Ralph Hooper has recorded the evolution of the propulsive nozzle design from 'bent pipe' with internal cascade to the, now familiar, exit vaned type.
In about November 1957 Frank Cross demanded to know what aerodynamic torque was to be expected on the nozzle drive system as he was in contact with Plesseys over possible air motor actuation.We had already made a stab at frictional torque and were ignoring the possible effect of exhaust flow swirl on the assumption that any such effect would be self cancelling, port and starboard. The problem was that the, then, 'bent pipe' nozzles undoubtedly projected into the forward flight air stream on deflection. We could have made a guesstimation but certainly could not wait for elaborate testing to provide guidance.
In pondering this impasse I got to wondering how much the end of the (bent pipe) ducts could be cut back, and a few doodles later the idea of oblique nozzles with guide vanes, which also provided the final contraction in area, looked promising. We dubbed these 'nozzling guide vanes', although 'cascade vanes' or 'oblique nozzles' became more popular. These now scarcely projected beyond the airframe nozzle fairings, when deflected downwards, and we felt able to claim negligible aerodynamic torque. The first formal Hawker drawing is dated January 1958. All subsequent aerodynamic design of the nozzles was, of course, done at Bristol.
In response, Gordon Lewis recalled extensive interchange of ideas between Bristols and Hawkers followed by a comprehensive series of rig tests on the nozzles, the rear 'trouser piece' and the fan outlet system. The solution adopted for the nozzles had a slightly higher internal loss than the original cascade bend followed by
final contraction, but with less projection into the airstream, and this configuration most likely originated at Kingston.