the gap dimension 40 thus it can be seen with reference to fig1 3 that there is a variety of flow areas ranging from least resistance to fluid flow to a maximum resistance to fluid flow passing through the nozzle the adaptation of the disc deflectors 20 and 25 enables a finite control of gases passing through the nozzle over a certain area range turning now to fig4 a preferred method to actuate the deflectors 20 and 25 is shown as heretofore mentioned the deflector 20 is slidable within a sector retaining wall or channel 22 in housing 12 the sector plate or wedge 20 is anchored to the actuator mechanism generally designated as 26 by retainer pin 24 the pin is secured to a piston 30 housed within piston housing 33 the deflector 20 in its retracted position within channel 22 positions the piston 30 against the inner wall 35 of housing 33 the chamber length 28 or distance between the upper surface 38 of piston 30 represents the distance the deflector 20 is permitted to extend beyond the peripheral edge 11 of disc housing 12 an o ring seal 32 is provided in the wall of the piston a deflector actuating force may be provided for example by a pyrotechnic explosive charge 36 actuated by actuator mechanism 18 which would be electric current carrying wires a passageway 39 is provided in housing 33 for the actuating gases.