Rotor-wing interaction phenomena for the ERICA tilt-wing rotorcraft configuration in the DNW-LLF wind tunnel

As part of the EU co-funded NICETRIP project a 1:5 scale model was tested in the 9.5x9.5 m2 test section of the \nlow speed DNW-LLF wind tunnel in June-July 2013 (see Ref. 1). The model design and manufacturing was \nlargely done by NLR, with inputs from TsAGI (fuselage shells), ONERA (rotor balances and blade design) and \nEurocopter (rotor hub design). Model pre-testing, including ground vibration tests and model control in the wind \ntunnel, was done by DLR. The overall project was led by Agusta Westland. \nThe test matrix consisted of 7 trimmed conditions in helicopter; conversion & aircraft mode. For each trimmed \ncondition a comprehensive number of variations (incidence, sideslip, nacelles, tilting outboard wing angles, flaps, \nflaperons, rudder and elevator angles, collective and cyclic blade pitch angle settings) were performed in order to \nprovide data for the flight dynamic model data-base. In total, over 400 different flight conditions, including an \nexploration towards the boundary of the conversion corridor, were measured. The model has a wing span of 3 m \nand two 1.48 m diameter rotors and is heavily instrumented. Model trimming was enabled by a model-pilot \ninterface from DLR to operate 16 (!) remote controls (Ref. 2). Total forces, rotor and tail forces were measured \nwith 6-component balances. Flaperon, flap, rudder and elevator moments were measured with one-component \nlocal balances. In addition various local loads and temperatures were measured and monitored for safety \nreasons. For each flight condition, over 800 parameters were recorded; consisting of about 50 parameters from \nbalance loads, strain gauges and accelerometer measurements, flight control positions, power required and 678 \nstatic and 55 dynamic model pressures. The tests resulted in an extensive and valuable database for the \nvalidation of the ERICA tilt-wing/tilt-rotor concept. \nThe relatively large rotors, placed at the wing tips and operating close to the wing leading edge, create \nsignificant wing-rotor interference effects, especially during high thrust conditions. Each blade passage over the \nwing leading edge not only leads to a periodic loading effect on the blade, but the blade wake and blade tip \nvortex passage over the wing also creates periodic loading of the wing. In turn these unsteady loadings can be a \ndriving factor for rotor and wing vibrations. In a previous paper the unsteady rotor loads and nacelle vibration \nlevels observed during the DNW-LLF tests have been investigated (Ref. 3). In the present paper the focus will be \non the steady but particularly on the unsteady pressures measured on the outer wing and their correlation with \nblade passage, observed vibration levels and flaperon loadings.