As conducted by TÜBITAK SAGE, external store flutter certification process mainly consists of
• Ground Vibration Test (GVT)
• Finite Element Model Updating
• Aeroelastic Analysis
• Flutter Flight Test
consecutive steps. The external stores subject to certification, are investigated and analyzed in terms of aeroelastic means.
Within this scope, the flight platform is investigated in terms of any aeroelastic instability problem within the prescribed flight envelope. The flight envelope is updated for the related external store configuration by examining the potential aeroelastic instabilities within the envelope.
TÜBITAK SAGE owns the facilities for the execution of all terms of an external store certification process with the support of 1st Air Supply and Maintenance Center Command/Turkish Air Force.
1. AEROELASTIC GROUND VIBRATION TESTS (GVT)
Aeroelastic Ground Vibration Test (GVT) is the initial step of a typical flutter certification process. The main goal of GVT is to determine the mode shapes, frequencies and the related damping ratios of the flight platform experimentally, regarding the external store configuration(s) specified. GVT is conducted in accordance with the MIL-HDBK-1763 military handbook.
Gvt System Specıfıcatıons
• Pneumatic Suspension System
• Electromagnetic Modal Shakers
• SCADAS III Data Acqusition System (168 channels)
• LMS Test.Lab Structures Acquisition
• LMS PolyMAX
• Single Axis Accelerometers (10 g, 50 g, 500 g)
• Triaxial Accelerometers (50 g)
• Dynamic Load Transducers
2. FINITE ELEMENT MODEL UPDATING
In FE Model Updating, the element properties of the flight platform/external store finite element model, which consists of shell and beam type finite elements are modified systematically. Thus the mode shapes and the natural frequencies of the finite element model are harmonized with the GVT modal data.
Design variables related to the finite element model are updated at the end of the optimization process. The model updating process is carried on until the discrepancy between the modal properties of the finite element model and the GVT modal results is minimized.
3. AEROELASTIC ANALYSIS
In this stage of the flutter certification process, where the aeroelastic analyses are conducted, prioritization of all external store configurations is done in terms of criticality level regarding aeroelastic considerations. Critical configurations for which the flutter flight test is necessary are determined and Mach-Altitude combinations, at which the flight flutter tests are to be conducted, are generated.
4. FLUTTER FLIGHTG TESTS
The ultimate goal of Flutter Flight Test, which is the final stage of the flutter certification process, is to substantiate that the flight platform with stores, which is to be qualified in accordance with the MIL-HDBK-1763 military handbook, will not undergo any critical aeroelastic instabilities and has satisfactory damping characteristics within the prescribed flight envelope for the external store configuration(s) of concern.
The aeroelastic modes of the flight platform are excited with the Flutter Excitation System and the real-time data are acquired during the Flutter Flight Test. The acquired data are transmitted to the Mobile Telemetry Station simultaneously and the data are used in modal analysis for real-time damping estimation.
- Flutter Excitation System
- Mobile Telemetry Station
- SCADAS III Data Acqusition System
- LMS Test.Lab Flutter Testing