An aircraft of the future that combines all the advantages of a helicopter with those of a fixed wing airplane will represent a massive step-change in the way we take to the skies. The team behind the necessary rotor technology plans to have it ready for the market before 2040.
The CROP project’s advances in developing an innovative cycloidal rotor technology to power such an aircraft brings this prospect much closer. An aircraft with cycloidal rotor technology can spin through 360 degrees around all axes, take off and hover like a helicopter, and perform the aerial acrobatics of fixed-wing planes. The potential applications are enormous and CROP has placed Europe at the forefront of this ‘disruptive’ technology.
“Our basic research has moved from a collection of ideas through to firm conceptual models,” explains CROP coordinator José Carlos Páscoa. “We are now working on the next steps – taking cycloidal rotor technology to the point that it can pass into production within around 20 years”.
A cycloidal rotor comprises several aerofoils rotating around a horizontal axis – it resembles the wheel on a watermill. Normally in such an arrangement the lift generated by each aerofoil would be cancelled out by opposing ones. However, by independently varying the pitch (angle to the airflow) of each aerofoil as it spins around, net lift can be generated in any direction.
Furthermore, this arrangement also allows both lift and propulsion to be generated simultaneously – offering the potential to power aircraft both upwards or downwards, and forwards or backwards. The concept was first suggested in the 1920s but considered not technically feasible at the time.
“We started the CROP project when we realised that new materials and computational tools are available today that could help us create a successful cycloidal rotor,” explains Páscoa. “In addition, Europe has just the right expertise CROP needed, such as drive train expertise and knowledge of high-performance bearings. Indeed, one partner had already built a tentative prototype.”
Research involved extensive simulations and mathematical modelling of all the components of an eventual aircraft – from power generation and transmission to the aerodynamics of the rotors. It explored integrating them into existing aircraft platforms, such as airships, fixed wing aircraft and helicopters. Innovative approaches were investigated, such as plasma generation over the rotor blades to give better control over turbulent airflow and thus greater performance and stability.
Laboratory testing helped to optimise rotor and bearing performance, and power-to-weight ratios. Experimental propulsion units indicated that this technology can offer 60% and 40% efficiency improvements when incorporated into helicopter and fixed wing platforms respectively.
Ready for take-off
Highly agile, fast and efficient aircraft based on cycloidal rotor technology would meet many of the demands of current and future air transport. The improved ability to fly and hover in rough weather and ‘stick’ to the decks of marine platforms and ships are alone sufficient to ensure success.
CROP has put Europe in a leading position. “We have demonstrated the scalability of this technology and how it could be implemented in real aircraft,” says Páscoa, from University of Beira Interior, in Portugal. “The next steps involve getting better lift efficiency and implementing intelligent control systems to manage stable flight. In CROP, we went from a basic idea to a clear concept – now we want an aircraft with a human pilot. If we can maintain the momentum, then we envisage that production of cycloidal rotor aircraft in Europe, capable of transporting two persons, could be achieved by 2030-2040, which is not such a long time for a truly breakthrough innovative technology.”
Project acronym: CROP
Participants: Portugal (Coordinator), Italy, Austria, UK, Germany