The development of a European tiltrotor, an aircraft that combines the characteristics of a helicopter and a regular airplane, is brought one step closer with the successful completion of a series of tests at DNW German-Dutch Wind Tunnels. This major leap forward in the European project was partly achieved thanks to the expertise of NLR engineers who succeeded in solving a design problem in 2012. The wind tunnel tests will clear the path for an airborne “technology demonstration”, a key step towards the realization of an operational tiltrotor aircraft. In 2006, NLR joined forces with a number of European sister organizations and helicopter manufacturers in the Novel Innovative Competitive Effective Tilt-Rotor Integrated Project (NICETRIP), which was partly funded by the European Union.
A tiltrotor aircraft , like the well-known Bell Boeing V-22 Osprey , is quicker than a helicopter in horizontal flight, consumes less fuel, and produces less noise. With vertical take-off and landing capabilities, a tiltrotor also offers the flexibility of a helicopter. The tiltrotor concept looks set to provide an efficient means of transport for niche applications like supplying oil platforms and flying goods and passengers to other locations that are not easily accessible.
One of the aims of NICETRIP was the construction of a scale model in order to generate a complete dataset to validate the concept. The motorized scale model was based on the Enhanced Rotorcraft Innovative Concept Achievement (ERICA) configuration. In addition to the advantages offered by the tiltable rotors of a tiltrotor aircraft like the Osprey, the ERICA configuration includes outer wings that can tilt independently of the rotors, thus achieving a significant increase in efficiency.
NLR engineers completed the assembly a few years ago and conducted an extensive preliminary testing programme. This proved to be a highly complex undertaking. To give just one example: the large number of embedded sensors and other electronics made it necessary to install 2.5 kilometres of pressurized lines and 5 kilometres of cables. The resulting scale model is the world’s most complex wind tunnel model ever constructed, partly due to the fact that the engine pod and a wing section can tilt independently of the aircraft body.
The main technical obstacle concerned the design of the rotor balance system, an essential component that must be able to accurately register the complex forces exerted by the tilting propellers. The European aerospace laboratories had to go back to the drawing board, whereupon NLR’s solution was selected as the best one.
The completed test programme examined the behaviour of the tiltrotor aircraft during take off and slow horizontal flight as well as upon tilting of the engine pods and wing sections, with engineers and researchers “pushing the envelope” in order to determine what is technically possible. Remotely adjustable model components enabled over 400 different flight conditions to be tested. During the last phase of the preparations and during the tests themselves, dedicated test teams were able to solve various final technical issues. This will be followed by research into the physical characteristics during horizontal flight, conducted in the high-speed wind tunnel of NLR’s French sister organization ONERA.