A control circuit and a method for controlling an operation of a power amplifier core are provided. The aerodynamic element is flexible and has a substantially cylindrical general shape and defines an upstream portion attached to the inner wall of the intake lip of the nacelle, and a downstream portion bearing radially against an inner face of the shroud. The proximal end of the length of coaxial cable is coupled to the first and second pole portions via a common-mode filter. A plug and a rotational shaft are installed in the cylinder to be rotated by the motor. A drive piston and cylinder assembly acts upon the resilient biassing compression springs for adjusting the resilient biassing force acting upon each arm.