the actuators 40 and is attached to the unison ring 36 the unison ring 36 is centered within and slides on track members 37 spaced around the outer housing structure 12 each actuating rod 39 extends through an opening 41 in the connecting member 16 a nozzle control 42 connects one side of the actuator to an actuating pressure while opening the opposite side to drain thereby movably positioning the main flaps 30 an arrangement of this type is shown in u s pat no 2 815 643 a plurality of balance flaps 50 extend forwardly of the main flaps 30 each flap 50 has its rearward end pivotally connected to the forward end of a main flap 30 while its forward end has cylindrical means 51 thereon which is mounted for axial movement in a track means 53 each track means 53 is formed between a rearward extension of the inner case 14 and a rearward extending flange 15 on the connecting member 16 while a simple cylinder and track means has been shown any type of device permitting axial movement along with a change in angular position of the balance flap 50 can be used a plurality of divergent flaps 60 extend rearwardly of the main flaps 30 each flap 60 has its forward end pivotally connected to the rearward end of a main flap 30 while its rearward end is pivotally connected to the rear end of an external flap 70 each external flap.