Aerospace industry is a place where sensors are used intensively. In order to monitor pressure, temperature, vibration, fuel level, landing gear status, wing and rudder position, an aircraft needs to use more than 100 sensors, so the size and weight of sensors become very important. This is also the reason why foreign military and aerospace fields pay so much attention to fiber grating.
NASA attaches great importance to the application of fiber grating sensors. They installed a fiber grating sensor network for measuring strain and temperature on the space shuttle X-33 to monitor the health of the space shuttle in real time. They also studied the multi-purpose optical fiber sensors for composite high-pressure vessels at normal temperature and low temperature, and their application objects are reusable launch vehicles and composite fuel tanks of McDonald-Douglas, Boeing North America and Rockfield-Martin, and it has been confirmed that the optical fiber grating sensor is an ideal technology. In 2008, NASA launched an experimental project to monitor the wing deformation of Ikhana UAV under static and dynamic loads by using fiber grating sensor network, and successfully realized the monitoring of the wing deformation when the aircraft was flying online, which was an important step towards intelligent sensor network. In this experiment, they used a total of 2880 FBG sensors, and each wing was equipped with 1440 FBG sensors to monitor the strain distribution and deformation of the wing. The United States Naval Research Laboratory and the Norwegian Naval Laboratory jointly conducted a study. They installed more than 100 fiber grating sensors on an active glass fiber demining ship, and used appropriate demodulation and processing methods to measure the hull statically and dynamically. The U.S. Naval Research Laboratory also embedded 60 fiber grating sensing systems in a 14-scale bridge model, and tested the damage of the model.
In 2012, the University of Tokyo and Japan Institute of Aeronautics (JAXA) carried out an experiment to measure the deformation of large wings by using fiber grating sensor network. They arranged 246 10mm FBG sensors, 6 300mm long FBG sensors and 6 500mm long FBG sensors on the wings of carbon fiber reinforced plates with a length of 6 meters and a width of 1.4 meters to detect the deformation of the whole wing frame and the strain change and deformation of local strain concentration points under loading.
Since 1996 in Germany, Daimler-Benz Research Center, Daimler-Benz Aerospace Airbus and Aerospace Research Institute have jointly studied fiber grating adaptive wings. Expecting to find a structural dynamic scheme to optimize the aerodynamic performance of the aircraft, they used the static distribution embedded fiber grating strain and temperature sensors in the structural change monitoring.
In France, several institutions cooperate to detect the interior of composite structures by embedding fiber grating sensors in the materials, in order to evaluate the perfection of fighter radar shielding, and are developing high-voltage warehouses embedded in fiber grating strain gauges.
Swedish Institute of Optics and FFA are carrying out a SMART national plan, aiming at developing a time-multiplexed strain and temperature measurement system for monitoring fighter composite structures with fiber grating sensors, and at the same time preparing to develop a real-time health and operation monitoring system based on advanced load monitoring and damage detection technology.
The Royal Australian Air Force (RAAF) and the Canadian Air Force (CF) have conducted an international continuous structure test project (IFOSTP) for a batch of F/A-18 fighters purchased from the United States. IFOSTP includes three main full-scale fatigue tests and independently supported mid-fuselage wing segment tests. The mid-fuselage test (designated as FT55) and wing test (FT245) were carried out in Canada, while the rear fuselage and tail test (FT46) was carried out in Australia. The loading and deformation experiments of the fuselage and wing are all conducted by comparing the fiber grating sensor network with the traditional resistance strain gauge sensor network. Some experiments have been completed before 2005 and 2008, and some experiments have been carried out until now.Fiber Bragg grating sensor has only one fiber, and the sensitive element (grating) is made in the fiber core. From the advantages of small size and light weight, almost no other sensor can compare with it. Therefore, military and aerospace industries attach great importance to fiber grating sensing technology, and Boeing Company alone has registered several technical patents for fiber grating sensors. It can be seen that internationally developed countries pay special attention to the application of fiber grating sensor network in aerospace, and the application technology is becoming more and more mature, and they have made phased achievements in monitoring the wing and overall deformation of aircraft by using fiber grating sensor network.