25/06/2020

Helicopter rotor blades regularly need inspecting, but this comes with challenges as they are manufactured with different internal and external materials. However, as evidenced by several helicopter crashes in recent years the early detection of fatigue cracks can mean the difference between life and death for the helicopter crew and its passengers.

A fatal helicopter crash in Ontario, Canada in 2011 was caused by blade defects that had been present since the blade was manufactured. Over time the rotor blades on the Bell 206L helicopter developed severe fatigue cracks, and as a result one of the rotor blades separated during flight, causing the helicopter to crash and three people on-board losing their lives.

Inspecting rotor blades is not simple. They are composed of composite materials that are designed and manufactured to withstand large vibratory loads and severe environments, often they are made of aluminium, steel, titanium, or a mix of these materials.

BladeSense

The BladeSense project is a £2 million programme supported with a £1 million grant from Innovate UK, via the Aerospace Technology Institute (ATI). The research programme is a collaboration between Airbus Helicopters UK, the Dynamics, Simulation and Control group and The Centre for Engineering Photonics at Cranfield University. Simone Weber, Technology Integration Manager at Airbus Helicopters in the UK was embedded at Cranfield University. Helitune of Torrington, UK provided the on-board vehicle monitoring unit, and fluid engineering specialists BHR Group (UK) of Cranfield supplied the mathematical model predicting the mechanical loads.

The project aims to develop accurate and robust measurement technologies for real-time measurement of rotorcraft blade deformation during flight. This holds out the prospect of substantially saving on lifecycle costs through continuous in-flight data collection, leading to improved predictive maintenance, higher operational reliability and enhanced safety to help protect the lives of helicopter crews and passengers.

In the course of the project, the rotor blades of an Airbus H135 helicopter were fitted with fibre optic instrumentation. Data was successfully transferred to a remote ground station through a Wi-Fi link from specially designed instrumentation mounted on top of the rotor hub, during some four hours of ground running with the 5m rotors operating at up to 400rpm.

The BladeSense system itself is made in the format of two separate strips composed of flexible materials and filled with multiple sensors. These sensors can determine a wide range of parameters during the movement of the blades, starting from their air resistance index to the internal pressure. When the helicopter flies, they measure the stress they experience and possible changes in shape.

In a real-world scenario, if the data detected a malfunction or indicated that one or more of the blades was close to failure then it would instantly inform the pilot and ground crew. If the problem was severe, the BladeSense could automatically trigger the helicopter's flight control systems to compensate, allowing the helicopter to stay airborne until it can land safely. It also could provide the opportunity to transform the regular, conservative, interval-based maintenance strategy of the helicopter rotor system to an adaptive, needs-based maintenance strategy.

Exploring future activities

Airbus Helicopters in the UK is now exploring future activities to follow on from the project. Future test scenarios under examination envisage flight-testing of the system and investigating the exploitation of the concept in the helicopter design phase.

Head of Design and Customisation at Airbus Helicopters in the UK, Richard Atack, said: “We’ve made real progress in an advanced field of work with the potential to bring important benefits in terms of performance monitoring and environmental impact. And we’ve done that by capitalising on people, skills and technical know-how right here in the UK at Airbus and with our partners. Now we are very interested to see what we can do next to advance our capabilities even further.”

Dr Mudassir Lone, Senior Lecturer in Flight Dynamics in the Dynamics, Simulation and Control Group at Cranfield University said: “The success of the final series of tests reflects the ability of the UK R&D environment to deliver unique and industrially relevant research, due to the close collaboration in both the available expertise and facilities.”

Professor Ralph Tatam, Head of the Centre for Engineering Photonics at Cranfield University added: “This was a fantastic team effort from all the partners to demonstrate that the novel interferometric fibre optic shape measurement, pioneered at Cranfield, works in this challenging environment. This opens the way for this technology to be applied across a range of sectors including aerospace, energy, transport and healthcare.”