FLIGHT VIBRATION TESTING - WE ALWAYS DID IT THIS WAY

Abstract

Aeroelasticity is a big issue in flight testing when it comes to external installations on the aircraft fuselage or wing. The issue requires quite a significant effort in terms of in-strumentation and real time data analysis. Flight test often requires telemetry in order to analyze the aeroelastic behavior of such an installation during flight envelope expansion. But what happens when you get stuck in flight test because no telemetry is available and time schedule is tight? We present an innovative solution which was created to solve this problem for a flight test of a large belly instrumentation pod with ventral fin on the German High Altitude and LOng Range Research Aircraft HALO. An inflight aeroelastic workspace was created which allowed to analyze spectral response and dampening coefficients of the installation directly after flying the respective test point. The solution helped to perform a highly efficient and fast test campaign for this aircraft modification. This paper describes the flight flutter test activities for the HALO. After a brief description of the main aircraft features and the requirements for aeroelastic certification, an overview of the ground vibration test and of the flutter analysis is presented. The report of the flight test activities is divided into the description of the aircraft instrumentation, flight envelope, test procedures and post-flight data reduction. The flight test results in combination with the aeroelastic analysis are discussed at the end.