Flutter Suppression

People involved:

POLIMI:  L.Marchetti, A.De Gaspari, F.Toffol, N.Fonzi, L.Riccobene and P.Mantegazza 

UWA: J.Berg, E.Livne

Developments of the capabilities and reliability of aircraft control system hardware and software, combined with the growing flexibility, and hence potential for flutter problems solutions and for related weight reduction of optimized composite airframes, seem to have made the implementation of Active Flutter Suppression (AFS) technology closer than ever before. This makes the experimental study of current state of the art AFS important, especially from the perspectives of uncertainty, reliability, and the safety of flight vehicles in which this technology will be used.

Contributing to AFS technology development, and to flight vehicle active control in general, for many years, the Politecnico di Milan (POLIMI) developed in the mid-2000s a scaled actively controlled aeroservoelastic model of a three-surface passenger airplane and tested it in its large low-speed wind tunnel. Motivated by the need to return to the wind tunnel with an aeroservoelastic model of a configuration that would capture the aeroelastic behavior of current and emerging commercial passenger and cargo flight vehicles that may benefit from AFS, a research program has been launched by the Polytechnic of Milan and the University of Washington - Seattle (UWA) in  in 2018 to focus on the reliability and safety of AFS-dependent flight vehicles using a wind tunnel model that would be representative in complexity and aeroelastic characteristic to real aircraft.

During the project ASDL Lab developed a modified version of the X-DIA aeroelastic platform to be used as a dedicated platform to experimentally validate active flutter control technologies. 

The project ended in January 2020 with a succesfully wind tunnel test campaign where four different active flutter suppression controllers were tested.

The short video below combines images of two cameras are reported, showing the entire F-XDIA model in the testing chamber, with a close-up to the left wing. The model is tested at flutter speed of 41.5 m/s, and excited with a low amplitude white noise. Two lights are reported into the screen, switching from RED to GREEN, showing when the AFS and the flutter safety mechanism are activated. The test shows what happens by switching off and on con AFS control system. Every time the AFS is switched off the model approach the flutter conditions, but then the stability is recovered every time by switching on the AFS control system. In the last part of the short video the AFS system is kept off, to force the safety futter mechanism intervention to stop the flutter when the max acceleration threshold is reached. It is possible to see a small light installed in the bottom part of the wing tip pod. Light on means mechanism engaged and moving mass in the rear position (flutter condition). Light off means mechanism activated, mass moved to the front position. It is very easy to see how the mechanism is fast and efficient in stopping the flutter. There is not any possibility to obtain a similar fast response by decreasing the velocity of the wind tunnel.

 

Click on the image to see the video

 

Related projects:

• FAA-UWA "Active Flutter Suppression (AFS) Project (2017-2019)": in collaborazione con University of Washington in Seattle (PI) and FAA (Funder).