  • Damage detection in composite aerospace structures
  • Impact Detection
  • Integrating sensing and data communication
  • Shape sensing on morphing wings
  • Affordable and high performance distributed FBG sensing

Landing gear load sensing

In the CleanSky 2 program PhotonFirst (then named Technobis TFT-FOS) was partner in the ALGeSMo project to develop a sensing system that will measure load at the landing gear. The objective for this system is to provide load data for use in aircraft systems that can be integrated with aircraft Health Monitoring, hard landing detection, flight management and flight controls. The project was taking a fully integrated system from post-TRL 4 through to flight test on a single-aisle aircraft and to the demonstration of a working aircraft-integrated system at TRL 6. This includes the integration of load and torque sensors into large passenger aircraft landing gear to provide robust, accurate, reliable load measurements and the potential for Health Monitoring capability. The sensors will measure loads using Fibre Bragg Grating technology integrated into Airbus-patented landing gear. The project covered a complete framework of activities, starting with the integration of dedicated optical fibers into composite structures, the readout of the optical fibre sensor with state-of-the-art miniature and reliable ASPIC-based FBG Interrogator Technology from PhotonFirst. For this purpose Technobis developed an OEM multi-channel and high speed FBG interrogator system. Although the system is developed in the context of the landing gear load sensing application, the system being qualified for the aerospace environment actually supports many more aerospace sensing applications where multiple fiber optic channels and high speed FBG interrogation is required, such as damage and impact detection, shape monitoring of morphing structures and structural load sensing.

Helicopter blade monitoring

The advancement of Fiber Optic Sensing Networks for load and vibration monitoring presents important possibilities for helicopter rotor health and usage monitoring. While main rotor blades account for the main source of lift for helicopters, rotor induced vibration establishes an important source for understanding the rotor performance and blade condition. Since December 2017 PhotonFirst FBG Interrogator systems are being Flight Tested on a helicopter with an Integrated Photonics based Multi-Channel Miniature fiber sensing system, directly mounted on the root of the helicopter blade. Measurement data was recorded and wirelessly transmitted to a central processing CPU located in the avionics area. The objective of these Flight tests is to demonstrate that the main rotor loads (bending moments, torsion and axial strain) recorded by the FBG sensor data system to be correlated by an existing strain gage data system. With this effort the system will achieve high TRL, constituting full functional prototype demonstrated airworthiness in a real operational flight environment.

UAV load monitoring

Todays Unmanned Aerial Vehicles (UAV’s) operate in extreme conditions and a variety of missions. This associates with the need to monitor the Structural Health of the aircraft over their lifespan. During their life, UAV’s subject to stringent environmental challenges as extreme dynamic loading conditions, material corrosion and degradation, being significant aspects that determine the structural health. They affect the reliability and economic impact with regards to maintenance. The PhotonFirst FBG interrogator system is integrated with UAV systems to add small footprint fiber sensing capability for the purpose of Structural Health Monitoring. The developed interrogator system is a miniature autonomous FBG interrogator with integrated (optional) capabilities for data processing, wireless data transfer, on-board data storage, battery power, GPS, etc. For one particular project the capability of load sensing is applied in order to improve efficiency of aerolastically tailored wing structures. Subsequently the very same integrated fiber optic sensing system provides a smart sensing platform that allows multi-parameter monitoring capability for damage and impact detection mechanisms to the extent that supports prognostic health management of existing and future aircraft.

Structural health monitoring in aircraft structures

In the Horizon2020 program PhotonFirst (earlier Technobis TFT-FOS) is partner in the EXTREME Dynamic Loading project for the development of a Fiber Optic Sensing system with the capability to perform extreme measurements. In this project the general objective is to push the boundaries of aerospace composite material structures. The aim of the project is to develop novel material characterization methods and in-situ measurement techniques, material models and simulation methods for the design and manufacture aerospace composite structures under EXTREME dynamic loadings leading to a significant reduction of weight, design and certification cost. PhotonFirst involvement concerns the development of an FBG interrogator with a Sampling Speed up to 1MHz, a Resolution of less than 0.1 pm, and Dynamic Range of 5%, which demonstrates high performance measurement capability utilizing standard optical telecom fiber for extreme loading conditions. This interrogator system is intended as an ideal measurement solution that provides high performance measurements on static, dynamic, high dynamic and extreme dynamic phenomena in aircraft structures with one single low footprint system. The system is considered a breakthrough in applicable and affordable sensing capabilities.

Damage detection in composite aerospace structures

Damage detection is a major challenge in the aviation industry, in particular with regard to the use of composites materials in aircraft structures. As composites materials prove to be cost effective for structures they also exhibit damage effects that require new perspectives for detection. Delamination effects and debonding of stringer runouts are examples that are barely visible and need NDT techniques in AOG situations for assessment of the damage. Although several approaches exist and are being developed, the damage detection algorithms currently applied in combination with integrated photonics based sensing equipment from PhotonFirst are based on a modal (vibration) approach with the ability to detect the presence and location of the damage in a composites structure with a relatively limited number of sensor positions. Different methodologies can be applied to measure the dynamic response of structures for assessment of damages, i.e. Modal Strain Energy Analysis, Acousto-Ultrasonic sensing (Acoustic Emission, and Lamb waves). The methodologies involve sample rates ranging from 1 kHz to 1Mhz. PhotonFirst is developing the technology that supports such wide range of sample rates maintaining the specification of sub micro-strain resolution for large dynamic strain ranges.

Impact detection

Impact detection in aeronautical structures allows predicting their future reliability and performance. An impact can produce microscopic fissures that could evolve into fractures or even the total collapse of the structure. FBG sensor networks applied for damage detection can also be applied as impact detection system during flight and even on the ground to determine the location of any significant impacts. Subsequently, based on the results from the less accurate impact detection system (using the same sensor network); a damage detection can be performed on the part of the structure where the impact was located. In the Dutch national program TAPAS (Thermoplastic Affordable Primary Aircraft Structures) PhotonFirst (earlier Technobis TFT-FOS) successfully performed impact tests on a thermoplastic composite aircraft wing structure, e.g. an overburdened torsion box representative for the load carrying box of an airliner flap of the tail of a business jet. The objective of the test was to obtain more information about impact detection on composite structures by measuring the time of arrival of the signals to the various sensors (Time Difference of Arrival, TDOA).

Integrating sensing and data communication

In practice, redundancy issues and smart sensing are addressed in solution developments allowing bidirectional interrogation combined with smart sensor networking and integrated data communication. PhotonFirstsuccessfully demonstrated continuous bi-directional FBG interrogation while maintaining high bandwidth data communication speeds. Such a concept allows a first degree sub-system failure, keeping remaining systems fully functional. Smart network management for instance allows immediate rerouting of both measurement and control data through distributed network nodes. The compatibility of PIC components for data communication and FBG sensing, enables the full integration of their functionalities on a single chip. In view of the trends towards miniaturization, the system concept combines many multiple features into a single high reliable PIC based system and subsequently highly applicable for multi-parameter sensing and datacommunication purposes.

Shape sensing on morphing wings

Conformal morphing technology is a new area to the aircraft industry. The ability of an aircraft to change the shape of its wings during flight allows it to perform a flight mission more efficiently than a fixed-wing aircraft (due to drag reduction and improved lift-to-drag ratios) and thus attracts much interest from both governments and the private aircraft industries. Shape sensing is one of the versatile applications in a wide market spread, made practical with Fiber Optic sensors for strain sensing. In the SARISTU project, a fiber optic based sensing approach for chord-wise shape reconstruction of an adaptive trailing edge device (ATED) is realized with the extrinsic implementation of fiber FBG sensors. With this implementation, the capability is provided for a closed-loop control of the morphing mechanism for a given set of the target shapes.

Affordable and high performance distributed FBG sensing

One of the key advantages of fiber sensing compared to electronics sensors is the ability to integrate multiple measurement points down a single fiber line. Probing particular FBG sensors is done by allocating a certain frequency bandwidth for each sensor, of which there is limited total window available (e.g. 8 for a regular interrogator). Sensor multiplexing in one fiber can, however, also be obtained in the time domain. A new method has been demonstrated to work with our standard interrogator architecture by the addition of a time-modulated optical amplifier in line between the interrogator and the sensor array. This time domain multiplexing allows for tens to hundreds of unique sets of FBGs to be interrogated in a single fiber consecutively, vastly extending the range of sensors into the thousands that can be analyzed with a single interrogation system. This highly demanded system will soon become available and is of particular interest to distributed sensing applications requiring many sensors for instance for thermal mapping and security monitoring.

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