Systems Control and Flight Dynamics

SACSO, Active Suspension for Wind Tunnel Tests

Sacso is an Onera Federating Research Project (PRF), proposed by Claude Reboulet in 1999, which is based on the skills of Onera's aerodynamics and robotics experts and model makers for designing and making a new type of Active Suspension (SACSO) for wind tunnel tests.

The purpose of this suspension is to achieve better modeling of aircraft behavior using much richer tests than those currently performed. In particular, the control of forces by the suspension's six degrees of freedom can simulate the model in free flight.

The suspension is a redundant parallel robot with cables (figures 5 and 6). The model is held by a carbon fiber support beam from a 6 component balance (figure 1). The beam is connected to the wind tunnel frame by nine tension-controlled motorized cables. A computer program is used to control the coordinated tensions. For free flight, these tensions are controlled in such a way that the resultant of the forces exerted on the model by the sting can simulate the thrust of the engines.

The model and its internal suspension

The model has three operational control surfaces whose control depends on the tests programmed.

The model's location is ensured by hybridizing the measurements from three gyros and seven accelerometers on the model, length measurements of the nine suspension cables, and processing the images taken by two location cameras.

The aerodynamic forces to which the model is subject are measured by numerical processing in which all the measurements taken are merged:

• The six balance measurements are used to reconstitute the tension coefficient of forces exerted on the model by the beam.
• The seven accelerometer measurements and three gyro measurements are used to reconstitute the model's inertial tension coefficient of force.
• The location system is used to specify the position, attitude and speeds at the same time as these tension coefficients.

This system allows us to carry out complex free flight type tests at less cost than real flight. New test methodologies now being defined will study the synthesis of control surface actuations that are particularly critical for identifying the aerodynamic coefficients, which are difficult to measure.

General technical characteristics:

• Model size: 1 m long
• Working volume: The volume in which the center of the model can move is a cube, 1 m on a side. The angular motions are –15° to +15° in heading, -45° to +45° in roll, and –20 to +45° in pitch.
• Speeds and accelerations: The maximum speeds and accelerations follow the similarity conditions for the motions of a military aircraft: 3 m/s2 and 15 m/s2 vertically and laterally, 80°/s2 and 1400°/s2 in yaw, 400°/s and 7000°/s2 in pitch and 440°/s2 and 8500°/s2 in roll.

History of preliminary studies

This short history of the preliminary studies, limited to the first year of the Federating Research Project (PRF), gives us the opportunity of mentioning the first team of engineers who contributed to the design of Sacso. These preliminary studies covered:

• definition of the setup's dynamic characteristics (M. Deschamps)
• definition of the control principles (M. Llibre)
• experimental verification of the control principles (C. Lambert and P. Carton)
• definition of the system specifications and the principles of use (J.P. Evrard, O. Rénier, D. Tristrant)
• study of the effect of the cables on the flow (C. Verbeke).

Last Update: 5 June 2006 - © ONERA 2009 - Terms of use