BLADE Flight Test Instrumentation for Transition Detection

'Clean Sky' is the biggest European research program that develops innovative breakthrough technologies for a future aircraft, which aim on CO2 reduction, decrease of emission and noise reduction. In the work package 'Natural Laminar Flow (NLF) Smart Wing with associated Advanced Flight Test Instrumentation' flight tests are performed on the 'Breakthrough Laminar Aircraft Demonstrator in Europe' (BLADE, Airbus A340), to pave the way for laminar wings on future commercial aircrafts. In order to measure the boundary layer status (laminar/turbulent) on the aircraft’s wing, the German Aerospace Center (DLR) used a planar imaging method (infra-red thermography) on the one hand, and a fast local measurement technique (hot-film anemometry) on the other hand. The technical challenges to use those measurement techniques were enormous and were realised by DLR in cooperation with Airbus on the A340 BLADE aircraft. During the pre-flight phase, ONERA has assessed the capability to use sun illumination for IR transition detection, based on an aerothermal model of the wing under flight conditions. An extensive flight test program helped to gather knowledge about the possibilities to establish a transport aircraft with laminar wings. The infra-red measurement system was able to detect the transition line on both wings with a remarkable spatial resolution. The presentation will describe how the IR-setup was engineered for the special situation of two vertical tail mounted IR-cameras together with a special calibration procedure and software development. The hot-film sensors measured the boundary layer status at the leading edge within smallest boundary layer thicknesses without biasing the transitional process. Moreover additional hot-film sensors were used to verify other transition measurement systems and gathered high frequency information from the boundary layer behind surface irregularities. The paper will describe the hot-film setup and installation for the special situation of thin boundary layers at the leading edge. Exemplary data from hot-film measurements as well as from transition measurements with the IR-system will be shown.