Flutter – a type of aeroelastic self-excited vibrations of the wing, ailerons, control surfaces or main rotor blades, arising after exceeding a certain speed, called the flutter critical speed, limiting the speed of the aircraft relative to the air. Since the discussed phenomenon is dangerous, it can also be the cause of air disasters, there is a need to carry out flutter tests of each airframe prototype.

Flutter tests consists of several stages:

• creating a dynamic FEM model of the structure – enabling the determination of the approximate aerodynamic properties of the structure,
• ground resonance tests,
• possible tests in a wind tunnel,
• flight tests.

During the flight tests, all resonances in the specified frequency range are monitored – their changes as a function of the flight speed in the full operational range. At a given altitude, a specific flight configuration is adopted, then structure vibrations are induced (noise, harmonic or impulse excitation) using control surfaces or additional devices (wings, rotating cylinders, mass exciters or rocket pulse generators).

Data from acceleration sensors mounted on the structure are analyzed.
After such a cycle, the aircraft continues testing in the next flight configuration.

Flutter tests – testing capabilities

We have over 40 years of experience in the field of aircraft resonance testing, having tested several dozen types of aircraft, gliders and helicopters, as well as their components manufactured by the domestic and foreign aviation industry. We carry out dynamic and aeroelastic analyses, including flutter analyzes in accordance with the requirements of aviation regulations. The data for analysis are the results of resonance tests or the results of calculations obtained using the finite element method (FEM).

The results of tests and analyzes carried out in the Łukasiewicz Research Network – Institute of Aviation are recognized by both Polish and foreign aviation supervisory authorities.

Flutter tests – scope of the tests

• aircraft resonance tests,
• determination of flutter velocity and form based on the results of resonance tests,
• calculations of natural vibrations and flutter using the finite element method (FEM),
• preparation of flutter test program in flight,

• support for flutter tests in flight,
• support for the certification of new or modified aircraft.

Flutter tests – software

• Nastran,
• JG2 (lPPT PAN),
• ZAERO (ZONA Technologies Inc.),
• SAF (Subsonic Aerodynamic Flutter),
• Patran, Siemens FEMAP.