62 affixed to the righthand end of linkage 55 rides in slot 60 to that axial movement thereof will cause member 44 to rotate about pivot point 46 for rotation of vane 42 relative to slot 43 and hence change its area as the aj is scheduled fig4 and 5 depict an actuation system when the vane varies the area the ejector slot 98 mounted in the side wall 100 in this actuation system the vane 102 is disposed adjacent the slot 104 formed between the upstream sidewall portion 106 and the downstream side wall portion 108 the vane 102 is similar to the one depicted in fig3 and is supported by the vane support 112 which is pivotally connected to the end of the downstream wall 108 by pin 114 the major link 116 is moved rectilinearly by the link 118 via the cam slot 120 and the follower 122 link 118 is connected to the hinge connection 12 of the convergent nozzle as shown in fig3 so that the position of link 118 is indicative of the throat area rotational movement of the vane 102 is obtained by the inclined cam slot 124 and the follower 126 hence the axial movement of link 116 rotates the vane 102 about the pivot 114 to position the vane 102 relative to the slot 98 fig6 9 schematically illustrate different configurations of the end edge of the wall for avoiding infra red detections fig6 depicts the edge 70 of the wall 16 is configured.