Abstract
The certification process of external loads designed for aircraft needs to satisfy various criteria where compatibility with existing systems is one of the essential requirements. Flight flutter testing is a critical part of a certification process that requires many preliminary studies. Computational flutter analysis must precede actual flutter test to determine an approximately safe flight envelope to ensure the safety of the personnel and aircraft. To be able to perform flutter analysis of an aircraft, an accurate structural model such as finite element (FE) model is required. An accurate FE model can be obtained from a coarse model using ground vibration test (GVT) which is also the primary test campaign for certification of a new external load, new aircraft design, or modification on existing aircraft. On the other hand, performing GVT for each configuration of an aircraft is both time consuming and costly. It would be more practical to determine the critical configurations for an aircraft using computational tools and perform actual GVT for those configurations. The objective of this study is to simulate GVT characteristics for downloading and fuel configurations of F‐16 aircraft. A novel methodology is proposed where various loading configurations can be simulated by subtractive modification from loaded GVT data so that joint stiffnesses between stores and aircraft need not be identified. The proposed technique decreases the number of necessary physical GVT testing campaigns.
Highlights
When designing an external store or ammunition for an existing fighter aircraft, the aircraft with the new store or ammunition should satisfy certification regulations of airworthiness authorities such as Federal Aviation Regulations (FAR), European Aviation Safety Agency (EASA), Joint Aviation Regulations (JAR), and Military (MIL)
The effect of fuel in fuselage tanks is shown to have no effect on the structural dynamics of F-16. e dynamics of the aircraft can be fully simulated for that change by this approach. e approach is applied to real ground vibration test (GVT) result data which show that minimization of the total number of test configurations and testing time is possible approximately to 80%
finite element (FE) model of an aircraft is crucial for the planning of a GVT campaign when the flutter characteristics are in consideration
Summary
When designing an external store or ammunition for an existing fighter aircraft, the aircraft with the new store or ammunition should satisfy certification regulations of airworthiness authorities such as Federal Aviation Regulations (FAR), European Aviation Safety Agency (EASA), Joint Aviation Regulations (JAR), and Military (MIL). Flutter performance and determination of safe flight envelope are the main concerns in these certification procedures. Flutter characteristics of an aircraft can be estimated using mathematical models and simulations which may be validated by flight testing when needed. In order to perform flutter analysis, either a validated finite element (FE) model or the modal parameters of the aircraft should be available. Flutter analysis is performed to identify the aeroelastic behavior of aircraft during various flight conditions and determine the flight speed when flutter occurs. Ground vibration testing (GVT) is an industryaccepted experimental methodology to identify elastic modal frequencies, modal damping ratios, mode shape vectors, and modal mass data of an aircraft, which are directly or indirectly used in flutter analysis of the same aircraft. GVT-related issues such as the decision on the number of sensors for attaining optimum spatial resolution for the motion of major structural elements and prevention of spatial aliasing, mounting style of accelerometers [1, 2], methods for exciting the structure using electrodynamic shakers [3], and providing the free-free boundary conditions using soft suspension systems are well studied and documented in the literature
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