Helicopters play a key role in many aspects of our modern society. They fly as air ambulances, search and rescue teams and in military operations. We also use them for urban transport and off-shore oil and gas operations. Some organisations even rely on helicopters for monitoring national electric grids.
Vibrations are one of the main considerations when designing and manufacturing rotorcraft vehicles. As well as causing damage to aircraft, excessive vibrations can result in higher fuel and maintenance costs, not to mention a bumpy ride for passengers. There are many causes of vibrations, but the prime source is the helicopter’s main rotor. In order to fly, the main rotor blades move through the air and create a force that lifts the helicopter. However, the interaction between the rotor blades and the air is very complex. As the blade moves in a circular trajectory, the aerodynamic forces change as it spins. This causes a type of vibration that is not encountered in fixed-wing planes.
Picking up good vibrations
Over the last decades, many initiatives have tried to cut out the vibrations of rotor blades. The latest in active vibration reduction for helicopters is ‘On-Blade Control’. This is a promising technique that embeds control mechanisms on the rotating blades.
These systems work by using a ‘feedback interconnection’. This means they measure the vibrations at key points on the helicopter and adjust for them in flight. Signals pass from the rotor to a computer, which processes the data and decides how the blades should respond. Control theory, a branch of computational mathematics, is a powerful tool to analyse and design feedback systems. This allows us to create the algorithms that enable the rotor’s computers to process data on the fly. By adjusting rotor performance in the air, we can greatly reduce vibrations. This can improve a helicopter’s airworthiness, flight comfort and running costs.
Taking the research to market
On-Blade Control can be performed via many devices. The most common is a simple flapping mechanism on the blades, like those found on aeroplane wings.
Recent wind tunnel and flight tests have shown the potential benefits of On-Blade Control in the USA and Europe. Leading rotorcraft manufacturers are now racing to take these technologies to production. However, the existing challenges of complexity, cost and the unknown effects on flight performance are a hindrance. This is where my research comes in. As an expert in control engineering, I support the development of OBC technologies right through to production.
In 2015, I was awarded a £27,000 Industrial Fellowship by the Royal Academy of Engineering. Through my fellowship, I teamed up with leading rotorcraft manufacturer, Leonardo, to test my research in industry. My role was to design, analyse and implement new vibration reduction algorithms. These have greatly improved both rotorcraft performance and stability. The potential benefits of this work show that in demanding operating regimes, we can almost halve vibrations, in comparison with existing algorithms. I have based this research work on studies of AW101 and AW139 helicopters.