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Advanced Landing Gear Sensing and Monitoring

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Novel sensor enables objective assessment of aircraft landing impact

Was that landing too hard? Pilots have always had to use their best judgement, but now an instrument eliminates the subjectivity.

Transport and Mobility icon Transport and Mobility

Aviation engineers like soft landings. Aircraft are designed to land within a narrow range of descent speeds. Anything faster means hitting the ground too hard and potentially damaging the aircraft. The question of whether a landing was too hard ultimately involves subjective pilot judgement. In European commercial operation, pilots would probably over-report hard landings. Then the aircraft will be sent for inspection, perhaps unnecessarily, which may also require the aircraft manufacturer’s assessment. Apart from direct maintenance costs, all such stages take time, during which the aircraft is unavailable, adding to indirect costs. The present system, based on subjective pilot judgement, is prone to maintenance inefficiency and unnecessary costs.

Photonic and fibre optic sensor

The aviation industry needs an objective landing impact sensor. The EU-funded ALGeSMo project developed the world’s first such sensor, intended for commercial passenger aircraft. The sensor removes the subjectivity from landing assessments. If a landing was too hard, engineers will immediately know for certain. The sensor is based on a combination of photonics and fibre optic technologies. “Optical sensors have many advantages,” explains project coordinator Jerry Symons. “Firstly, they are inherently safe, being immune to electromagnetic interference. They also offer multiplexing capability, which means that many sensing elements can be included in a single optical fibre to measure numerous parameters. Optical sensors also allow the high accuracies we need for this application.” ALGeSMo’s system consists of two main components, both developed from scratch by the project team. The system’s ‘brain’ is a fibre optic processing unit (FOPU), installed in the aircraft’s avionics bay. This unit generates infrared light, which it sends to each axle sensor. Each axle has two wheels, and each wheel has its own sensor. The sensors consist of optical fibres with Fibre Bragg Gratings (FBG) inside a composite material carrier. Each FBG reflects a difference wavelength of light back to the FOPU. Any loading on the axles is transmitted through the composite to the FBG and causes a change in the wavelength of the reflected light. The FOPU receives light returning from each sensor and converts any change in wavelength into a load value. Sensors are held in place with a new clamping mechanism specially designed for the Airbus A320 axle.

Cleared for further development

“Our key final outcome is that the system demonstrates the capability of optical technology to meet the aircraft need,” adds Symons. “We achieved most of our objectives. The system has not been flight tested yet, but has been demonstrated on a landing gear test rig, which reproduced the loads seen by medium-sized passenger aircraft.” Testing proved that the system accurately calculates landing load. The load data also aid the automation of other aircraft functions. These include optimisation of braking and of trim and thrust settings for take off. Next, the team will begin refining the new functions to technology readiness level 6, leading to subsequent implementation on future commercial aircraft. This will eventually mean less unnecessary maintenance and lower costs. The project received funding from the Clean Sky 2 Joint Undertaking (JU). The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union.


ALGeSMo, sensor, aircraft, landing, optical, aviation, photonic, Airbus A320

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