The wind tunnel model built by NLR weighed about 1,000 kilograms and was on a scale of 1:5.The main engineering obstacle was the design for the rotor balance system, which was successfully solved by NLR. The system had to be able to register very accurately the complex forces of the tilting propellers and of global aerodynamic lift, drag and moment acting on the model, NLR did most of the rotor balance design, including the instrumentation. Eventually, the model could test over 400 different flight conditions.
“NLR was very important for the development of the model as a whole, of key model systems, like rotorsâ€™ load balances, modelâ€™s control system, lubrication, etc. and of tubing, wires, data acquisition systems etcetera”, says Arra. “Cooperation with NLR was very good. They provided technical professionals, in terms of technical expertise, technical cooperation, communication and the management point of view. Everything was delivered in time and they had an open line of communication.”
“Finally, the model was used to validate aerodynamics characteristics in helicopter mode in the DNW low speed wind tunnel in the Netherlands and at ONERA (France) high speed wind tunnel facility to test airplane mode at fast speeds. As far as I know it was the first test in Europe with such a complex model”, says Arra.