Flight testing using fast online aeroelastic identification techniques with DLR research aircraft HALO

Kurzfassung

The research aircraft HALO (High Altitude and Long Range Research Aircraft) of the German Aerospace Center (DLR) can be equipped with under-wing stores at different wing positions to transport scientific instruments for atmospheric research. The PMS (Particle Measurement System) carrier is one example of such an external store which can carry three instruments at the same time per wing to detect and count particles of different size (ice, carbon, dust, etc.) in different layers of the atmosphere. Any modification on an aircraft must be investigated numerically and experimentally to ensure the structural integrity and safe operation of the aircraft for all flight conditions. For loads and flutter analyses, flight test data is the essential means for validation. In preparation of the flight test, the airframe and the under-wing stores must be instrumented with acceleration sensors and strain gauges. In order to reduce flight test time and to maintain safety it is important to have tools available that indicate relevant safety margins to support the flight test engineers in making decisions for continuation of cancellation of a flight test. The DLR Institute of Aeroelasticity in Göttingen (Germany) has developed a real-time analysis procedure for online identification of modal parameters like eigenfrequencies, damping ratios and mode shapes. These parameters vary with flight conditions, payload and fuel configuration and must be monitored to assess the aeroelastic stability margin of the system. In a joined flight test campaign, the department of Loads Analysis and Aeroelastic Design and the department of Structural Dynamics and System Identification of the DLR-Institute of Aeroelasticity have tested the newly developed flight test procedure in 14 flight hours using the HALO research aircraft. A network of three distributed data acquisition modules enabled the recording of the flight test instrumentation with 51 accelerometers and 16 strain gauges integrated in Wheatstone bridges. The measured data were distributed online to several computers on which the newly developed software was implemented, allowing an instantaneous analysis of the structural dynamics and dynamic loads in flight. This paper provides an overview of the flight vibration tests (FVT) conducted with HALO. It also shows the capability of the newly developed online monitoring system for aeroelastic identification.