Abstract
HALO (High Altitude and Long Range Research Aircraft), the atmospheric 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 particle measurement system (PMS) carrier is such an external store which can carry three instruments at the same time per wing. Any modifications on an aircraft must be tested numerically and experimentally to ensure the structural integrity of the aircraft for all flight conditions. Load and flutter analyses can be validated with flight test data. For flight test, the aircraft and the under-wing stores of HALO must be equipped with acceleration and strain sensors. To reduce flight test time it is necessary to make quick decisions during the flight test. Therefore the DLR Institute of Aeroelasticity in Göttingen 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 and are necessary to analyse the aeroelastic stability of the system. The department of loads analysis and aeroelastic design and the department of structural dynamics and system identification have tested the newly developed procedure in 14 flight hours on the HALO. A network of three distributed data acquisition modules enabled the recording of the flight test instrumentation with 51 accelerometers and 16 strain gauge bridges. The measured data were distributed online on several computers where the newly developed software was implemented, allowing an instantaneous analysis of the structural dynamics behaviour and loads in flight. This paper provides an overview of the conducted flight vibration tests with HALO. It also shows the capability of the newly developed online monitoring system for aeroelastic identification.
Highlights
The aeroelastic stability of aircraft prototypes and major modifications on existing aircrafts is calculated on the basis of a finite element model during design phase
This paper provides an overview of the conducted flight vibration tests with HALO
Defined movements of the control surfaces are only possible via an electronic flight control system (EFCS) or a fly by wire (FBW) control and external exciters installed at the wing tips, are quite expensive and not easy to install
Summary
The aeroelastic (flutter) stability of aircraft prototypes and major modifications on existing aircrafts is calculated on the basis of a finite element model during design phase. In the context of the iLOADS [5] flight test campaign, modal identification methods, e.g. Operational Modal Analysis (OMA), as well as methods for load determination are tested by DLR for the first time in a flight vibration test. Appropriate flight test instrumentation (FTI) suitable for vibration tests and loads identification was not available and had to be planned for the iLOADS campaign This FTI consisted of sensors, cabling, a measurement system as well as a data acquisition PC and four analysis PCs. To analyse the measured time signals efficiently in flight a network was established between the PCs for live data distribution. For the flight vibration tests several altitudes with different flight speeds have been flown to identify the changes in the structural dynamical behaviour of the aircraft. Some acceleration signals of a typical flight are plotted behind the two parameter variations and provide different excitation levels, e.g. by extending the spoilers, impulse inputs via the control surfaces or the Take off at the beginning of the time data plot
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